Colorimetric sensor for oxygen and use thereof

Abstract

The present invention relates to a non-toxic luminescence-based colorimetric sensor and a method of using the sensor in food contact and similar applications. The luminescence-based sensor can be used to assess oxygen concentration, in particular in a controlled oxygen atmosphere such as in food packaging.

Description

Technical Field

[0001] This invention relates to a non-toxic, light-emitting colorimetric sensor and a method for using the sensor in food packaging and other applications. The sensor can be used to assess oxygen concentration, particularly in controlled oxygen atmospheres such as those found in food packaging.

[0002] background In recent years, the use of protective atmosphere packaging has increased significantly due to a number of factors, including stringent food safety requirements, increased demand for fresh products, imports of non-local and non-seasonal foodstuffs, and the push toward reducing food waste and associated CO2 and CO2 equivalent emissions.

[0003] Protective atmosphere packaging typically includes gas-free packaging (i.e., vacuum packaging) and modified atmosphere packaging (MAP). A gas-free environment is created by removing all air from the packaging under vacuum, thus eliminating oxygen. A gas-free environment is beneficial for packaging products that are prone to oxidative degradation, including electronic components, pharmaceuticals, and food. MAP is generated by altering the normal gas composition of the air inside the packaging (78% nitrogen, 21% oxygen, 1% trace gases). These processes provide an atmosphere that inhibits major food spoilage processes, thereby extending the product's shelf life and improving food quality and safety.

[0004] Oxygen (O2) and carbon dioxide (CO2) are the most commonly used gases for modified atmospheres (MAPs). Typically, modified atmospheres are tailored to the product to be packaged, with fruits and vegetables, as well as cooked meats, usually stored in low-oxygen atmospheres (0%–20%), and raw red meat and poultry products typically stored in higher-oxygen atmospheres (20%–80%). The partial pressures (pCO2, pO2) of these gases within the top space of the package can fluctuate over time and are affected by factors such as product type, microbial activity, storage conditions, packaging materials, and integrity. Since any leakage or damage to the packaging will result in the loss of the modified atmosphere and its return to ambient air conditions, and improper gas flushing can lead to an incorrect atmosphere within the package, the composition of the gases in the top space of the package, and particularly the O2 concentration, can provide a useful indicator of packaging integrity, the reliability of gas flushing, and the freshness and safety of the packaged food.

[0005] Thin-film oxygen sensors for assessing oxygen in food packaging are known. In these known sensors, the sensor response is typically based on changes in optical properties such as absorbance or luminescence as a function of oxygen concentration. Luminescence-based sensors can be particularly advantageous because they provide a non-destructive means of quantitative detection. Incorporating these sensors into the supply chain can allow for the removal of individually damaged or spoiled goods from the supply chain without disposing of the entire batch, thus preserving any remaining fresh and safe-to-eat product. On a commercial scale, this can lead to increased efficiency and a significant reduction in food waste and food waste packaging.

[0006] However, for sensors to monitor real-time conditions in enclosed environments such as modified atmosphere packaging (MAP), the sensor must be in direct contact with the atmosphere; that is, it needs to be positioned within the top space of the packaging and in direct contact with the food or other ingestible product that the MAP is designed to preserve. This is problematic because known lumophores tend to exhibit a variety of toxicities, including organ toxicity, cytotoxicity, and / or genotoxicity, and are therefore inherently unsuitable for applications involving direct contact with food or other ingestible products. Rigorous testing of proposed food contact materials is also required before legislative approval for their use can be cumbersome in terms of time and cost. This is especially true if a multi-component system is being developed, requiring comprehensive testing of each individual component before market approval. These factors, among others, have to date limited the widespread adoption of lumophore-based sensors in modified atmosphere packaging for food or other ingestible products such as pharmaceuticals and veterinary drugs.

[0007] The objective of this invention is to avoid or reduce one or more of the disadvantages associated with the prior art. Ideally, it would be advantageous to provide a non-toxic colorimetric oxygen sensor that can be positioned in use to come into direct contact with food and / or other ingestible products, for example, in the top space of modified atmosphere packaging. An adjustable colorimetric sensor capable of transmitting color changes within a relevant oxygen concentration range, such as the oxygen levels required for preserving specific food articles like meat or vegetables in modified atmosphere packaging, would be particularly advantageous. Invention Overview According to the present invention, a colorimetric oxygen sensor is provided, comprising a first luminescent element and a second luminescent element, each luminescent element being dispersed in a polymer matrix, wherein the first luminescent element is selected from ruthenium (II) 4,7-diphenyl-1,10'-phenanthroline [Ru(dpp)3]. 2+; octaethylporphyrin (PtOEP); 5,10,15,20-tetrakis(2,3,4,5,6-pentafluorophenyl)porphyrin (PtTFPP) and meso-tetraphenylporphyrin (PtTPP); and the second luminescent body is a naturally occurring compound or its synthetic analogue selected from diarylheptanoids, flavonols, carotenoids, coenzymes, minor flavonoids, or the naturally occurring compound or its synthetic analogue is paeonol or ellagic acid.

[0009] The inventors have advantageously discovered that certain naturally occurring compounds possess surprising utility in luminescent oxygen sensors. While some naturally occurring compounds are known to exhibit fluorescence, these compounds typically exhibit low color intensity and fastness, as well as poor emission brightness. Therefore, their inherent fluorescence properties are generally considered disadvantageous and tend to make detection and analysis more difficult, rather than less difficult. This is due to a number of factors, including low levels of fluorescence, which makes the independent use of fluorescence properties impractical; the presence of numerous competing analytes in the whole food in which they may be present; and interference from food-derived autofluorescence with external detection systems. Furthermore, these naturally occurring compounds typically exhibit poor photostability and / or poor chemical stability. These properties mean that naturally occurring products, such as diarylheptane compounds, flavonols, carotenoids, coenzymes, minor flavonoids, and other compounds described herein, have not previously been incorporated into luminescent sensors and would generally be considered entirely unsuitable for use in commercial sensor applications.

[0010] In another aspect of the invention, a method for determining the oxygen content of an atmosphere is provided, the method comprising exposing a colorimetric sensor described above to the atmosphere; applying a UV excitation source or a UV-visible light excitation source to the sensor; and observing the color of the sensor.

[0011] The atmosphere can be a food packaging atmosphere. Advantageously, the sensor of the present invention is suitable for direct contact with food and other ingestible products, such as direct contact within the headspace of a MAP, due to its natural and non-toxic properties. Alternatively, the atmosphere can be any environment in which a vacuum or controlled oxygen concentration is preferred; such as in the packaging of pharmaceutical or veterinary products, disposable medical products, or electronic components; or in the packaging or storage of preservation / protection areas (e.g., works of art or antiques).

[0012] This article also describes laminates and labels including printed colorimetric oxygen sensors, and the uses of such laminates and labels in packaging applications.

[0013] Several additional features and aspects of the invention are defined in the claims. Brief description of the attached diagram Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, wherein the same parts are provided with corresponding reference numerals, and in the drawings: Figure 1 The oxygen sensors shown are (a) PtOEP:curcumin (1:3.0) and (b) [Ru(dpp)3]. 2+ Curcumin (1:2.8) and (c) [Ru(dpp)3] 2+ Color response of curcumin (1:7.5).

[0015] Detailed Explanation This invention relates to a colorimetric oxygen sensor comprising a first luminescent element and a second luminescent element, each luminescent element being dispersed in a polymer matrix, wherein the first luminescent element is selected from 4,7-diphenyl-1,10'-phenanthroline ruthenium(II)[Ru(dpp)3]. 2+ ; Octaethylporphyrin platinum (PtOEP); 5,10,15,20-tetra(2,3,4,5,6-pentafluorophenyl)porphyrin platinum (PtTFPP) and meso-tetraphenylporphyrin platinum (PtTPP); and the second luminescent body is a naturally occurring compound selected from diarylheptane compounds, flavonols, carotenoids selected from bixin, capsanthin and capsorubin, coenzymes, minor flavonoids; or the naturally occurring compound is paeonol or ellagic acid.

[0016] Throughout this specification, the terms "lumophore" and "luminophore" are used synonymously, referring to the radiative relaxation (radiative energy release) from a higher energy electronically excited state (unstable) to its lowest energy ground state (stable). LightColorimetric sensors are chemical substances that emit light spontaneously. When a light-emitting body absorbs radiation, it forms a higher-energy electronic state. The energy of this radiation is usually, but not always, greater than the energy of the light subsequently emitted. Colorimetric sensors are oxygen-sensitive, meaning they exhibit observable color changes in response to changes in the oxygen concentration of the atmosphere or local environment in which they are exposed.

[0017] Colorimetric sensors are based on light emission. Color changes are caused by the preferential quenching of light emitted by at least one light-emitting element in the sensor. Color changes are only visible to the naked eye when the sensor is exposed to UV or UV-visible light. This can be advantageous in monitoring consumer products because, if preferred, the sensor can be concealed from general visibility.

[0018] The colorimetric sensor is an oxygen sensor. Throughout this specification, "oxygen sensor" is intended to refer to a single-parameter sensor that is sensitive to oxygen as an analyte.

[0019] In the colorimetric sensor of the present invention, each of at least two luminescent elements is dispersed in a polymer matrix. The at least two luminescent elements may be dispersed in the same polymer. In this embodiment, the sensor comprises a single luminescent element layer. Alternatively, the at least two luminescent elements may be dispersed in different polymers. In this embodiment, the sensor comprises two luminescent element layers.

[0020] Throughout this specification, the term "naturally occurring" is used to mean a compound or its synthetic analogues that can be found or isolated from nature. This term covers compounds derived from nature, as well as those identical compounds prepared synthetically. As will be apparent to those skilled in the art, any synthetic analogues of naturally occurring products will need to have food-grade purity.

[0021] In some embodiments, the naturally occurring compound is of natural origin, i.e., it has been extracted or isolated from nature. Examples of naturally occurring compounds include, for example, curcumin, capsanthin, capsanthin, annatto, and safflower extract. As those skilled in the art will understand, when the naturally occurring compound is a naturally occurring extract, such as safflower extract, the extract may contain, in addition to the major component, a minor component of the extract (e.g., for safflower, the major component is hydroxysafflower yellow A / (6E)-2,5-dihydroxy-6-[(E)-1-hydroxy-3-(4-hydroxyphenyl)prop-2-eneyl]-2,4-bis[(2S,3R,4R,5S,6R)-3,4,5-trihydroxy-6-(hydroxymethyl)oxacyclohexane-2-yl]cyclohex-4-en-1,3-dione), which is used as a luminescent agent in the sensor. For natural curcumin extracts, demethoxycurcumin (13%-20%) and didemethoxycurcumin (1%-4%) can coexist in the extract along with curcumin, which serves as a secondary luminescent agent. When the extract is a carotenoid extract from capsicum, both capsanthin and capsanthin can be present, and both can serve as secondary luminescent agents.

