WO2006009810A1 - Devices and methods for product authentication and/or monitoring - Google Patents

Abstract

Aspects of the invention provide stabilized light-sensitive compounds and methods for their use in product authentication and/or monitoring. A light sensitive compound, such as a fluorescent dye, is combined with an isolating material to form a liquid mixture. The mixture is applied onto the surface of a solid base. The isolating material isolates the light sensitive compound from adverse environmental effects and serves to control the rate of hydration of the light sensitive compound. Preferably, liquid samples are authenticated with the stabilized light sensitive compound.

Description

DEVICES AND METHODS FOR PRODUCT AUTHENTICATION AND/OR

MONITORING

Related Applications This application claims the benefit under 35 U.S. C. §119(e) of U.S. Provisional

Application Serial No. 60/580,580, filed June 17, 2004, the entire contents of which are incorporated herein by reference.

Field This invention relates generally to methods and apparatuses for authenticating and/or monitoring a sample product, and more specifically, to substrates and methods for stabilizing light-sensitive compounds for use with product authentication and/or monitoring equipment and for improving the functionality of product authentication and/or monitoring.

Background

Authenticating and monitoring products to discriminate between very similar complex mixtures are useful for various reasons. For example, the use of counterfeit substances (e.g., misbranded product from a competitor or misformulated product from a licensee/franchisee) should be detected to preserve the integrity of a brand. Also, low quality substances (e.g., diluted or misformulated product) should be quickly and conveniently detected for appropriate correction.

One particular industry that could benefit from such authenticity testing and monitoring is the beverage industry. With respect to monitoring production of the beverage, a simple, quick, and product specific at-line test to determine whether the beverages being produced are within specification is desirable. Typically, the beverages are being bottled at a rate of 2000 bottles/minute. Therefore, standard off-line analytical techniques for monitoring product quality, such as GC/MS or HPLC, are complex and time consuming in that beverages that are being tested have already been introduced to the market. A desirable monitoring procedure should provide relatively quick response time, be usable by non-scientific personnel, be accurate (e.g., having an error rate of less that 2.5%) and survive harsh plant environments. With respect to product authentication, a determination as to whether a particular branded bottle includes the correct product may be made.

Commonly assigned U.S. Patent No. 5,753,511, which is herein incorporated by reference in its entirety, discloses an automated method of developing a database to store information for "fingerprint"-type analysis of products (even as to product lot numbers and batch). The automated analysis is a method of evaluating and discriminating products, even within a narrow field or industry, competing and otherwise, to establish authenticity or point of origin of the product. The invention therein relates to an automated method for identifying key ingredients and/or the relative amounts of key ingredients in products mixed with light- emissive compounds. Scanning for light emission of a predetermined wavelength when the sample product is mixed with the light-emissive compound is used when comparing the sample product to a fingerprint to determine whether the product is authentic or to otherwise monitor the production of the product.

Commonly assigned U.S. Patent Nos. 6,490,030 and 6,512,580 each of which is herein incorporated by reference in its entirety, disclose a portable product authentication device and a method of authenticating products, where light-sensitive compounds are delivered to a sample by way of a substrate that immobilizes the compound and receives a sample product. The light-sensitive compound may also be brought to the sample using a standard microtitre plate having, for example, 96 test wells, each including one or more light- sensitive compounds dried in the well into which an amount of sample product is placed. Testing is thereafter performed by a device that detects light interactions (emission and/or absorption) with the light-sensitive compound and the sample product and compares the emission and/or absorption to a standard.

Summary

Aspects of the invention provide compositions and methods for stabilizing light- sensitive compounds for use in product authentication and/or monitoring.

In one aspect, the invention provides a method for preparing a stabilized light- sensitive compound by combining a light-sensitive compound with an isolating material to form a liquid mixture, depositing a volume of the liquid mixture onto a surface of a solid base, and drying the deposited liquid mixture to form a stabilized light-sensitive compound on the solid base, in which the isolating material acts to isolate the lights-sensitive compound from adverse environmental effects and to control the rate of hydration of the light-sensitive compound. In one embodiment, a film of stabilized light-sensitive compound is formed by drying the liquid mixture onto the solid base. The isolating material may be a polymer, a carbohydrate (e.g., a carbohydrate with a sharp melting point), a hydrocolloid, or a combination of two or more thereof. In certain embodiments, the isolating material may include a water soluble methylcellulose, a water soluble hydroxypropyl methylcellulose, a polymer of one or more thereof, or a combination of two or more thereof. In further embodiments, the isolating material may include sucrose, fructose, galactose, starch, or any combination of two or more thereof. In another aspect, the invention provides a method for preparing a stabilized light- sensitive compound by combining a light-sensitive compound with an isolating material to form a liquid mixture, and depositing a volume of the liquid mixture onto a surface of a solid base, wherein the deposited liquid mixture forms a gel on the solid base thereby producing a stabilized light-sensitive compound on the solid base. In one embodiment, the gel is dried on the surface of the solid base.

In another aspect, the invention provides a method for preparing a stabilized light- sensitive compound by depositing two or more layers of material onto a surface of a solid base, wherein at least one of the two layers includes a light-sensitive compound in association with an isolating material. In certain embodiments, 2-10 layers of material may be deposited onto the solid base. For example, about 5 layers of material may be deposited onto the solid base. However, other numbers of layers may be used. The different layers may include different material and have different properties as described herein.

In another aspect, the invention provides a film of stabilized light-sensitive compound, wherein the film includes a light-sensitive compound and an isolating material. In one embodiment, the film may be disposed on a surface of a solid base. In one embodiment, the film may be disposed on a surface of a well in a multi-well plate. In another embodiment, the film may be disposed on a packaging material. In a further embodiment, a film may be disposed on a test area of a solid base. It should be appreciated that a film may include two or more layers of material (e.g., two or more layers of different material). In yet another aspect, the invention provides a stabilized light-sensitive compound preparation including a substantially uniform dispersion of a light-sensitive compound within a matrix of isolating material. The matrix of isolating material may be disposed on a surface of a solid base. In one embodiment, the matrix is a gel. In another embodiment, the light- sensitive compound and isolating material form a film on the surface of the solid base.

In further aspects, the invention provides methods of characterizing a liquid sample by adding the liquid sample to a stabilized light-sensitive compound described herein (e.g., a stabilized light-sensitive compound prepared according to any of the methods described herein), and obtaining a characteristic signal of the liquid sample by detecting a signal from the light-sensitive compound that is in contact with the liquid sample. In one embodiment, the assay is performed after allowing the liquid sample to react with the isolating material and the light-sensitive compound for an incubation period that is sufficient for the liquid sample to contact the light-sensitive compound and form a mixture suitable for analysis (e.g., a stable mixture). The incubation period may be less than about 20 minutes (e.g., less than about 10 minutes, less than about 5 minutes, about 2 minutes, etc.). However, shorter or longer time periods may be used.

In any aspects or embodiments of the invention described herein, the liquid sample being tested may be a sample of a commercial liquid product (e.g., a sample obtained at a field site, a beverage, or other commercial or consumer product). In other embodiments, the liquid sample may be obtained by incubating a liquid (e.g., a liquid solvent) with a solid sample of interest (e.g., a sample of a solid commercial or consumer product). It should be appreciated that a sample may be diluted or treated (e.g., to remove one or more coloring agents) prior to analysis. The volume of sample being analyzed (e.g., added to the stabilized light-sensitive agent) may be between about 0.1 μl and about 5 ml. For example, the volume of added liquid sample may be about 0.5 mis. However, smaller or larger volumes may be used as the invention is not limited in this respect. In certain embodiments, the liquid sample may be physically mixed with the stabilized light-sensitive compound prior to analysis. The physical mixing may include shaking. In certain embodiments, the liquid sample may cause the isolating material to dissolve and/or swell and/or form a colloid. In certain embodiments, the liquid sample may penetrate the isolating material and re-hydrate the light-sensitive compound. In certain embodiments, the light-sensitive compound (or a fraction thereof) may be released from the isolating material and dispersed in the liquid sample. In any aspects or embodiments of the invention described herein, an assay may include illuminating a light-sensitive compound that is in contact with a liquid sample and detecting an absorbance and/or fluorescence signal at one or more wavelengths (e.g., a spectrum of signals). Accordingly, the assay may include a colorimetric detection step and/or a fluorescence detection step. In certain embodiments, the signal obtained from the liquid sample may be compared to a reference signal to determine whether the liquid sample is authentic, fresh, and/or to determine the origin of the liquid sample. The reference signal may be obtained from one or more reference samples that are processed along with the sample(s) being tested. Alternatively or additionally, the reference signal may be a standard signal that is stored, for example, in a memory of a computer or processor associated with the test device.

Other aspects of the invention include a kit for assaying a liquid sample. The kit may include one or more (e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, etc., or more) stabilized light-sensitive compounds described herein (e.g., prepared according to any one of the methods described herein). Accordingly, a kit may include one or more isolating materials that are permeable to a liquid sample, miscible with a liquid sample, and/or soluble in a liquid sample. In one embodiment, the kit may include or consist of a multi-well plate having two or more wells, wherein each well includes a stabilized light-sensitive compound. The multi-well plate also may include one or more wells containing one or more different stabilized light-sensitive compounds. The multi-well plate also may include one or more control wells and/or one or more reference wells. In another embodiment, the kit may include or consist of a test strip with one or more stabilized light-sensitive compounds on its surface. In certain embodiments, the kit may include two or more different layers of isolating material, wherein the light-sensitive compound is present in at least one of the layers of isolating material. The different layers of isolating material may have different hydration rates, porosities, buffering properties, or any combination thereof. For example, the kit may include a buffering layer, a filtering layer, a capping layer, or any combination thereof. It should be appreciated that in any of the aspects or embodiments described herein, one or more light-sensitive compounds may be used, and the light-sensitive compounds may be dyes (e.g., different dyes) such as fluorescent dyes or other dyes, as the invention is not limited in this respect.

It also should be appreciated that in any of the aspects or embodiments described herein, an isolating material may be a combination of two or more suitable materials described herein. In certain embodiments, the isolating material may be opaque or transparent. In certain embodiments , the isolating material may include a humectant. The amount of isolating material used may represent between 0.05% and 5% weight/weight of the liquid mixture (e.g., between about 0.2% and 2.0%, about 0.5%, etc.). However, lower or higher amounts may be used. In one embodiment, the ratio of isolating material to light- sensitive material in the liquid mixture may be greater than 1:1. However, lower or higher ratios may be used. In certain embodiments, the light-sensitive compound(s) may be cross- linked to the isolating material(s). In other embodiments, the light-sensitive material(s) may be retained within a cross-linked matrix of isolating material(s). Accordingly, the isolating material(s) may entrain the light-sensitive compound(s).

It also should be appreciated that in any of the aspects or embodiments described herein, a liquid mixture may be deposited onto a solid body surface that is etched and/or includes a porous substrate.

Brief Description of the Drawings Figure 1 shows a cross-section of one embodiment of a test well with several test layers.

Figures 2A and 2B illustrate one embodiment of a multi-well plate containing wells with a dry dye coating.

Figure 3 illustrates one embodiment of a dye-ready plate (DRP) system including examples of steps taken to analyze collected samples.

Figure 4 illustrates one example of results obtained in a multivariate sample analysis.

Figures 5A-5D illustrate additional examples of multivariate analytical results.

Figure 6 illustrates one embodiment of a dye-ready plate showing an example of a configuration of reference samples, test samples, and negative controls.

Description

The inventors herein have found that substrates (e.g., solid bases such as microplates or products or product packaging) containing light-sensitive compounds may produce inconsistent results, and in particular, substrate-to-substrate variability. It is believed that this variability is due to a number of factors, including, for example, 1) the susceptibility of the light-sensitive compounds to environmental effects (e.g., effects of the solvent used with the light-sensitive compounds; the pH; the shelf-life of the compound; exposure to air, oxygen, carbon dioxide, light, bacteria, molds or other contaminants), and 2) the rate of hydration of the light-sensitive compound, for example, the rate of hydration of a film of light-sensitive compound at the bottom of a microtitre plate. However, it should be appreciated that the invention is not limited in this respect and that these factors, alone or in combination, need not contribute.

According to one aspect, substrate-to-substrate variability may be overcome by isolating a light-sensitive compound on a delivery substrate. In one embodiment, this is accomplished by mixing the light-sensitive compound with an isolating material and placing a suitable amount of the mixture onto the surface of a solid base (e.g. a microplate or into a microplate well) and thereafter allowing the isolating material to cure, set, and/or dry, thereby forming a gel or a film on the surface of the solid base. In this respect, the light-sensitive compound is held in the material and is isolated from environmental effects. In a sense, the light-sensitive compound is placed in a controlled microevironment where otherwise naturally occurring environmental effects are controlled or completely eradicated. In another embodiment, a layer of isolating material may be placed over a layer of light-sensitive compound on a substrate surface.

In certain embodiments, a light-sensitive compound may be a dye (e.g., a light- emitting compound such as a fluorescent dye) that generates a specific pattern or fingerprint (e.g., a specific spectrum of color and/or fluorescence) when contacted (e.g., mixed) with a sample of interest. The resulting fingerprint may be used to identify or characterize the sample. For example, the fingerprint may be used to determine whether the sample is an authentic product or whether the sample is in a desired condition (e.g., not degraded or otherwise tainted or contaminated). In another embodiment, the fingerprint may be used to determine the origin of the sample (e.g., the manufacturing plant). In one aspect of the invention, one or more light-sensitive compounds may be stabilized in order to provide a product that generates a reproducible fingerprint when contacted with a sample of interest. According to the invention, stabilization may be important to prevent minor changes in the light-sensitive compound from affecting the characteristics of the fingerprint that is obtained when contacted with the sample of interest. In one embodiment, one or more light-sensitive compounds may be stabilized in an isolating material (e.g., in the form of a matrix, a gel, a film, or a combination thereof) as described herein in either a hydrated or a dehydrated form. Accordingly, in one embodiment, addition of a sample to the stabilized light-sensitive compound may result in rehydration of the light- sensitive compound. However, in other embodiments, addition of a sample may result in dissolution of the isolating material as described herein. In yet further embodiments, addition of a sample may result in other reactions that promote contact between the stabilized compound and the sample (and/or one or more components of the sample). It should be appreciated that any combination of two or more of these reactions may be involved when a sample is contacted to a stabilized light-sensitive compound. According to aspects of the invention, the sample may be incubated with the light-sensitive compound for a time sufficient to obtain a stable mixture of the sample and the light-sensitive compound. As used herein, a stable mixture is one where all of the light-sensitive compound (or substantially all of it) is mixed with the sample. Accordingly, a stable solution may be obtained when all (or substantially all) of a stabilized light-sensitive compound is rehydrated (e.g., solubilized, penetrated, permeated, released, or otherwise able to come in contact with a sample solution). In another embodiment, a stable solution may be obtained when all (or substantially all) of a matrix material containing a light-sensitive compound has dissolved (e.g., dissolved by a sample solution). In one embodiment, a stable mixture is a homogeneous mixture of sample and light-sensitive compound. It should be appreciated that a stable mixture may be important to obtaining reproducible and reliable assay results. It also should be appreciated that the conditions of sample incubation with the light-sensitive compound may affect the time required to obtain a stable mixture. In one embodiment, the time may be shortened by physical mixing (e.g., shaking, agitating, stirring, or other form of mixing) during the incubation time. In another embodiment, the time may be shortened by elevating the incubation temperature.