[0022] Alternatively, the second luminescent body may be a synthetic analogue of a naturally occurring compound, such as synthetic curcumin (typically 98+% pure).

[0023] The first luminescent body is an oxygen-sensitive luminescent body, meaning its emission is quenched in the presence of oxygen. The emission of the first luminescent body is generally insensitive to pH and temperature.

[0024] According to the present invention, the first luminescent material is 4,7-diphenyl-1,10'-phenanthroline ruthenium(II)[Ru(dpp)3] 2+ (Also known as ruthenium tri(II)4,7-diphenyl-1,10'-phenanthroline [Ru(dpp)3]) 2+ ); octaethylporphyrin platinum (PtOEP); 5,10,15,20-tetra(2,3,4,5,6-pentafluorophenyl)porphyrin platinum (PtTFPP); or meso-tetraphenylporphyrin platinum (PtTPP). These luminescent substances are non-toxic, and 4,7-diphenyl-1,10'-phenanthroline ruthenium(II)[Ru(dpp)3] is known. 2+ 5,10,15,20-tetra(2,3,4,5,6-pentafluorophenyl)porphyrin platinum (PtTFPP) complies with EU regulations for use in food packaging applications.

[0025] The second luminescent body is oxygen-insensitive, meaning its emission is not significantly quenched in the presence of oxygen. The second luminescent body typically absorbs UV and / or UV-visible light in substantially the same spectral region as the first luminescent body. This is advantageous because it allows the use of a single excitation source. However, if the first and second luminescent bodies do not absorb in substantially the same spectral region, multiple excitation sources can be used. The second luminescent body emits in substantially a different spectral region than the first luminescent body. 'Substantially' means that the maximum emission of each luminescent body should differ by at least ~20 nm to allow for the observation of color changes. The emission of the second luminescent body in the sensor is also generally insensitive to pH and temperature.

[0026] According to the present invention, the second luminescent body is a naturally occurring compound selected from diarylheptane compounds, flavonols, carotenoids, coenzymes or minor flavonoids, or the second luminescent body is paeonol or ellagic acid.

[0027] To date, naturally occurring compounds have not been widely used in commercially available luminescent sensors due to a combination of factors including low levels of fluorescence, poor photostability, and poor formulation properties. However, the inventors have demonstrated that some naturally occurring luminescent materials are surprisingly effective in colorimetric oxygen sensors, allowing their use in many oxygen sensor applications where non-toxicity is critical. Advantageously, since these naturally occurring compounds are approved for other food safety applications in most cases, such as, for example, as food coloring agents (e.g., curcumin, annatto, and FMN), the luminescent materials can be commercially used in food-related applications without undergoing significant toxicity testing. This paves the way for the widespread commercial adoption of the colorimetric sensors of this invention.

[0028] In the colorimetric sensor of the present invention, each luminescent element is directly dispersed in a polymer matrix, and the luminescent element is not encapsulated or otherwise embedded (e.g., in a gel) before being dispersed in the polymer matrix. The luminescent element is not incorporated into the surface of the microspheres. The luminescent element is not incorporated into the mesoporous structure. At any point during the formation of the polymer matrix, the luminescent element is not incorporated into the microspheres. For example, when incorporated into a sensor label or laminate, the luminescent element may be dispersed in a single luminescent element-polymer layer, or it may be dispersed individually in separate, continuous polymer layers. Therefore, the sensor can be a monolayer or multilayer structure, depending on the dispersion of the luminescent element. When the sensor comprises multiple layers, these layers preferably have the same thickness.

[0029] Due to the preferential and quantitative reduction (quenching) of luminescence in oxygen-sensitive luminescent materials, the sensor changes color in response to changes in the oxygen concentration in the atmosphere or local environment to which it is exposed. Advantageously, the color change is reversible, allowing it to proceed both forwards and backwards along the response range with increases or decreases in local oxygen concentration. This provides broad applicability for the commercial application of oxygen sensors.

[0030] The emission of each luminescent element is typically insensitive to pH and temperature, allowing the sensor to be applied directly to a wide variety of environments and ensuring that colorimetric changes are directly attributable to changes in oxygen concentration.

[0031] The second luminescent material in the sensor is a naturally occurring compound selected from diarylheptane compounds, carotenoids, coenzymes, flavonols, minor flavonoids, or paeonol or ellagic acid.

[0032] The term "diarylheptane compound" refers to a polyphenol consisting of two aromatic rings linked by a C7 chain, and the polyphenol may have various substituents. Diarylheptane compounds can be linear (curcuminoid) or cyclic. Suitable diarylheptane compounds for use in this invention include curcumin.

[0033] The term "carotenoid" refers to tetraterpenes that are formally derived from the acyclic parent compound Ψ,Ψ-carotene I through hydrogenation, dehydrogenation, cyclization, oxidation, or a combination of these processes. The term "carotenoid" includes carotenes, lutein, and certain compounds produced by skeletal rearrangement of I or by the loss of a portion of that structure. Suitable examples of carotenoids used in this invention include annatto, capsanthin, and capsanthin. Both capsanthin and capsanthin can be present in the same extract and can be used in combination as a secondary luminescent agent. Alternatively, they can be used independently, i.e., where only capsanthin or only capsanthin is used as a secondary luminescent agent.

[0034] The term "coenzyme" refers to an organic, non-protein compound that binds to an enzyme to catalyze a reaction, and in some embodiments, may be a vitamin. Suitable coenzymes according to the invention include riboflavin, nicotinamide adenine dinucleotide (NADH), flavin adenine dinucleotide (FAD), and flavin mononucleotide (FMN). Riboflavin, NADH, FAD, and FMN may be used in their acidic form or in their salt (sodium or disodium) form.

[0035] The term "flavonoid" refers to natural products derived from 2-phenylchromen-4-one (flavonoids). According to the invention, the second luminescent body can be a flavonol or a minor flavonoid. Flavonols are a class of flavonoids comprising a 3-hydroxyflavonoid backbone. Suitable examples of flavonols include quercetin, fisetin, kaempferol, myricetin, 3-hydroxyflavonoids, and morin. The term "minor flavonoid" refers to five minor classes of flavonoids: chalcone, aurone, dihydrochalcone, flavanone, and dihydroflavonol. Suitable examples of minor flavonoids used in the invention include safflower extract.

[0036] Other compounds used in this invention include phenol, paeonol, and polyphenolic ellagic acid.

[0037] According to an embodiment of the present invention, the second luminescent body is a naturally occurring compound selected from: Diarylheptane compounds, selected from curcumin; Carotenoids, selected from annatto, capsanthin and capsanthin; Coenzymes, selected from riboflavin, NADH, FAD, and FMN; Flavonols or minor flavonoids selected from quercetin, fisetin, kaempferol, myricetin, 3-hydroxyflavone, morin and safflower extract; Paeonol; and ellagic acid.

[0038] The use of these naturally occurring compounds in luminescent oxygen sensors is novel and offers significant advantages over existing technologies.

[0039] In the implementation scheme, the naturally occurring compound is a diarylheptane or a flavonol.

[0040] In the embodiments, the naturally occurring compounds are curcumin, quercetin, fisetin, kaempferol, myricetin, 3-hydroxyflavone, or morin. In particular, these compounds have demonstrated surprising utility in the luminescent oxygen sensors of the present invention, which exhibit good emission and brightness characteristics and visible color changes within the range of oxygen concentration of interest.

[0041] According to an embodiment of the invention, a colorimetric oxygen sensor as previously described is provided, wherein the sensor further comprises an antioxidant.

[0042] Advantageously, it has been demonstrated that adding antioxidants to the sensor of the present invention improves the photostability of the sensor. In embodiments, the antioxidants are carotenoids, phenolic compounds, or vitamins.

[0043] In some instances, the second luminescent agent itself can be an antioxidant compound that imparts photostability to the sensor. For example, annatto, capsanthin, and capsanthin are non-limiting examples of second luminescent agents that can be considered antioxidant compounds themselves. In this embodiment, an additional antioxidant may not be necessary; however, an antioxidant compound can still be added to the sensor to further improve photostability. In this case, the second luminescent agent and the antioxidant compound can be the same compound or they can be different compounds. In embodiments, the second luminescent agent and the antioxidant are different compounds. As a non-limiting example, fisetin can be used as the second luminescent agent, and annatto can be used as the antioxidant.

[0044] Antioxidants can be added to polymers along with one or more luminescent substances (lumophores or lumophores).

[0045] When adding antioxidants to a multilayer sensor, the antioxidants can be added to the polymer containing the second luminescent element.

[0046] In one embodiment, the molar ratio of the second luminescent material to the antioxidant compound is from 1:1 to 1:10, preferably from 1:1 to 1:5. In another embodiment, the molar ratio of the second luminescent material to the antioxidant compound is 1:2.

[0047] In the implementation scheme, the antioxidant may be selected from vitamins (vitamin A, vitamin C or vitamin E), carotenoids (lutein, beta-carotene, capsanthin, capsicumin, annatto, norostatin), flavonoids (quercetin, fisetin, morin, catechin, epicatechin, luteolin, baicalin) and / or phenolic acids (caffeic acid, vanillin, ferulic acid).

[0048] In the implementation plan, the antioxidant is annatto, quercetin, or vitamin E (DL-α-tocopherol).

[0049] In the implementation plan, the antioxidant is DL-α-tocopherol.

[0050] In embodiments of the invention, the second luminescent material may be complexed with aluminum, boron, or zinc. The inventors have advantageously discovered that when the second luminescent material is complexed with Al(III), B(III), or Zn(II), the photostability of the sensor formulation is surprisingly improved compared to using a second luminescent material in an uncoordinated state. Even more surprisingly, complexation has been shown to result in increased emission and enhanced oxygen sensitivity in the sensor formulation.

[0051] In the implementation scheme, quercetin, curcumin, fisetin, kaempferol, morin, safflower extract, ellagic acid, paeonol, riboflavin, FMN or FAD can be complexed with Al(III), B(III) or Zn(II).