In one embodiment, a sample reacts rapidly with the stabilized form of the light- sensitive compound. For example, rehydration, penetration, dissolution, or other reaction may provide a stable fingerprint (e.g., reach saturation or approach saturation) within less than about 20 minutes, for example between about 2 and about 20 minutes, or less than about 15 minutes, less than about 10 minutes, less than about 5 minutes, about 2 minutes, or less (e.g., about 1 minute, about 30 seconds, or less). In some embodiments of the invention, sample reaction time may be shortened by using an isolating material and/or light/sensitive compound that is readily miscible with the sample of interests. For example, hydrophilic isolating material(s) and/or light/sensitive compound(s) may be used to test an aqueous sample. In certain embodiments, one or more carbohydrates that readily dissolve in the sample liquid may be used. In certain embodiments, one or more (e.g., a combination of two or more) material(s) (e.g., glucose) and/or material(s) that shield and/or material(s) that form a colloid may be used. As used herein, a sample may be a liquid product that is being tested. A liquid sample of interest also may be generated by contacting a solid product with a suitable liquid (e.g., a solvent) that subsequently may be tested.

In one aspect, the invention provides sample-ready testing products for use in portable readers. In one embodiment, a testing product may be a "coated" plate that is coated with one or more dyes in a stabilized form and to which a sample may be added for testing (e.g., for authentication and/or monitoring). The plate may be a multi-well plate containing a plurality of wells each with a coating of one or more stabilized dyes. In other embodiments, a testing product may be a surface that includes one or more dye-coated strips or stripes. As used herein, a dye coating may include one or more layers of material (including at least one layer containing at least one isolating material) as described herein. It should be appreciated that other dye-coated surfaces or containers may be used as the invention is not limited in this respect. A sample to be tested may be added to a dye coating on any suitable surface or in any suitable container. The resulting sample/dye interaction may be detected or assayed using a suitable reader (e.g., a portable reader) that can detect a signal at one or more sites to which sample was added. The signal may be any detectable signal, including a color signal, an intensity signal, a fluorescent signal, etc., or a combination of two or more thereof. In one embodiment, a sample-ready testing product may be a dye-ready plate containing one or more dyes (e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, etc.) stabilized with one or more isolating materials (e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, etc.). According to aspects of the invention, a plate may contain a plurality of wells (e.g., 16, 32, 64, 96, 192, 384, etc., or any other suitable number) each with one or more stabilized dyes. In other aspects, a plate may contain a plurality of distinct locations (e.g., test areas, micro-areas, etc.) coated with one or more stabilized dyes. In other embodiments, one or more stabilized light-sensitive compounds may be deposited on other solid bases, including discs (e.g., CDs, etc.), capillaries, and other devices (e.g., micro-fluidic devices and/or channels, etc.).

In aspects of the invention, the volume of mixture (containing isolating material(s) and light-sensitive compound(s)) that is deposited on a solid base may be a function of the size of the selected reaction area (e.g., the size of a well in a multi-well plate). For example, the amount of mixture may be between about 1 μl and about 10 ml (e.g., about 10 μl, about 100 μl, about 1 ml, etc.). However, lower, higher, or intermediate amounts may be used. It should be appreciated that the size of the reaction area (related to the amount of stabilized light-sensitive compound) may determine the amount of liquid sample that is added.

Accordingly, liquid sample volumes may range from about 1 μl to about 10 ml (e.g., about 10 μl, about 100 μl, about 1 ml, etc.). However, lower, higher, or intermediate amounts also may be used. Mixtures and/or samples may be delivered using any suitable method including, but not limited to, a pipette (e.g., an automatic pipette), a dropper, a spoon, capillary action, or any other suitable device (e.g., any other device that may be used to deliver a predetermined volume of liquid). In the example of a disk, centrifugal force may be used to deliver a liquid to a target area. For example, a volume of liquid may be delivered to a central deposit area and the disk may be spun to send the liquid to target areas further out from the center of the disk (this may be particularly useful in connection with micro-fluidic channels on the disk).

In one embodiment, authentication or monitoring may occur whereby a sample of the product to be tested is placed on the microplate or in the microplate well. In one embodiment, the liquid sample (or a key ingredient(s) or analyte(s) thereof) percolates diffuses or otherwise penetrates into the isolating material and interacts with the light- sensitive compound(s). In another embodiment, the liquid sample (or a key ingredient(s) or analyte(s) thereof) dissolves the isolating material and interacts with the light-sensitive compound(s). It should be appreciated that the invention is not limited in this respect and other driving arrangements, such as pressure, vacuum, mechanical pumping, centrifugation, or electrical, magnetic, or chemical forces can be used to move the sample into the isolating material. An authentication or monitoring device and methodology, such as those described in U.S. Patent Nos. 6,490,030 and 6,512,580, can be used to then record the amount and/or intensity of light emission or absorption and compares that data to a standard. A result is thereafter produced informing a tester of the authenticity and/or purity of the sample product. Of course, the present invention is not limited in this respect and other suitable detection arrangements or devices may be employed.

In one embodiment, the detection device includes an optical detector that detects light emission and/or absorption of light from the light-sensitive compound interacting with the sample. In this embodiment, the light travels through air. However, the present invention is not limited in this respect as other suitable arrangement for detecting the light emission and/or absorption can be employed. For example, in one embodiment, the light may travel through a fiber optic cable or cables that extends from the test site where the interaction occurs to the optical detector.

In one embodiment, rather than provide an optical detector, a photographic film material may lie adjacent the test site such that when incident light irradiates the light- sensitive compound and the sample and thereafter emits or absorbs light, the photographic film material is exposed. Upon subsequent development of the photographic paper, a determination can be made as to the authenticity of the sample based on exposure, color, and/or pattern.

It has been found by the inventors that plate to plate variability has dropped. In particular, internal test cross validations (CVs) have dropped by approximately 5%. In one embodiment, a relatively large batch of material (light-sensitive compound and isolating material) can be made and dispensed in multiple microplates, again reducing plate to plate variability, although the present invention is not limited to bulk formation.

The light-sensitive compounds may by dispersed into the isolating material using any suitable means, as the present invention is not limited in this respect. In one embodiment, the light-sensitive material is mixed with the isolating material. In another embodiment, the light-sensitive material is entrained with the isolating material. In yet another embodiment, the light-sensitive compound is cross-linked with the isolating material (e.g., directly or indirectly cross-linked to the isolating material or retained within a cross-linked matrix of isolating material without being cross-linked to the isolating material). Cross-linking can occur using any suitable technique, as the present invention is not limited in this respect. In yet another embodiment, the light-sensitive compound is merely entrained into the isolating material. It should be appreciated that one or more than one arrangement for imparting and/or holding the light-sensitive compound in the isolating material may be employed, as the present invention is not limited in this respect. When isolating material(s) and light-sensitive compound(s) are mixed, either one or both may be provided as a dry solid or in a liquid (e.g., a solution, a suspension, a colloid, etc.). Accordingly, in one embodiment a dry mixture may be prepared and a liquid may be added to the dry mixture to prepare a mixture fluid that may be deposited on a base surface. In other embodiments, one of the isolating material and the light-sensitive compound may be a solid (e.g., a dry powder) and the other may be in a liquid form. After mixing, additional liquid may be added if necessary. Alternatively, both the isolation material and the light-sensitive compound may be provided in liquid forms. The liquid(s) used for either the light-sensitive compound or the isolating material may be any suitable liquid (e.g., a solvent, water, alcohol, an organic solvent, a buffer, an aqueous buffer, a saline solution, etc., or any combination thereof). Similarly, a sample may be diluted with any suitable liquid including, but not limited to, one or more of the above.

Although the present invention is not limited to any particular isolating material, in one embodiment, the isolating material may form a gel. Non-limiting examples of gels include hydrogels, hydrocolloid gels, gels formed by a cross-linked matrix, polymers (including synthetic and natural polymers, either of which can be cross-linked in some embodiments) and combinations of all of the above.

Accordingly, an isolating material may be a gelant. According to the invention, a gelant may be any material or combination of materials that start as a liquid but form a semi- solid or solid matrix (gel) that tends to hold the shape of its container. Mechanisms to produce a gel vary widely, but may include one or more of the following: covalent cross- linking of one component with another (e.g., multivalent metal ion cross-linking of carboxyl groups in many biopolymers/polysaccharides), hydrogen bonding (primary mechanism in creating hydroxypropylmethylcellulose gels by adding isopropyl alcohol), polymerization/copolymerization (e.g., reaction of acrylamide and/or methyacrylamide monomers with bis-acrylamide in presence of appropriate initiator and buffer). Alternative or additional mechanisms may include pH adjustment (guar-borate gels only subsist above pH 7.5), energy input (e.g., heat, ultraviolet, infrared), evaporation, sufficiently high concentration, or oxidation. Accordingly, a resulting gel may have a specific structure that is held together by a stable lattice of gel molecules (e.g., a lattice of cross-linked molecules). A gel may have a long term order imposed by the stable lattice structure, including pores in the spaces defined by the lattice structure. The porosity of a gel may be determined by the size of the pores defined by the lattice. A gel may contain liquid within the pores (e.g., it may be hydrated). However, a gel also may be dried (e.g., dehydrated) and a dry gel may collapse, at least partially, depending on the properties of the lattice molecules. In another embodiment, the isolating material may form a film. Accordingly, an isolating material may be a film-former (a film-forming material). According to the invention, a film-former may be any liquid that, on evaporation of solvent (with or without external heating) and/or by reaction with air (oxygen), and/or by reaction of components within the liquid, is capable of forming a thin sheet (film) of homogeneous solid. The resulting solid may or may not be transparent, may or may not be "peelable" (be capable of being removed from surface without destroying its integrity), and may or may not require "draw-down" (knife-edge device used to level film-former and set its thickness). In certain embodiments, film-formers can also act as binders, i.e., film-former liquids may contain components with functions unrelated to forming the films. However, in the process of forming a thin sheet of homogenous solid, those components may be dispersed evenly and become attached to the surface due to particular film-adhesion properties for that surface.

Accordingly, in one embodiment, a film may be formed by any molecule that does not form a gel lattice described above. Non-limiting examples of film forming molecules include biopolymers, starches, cellulose, carbohydrates, hydrocolloids, etc. It should be appreciated that certain molecules may form gels (e.g., when they are cross-linked, for example with a cross-linker or by physical activation), but also may form films (e.g., when they are dried under different conditions, and/or prepared under non-cross-linking conditions, etc.). In one embodiment, a film may be an amorphous structure composed of packed macromolecules. A film may not have a long range order imposed by a lattice. A film may be permeable if it contains space that is not occupied by the macromolecules (e.g., the shape and size of the molecules may not allow them to be packed to fill all of the space in the film). However, this space does not constitute a pore such as the pore of a gel defined by a specific lattice structure. However, in some embodiments a film may be cross-linked (e.g., to stabilize it, to bind it to a surface, to bind a molecule such as a light-sensitive compound).

Accordingly, a gel and/or a film may include one or more of the following non- limiting isolating materials: a hydrocolloid, a polymer (naturally occurring or otherwise), acrylamide, cellulose, methyl-cellulose, cellulose acetate, agarose, acrylic, starch, xantham gum, carboxymethylcellulose (CMC), hydroxypropyl cellulose, hydroxypropyl methocellulose (HPMC), polyvinyl alcohol, and polyacrylamide. In certain embodiments, the isolating material may include a carbohydrate or similar material having a sharp melting point (e.g., dissolves rapidly, for example within about 20 minutes, 15 minutes, 10 minutes, 5 minutes, 2 minutes, or less). Examples of carbohydrates with sharp melting points include, but are not limited to, sucrose, glucose, and fructose. In certain embodiments, one or more isolating materials (e.g., carbohydrates) may be included at between about 0.05% and 1% (weight/volume, weight/weight, or volume/volume), for example between about 0.1% and 0.5%, or between about 0.1% and 0.2%. However, lower, higher, or intermediate concentrations may be used. It should be appreciated that the isolating material may include two or more different materials described herein.

Further non-limiting examples of isolating materials are provided in the following table.

Table 1. Examples of gelants and some of their common cross-linkers that may be employed to cross-link the gelants, if desired:

GELANTS CROSS-LINKERS*

Biopolymers

Titanium, chromium, iron, succinoglycan aluminum borate (pH above 7.5), guar gum titanium, aluminum xanthan chromium, iron, aluminum aluminium, zirconium, carboxymethylcellulose chromium hydroxypropylcellulose isopropyl alcohol agar gum arrabic hydroxypropylmethylcellulose scleroglucan

Synthetic polymers

Often insitu using monomer, a persulfate, polyacrylamide (low hydrolysis) and/or TED, TEMED, or

SDS buffer copolymers of acrylamide and t-butyl acrylate polyethyleneimine polyacrylamide/polyacrylate/polymethacrylate copolymers

Inorganic acid added to sodium silicate silica gels solution * cross-linkers usually include a multivalent cation. As used herein, however, "cross-linkers" can be any material that causes liquid to solidify

In some cases, liquid solutions may become gels by simply adjusting concentration, pH, degrees of hydrolysis or degrees of substitution, and/or application of heat

In one embodiment, the isolating material has properties that can be utilized to obtain desired performance characteristics. For example, the type of isolating material used can be selected to render the isolating material more or less permeable to certain impurities, molecules or sizes thereof, render the material less susceptible to evaporation, control hydration rates, increase shelf life, and impact kinetics and rheology. Humectants may also be added to keep the isolating material moist.