[0052] In particular, quercetin, curcumin, fisetin, kaempferol, morin, safflower extract, ellagic acid, and paeonol show significant advantages when complexed with Al(III), B(III), or Zn(II).

[0053] In the implementation scheme, the second luminescent agent is curcumin, which is complexed with Al(III).

[0054] According to the present invention, each luminescent element in the colorimetric oxygen sensor is dispersed in a polymer matrix.

[0055] In the embodiments, the polymer is selected from polystyrene, polyvinyl, polyamide, polyurethane, acrylate, shellac, rosin, rosin ester, siloxane, cellulose and cellulose derivatives; and mixtures thereof.

[0056] One or more polymers may be, for example, polystyrene, siloxanes, or one or more cellulose-based polymers. Suitable siloxanes include polydimethylsiloxane (PDMS). Suitable cellulose-based polymers include, but are not limited to, ethyl cellulose (EC), cellulose acetate (CA), cellulose acetate propionate (CAP), cellulose acetate butyrate (CAB), nitrocellulose (NC), hydroxypropyl cellulose (HPC), hydroxypropyl methylcellulose (HPMC), or carboxymethyl cellulose (CMC).

[0057] In one embodiment, the first and second light emitters are dispersed in the same polymer, for example, in a single polymer layer. In other embodiments, the first and second light emitters are dispersed in different polymers, for example, in multiple consecutive polymer layers.

[0058] In the implementation scheme, one or more polymers are one or more of polystyrene, PDMS, EC, CAP or CAB, HPMC and HPC.

[0059] In embodiments of the present invention, the first light emitter is a red light emitter, and the second light emitter is a blue, green, or orange light emitter. However, as those skilled in the art will understand, the coordination of the second light emitter with Al(III), B(III), or Zn(II) can lead to a shift in both absorption and emission.

[0060] In the implementation scheme, the second luminescent agent is curcumin or fisetinone.

[0061] In the implementation scheme, the second luminescent body is already complexed, preferably with aluminum-complexed curcumin or fisetone.

[0062] Curcumin and fisetin are particularly useful for the sensors of the present invention due to factors such as their availability, relatively low cost and good photophysical properties.

[0063] In the embodiment, the first luminescent material is 4,7-diphenyl-1,10'-phenanthroline ruthenium(II)[Ru(dpp)3]. 2+ Or octaethylporphyrin platinum (PtOEP).

[0064] In the embodiment, the first luminescent material is 4,7-diphenyl-1,10'-phenanthroline ruthenium(II)[Ru(dpp)3]. 2+ Alternatively, octaethylporphyrin platinum (PtOEP) may be used, and the second luminescent agent is curcumin or fisetinone. Curcumin or fisetinone may be complexed. In an embodiment, curcumin or fisetinone is complexed with Al(III).

[0065] Complexation with Al(III) can lead to enhanced emission, enhanced color response, and stronger absorption. Advantageously, this means that a lower amount of the second emitting element is required to achieve a similar brightness output as its uncomplexed counterpart.

[0066] In the embodiment, the first luminescent material is 4,7-diphenyl-1,10'-phenanthroline ruthenium(II)[Ru(dpp)3]. 2+ Furthermore, the second luminescent substance is curcumin.

[0067] In the embodiment, the first luminescent material is 4,7-diphenyl-1,10'-phenanthroline ruthenium(II)[Ru(dpp)3]. 2+ Furthermore, the second luminescent body is fisetin.

[0068] In the implementation scheme, the molar ratio of light emitter 1 to light emitter 2 is from 1:1.9 to 1:10.

[0069] In the implementation scheme, the sensor comprises [Ru(dpp)3]. 2+ Curcumin and DL-α-tocopherol. Optionally, curcumin may be complexed, preferably complexed with Al(III). In this embodiment, the molar ratio of the components may be L1:L2:AO 1:2.8:5.6. The polymer may be EC, CAB, CAP, or polystyrene. Preferably, the polymer is EC. In this embodiment, the sensor is preferably formed of a monolayer comprising [Ru(dpp)3] dispersed in EC. 2+Curcumin (optionally complexed with Al(III)) and DL-α-tocopherol.

[0070] In an alternative implementation, the sensor comprises [Ru(dpp)3]. 2+ The polymer consists of fisetin and DL-α-tocopherol. Optionally, fisetin may be complexed, preferably complexed with Al(III). In this embodiment, the molar ratio of the components may be L1:L2:AO 1:3:6. The polymer may be EC, CAP, CAB, or polystyrene. Preferably, the polymer is EC. In this embodiment, the sensor is preferably formed of a monolayer comprising [Ru(dpp)3] dispersed in EC. 2+ Fissone (optionally complexed with Al(III)) and DL-α-tocopherol.

[0071] The colorimetric sensor includes a first luminescent element and a second luminescent element, each dispersed in a polymer matrix. One or more polymer matrices containing the luminescent elements are formulated to be printable onto a substrate. In one embodiment, the colorimetric oxygen sensor includes a first luminescent element and a second luminescent element, each dispersed in a polymer matrix, wherein the polymer matrix is ​​printed onto the substrate, or, in the case of using different polymers, the polymer matrices are continuously printed onto the substrate such that the polymer layers containing the luminescent elements are in direct contact. The substrate can be a polymer substrate, such as a PET, PE, or PP substrate.

[0072] Colorimetric sensors can be in the form of one or more inks, and particularly printable inks. In embodiments, the sensor consists of a single ink formulation in which the luminescent material is dispersed in a polymer, optionally together with printing additives. However, as will be clearly understood, in cases where the luminescent material is in a different polymer matrix, the sensor may comprise two ink formulations that are sequentially printed to form a continuous layer, i.e., where the two layers are in direct contact. Either or both inks may contain printing additives.

[0073] Throughout this specification, the term "ink" refers to a fluid or viscous substance that can be printed using suitable printing techniques. Suitable printing techniques include, for example, inkjet printing such as piezoelectric-based inkjet or thermal inkjet, flexographic printing, gravure printing, offset lithography, screen printing, and letterpress printing. In embodiments, printing is performed by inkjet printing, flexographic printing, or gravure printing.

[0074] The ink may consist of a first luminescent body and / or a second luminescent body dispersed in a polymer matrix, optionally together with any solvent used in the preparation process. Alternatively, the ink may contain additional luminescent bodies and / or additional components. Thus, the polymer acts as a binder, and any solvent acts as a medium for the luminescent body to facilitate printing.

[0075] Ink formulations may additionally contain one or more printing additives. Such additives include, for example, rheology modifiers, dispersants, wetting agents, plasticizers, etc., as are well known to those skilled in the art.

[0076] The rheological properties of inks can be controlled to ensure compatibility with the printing process used, enabling high-throughput printing and minimizing ink bleeding, and in the case of inkjet printing, minimizing nozzle clogging. For flexographic and gravure printing, ink viscosity is typically controlled in the range of 20 mPa·s–70 mPa·s, while for inkjet printing, it is typically controlled in the range of 2 mPa·s–10 mPa·s. In the latter case, additional properties of the ink formulation can be controlled to obtain a formulation with ideal droplet formation, continuous jetting, and to prevent nozzle clogging and “skinning” effects, which lead to poor printing quality and / or jetting interruptions. The rheological properties of inks are important for achieving good printing quality using flexographic or gravure printing. Furthermore, proper selection of the printing plate design, anilox roller, material (flexographic printing), and / or cylinder unit geometry and depth (gravure printing) ensures optimal ink transfer to the substrate. Finally, regardless of the printing technology, the surface tension of the ink should be lower than the surface energy of the substrate to allow for good wetting. These properties can be easily optimized by those skilled in the art.

[0077] The present invention also relates to a method for determining the oxygen content of an atmosphere. The method includes the steps of: exposing the colorimetric sensor described above to the atmosphere; applying a UV excitation source or a UV-visible light excitation source to the sensor; and observing the color of the sensor. The step of exposing the colorimetric sensor to the atmosphere may include positioning the sensor within a modified atmosphere package. Advantageously, due to the non-toxic nature of the sensor, embodiments of the invention include positioning the sensor in a location where it can come into direct contact with food or other ingestible products, such as, for example, on the inner surface of food packaging.

[0078] As technicians typically understand it, the UV region is from 190 nm to 400 nm, and the visible light region is from 400 nm to 700 nm.

[0079] In the implementation scheme, the excitation wavelength ranges from 340 nm to 465 nm.

[0080] The process of observing the color of a sensor can be performed by the naked eye, by using spectroscopy, or by using digital imaging equipment / machine vision systems.

[0081] Advantageously, the color change is only visible to the naked eye after a UV / UV-visible light source is applied to the sensor. This means the sensor can be concealed, for example, inside food packaging, which could be beneficial when supplying consumer products. The non-toxic nature of the sensor makes it particularly suitable for such applications, as it can be concealed within the top space of modified atmosphere packaging.

[0082] Another advantage is that the color change occurs very quickly, typically within milliseconds of exposure to the MAP. This allows the sensor to be used for real-time monitoring.

[0083] The color of the sensor when exposed to the atmosphere can be compared to a reference color to determine the oxygen content. For example, the color of the sensor can be observed visually and compared to a reference color, color chart, or color indicator for the specific sensor used, which can provide a rapid, semi-quantitative result regarding the oxygen concentration in the atmosphere. Alternatively, a camera can be used to observe and compare with a calibration curve to obtain a fully quantitative result. Therefore, in this embodiment, the method also includes comparing the color of the sensor to a reference color to assess the oxygen content. Advantageously, the sensor can be customized for the specific atmosphere being monitored, wherein [Ru(dpp)3] 2+ Curcumin-Al(III) and [Ru(dpp)3] 2+ Both fisetin and fisetin are suitable for atmospheres with high oxygen concentrations (e.g., atmospheres commonly used for packaging raw red meat and poultry).

[0084] Alternatively, fluorescence spectroscopy can be used to achieve complete quantitative analysis.