In one embodiment, the isolating material can be manipulated and/or selected to provide a certain porosity that acts to filter undesirable attributes from the sample so that they do not interact with or otherwise interfere with the key ingredients interaction with the light- sensitive compound. In one embodiment, the isolating material is selected to filter out dissolved or entrained gas (carbon dioxide and/or air and/or oxygen) bubbles that may exist when testing carbonated beverages. Also, the isolating material may filter out coloring agents, such as the caramel coloring often found in cola-type beverages. Further, solid or particulate matter may also be filtered by controlling the make-up and/or type of isolating material.

The porosity or permeability of the isolating material may also be manipulated to obtain a desired diffusion and/or reaction rate. That is, a more porous isolating material may reduce the amount of time required for the sample to diffuses into the isolating material and therefore increase the overall testing time. Conversely, a denser, or less porous material, may increase the diffusion and/or reaction rate.

Controlling the porosity of the isolating material can also occur by controlling the amount and/or type of cross-linking that may be employed (e.g., if the isolating material is a gel that contains cross-linked material). For example, a highly cross-linked isolating material and light-sensitive compound combination may produce a relatively low porosity material, again having the effect of decreasing diffusion/reaction rate and increasing the effect of filtering undesired components of the test sample. Again, the converse holds, wherein a low cross-linked combination may produce a relatively high porosity material, thereby resulting increased diffusion/reaction rates and low filtering properties. Although the present invention is not limited to any particular cross-linking methodology, in one embodiment, cross-linking may occur by utilizing one or more cross-linking agents, such as Al+3, Cr+3, Fe+3, Ti+4, UV, oxidizing agents, heat, and ionizing radiation, alone or in combination. Other non- limiting cross-linking agents include bi-functional cross-linking agents such as bisacrylamides (e.g., methylenebisacrylamide) and diacrylylpiperazine. Porosity changes may also occur using other suitable techniques, as the present invention is not limited in this respect.

In one embodiment, the light-sensitive compound is mixed with the isolating material, transferred to 96 well plates and then cross-linked in the plate itself by the addition of cross linking agents, such as those mentioned above. In another embodiment, the isolating material and light-sensitive compounds are blended and cross-linking agents are added before the resulting mixture is placed into the plate. The blend is then pipetted before the setting. The curing time is controlled by the pH and the level of cross linker and the isolating material is allowed to cure (e.g., cross-link/harden) in the well.

The ratio (concentration) of the light-sensitive compound to the isolating material may depend upon a number of factors including the ability of the particular isolating material to hold the compound, the level of cross-linking, the type of cross-linking material, the type and characteristics of the light-sensitive compound(s) employed (for example, its ability and propensity to react with the sample, how effectively it emits and/or absorbs light, etc.) and other factors that are recognizable to those skilled in the art.

The isolating material can have any level of optically suitable transparency, as the present invention is not limited in this respect. Thus, the isolating material may be transparent, semi-transparent, and opaque to visible light. Importantly, though, the transparency of the isolating material is dependent upon the incident radiation (whether visible, near IR, far IR, etc.) necessary to cause the light-sensitive compounds, when interacting with the sample or key ingredients thereof, to emit or absorb light. Similarly, the level of transparency should allow the emission or absorption to be detectable by the detecting device. Thus, although the resulting isolating material and light-sensitive compound may appear to be opaque to the naked eye, testing may nonetheless occur.

In one embodiment, some of the wells of a microplate (or portions of a microplate not having wells) may include the combination of light-sensitive compounds and isolating material together with a predetermined amount of a sample to allow a known standard to accompany the substrate so that, upon subsequent testing, the emission and/or absorption from the known sample can be compared to the emission and/or absorption of the test sample. Similarly, the wells or portions of the microplate may contain the light-sensitive compounds and isolating material combination together with a predetermined amount of a fake sample. Thus, upon subsequent testing, the emission and/or absorption from the fake sample can be compared to the emission and/or absorption of the test sample.

In one embodiment, the light-sensitive compound and isolating material combination can be prepared so that, upon subsequent testing, the sample is adequately drawn into the material. In one embodiment, after the light-sensitive compound is disposed within the isolating material, the resulting combination can be fully or partially dried (e.g., freeze dried). Thus, upon subsequent testing, the liquid sample is drawn into the combination and rehydrates the material in a manner similar to a sponge. Depending upon the amount of drying, the rehydration can occur at desired rates, which can then impact the reaction time of the sample with the light-sensitive compound, as desired.

A dry material may offer additional benefits. For example the material may be formed into a film. The film may thereafter be rolled or otherwise packaged for bulk distribution and subsequently metered out for a particular test. Alternatively, the film may be used in a continuous monitoring process. The performance characteristics of the light-sensitive compound/isolating material may be enhanced by stratifying or layering differently formatted materials. For example, a cross-section of a test site 10, including microplate 12 and test well 14, shown in the embodiment depicted in Figure 1, may include test layers 16, 18, 20, 22having different porosities effecting diffusion and/or reaction times, as discussed above. It should be appreciated that test layers 16, 18, 20, 22 may be gels, films or any combination thereof. Each layer may have differing hydration rates or hydrophobicity and selectivity. Different layers can have different amounts of light-sensitive compounds or different types, with each layer being used in a particular portion of the overall analysis of the sample. In this regard, the testing density of a particular microplate may be increased. That is, more tests per microplate may be conducted. Additional layers may be included to provide additional features. Layers with or without light-sensitive compounds may be applied to provide desired filtering (e.g., particulate, molecular, gaseous, and/or color filtering, as described above). In addition, a layer may be used as a buffer or to contain a buffer. That is, it may include a buffering agent or other pre-conditioning agent to precondition or otherwise manipulate the sample prior to testing. A capping layer may also be employed, further acting to isolate the layers used for testing. It should be appreciated that the present invention is not limited to the use of any or all of these additional layers. Further, any combination of these layers may be employed, as the present invention is not so limited. In addition, each layer need not represent a clear distinct layer. Rather, each layer may be a zone that acts to impart the desired properties. Each such layer may also be partially or completely dried and thereafter formed in to a film, as described. Although in the figure shown, the layers are depicted as being horizontal, the present invention is not limited in this respect, as vertical or other inclined layers may be formed.

In one embodiment, to form the stratified test site, each layer is formed separately. For example, a first layer is allowed to cure completely before applying the second layer. Alternatively, the first layer may only be partially cured or set prior to the addition of the adjacent layer. In either case, in one embodiment, it may be preferable to cure the layers in a manner that creates a relatively intimate bond so that the potential to delaminate is reduced. In embodiments where the test site is partly or completely dried, the additional layers may be applied either before or after the first layer is dried, as the present invention is not limited in this respect. In another embodiment, one or more layers may form spontaneously after a solute is added (e.g., pipetted) into a container (e.g., a well of a multi-well plate) based on the miscibility properties of the different components in the container.

In one aspect, different light-sensitive compounds (or different combinations of light- sensitive compounds) may be immobilized at distinct positions on a substrate (e.g., in different wells on a plate) and one or more ratios of signal intensities (e.g., at one or more different wavelengths or over a range of wavelengths) may be obtained and used to characterize the sample being tested (e.g., the ratio(s) may be compared to one or more reference ratio(s)).

The substrate and method may include one or more of the above-described or other features, each independently or in combination, contributing to increasing the performance and/or functionality of the authentication and/or monitoring and isolating the light-sensitive compound(s) from the environment. That is, the invention is not limited to the particular embodiments described herein as other suitable combination of the various features discussed may be employed.

Examples

Example 1 : Light-sensitive Compound Ready Plates for Pepsi Authentication (Global Authentication^') .

A solution is made at a concentration of 0.4mM/ml as follows: A large stock solution of compounds 4, 25, 33, 335, 191, 233 dyes (see identities below) is made from 10 mM stocks and diluted to the final operating concentration of- 0.046 mM/ml in 0.1% methocel.

The compounds utilized are purchased from Molecular Probes, Inc. of Eugene, OR, USA and are listed below:

Compound Identities: Compound 4 3, 6-diaminoacridine hemisulfate (proflavine hemisulfate)

Compound 25 5 -carboxy fluorescein

Compound 33 5 -(and-6)-carboxy fluorescein (also Aldrich 44,729-3)

Compound 335 7-methoxycoumarin-3 -carboxy lie acid

Compound 191 Lucigenin(bis-N-methylacridinium nitrate) Compound 233 l,r,3,3,3',3'-Hexamethylindodicarbocyanine Iodide

The stock solutions are then placed into 250ml glass jars and transferred into 96 well plates using a ThermoLab systems Multidrop (ThermoLab Systems, Finland). Plates are then air dried for two (2) days. This procedure and examples of data from these tests are shown in Figures 2-6.

An embodiment of a dye-ready plate (DRP) 24 is depicted in Figures 2 A and 2B. DRP 24 may be a multi-well plate and may contain individual well inserts 26 with a dried dye film 28. This embodiment may enable dyes to be transported to a test site in the well inserts 26. The dried dye film 28 may contain one or more light-sensitive compounds, isolating materials, such as film formers, and/or stability additives. In one embodiment, fluorescence of the dyes, e.g., the light-sensitive compounds, may be measured with an OEM Fluorescence Reader. An embodiment of a DRP system, including examples of steps taken to analyze collected samples is shown in Figure 3. During step S30, samples, such as those from cola bottles 32, may be collected. The samples may be placed into tubes 34 and prepared in step S36. Preparation of the samples may include decolorization, such as by precipitation, any method described in U.S. Patent Application Serial No. 10/694,637, filed October 24, 2003, the entire contents of which is incorporated herein by reference, or any other method. In step S38, the samples may be transferred to a DRP 40. The samples may be read by an OEM Reader 44 in step S42. In step S46, a report, such as Preliminary Analysis 48, may be produced and any corrective actions may be taken in S50. Results of the DRP system may include saved revenue.

Analysis of data, such as data produced in step S42, may be performed by a variety of methods, such as those described in U.S. Patent Application Serial No. 10/212,334, filed August 5, 2002, the entire contents of which is incorporated herein by reference, including by developing plots having distinct clusters summarizing the similarities and differences among the samples being analyzed to a scored standard. Such analysis may be performed, for example, by multivariable pattern recognition.

An example of such a plot is shown in the embodiment depicted in Figure 4, which shows a filed sample testing in Cork, Ireland on May 21, 2004. The plot may contain a main "swarm" of field samples 52, plate controls (Zam Zam) 54, identified outliers or potential fakes 56, and inserted fakes 58. Additional examples of multivariate analytical results are shown in Figures 5A, 5B, 5C and 5D.

It should be appreciated that all plates may include some combination of standards and references. Empirical testing utilizing real world sample sets may be used to determine plate and/or test designs. Elements to be considered may include use of selected "gold standard," incorporation of inorganic fluorophore, use of negative controls (RC etc.), and blanks. A goal may be a plate/test design that is able to run 6-8 samples per plate. As shown in the embodiment depicted in Figure 6, plate 60 may include three columns of references 62, eight columns of samples 64 and a negative control column 66.

Example 2. Light-sensitive compound "fixed" in a highly soluble film.

In some embodiments, it is helpful to maintain an even dispersion of light-sensitive compounds such as those discussed in Example 1 by "fixing" them in place using a highly soluble nonionic matrix such as a 0.1 to 0.2% sucrose solution containing 0.1 to 0.2% methylcellulose (e.g., Methocel, preferably MW of 250,000 with a dispersivity of < 1 ,2). The light-sensitive compounds may be prepared as discussed in Example 1 , but the level of methylcellulose is adjusted between 0.1 to 0.2% (the higher level is more resistant to cracking and more porous) and sufficient sucrose is added to bring the concentration in the final solution to between 0.1 to 0.2% (the higher level provides a larger surface area to adsorb light-sensitive compounds and is particularly useful when higher concentrations of light- sensitive compounds are used to obtain an effective level of signal intensity).

The above example may be adapted, for example, using one or more relatively non- ionic film-formers such as methylcellulose and hydroxypropylcellulose both for their non- reactivity to both light emitting compounds and test samples and for their ability to produce relatively flat films without other additives or mechanical "drawing" or timed dipping procedures. If the light-sensitive compound is particularly sensitive to oxygen-induced degradation, 0.1-1.0% polyvinyl alcohol (e.g., up to -50% PVA) that has relatively low permeability to oxygen, may be used in place of or in addition to other film-formers. Many other adaptations also may be employed such as plasticizers (e.g., polyethylene glycol)~both to increase film flexibility and to increase permeability to water vapor for more rapid drying. The above example in no way is intended to constrain use of film-formers or associated additives or otherwise limit the scope of this invention.

Example 3. Light sensitive compound isolated in a gel or gel layers

In other embodiments, it may be desirable to isolate one or more light-sensitive compounds in single or multiple layers of gels either to permit separation of one or more light-emitting compounds in each test well, or to provide a variable level of permeability to test sample components. One example of a nonionic gel layer may be made by mixing the light-sensitive compound at the desired effective level such as those provided in Example 1 with 0.1 to 1% hydroxypropyl cellulose (HPC, MW of 50,000 to 500,000) depending on thickness, permeability and gel strength desired. More specifically, a 0.5% solution of HPC (MW~ 200,000) may be used as the final diluent in Example 1 (in place of 0.1% methocel). By itself, the HPC does not form a gel. Just before dispensing into a well, approximately 500 ppm of isopropyl alcohol may be mixed into the solution of light-sensitive compound. Once dispensed, brief air drying or drying in an oven will produce a gel layer whose thickness will depend on the volume of mixture dispensed into each well.

Additional layers of gel containing other light emitting compounds or just HPC gelant with different permeability properties may be added (e.g., to "filter" some test sample components).

Any suitable light-sensitive compound may be employed, as the present invention is not limited in this respect, such as any one or more of the compounds described or incorporated in U.S. Patent Nos. 6,490,030 and 6,512,580, and commonly assigned co- pending U.S. Patent Application Serial Nos. 09/556,280 and 10/694,637, each of which is hereby incorporated by reference in its entirety.

Light-sensitive compounds emit and/or absorb light in response to irradiation with light. Light emission or absorption can be a result of phosphorescence, chemiluminescence or more preferably fluorescence. Specifically, the term "light-sensitive compounds", as used herein, means compounds that have one or more of the following properties: 1) they are fluorescent, phosphorescence or luminescent; 2) react, or interact, with components of the sample or the standard or both or with the sample or standard itself to yield at least one fluorescent, phosphorescence, or luminescent compound; or 3) react, interact, with at least one fluorescent, phosphorescence, or luminescent compound in the sample product, the standard, or both to alter emission and/or absorption at the emission and/or absorption wavelength.