[0085] The present invention also relates to an automated method for assessing the oxygen concentration of an atmosphere using the sensors described above. For example, in an embodiment of the invention, a camera can be used to acquire a digital image of the color signature of the sensor. The digital image can then be processed, and the color is converted into a numerical value, which can be automatically correlated with a pre-measured calibration curve to produce an oxygen content value. The software can be designed to locate the sensor (e.g., in the packaging of a product or in the top space of a food package) and identify and eliminate optical variations (e.g., reflections, scattering, etc.) in the image and attribute them to the oxygen percentage before processing the image with an empirical calibration file for a particular combination of sensors. This method enables real-time, non-destructive, high-throughput, and remote analysis of multiple samples (e.g., each packaged product on a manufacturing line). The oxygen percentage determined according to this method can then be used to eliminate packaging that falls outside specified specifications. For example, a linked rejection mechanism can be incorporated into the manufacturing / packaging production line, which can remove such eliminated packaging from the production line, thereby preventing these products from moving down the supply chain. This has significant advantages in reducing food waste and food waste packaging because it can isolate and remove individually damaged or spoiled food from the supply chain without removing the unspoiled or undamaged remainder of the batch.

[0086] Advantageously, the sensor of the present invention allows for visual observation of color changes in many cases, i.e., color changes are visible to the naked eye after exposure to UV / UV-visible light. This eliminates the need for expensive external inspection equipment (such as spectrometers) and also allows for inspection by laypeople (i.e., no specific technical skills are required). Another advantage is that inspection can be performed using standard vision systems. In many cases, these already exist in the production line, for example, for label inspection, damage inspection, product color, etc., thus avoiding the need to install expensive inspection systems in these situations. Quantitative determination can be made by comparing the color with a database of calibration curves or color charts specific to the pair of luminescent elements used (or lumophore trio, etc.). The use of a camera and the comparison of color changes with calibration curves provide a sensitive method that allows for the determination of even small changes in oxygen concentration. This can be particularly useful for monitoring oxygen concentration in modified atmosphere packaging, where, as an example, the difference between 70% and 80% oxygen can be crucial in determining whether packaged food articles are compliant or non-compliant with specifications regarding their headspace gas mixture.

[0087] However, if needed, color changes can be monitored via spectroscopy and fully quantitative analysis can be performed. Embodiments of the invention also relate to electronic means for detecting color changes, i.e., by using software that can be coded into an "app" and can detect the color of the atmosphere and compare it with a pre-programmed database to produce results regarding the freshness or safety or packaging integrity of the packaged goods. Such results can be binary (i.e., fresh = yes / no; safe = yes / no), or they can be quantitative values ​​indicating the degree of freshness of the packaged product (e.g., instructing sellers to "maintain normal inventory," "reduce product prices," "discard product," etc.).

[0088] In the implementation plan, the atmosphere is the food packaging atmosphere.

[0089] As indicated above, the sensor of the present invention is particularly suitable for use in the context of food packaging atmospheres and is ideally suited for packaging food and other ingestible products due to its non-toxic properties. However, the invention is not particularly limited thereto, and it can find applicability in other areas of monitoring oxygen concentration, such as in pharmaceutical storage, packaging of disposable sterile medical products, preservation of works of art and cultural artifacts, or packaging of electronic components. For all these applications, an anaerobic or controlled oxygen environment (i.e., 0% O2) may be advantageous. Furthermore, the luminescent colorimetric sensor of the present invention can find application in monitoring gas supply products, such as premixed gas cylinders in which a controlled oxygen concentration (~0%-100%) is required.

[0090] As mentioned above, the colorimetric sensor can be tailored to the application of interest; that is, by controlling the selection of luminescent elements and their molar ratio, a colorimetric response can be obtained within a range of O2 concentrations of interest. In implementations, the colorimetric sensor is configured to provide color changes within an O2 concentration range of 0%–20% (suitable for fruits, vegetables, and oxygen-sensitive foods such as cooked meats, nuts, fish, and cheeses) or 20%–80% (suitable for meat products and other foods requiring high O2 MAP). Other defined concentration ranges can be customized based on the application of interest.

[0091] This paper also envisions a method for preparing a laminated film or label containing a colorimetric oxygen sensor, the method comprising printing the sensor onto a substrate film. The sensor can be printed as ink in a single layer, or as ink in two or more consecutive layers. The substrate film can be a polymer substrate film. Lamination can be performed by thermal means, by using an adhesive, or by a combination thereof.

[0092] The substrate film itself can be a laminated film and may comprise more than one layer, or it can be a single-layer film printed with one or more sensor inks to form a sensor-printed laminated or single-layer film. For example, a printed polymer substrate film can be laminated with a second polymer substrate film such that one or more ink layers are trapped between the polymer substrate films. However, it is generally envisioned that the sensor will not be trapped between the polymer substrate films, but will be exposed to and directly within the top space of the MAP, such as in food packaging. As an example, the sensor can be directly printed (in a single ink layer or multiple ink layers) onto the inner surface of the food packaging itself. For example, the sensor can be printed as a single layer containing multiple light emitters or multiple consecutive single light emitter layers onto the inner surface of a conventional food packaging polymer film, such that at least one layer of the sensor is in direct contact with the atmosphere. Preferably, the layer containing the first light emitter is in direct contact with the atmosphere.

[0093] Polymer substrates may undergo surface treatment prior to printing to improve the wettability of one or more sensor inks on the film. Such surface treatment steps include, for example, corona discharge, flame activation, low-pressure oxygen plasma, laser beam, focused ion beam or electron beam treatment, as well as chemical treatment via the application of organic or inorganic coatings.

[0094] Integrating the sensor ink formulation into the packaging material is a key component of this invention, allowing sensors to be placed within the packaging for on-site detection and / or monitoring of oxygen concentration in controlled or modified atmospheres. Due to the non-toxic nature of the sensors, one or more sensor formulations can be printed within modified atmosphere packaging, even when the sensors come into direct contact with food and other ingestible products. Therefore, the polymer substrate should be compatible with conventional / commercially available laminated polymer films used for sealing MAP food trays, or with plastic film coverings commonly used in vacuum-packed food trays or packaging for electronic / medical products.

[0095] The polymer substrate film can be a layer of a laminated film. For example, a polymer substrate film with high O2 permeability can be printed with a sensor ink formulation, and then the printed polymer substrate film is adhered to a lidding film, which is preferably a gas-impermeable film, such as PA or PET, so that the sensor ink is trapped between the polymer substrate film and the lidding film.

[0096] Alternatively, one or more sensor ink formulations can be reverse-printed onto a polymeric film substrate with low or very low O2 permeability before lamination onto a high O2 permeability substrate such as PE or PP. Suitable polymeric film substrates with low or very low O2 permeability include polyamides (PAs) (including nylon, cast nylon, and the like), polyvinylidene chloride (PVDC), polyesters (PET), and oriented polyesters (OPET). The low or very low O2 permeability layer can maintain a modified atmosphere within the packaging. In this embodiment, the oxygen sensor is in direct contact with the product (e.g., food or other ingestible products) that the MAP is designed to protect, which is facilitated by its non-toxic properties. Advantageously, this direct contact between the atmosphere and the sensor results in a robust sensor response.

[0097] Suitable commercial cover films that can be used with these technologies include, for example, polyamide (PA) / polyethylene (PE) films, polyester (PET) / polyethylene (PE) films, polyester (PET) / ethylene vinyl alcohol (EVOH) / polyethylene (PE) films, polypropylene (PP) / ethylene vinyl alcohol (EVOH) / polyethylene (PE) films, and polypropylene (PP) / polyamide (PA) / polyethylene (PE) films. In an embodiment, the film is a PP or PE film.

[0098] Advantageously, the sensors are invisible to the naked eye when printed onto the laminate or label. This means that integrated or embedded sensors, for example, used to monitor the integrity of packaging on a manufacturing line, are invisible to consumers. This is particularly suitable for sensors embedded in food packaging, for example, where the sensor is positioned within the top space of the food's map. This allows for non-destructive, real-time monitoring of the freshness of the food within the packaging.

[0099] A system for monitoring the oxygen content in modified atmosphere packaging is also envisioned. This system may include a laminated packaging film or label comprising a colorimetric oxygen sensor as described in detail above, a UV or UV-visible light source, and an image reader or vision system.

[0100] The invention will now be described with reference to the following embodiments, which are intended to be illustrative only.

[0101] Throughout the embodiments, when ethyl cellulose is used, the ethyl cellulose is EC Standard 4 (i.e., a 5% solution in toluene:ethanol 80:20 (v / v) with a viscosity of 4 cP). When curcumin is used, the curcumin is derived from turmeric (…). Curcuma longa LThis is a natural extract from the rhizome of turmeric (turmeric rhizomes). The natural extract contains over 70% curcumin, as well as demethoxycurcumin (13%-20%) and didemethoxycurcumin (1%-4%).

[0102] Example: 1.1 4,7-Diphenyl-1,10'-Phenanthrolineruthenium(II) and (1E,6E)-1,7-bis(4-hydroxy-3-methoxyphenyl)hept-1,6-diene-3,5-dione [Ru(dpp)3] in ethyl cellulose (EC) 2+ Curcumin (1:7.5 molar ratio) 28.8 g of dried ethyl cellulose polymer (4 cP) was added to a 69:31 (v / v) mixture of ethanol and ethyl acetate (140.9 ml ethanol; 63.9 ml ethyl acetate) and stirred overnight to ensure complete dissolution of the polymer. Then, 146.6 mg (1.088 mg) of the polymer was added. 10 -4 4,7-Diphenyl-1,10'-phenanthroline ruthenium(II) ([Ru(dpp)3) mol) 2+ 1) and 300.5 mg (8.158) 10 -4 (1E,6E)-1,7-bis(4-hydroxy-3-methoxyphenyl)hept-1,6-diene-3,5-dione (curcumin, luminescent material 2) was added sequentially in powder form to the solution, and the solution was stirred until complete homogenization was achieved and no sedimentation of the luminescent material was observed.

[0103] To evaluate sensor performance, data from Elcometer was then used. TM The 20 µm spiral coating rod prints the formulation onto the self-adhesive PE substrate (EZ-Pierce). TM The coated substrate was then dried in a constant temperature oven at 40°C for 2 hours, followed by cutting into 1 cm × 1 cm cubes and storing at room temperature in the dark until needed. The color change response of the printed sensor formulation was measured as outlined in Example 2 below.