The term "fingerprint" as used herein, means light emission and/or absorption quantity and/or intensity and/or intensity decay or changes thereof from one or more light- sensitive compounds in combination with a standard (e.g., authentic) product. Accordingly, each product can have a particular fingerprint. The term fingerprint "profile" as used herein, means an assembly of fingerprints of a standard in combination with a series (or profile) of different light-sensitive compounds.

The term "sample characteristic" as used herein refers to light emission and/or absorption quantity and/or intensity and/or intensity decay or changes thereof in combination with the sample product. Detection of the light emitted and/or absorbed from the light-sensitive compound may be used using any imaging technique, such as infra red, near infra red, far infra red, foyer transformed infra red, ramonspectroscopy, time resolved fluorescence, fluorescence, luminescence, phosfluorescence and visible light imaging.

A change in spectroscopy, such as light emission, due to the presence of light- emissive compounds alone can be determined from the formula [(Fd-Fp)/Fd] x 100 where the light-emission of the light emissive compound and the absence of the sample product is Fd, and the light emission after adding the sample product to the microplate is Fd. The light- emission changes as a result of interaction of the light-emissive compound with the sample product. The emission filters may be used to filter undesired wavelengths of light emitting from the sample and the light-emissive compounds such that, for example, only peak wavelengths of light are passed through. The light is then directed to the optical detector, which generates a voltage level indicative of the amount of light emitted.

It is also to be appreciated that the intensity or quantity of light-emission from the sample is detected. However, according to one aspect of the invention, intensity, decay or change in the quantity of light-emission over time may be used to provide the sample characteristic. Alternatively, any such combinations may be used to provide the sample characteristic. Thus, "light-emission" or "light-absorption" means intensity or quantity or intensity, decay or change in quantity of light emitted and/ or absorbed from the sample. Rather than, or in addition to, comparing certain spectral properties, such as light emission and/or absorption from the light-sensitive compound to a stored fingerprint, in some instances it may be desirable to compare a ratio of light emission and/or absorption of two different wavelengths of light to a stored ratio fingerprint. This may be accomplished by providing a light-sensitive compound that is capable of emitting and/or absorbing at two different peak wavelengths of light or, alternatively, providing two or more different light- sensitive compounds, each producing a characteristic peak wavelength having a certain light emission and/or absorption. For example, two light-sensitive compounds are applied to the substrate. An excitation wavelength is applied such that the first light-sensitive compound may have a relative fluorescence unit (RFU) of 98 at a peak wavelength (λl) of 575 μm and the second light-sensitive compound has an RFU of 76 at a peak wavelength (λ2) of 525 μm. The ratio of the RFU values at the peak wavelengths 575 to 525 is approximately 1.3. This ratio of 1.3 may then be used in comparison to the stored fingerprint ratio. Although relative fluorescence units are used in this example to indicate the value of the amount of light emitted, other units may be used, such a photon count, for example. It is to be appreciated that the sampling rate of the device may include about 10,000 readings. Thus, a high degree of confidence may be obtained in providing the sample characteristics.

With such a large amount of data generated, although possible, conventional data analysis comparing one or two variables at a time, is not practical. Thus, according to one aspect of the invention, multivariable analysis or multivariable pattern recognition may be used. In a preferred embodiment, Tukey's analysis and Principle Component Analysis (PCA) are used. Other multivariable techniques that may be utilized include Hierarchical Cluster Analysis, K Nearest Neighbor, Pineapple Component Regression, Partial Least Squares Regression, and Soft Independent Modeling of Class Analogy (SIMCA). These multivariable techniques reduce the dimensionality of the data to two or three dimensions, allowing the pattern or relationships to be generated.

Analysis of the data may also be performed by developing plots having distinct clusters summarizing the similarity and differences among the samples being analyzed to a stored standard. Such analysis may be performed in addition to or in the alternative to the above-mentioned multivariable or multivariable pattern recognition.

We claim:

Claims

Claims

1. A method of preparing a stabilized light-sensitive compound, the method comprising: combining a light-sensitive compound with an isolating material to form a liquid mixture; depositing a volume of the liquid mixture onto a surface of a solid base; and, drying the deposited liquid mixture to form a stabilized light-sensitive compound on the solid base whereby the isolating material acts to isolate the light-sensitive compound from adverse environmental effects and to control the rate of hydration of the light-sensitive compound.

2. The method of claim 1 , wherein drying the deposited liquid mixture comprises forming a film of stabilized light-sensitive compound.

3. The method of claim 1, wherein combining a light-sensitive compound with an isolating material comprises combining the light-sensitive compound with one of a polymer, a carbohydrate, a hydrocolloid, or a combination of two or more thereof.

4. The method of claim 3, wherein combining a light-sensitive compound with an isolating material comprises combining the light-sensitive compound with one of a water soluble methylcellulose, a water soluble hydroxypropyl methylcellulose, a polymer of one or more thereof, or a combination of two or more thereof.

5. The method of claim 3, wherein combining a light-sensitive compound with an isolating material comprises combining the light-sensitive compound with one of sucrose, fructose, galactose, starch, or a combination of two or more thereof.

6. The method of claim 1 , wherein combining a light-sensitive compound with an isolating material comprises combining the light-sensitive compound with the isolating material such that the isolating material represents between 0.05% and 5% weight/weight of the liquid mixture.

7. The method of claim 1, wherein combining a light-sensitive compound with an isolating material comprises producing a ratio of isolating material to light-sensitive material in the liquid mixture of greater than 1 :1.

8. The method of claim 1, wherein combining a light-sensitive compound with an isolating material comprises combining a dye with the isolating material.

9. The method of claim 8, wherein combining a dye with the isolating material comprises combining a fluorescent dye with the isolating material.

10. The method of claim 1 , wherein combining a light-sensitive compound with an isolating material comprises mixing two or more light-sensitive compounds with the isolating material.

11. The method of claim 1, wherein depositing a volume of the liquid mixture onto a surface of a solid base comprises depositing the volume of the liquid mixture into a well on the solid base.

12. The method of claim 1, wherein depositing a volume of the liquid mixture onto a surface of a solid base comprises depositing the volume of the liquid mixture into a well of a multi-well plate.

13. The method of claim 1 , wherein depositing a volume of the liquid mixture onto a surface of a solid base comprises depositing the volume of liquid mixture onto a test area on the solid base.

14. The method of claim 1, wherein depositing a volume of the liquid mixture onto a surface of a solid base comprises depositing the volume of the liquid mixture onto a test strip surface.

15. The method of claim 1, wherein depositing a volume of the liquid mixture onto a surface of a solid base comprises depositing the volume of the liquid mixture onto an etched surface.

16. The method of claim 1, wherein depositing a volume of the liquid mixture onto a surface of a solid base comprises depositing the volume of the liquid mixture onto a porous substrate.

17. A method of preparing a stabilized light-sensitive compound, the method comprising: combining a light-sensitive compound with an isolating material to form a liquid mixture; and depositing a volume of the liquid mixture onto a surface of a solid base, wherein the deposited liquid mixture forms a gel on the solid base, thereby producing a stabilized light-sensitive compound on the solid base.

18. The method of claim 17, further comprising drying the gel on the surface of the solid base.

19. A method of preparing a stabilized light-sensitive compound, the method comprising: depositing two or more layers of material onto a surface of a solid base, wherein at least one of the two layers comprises a light-sensitive compound in association with an isolating material.

20. The method of claim 19, wherein depositing two or more layers of material onto a surface of a solid base comprises depositing 2-10 layers of material onto the solid base.

21. The method of claim 20, wherein depositing 2-10 layers of material onto the surface of the solid base comprises depositing about 5 layers of material onto the solid base.

22. The method of claim 19, wherein depositing two or more layers of material onto a surface of a solid base comprises depositing a first layer comprising a first material and depositing a second layer comprising a second material that is different from the first material each layer comprises a different material.

23. An apparatus comprising: a solid base having a surface; and a film of stabilized light-sensitive compound disposed on the surface, the film comprising a light-sensitive compound and an isolating material acting to isolate the light- sensitive compound from adverse environmental effects.

24. The apparatus of claim 23, wherein the solid base comprises a plate having multiple wells, each well having a surface, and wherein the film is disposed on the surface of the well.

25. The apparatus of claim 23, wherein the solid base comprises a packaging material and wherein the film is disposed on the packaging material.

26. The apparatus of claim 23, wherein the film comprises two or more layers of material.

24. A stabilized light-sensitive compound preparation comprising: a solid base having a surface; a matrix of isolating material disposed on the surface of the solid base; and a substantially uniform dispersion of a light-sensitive compound within the matrix of isolating material.

25. The preparation of claim 24, wherein the matrix is a gel.

26. The preparation of claim 24, wherein the light-sensitive compound and isolating material form a film on the surface of the solid base.

27. A method of characterizing a liquid sample, the method comprising: adding a liquid sample to a stabilized light-sensitive compound prepared according to a method of any one of claims 1-22; and, obtaining a characteristic signal of the liquid sample by detecting a signal from the light-sensitive compound in contact with the liquid sample.

28. The method of claim 27, wherein the liquid sample is added in a volume of between about 0.1 μl and about 5 ml.

29. The method of claim 28, wherein the volume is about 0.5 ml.

30. The method of claim 27, wherein the characteristic signal of the liquid sample is compared to a reference sample to determine whether the liquid sample is authentic.

31. The method of claim 27, wherein the characteristic signal of the liquid sample is compared to a reference sample to determine whether the liquid sample is fresh.

32. The method of claim 27, wherein the characteristic signal of the liquid sample is compared to a reference sample to determine the origin of the liquid sample.

33. The method of claim 27, wherein the liquid sample is a sample of a commercial liquid product.

34. The method of claim 27, wherein the liquid sample was obtained by incubating a liquid solvent with a solid sample.

35. The method of claim 27, wherein the liquid sample is a diluted product sample.

36. The method of claim 27, wherein the liquid sample is a treated product sample.

37. The method of claim 27, wherein the product sample was treated to remove one or more coloring agents.

38. The method of claim 27, wherein the assay comprises a colorimetric detection step.

39. The method of claim 27, wherein the assay comprises a fluorescence detection step.

40. The method of claim 27, wherein the isolating material dissolves upon addition of the liquid sample.

41. The method of claim 27, wherein the isolating material swells upon addition of the liquid sample.

42. The method of claim 27, wherein the isolating material forms a colloidal liquid upon addition of the liquid sample.

43. A method of characterizing a liquid sample, the method comprising: adding a liquid sample to the apparatus of any one of claims 23-26; and, obtaining a characteristic signal of the liquid sample by detecting a signal from the light-sensitive compound in contact with the liquid sample.

44. A kit for assaying a liquid sample, the kit comprising a stabilized light-sensitive compound prepared according to any one of methods 1-22.

45. The kit of claim 44, wherein the isolating material is permeable to a liquid sample.

46. The kit of claim 44, wherein the isolating material is miscible with a liquid sample.

47. The kit of claim 44, wherein the isolating material is soluble in a liquid sample.

48. The kit of claim 44, wherein the isolating material entrains the light-sensitive compound.

49. The kit of claim 44, wherein the solid base is a multi-well plate comprising two or more wells, each well comprising a first stabilized light-sensitive compound.

50. The kit of claim 49, further comprising one or more wells with a second stabilized light-sensitive compound.

51. The kit of claim 49, further comprising one or more control wells.

52. The kit of claim 49, further comprising one or more reference wells.

53. The kit of claim 44, wherein the surface is the surface of a test strip.

54. The kit of claim 44, wherein the light-sensitive compound is cross-linked to the isolating material.

55. The kit of claim 44, wherein the light-sensitive material is retained within a cross- linked matrix of isolating material.

56. The kit of claim 44, further comprising two or more different layers of isolating material.

57. The kit of claim 56, wherein the light-sensitive compound is present in at least one of the layers of isolating material.

58. The kit of claim 56, wherein two or more layers of isolating material have at least one of different hydration rates, porosities, buffering properties, or any combination thereof.

59. The kit of claim 44, wherein the isolating material is opaque.

60. The kit of claim 44, wherein the isolating material is transparent.

61. The kit of claim 44, further comprising a humectant.

62. The kit of claim 44, further comprising a buffering layer.

63. The kit of claim 44, further comprising a capping layer.

64. A method of characterizing a liquid sample, the method comprising: adding a liquid sample to a stabilized light-sensitive compound that comprises an isolating material associated with a light-sensitive compound on a surface of a solid base; allowing the liquid sample to react with the isolating material and the light-sensitive compound for an incubation period that is less than about 20 minutes, thereby obtaining a mixture of the liquid sample and the light-sensitive compound; assaying the mixture to obtain a light signal that is a characteristic signal of the liquid sample.

65. The method of claim 64, wherein allowing the liquid sample to react with the isolating material and the light-sensitive compound for an incubation period that is less than about 20 minutes comprises allowing the liquid sample to react with the isolating material and the light-sensitive compound for an incubation period that is less than about 10 minutes.

66. The method of claim 65, wherein allowing the liquid sample to react with the isolating material and the light-sensitive compound for an incubation period that is less than about 20 minutes comprises allowing the liquid sample to react with the isolating material and the light-sensitive compound for an incubation period that is less than about 5 minutes.

67. The method of claim 66, wherein allowing the liquid sample to react with the isolating material and the light-sensitive compound for an incubation period that is less than about 20 minutes comprises allowing the liquid sample to react with the isolating material and the light-sensitive compound for an incubation period that is less than about 2 minutes.

68. The method of claim 64, wherein allowing the liquid sample to react with the isolating material and the light-sensitive compound for an incubation period that is less than about 20 minutes comprises allowing the liquid sample to react with the isolating material and the light-sensitive compound for an incubation period that is sufficient to obtain a stable mixture of the liquid sample and the light-sensitive compound.

69. The method of claim 64, further comprising physically mixing the liquid sample with the stabilized light-sensitive compound during the incubation period.

70. The method of claim 69, wherein physical mixing comprises shaking.

71. The method of claim 64, wherein allowing the liquid sample to react with the isolating material and the light-sensitive compound for an incubation period causes the liquid sample to dissolve the isolating material.

72. The method of claim 64, wherein allowing the liquid sample to react with the isolating material and the light-sensitive compound for an incubation period causes the liquid sample to penetrate the isolating material and re-hydrates the light-sensitive compound.

73. The method of claim 64, wherein allowing the liquid sample to react with the isolating material and the light-sensitive compound for an incubation period releases the light-sensitive compound from the isolating material and disperses the light-sensitive compound in the liquid sample.