[0104] 1.2 4,7-Diphenyl-1,10'-Phenanthrolineruthenium(II) and (1E,6E)-1,7-bis(4-hydroxy-3-methoxyphenyl)hept-1,6-diene-3,5-dione [Ru(dpp)3] in ethyl cellulose (EC)-based inks 2+ Curcumin (1:2.8 molar ratio) 720 g of dried ethyl cellulose polymer (4 cP) was added to a 69:31 (v / v) mixture of ethanol and n-propyl acetate (3.18 L ethanol; 1.44 L n-propyl acetate) and mechanically stirred to ensure complete dissolution of the polymer. Then, 2-acetoxypropane-1,2,3-tributyl triacetate (ATBC, 25.0 g) and polyethylene wax (40% dispersion in isopropanol) (50.0 g) were added to the polymer solution as printing additives. 3.66 g (2.720) 10 -3 [Ru(dpp)3] mol) 2+ The first luminescent solution was prepared by dissolving the luminescent agent in a 69:31 (v / v) mixture of ethanol and ethyl acetate (345 ml ethanol; 155 ml ethyl acetate), while separately dissolving 2.85 g (7.615 g) of the luminescent agent. 10 -3 A second luminescent solution was prepared by dissolving curcumin (mol) in a 69:31 (v / v) mixture of ethanol and ethyl acetate (345 ml ethanol; 155 ml ethyl acetate). After complete dissolution, the two luminescent solutions were added to the polymer solution prepared above.

[0105] After ensuring complete homogenization of the formulation, a pattern consisting of 1 cm × 1 cm squares was printed onto the inside of a multilayer LINTOP PE HB film from Klöckner Pentaplast using a rotary gravure printing press. The printed film was passed through a drying tunnel set at 75°C and then rewound at the end of the production line. A 1,000 m long roll was protected from light using protective foil and stored at room temperature. The printed film was mounted onto a roll-to-roll feeder, and hundreds of meters of the printed film were tested using a prototype vision system. After testing, the printed film was used in trials with MAP food products. The color change response of the printed sensor formulation was measured as outlined in Example 2 below.

[0106] 1.3 4,7-Diphenyl-1,10'-Phenanthrolineruthenium(II) and 2-(3,4-Dihydroxyphenyl)-3,7-Dihydroxychromene-4-one [Ru(dpp)3] in ethyl cellulose (EC) 2+ Fischerone (1:2.8 molar ratio) 28.8 g of dried ethyl cellulose polymer (4 cP) was added to a 69:31 (v / v) mixture of ethanol and ethyl acetate (140.9 ml ethanol; 63.9 ml ethyl acetate) and stirred overnight to ensure complete dissolution of the polymer. Then, 146.6 mg (1.088 mg) of the polymer was added. 10 -44,7-Diphenyl-1,10'-phenanthroline ruthenium(II) ([Ru(dpp)3) mol) 2+ , luminescent 1) and 88.4 mg (3.089 10 -4 2-(3,4-dihydroxyphenyl)-3,7-dihydroxychromen-4-one (Fissone, luminescent agent 2) was added sequentially in powder form to the solution, and the solution was stirred until complete homogenization was achieved. The formulation was then printed using the same method described in Example 1.1. The film incorporated into the printed sensor cube was measured, and the color change response was evaluated as outlined in Example 2 below.

[0107] 1.4 5,10,15,20-tetrakis(2,3,4,5,6-pentafluorophenyl)porphyrin platinum(II)-22,24-dioxide in ethyl cellulose (EC) and sodium hydrogen phosphate [(2S,3R,4R)-5-(7,8-dimethyl-2,4-dioxobenzo[g]pterodin-10-yl)-2,3,4-trihydroxypentyl] in hydroxypropyl cellulose (HPC) PtTFPP:Flavin Mononucleotide Sodium (FMN) in Ethyl Cellulose / Hydroxypropyl Cellulose (EC / HPC) (1:6.0 molar ratio) 2.88 g of dried ethyl cellulose polymer (4 cP) was added to a 69:31 (v / v) mixture of ethanol and ethyl acetate (14.1 ml ethanol; 6.4 ml ethyl acetate) and stirred to ensure complete dissolution of the polymer. First, 12.7 mg (3.1 ml, 1.087) was added. 10 -5 5,10,15,20-tetrakis(2,3,4,5,6-pentafluorophenyl)porphyrin platinum(II)-22,24-dioxide (PtTFPP, luminescent 1) was dissolved in THF and then added to the EC polymer solution. Separately, 2.00 g of dried hydroxypropyl cellulose (HPC) was dissolved in 34.6 ml of ethanol and stirred until completely dissolved. Then, 33.3 mg (0.74 ml, 6.539 mol) was added. 10 -5 A sodium salt of flavin mononucleotide (FMN) was added to the HPC polymer solution, and the solution was stirred until complete homogenization was achieved. The FMN formulation was then printed onto a self-adhesive PE substrate (EZ-Pierce) using a 20 µm spiral coating rod. TMThe printed substrate was then dried in an oven at 40°C for 2 hours. The printed substrate was then coated with the PtTFPP / EC formulation using the same 20 µm coating rod. The printed substrate was cut into 1 cm × 1 cm cubes and stored at room temperature in the dark until use. The color change response of the printed sensor formulation was measured as outlined in Example 2 below.

[0108] 1.5 Other formulations An additional formulation was prepared using the method described in Example 1.1, which contained [Ru(dpp)3] in HPMC. 2+ Riboflavin (1:2.8 molar ratio); PtTFPP in polystyrene (PS): curcumin (1:3.0 molar ratio); PtOEP in CAP / EC: paeonol (1:10.0 molar ratio); PtTFPP in EC / HPC: ellagic acid (1:6.0 molar ratio); PtTPP in EC: curcumin (1:3.0 molar ratio); PtTPP in CAB: morin (1:3.0 molar ratio). PtTPP: Safflower Extract in EC / HPMC (1:1.9 molar ratio); PtOEP: Curcumin in CAP (1:3.0 molar ratio); PtOEP: Riboflavin in CAB (1:6.0 molar ratio); PtTFPP: Natrazine in EC / HPC (1:3.0 molar ratio); PtOEP: Fisexin in EC (1:3.0 molar ratio); [Ru(dpp)3] in EC 2+ Quercetin (1:2.8 molar ratio); PtTPP:FMN (1:6.0 molar ratio) in EC / HPC and PtTFPP:3-hydroxyflavone (1:4.0 molar ratio) in EC / CAB. For [Ru(dpp)3] in HPMC... 2+ Example of riboflavin (1:2.8 molar ratio), using a 10 µm spiral coating bar.

[0109] The formulations prepared in Examples 1.1 to 1.5 are summarized in Table 1 below: Table 1: Preparation of oxygen sensors Example 2: Measurement of Color Response The following measurements were taken to determine the color response of the sensor formulation to changes in oxygen concentration: For Examples 1.1 and 1.3 through 1.5, data from Elcometer was used. TM Spiral coating rod printing is available on commercially available self-adhesive PE and PET substrates (from Excel Scientific's EZ-Pierce). TMMembrane and SealPlate TM On the non-sticky side of the membrane, a wet ink film with a thickness of 10 μm or 20 μm is deposited (see Table 1). The coated substrate is then dried, cut into 1 cm × 1 cm squares, and stored at room temperature in the dark until use (up to 6 months). For Example 1.2, the sensor is printed using a rotary gravure printing press as outlined in this example.

[0110] Spectrophotometric evaluation of the sensor response (i.e., measurement of the spectral response) is performed by attaching a single sensor to a pre-cut glass slide and placing it in a disposable poly(methyl methacrylate) (PMMA) cuvette or cell under a controlled gas atmosphere. The sensor is held in the LED excitation path at a fixed angle of 45° using a Teflon-based sample holder (at 385 nm for PtOEP and PtTPP, or for [Ru(dpp)3]). 2+ The PtTFPP (at 405 nm) ensures that the sample position of each sensor is identical for every measurement. The atmosphere within the cuvette is altered by mixing O2 and N2 gases in the desired ratio (0%-100% O2, corresponding to 100%-0% N2) using a computer-controlled gas mixer. Two holes on the top of the sample holder allow the gas mixture to flow in and out.

[0111] A vision system equipped with a CMOS camera and two LED strip lights was used to evaluate the sensor response (i.e., color response). Before placing the membrane in the measurement chamber, a 1 cm... 2The cubic sensors are adhered to the underside (i.e., the food contact side) of the commercial multilayer cover film. Typically, six sensors are used to prevent sensor failure and provide an average sensor response. [Although not done here, the printed film rolls can optionally be dispensed onto the measuring chamber using a roll-to-roll feeder]. The gas atmosphere in the chamber can be continuously altered by using a computer-controlled gas mixer to flow in the desired gas mixture and by analyzing the outflow using a gas analyzer to confirm the modified atmosphere within the chamber. Once the desired oxygen level in the chamber is reached, a manually triggered strobe LED bar light is activated, and a camera captures RGB images of the sensors during the illumination pulse. The gas is then changed within the chamber, and image capture is repeated after the gas atmosphere set on the gas mixer is matched with the gas reading from the gas analyzer. For low O2 formulations (i.e., operating at oxygen levels ≤ 21%), images are captured at O2 levels of 0%, 1%, 3%, 5%, 10%, and 21%. For high-O2 formulations (i.e., operating at oxygen levels ≥35%), images were recorded at O2 levels of 0%, 20%, 35%, 50%, 60%, 70%, and 80%. The RGB and HSI outputs from the camera were then analyzed to obtain the color response for the various formulations tested. To standardize the reporting of color responses, relative percentage changes are presented as follows: For formulations with applications for high-O2 packaging, hue differences are represented using the 80% O2 hue value as a reference (Δhue = hue). 80 -tone i , among which the hue i (This is the value measured at 1% O2), therefore the relative percentage change is obtained by dividing the hue difference by the hue at 80% O2, i.e., Δhue / hue. 80 Similar reports are made for formulations operating at low O2, but in this case, the 0% O2 hue value is used as a reference, so the relative percentage change is determined by (hue value). i -hue0) / hue0 is given.

[0112] PtOEP:curcumin (1:3) in CAP (Example 1.5) and [Ru(dpp)3] in EC 2+ Curcumin (1:2.8) (Example 1.2) and [Ru(dpp)3] in EC 2+ The results of these measurements of curcumin (1:7.5) (Example 1.1) were in Figure 1 As shown in the image.

[0113] Figure 1(a) illustrates a discernible color change from an initial bright orange to a final green for the PtOEP:curcumin [in CAP (1:3), Example 1.5] sensor between 0% and 21% O2. This tricolor transition from orange to yellow to green within this specific oxygen range correlates with the MAP of vacuum-packed products, oxygen-sensitive MAP foods (cooked meats, nuts), and fresh products. Average hue and % change were measured, and the results are included in Table 2 below. These results show that for this combination of luminescent materials, the color change results in a relative change in hue (hue 5 - hue 0 / hue 0) of 210% between 0% and 5% O2. Table 2: Hue variation of PtOEP:curcumin sensor [in CAP (1:3), (Example 1.5)] Figure 1 (b) shows that for [Ru(dpp)3] 2+ Curcumin [in EC (1:2.8)(Example 1.2)] sensor, the color change from orange to green was evident between 0% and 80% O2. Average hue and % change were measured, and the results are included in Table 3 below. Relative hue change between 80% and 50% O2 (hue) 50 -tone 80 / tone 80 The oxygen content reached -19.3%. The range of oxygen that causes color change is related to MAP gas mixtures used in products, such as raw meat packaged in an O2-rich atmosphere (70%-80% O2). Table 3: [Ru(dpp)3] 2+ Hue variation of curcumin sensor [in EC (1:2.8) (Example 1.2)]: Figure 1 (c) shows that for [Ru(dpp)3] 2+ Curcumin [in EC (1:7.5) (Example 1.1)] produces a color change from yellow to green in a modified atmosphere containing 0%–21% O2. The average hue and % change were measured, and the results are shown in Table 4 below. The color change resulted in a hue difference of >20% between 0% and 10% O2, or a relative change of 46% (hue). 10 - Hue 0 / Hue 0). The color change occurs within the oxygen range suitable for oxygen-sensitive foods such as bagged lettuce in MAP packaging. Table 4: [Ru(dpp)3] 2+Hue variation of curcumin sensor [in EC (1:7.5), (Example 1.1)] Example 3: Effects of antioxidants on sensor performance The effect of adding antioxidants on the photostability of sensor formulations was investigated below.

[0114] The formulations of Examples 1.1 to 1.5 were prepared as described above. After homogenization, the formulations were then aliquoted into two vials. The first vial served as a control, while the antioxidant was added directly to the formulation in the second vial to give the luminescent agent 2: antioxidant molar ratio indicated in Table 5 below. The control and antioxidant-containing formulations were then coated onto a PE self-adhesive substrate using a spiral coating bar as described in Example 2 above. The photostability of the printed sensor cubes from the formulations was then evaluated by continuously illuminating the sensors at full power for 5 min with a 405 nm LED strip light (FWHM = 20 nm), the illumination being (i) in an 80% O2 atmosphere for formulations associated with products packaged in O2-rich MAP packaging, or (ii) in a 21% O2 (air) atmosphere for formulations developed for oxygen-sensitive products (low O2). Images were captured every minute and changes in RGB and HSI were compared. The results are shown in Table 5 below. Table 5: Effects of antioxidants on the photostability of sensor formulations The results showed that incorporating antioxidants into the formulation resulted in a surprisingly significant enhancement in photostability compared to formulations that did not contain antioxidants, specifically for [Ru(dpp)3]. 2+ The formulation is >30% (hue). For example, for [Ru(dpp)3] in Example 1.2. 2+ The curcumin luminescent complex (1:2.8 molar ratio) exhibited a significant reduction in both RGB and HSI values ​​within 5 minutes. Specifically, during the 5-minute illumination period, the green (G), red (R), and hue (H) values ​​decreased by 12.3%, 4.0%, and 7.5%, respectively. Conversely, when an antioxidant was included in the formulation (in this case, tocopherol, at a 1:2 L2:AO ratio), the green (G), red (R), and hue (H) values ​​decreased by 7.2%, 2.2%, and 3.8%, respectively, during the same 5-minute illumination period. This indicates an improvement in photostability of approximately 50% for hue, approximately 45% for red, and approximately 41% for green when an antioxidant is included in the formulation.

[0115] Similarly, when annatto (1:1 L2:AO molar ratio), which can act as both an antioxidant and a secondary luminescent agent, is added to [Ru(dpp)3] comprising Example 1.3...2+ When the formulation of the Fissone luminescent combination (1:2.8 molar ratio) is used, the photostability is improved by 48% for hue, 108% for red, and 61% for green.

[0116] When quercetin, which can act as both an antioxidant and a secondary luminescent agent, was added to a formulation containing the PtTPP:FMN luminescent combination (1:6 molar ratio) of Example 1.5, photostability was significantly improved by 87% and 57% for red (R) and green (G), respectively, while a smaller 5% stabilization was observed for hue. The lower stability observed in hue is a direct result of the greater stability improvement in red compared to green.

[0117] Smaller and simpler compounds such as vanillin also showed surprising contributions to the stability of the PtTPP:FMN luminescent pair, with improvements in photostability observed for 8% for hue, 11% for red, and 8% for green.

[0118] The surprising potency of the added antioxidants means that naturally occurring luminescent materials and their synthetic analogues can be effectively used in the luminescent-based sensors of this invention.

[0119] Example 4: The effect of coordination between metal and light emitter 2 on the sensor response The effect of coordination between metal ions and luminescent material 2 on the sensor performance was investigated below.

[0120] The formulations listed in Table 1 were prepared according to a scheme similar to that described in Example 1, wherein a metal was added to generate a coordination complex having a luminescent body 2, as described in Examples 4.1-4.3 below.

[0121] In summary, the metal complex was formed by (i) directly adding an aliquot of the metal stock solution to the formulation, or (ii) pre-forming the metal complex by mixing a solution of luminescent material 2 (if necessary, by adding a base for deprotonation) with metal ions to give the luminescent material 2:M molar ratio indicated in Table 6 below, and then adding it to the formulation. After adding luminescent material 1 and homogenizing, the control and metal-containing formulations were coated onto a self-adhesive PE substrate (EZ-Pierce from Excel Scientific) using a spiral coating bar as described in Example 2 above. TM )superior.

[0122] 4.1 4,7-Diphenyl-1,10'-Phenanthrolineruthenium(II) and 2-(3,4-dihydroxyphenyl)-3,5,7-trihydroxychromene-4-one with Al(III) [Ru(dpp)3] in ethyl cellulose (EC) 2+ Quercetin-Al(III) (1:2.8 molar ratio) 28.8 g of dried ethyl cellulose polymer (4 cP) was added to a 69:31 (v / v) mixture of ethanol and ethyl acetate (140.9 ml ethanol; 63.9 ml ethyl acetate) and stirred overnight to ensure complete dissolution of the polymer. Then, 146.6 mg (1.088 mg) of the polymer was added. 10 -4 4,7-Diphenyl-1,10'-phenanthroline ruthenium(II) ([Ru(dpp)3) mol) 2+ 1) and 105.9 mg (3.089) 10 -4 2-(3,4-dihydroxyphenyl)-3,5,7-trihydroxychromene-4-one (quercetin hydrate, luminescent 2) was added sequentially in powder form to the solution, and the solution was stirred until complete homogenization was achieved. In this case, aluminum(III) hexahydrate (AlCl3·6H2O, 77.9 mg, 3.195 mol) was added sequentially to the solution, and the solution was stirred until complete homogenization was achieved. 10 -4 A metal salt (1 mol or 1.05 molar equivalent) is added to the formulation, and the mixture is stirred further. Sufficient time (1-2 hours) is allowed between the addition of Al(III) and printing to ensure complete formation of the coordination complex L2-M. The sensor cubes are printed and prepared as described in Example 1.1. The color change response of the sensor is then evaluated as outlined in Example 2 above.

[0123] 4.2 5,10,15,20-tetrakis(2,3,4,5,6-pentafluorophenyl)porphyrin platinum(II)-22,24-dioxide in ethyl cellulose (EC) and 6,7,13,14-tetrahydroxy-2,9-dioxatetracyclo[6.6.2.0] in hydroxypropyl cellulose (HPC). 4 ,16 .0 11,15 Hexadecane-1(15),4,6,8(16),11,13-hexane-3,10-dione and B(III) PtTFPP:ellagic acid-B(III) in ethyl cellulose / hydroxypropyl cellulose (EC / HPC) (1:6.0 molar ratio) 2.88 g of dried ethyl cellulose polymer (4 cP) was added to a 69:31 (v / v) mixture of ethanol and ethyl acetate (14.1 ml ethanol; 6.4 ml ethyl acetate) and stirred to ensure complete dissolution of the polymer. First, 12.7 mg (1.087 g) was added. 10 -5 5,10,15,20-tetra(2,3,4,5,6-pentafluorophenyl)porphyrin platinum(II)-22,24-dioxide (PtTFPP, luminescent 1) was dissolved in THF and then added to the EC polymer solution. 2.00 g of dried hydroxypropyl cellulose (HPC) polymer was dissolved in a 75:25 (v / v) mixture of ethanol:water (54.2 ml ethanol; 18.0 ml deionized water) and stirred overnight. Coordination of B(III) with ellagic acid was performed prior to addition to the HPC solution. A 4 g / L stock solution of ellagic acid in alkaline water (pH 11) and a 0.067 M stock solution of borax (sodium tetraborate) in deionized water were prepared. Then 10.0 mg (2.5 ml, 3.31 mol) was added to the EC polymer solution. 10 -5 A stock solution of ellagic acid (25.3 mg, 6.62 mol) was added to 0.994 ml (25.3 mg, 6.62 mol) of ellagic acid. 10 -5 A borax solution of mol was prepared to obtain an L2:M molar ratio of 1:2.

[0124] Then, the ellagic acid:B(III) coordination compound was added to the HPC polymer solution and stirred until homogenization was achieved.

[0125] The formulation, namely PtTFPP in EC and ellagic acid-B(III) in HPC, was printed onto a self-adhesive PE substrate (from Excel Scientific's EZ-Pierce). TM The substrate was printed as described in Example 2. To ensure a rapid response to oxygen, an oxygen-sensitive layer (PtTFPP in EC) was printed after the ellagic acid-HPC layer. The printed substrate was dried in an oven at 40°C for 2 hours. The printed PE substrate was then cut into 1 cm × 1 cm squares and stored in the dark at room temperature until needed. The sensor squares were then placed inside the MAP cover film (i.e., a commercial multilayer film (ToplexHB44) from Plastopil). The color change response of the multilayer print was measured as outlined in Example 2.

[0126] 4.3 4,7-Diphenyl-1,10'-phenanthroline ruthenium(II) and (1E,6E)-1,7-bis(4-hydroxy-3-methoxyphenyl)hept-1,6-diene-3,5-dione with Al(III) [Ru(dpp)3] in ethyl cellulose (EC) 2+ Curcumin-Al(III) (1:2.8 molar ratio) 28.8 g of dried ethyl cellulose polymer (4 cP) was added to a 69:31 (v / v) mixture of ethanol and ethyl acetate (140.9 ml ethanol; 63.9 ml ethyl acetate) and stirred overnight. When 146.6 mg (1.088) was added... 10 -4 4,7-Diphenyl-1,10'-phenanthroline ruthenium(II) ([Ru(dpp)3) mol) 2+ When luminescent agent 1) is added from a freshly prepared stock solution to an EC solution, (1E,6E)-1,7-bis(4-hydroxy-3-methoxyphenyl)hept-1,6-diene-3,5-dione (curcumin, luminescent agent 2) first coordinates with Al(III) before being added to the polymer. In short, 1 ml of curcumin stock solution (20.4 g / L in ethyl acetate:ethanol 2:1 (v / v)) 5.543 10 -5 1 mol) and 1 equivalent of 1 M NaOH (0.055 ml, 5.543 mol) 10 -5 The curcumin was mixed with 13.4 mg of AlCl3·6H2O (1 equivalent, 5.543 mol) to deprotonate the enol functional group of curcumin. This step was followed by the addition of 13.4 mg of AlCl3·6H2O (1 equivalent, 5.543 mol). 10 -5 0.549 ml (3.043 mol) was added to allow for the formation of a coordination complex in solution. The solution was vigorously stirred to ensure complete coordination of Al(III). Finally, 0.549 ml (3.043 mol) was added to the solution to allow for the formation of a coordination complex in solution. 10 -5 A curcumin-Al(III) solution containing 1 mol of curcumin was added to the EC polymer containing the first luminescent material to obtain an L1:L2 molar ratio of 1:2.8. The formulation was then stirred until complete homogenization was achieved and no sedimentation of the luminescent material was observed. After printing the formulation onto a self-adhesive PE substrate, the backing paper was removed, and the sensor cube was placed on the inside of a MAP cover film (i.e., a commercial multilayer film (Toplex HB44) from Plastopil) for testing. The color change response of the printed sensor formulation was measured as outlined in Example 2 below.

[0127] 4.4 5,10,15,20-tetrakis(2,3,4,5,6-pentafluorophenyl)porphyrin platinum(II)-22,24-dioxide in ethyl cellulose (EC) and 3-hydroxy-2-phenylchromene-4-one in cellulose acetate butyrate (CAB) with Zn(II) PtTFPP:3-hydroxyflavone-Zn(II) in ethyl cellulose / cellulose acetate butyrate (EC / CAB) (1:4.0 molar ratio) 2.88 g of dried ethyl cellulose polymer (4 cP) was added to a 69:31 (v / v) mixture of ethanol and ethyl acetate (14.1 ml ethanol; 6.4 ml ethyl acetate) and stirred to ensure complete dissolution of the polymer. First, 12.7 mg (1.087 × 10⁻⁶) was added. -5 5,10,15,20-tetratetra(2,3,4,5,6-pentafluorophenyl)porphyrin platinum(II)-22,24-dioxide (PtTFPP, luminescent 1) was dissolved in THF and then added to the EC polymer solution. 4.20 g of dried cellulose acetate butyrate (CAB) polymer was dissolved in a 69:31 (v / v) mixture of ethanol and ethyl acetate (14.1 ml ethanol; 6.4 ml ethyl acetate) and stirred overnight. Prior to addition to the CAB solution, coordination of Zn(II) with 3-hydroxyflavone was performed. A 13 g / L stock solution of 3-hydroxyflavone in ethanol:THF 75:25 (v / v) and a 0.076 M stock solution of zinc(II) chloride (ZnCl2) in ethanol were prepared. Then 10.4 mg (0.804 ml, 4.35 × 10⁻⁶) was added to the EC polymer solution. -5 3-hydroxyflavone stock solution (mol) with 0.570 ml (5.9 mg, 4.35 × 10⁻⁶) -5 Mix mol) of ZnCl2 solution to obtain a 1:1 L2:M molar ratio.

[0128] Then, the 3-hydroxyflavone:Zn(II) coordination compound was added to the CAB polymer solution and stirred until homogenization was achieved.

[0129] The formulation, namely PtTFPP in EC and 3-hydroxyflavone-Zn(II) in CAB, was printed onto a self-adhesive PE substrate (from Excel Scientific's EZ-Pierce). TM The substrate was printed as described in Example 2. To ensure a rapid response to oxygen, an oxygen-sensitive layer (PtTFPP in EC) was printed after the CAB layer containing 3-hydroxyflavone. The printed substrate was dried in an oven at 40°C for 2 hours. The printed PE substrate was then cut into 1 cm × 1 cm squares and stored in the dark at room temperature until needed. The sensor squares were then placed inside the MAP cover film (i.e., a commercial multilayer film (Toplex HB44) from Plastopil). The color change response of the multilayer print was measured as outlined in Example 2.

[0130] 4.5 Evaluation of Color Response and Light Stability The color response of the evaluation control (Table 1) and metal-containing formulations (Examples 4.1 to 4.4) as described in Example 2 was compared, and the relative increase / decrease in sensitivity (color response) is reported in Table 6. The photostability of printed sensor cubes from the formulations was then evaluated by continuous full-power illumination of the sensor for 5 min using a 405 nm LED strip lamp (FWHM = 20 nm), the illumination being (i) in an 80% O2 atmosphere for formulations associated with products packaged in O2-rich MAP packaging, or (ii) in a 21% O2 (air) atmosphere for formulations developed for oxygen-sensitive products (low O2). Images were captured every minute, and changes in RGB and HSI were compared. The results are shown in Table 6 below and indicate improved stability with the same illumination exposure (i.e., considering absorption changes due to metal coordination). Table 6: Effects of metal coordination on fluorescence, color response and photostability of sensor formulations.

[0131] As can be seen from the results in Table 6, compared with the same formulation without the addition of Al(III), the formulation prepared in Example 4.1 containing [Ru(dpp)3] 2+ Quercetin-Al(III) sensors exhibited a significantly increased brightness, with a distinct color change from red to green clearly discernible to the naked eye. The O2 sensitivity of the complexed quercetin formulation was also significantly improved compared to its free metal analogue, with a 27% increase observed. The change in hue observed at oxygen concentrations between 80% and 50% was 15.4% for the control (non-complexed sensor) and 19.3% for the metal-containing formulation. A significant 33% improvement in photostability (based on hue value) was also observed in the Al(III)-complexed quercetin sensors compared to their non-complexed counterparts.

[0132] Regarding Example 4.1, the luminescent pair (i.e., PtTFPP:ellagic acid-B(III)) of Example 4.2 showed improved brightness compared to the same formulation without the addition of B(III). Similar to what was observed with Al(III) in Example 4.1, the addition of sodium tetraborate (as a source of B(III)) also contributed to improved O2 sensitivity, with a recorded increase in sensitivity of 24%. Photostable stability was tested and compared with a metal-free control formulation. Similar improvements in photostable stability (23%–25%) were observed in hue, red, and green output.

[0133] For the complexed formulation of Example 4.3 (i.e., [Ru(dpp)3]) 2+Curcumin (1:2.8, in EC) was used in this formulation, which exhibited an increase in brightness, which (as also seen in Examples 4.1 and 4.2) enhanced the color response, resulting in an 11% improvement in O2 sensitivity. Furthermore, the metal-containing formulation showed significantly higher photostability compared to its corresponding metal-free formulation, achieving a 42% improvement in hue, 34% in red, and 38% in green. The hue reduction was from 4.3% in the absence of Al(III) to 2.5% after coordination with Al(III), while red and green were reduced from 5.3% and 12.6% in the metal-free formulation to 3.5% and 7.8% in the presence of Al(III), respectively.

[0134] For the complexed formulation of Example 4.4 (i.e., PtTFPP:3-hydroxyflavone (1:4.0, in EC / CAB)), this formulation exhibits an increase in brightness, which (as also seen in Examples 4.1 and 4.2) enhances the color response, resulting in a 61% improvement in O2 sensitivity. Furthermore, the metal-containing formulation exhibits significantly higher photostability compared to its corresponding metal-free formulation, achieving a 31% improvement in photostability in red and a 62% improvement in photostability in green. Compared to the previous examples, 3-hydroxyflavone and its Zn(II)-coordinated counterparts exhibit sufficient blue emission to identify a significant 58% improvement in photostability in blue. The reduction in red intensity decreased from 0.9% in the absence of Zn(II) to 0.6% after coordination with Zn(II), while green and blue intensity decreased from 4.2% and 2.8% in the metal-free formulation to 2.6% and 1.7% in the presence of Zn(II), respectively.

[0135] It is important to note that in some cases, the relationship between the luminescent material and [Ru(dpp)3] is different. 2+ Fischerone (1:2.8 molar ratio, in EC) was observed to have photostabilization disproportionately favor one of the photoelectrophores. In this case, it originated from [Ru(dpp)3]. 2+ The red output of the sensor showed a 3-fold improvement in photostable stability compared to the green output from fisetin. The sensor's color, as represented by the hue value, shifted towards redder colors (i.e., lower hues), which resulted in a significant decrease in stability.

[0136] Example 5: Combined Effect of Antioxidants and Metal Coordination on Sensor Response [Ru(dpp)3] in ethyl cellulose (EC) (4 cP) was prepared as outlined in Example 1.1, but at a molar ratio of 1:2.8. 2+Curcumin (1:2.8 molar ratio). In short, 14.4 g of dried ethyl cellulose polymer was added to a 69:31 (v / v) mixture of ethanol and n-propyl acetate (70.5 ml ethanol; 32.0 ml ethyl acetate) and stirred overnight. 73.3 mg (5.438) 10 -5 [Ru(dpp)3] mol) 2+ That is, luminescent material 1 and 56.1 mg (1.523 mg). 10 -4 DL-α-tocopherol (2 mol), i.e., luminescent material 2, was dissolved in a 69:31 (v / v) mixture of ethanol and ethyl acetate and then added to the polymer solution. After complete homogenization, the formulation was divided equally into two different flasks. The first flask remained as prepared, while DL-α-tocopherol (2 equivalents, 1.523 mol) was added. 10 -4 mol) was added to the second flask.

[0137] Incidentally, the metal-containing formulation described in Example 4.3 was prepared and equally separated into two different flasks; flask 3 contained the Al(III)-based formulation as prepared, namely [Ru(dpp)3]. 2+ Curcumin-Al(III) (1:2.8 molar ratio). DL-α-tocopherol was added to flask 4 to obtain a formulation in which both an antioxidant and a metal coordination are used.

[0138] Therefore, the following formulations are obtained: Flask 1: [Ru(dpp)3] 2+ Curcumin; Flask 2: [Ru(dpp)3] 2+ Curcumin and TP; Flask 3: [Ru(dpp)3] 2+ Curcumin-Al(III); Flask 4: [Ru(dpp)3] 2+ Curcumin-Al(III) and TP.

[0139] Each formulation in flasks 1-4 was printed onto a self-adhesive PE substrate (from Excel Scientific's EZ-Pierce). TM Afterward, the sensor was cut and placed on the inner layer of a MAP cover film (Toplex HB44) from Plastopil for testing. The photostability of curcumin in each of the four formulations was then evaluated, and the stabilization effect was measured as described in Example 4.5.

[0140] While both tocopherol and Al(III) coordination individually lead to a significant increase in the photostability of curcumin (see Tables 5 and 6), combining the two additives in the same formulation results in further improvements. When comparing with reference only [Ru(dpp)3]... 2+ When curcumin was combined with formulations containing metals and antioxidants, stabilization was observed in hue, red, and green by 72%, 66%, and 63%, respectively. The reference formulation showed reductions in hue, red, and green by 4.3%, 5.3%, and 12.6%, respectively, while for [Ru(dpp)3]... 2+ Curcumin-Al(III) + tocopherol, with the same values ​​of 1.2%, 1.8%, and 4.6%. The results indicate that the metal coordination of the naturally occurring luminescent material, combined with the addition of an antioxidant to the formulation containing the second luminescent material, leads to a very significant improvement in sensor performance.

[0141] Example 6: Application of colorimetric sensors in low-O2 MAP packaging - MAP bagged lettuce Two formulations [Ru(dpp)3] 2+ Curcumin (1:7.5 molar ratio) and PtTFPP-kaempferol-Al(III) (1:3.0 molar ratio) were prepared as outlined in Examples 1.1 and 4.1, respectively. The curcumin was printed on PE self-adhesive sheets (from Excel Scientific's EZ-Pierce). TM Cut into 1 cm pieces 2 Following the cubic sensor, four sensors are placed inside the commercial film used to package the chopped lettuce in bags. The lettuce is placed inside the bag before sealing using a heat-sealing device. To create a modified atmosphere, air is extracted from the bag by inserting a needle through the rubber diaphragm and connecting it to a vacuum. After most of the air has been removed (approaching vacuum), the vacuum is stopped, and the needle is connected to an N2 gas line. The bagged lettuce is then rinsed with N2. This cycle is repeated three times to achieve an O2 level of 1% or lower in the top space of the bagged lettuce. Following this procedure, 30-40 bags of chopped lettuce are produced and imaged using the vision system described in Example 2 above. The O2 level in the top space of the bagged lettuce is first calculated using the vision system, and tonal values ​​are obtained from the captured images. The bags are then subjected to a destructive test using a gas analyzer, and the readings from the gas analyzer are compared with the readings provided by the vision system. For [Ru(dpp)3] 2+Curcumin showed a distinct color change from orange-yellow to green, and PtTFPP-kaempferol-Al(III) showed a distinct color change from orange to green. For both sensors, the O2 level determined using a vision system was within ±1% of the gas analyzer readings for most bags. A significant increase in O2 between measurements was immediately detected in lettuce bags with poor sealing, indicating that air was entering through gaps or creases in the seal.

[0142] Example 7: Application of colorimetric sensors in high-O2 MAP packaging - MAP ground beef [Ru(dpp)3] was prepared as described in Example 1.2. 2+ 5 kg of ink batch containing curcumin (1:2.8 molar ratio). Then, the antioxidant DL-α-tocopherol (2 equivalents, 1.523 g / L) was added. 10 -4 (mol) was added to the sensor formulation, and the viscosity of the formulation was then adjusted by adding a solvent mixture for printing on a rotary gravure printing press until the desired viscosity, as measured using a Zahn Cup #2, was obtained. The ink formulation was printed onto a 285 mm wide, 1,000 m long co-extruded film roll that had been pretreated with corona discharge to increase the ink's adhesion to the substrate film.

[0143] On a commercial food packaging production line, a printed film was used to seal the top space of raw ground beef in modified atmosphere (MAP) packaging at 80% O2 / 20% CO2. The MAP ground beef packages were stored at 4°C for 12 days in retail display cases. Two shelf-life tests (36 packages per test) involved daily measurements of each package to monitor sensor color output using the vision system described in Example 2. The purpose of this test was to non-invasively monitor O2 levels within the MAP ground beef packages throughout the product's shelf life. Changes in O2 levels observed within the top space of the packages were grouped into three categories: Group I: Leakage / Damage: A significant decrease in O2 levels is attributed to leakage or damage to the packaging pallet or covering film; Group II: Stable / no significant decrease in O2 levels observed during the shelf life; Group III: Decreased O2 levels observed during the shelf life.

[0144] Due to the significant decrease in oxygen levels, the packaging from Group I exhibited a visible color change from green to orange, a typical behavior of packaging that has lost its integrity due to leakage, poor sealing, or other structural damage.

[0145] The second group of packages showed stable O2 readings and therefore no color change was observed during the shelf life of the packaged product.

[0146] The third group of packages showed no color change or only slight color change in the first few days, but sensor readings decreased a few days before the product's "use" date (i.e., typically 3 days before the "use" date), indicating a lower oxygen level within those packages. This decrease resulted in a small but measurable change in color during the last three days of the shelf life.

[0147] As a control, destructive testing was performed on six packages of MAP ground beef using a Mocon Dansensor O2 and CO2 gas analyzer (model: Checkpoint 3), and the results were compared with the sensor output. The correlation between the gas analyzer readings and the non-destructive testing was within ±5%.

[0148] As demonstrated by the inventors, the non-toxic, luminescent-based colorimetric sensor of the present invention combines high sensitivity to oxygen with tunability to specific oxygen concentrations, such as those associated with the MAP of a particular type of food, via a color change induced by luminescence quenching. Due to the non-toxic nature of the formulation, the sensor can be embedded in food packaging atmospheres, for example, where the sensor may come into direct contact with food or other ingestible items, and legislative approval of the sensor is simplified due to the non-toxic and naturally occurring nature of the second luminescent element. The sensor enables semi-quantitative analysis based solely on the induced colorimetric change, while ratiometric measurements can be used if full quantitative measurements are required. The sensor can be used in conjunction with digital image analysis, performed via software or an app pre-programmed with internal sensor calibration, to provide high-throughput visualization and evaluation of the sensor response. The non-destructive nature of the sensor allows for continuous quality control, e.g., on-site analysis of each packaged product on the manufacturing line and throughout the supply chain. This means that any defective or spoiled item can be removed from the supply chain upon identification without affecting the remainder of that batch, resulting in significant environmental benefits due to reductions in food waste and associated packaging.

[0149] All features disclosed in this specification (including any appended claims, abstract, and drawings) and / or all steps of any method or process so disclosed may be combined in any combination, except that at least some of such features and / or steps are mutually exclusive combinations. Unless otherwise expressly stated, each feature disclosed in this specification (including any appended claims, abstract, and drawings) may be replaced by an alternative feature for the same, equivalent, or similar purpose. Therefore, unless otherwise expressly stated, each disclosed feature is merely one example of a general series of equivalent or similar features. The invention is not limited to the details of the foregoing embodiments. The invention extends to any novel feature or any novel combination of features disclosed in this specification (including any appended claims, abstract, and drawings), or to any novel step or any novel combination of steps in any method or process so disclosed.

[0150] Regarding the use of virtually any plural and / or singular terms herein, those skilled in the art can convert from plural to singular and / or from singular to plural where appropriate for the context and / or application. For clarity, various singular / plural permutations may be explicitly described herein.

[0151] Those skilled in the art will understand that, generally, the terms used herein, and especially in the appended claims, are generally intended to refer to “open-ended” terms (e.g., the term “including” should be understood as “including but not limited to,” the term “having” should be understood as “having at least,” the term “includes” should be understood as “including but not limited to,” etc.). Those skilled in the art will further understand that if a particular number is intended to be presented in the claims, such intention will be explicitly stated in the claims, and if such a statement is absent, such intention does not exist. For example, as an aid to understanding, the appended claims may include the use of the introductory phrases “at least one” and “one or more” to introduce the claim statement. However, the use of such wording should not be construed as meaning that the introduction of the indefinite article "a(a)" or "an" limits any particular claim containing such an introduction to embodiments containing only one such introduction, even when the same claim includes the introductory phrase "one or more" or "at least one" and indefinite articles such as "a(a)" or "an" (e.g., "a(a)" and / or "an" should be interpreted as meaning "at least one" or "one or more"); this also applies to the use of definite articles used to introduce the claim statements. Furthermore, even if a specific number of introduced claim statements are explicitly stated, those skilled in the art will recognize that such statements should be understood to mean at least the number stated (e.g., a plain statement of "two statements" without other modifiers means at least two statements, or two or more statements).

[0152] It will be understood that, for illustrative purposes, various embodiments of this disclosure have been described herein, and various modifications may be made without departing from the scope of this disclosure. Therefore, the various embodiments disclosed herein are not intended to be limiting, and the true scope is indicated by the appended claims.

Claims

1. A colorimetric oxygen sensor comprising a first luminescent element and a second luminescent element, each luminescent element being dispersed in a polymer matrix, wherein the first luminescent element is selected from 4,7-diphenyl-1,10'-phenanthroline ruthenium(II)[Ru(dpp)3]. 2+ ; Octaethylporphyrin platinum (PtOEP); 5,10,15,20-tetra(2,3,4,5,6-pentafluorophenyl)porphyrin platinum (PtTFPP) and meso-tetraphenylporphyrin platinum (PtTPP); and the second luminescent body is a naturally occurring compound or its synthetic analogue selected from diarylheptane compounds; flavonols; carotenoids selected from annatto, capsanthin and capsanthin; coenzymes; minor flavonoids; paeonol or ellagic acid.

2. The colorimetric oxygen sensor according to claim 1, wherein the diarylheptane compound is selected from curcumin; the flavonol is selected from quercetin, fisetin, kaempferol, myricetin, 3-hydroxyflavone and morin; the coenzyme is selected from riboflavin, NADH, FAD and FMN; the minor flavonoid is safflower extract; or the second luminescent agent is paeonol, ellagic acid, annatto, capsanthin or capsanthin.

3. The colorimetric oxygen sensor according to claim 1 or claim 2, wherein the naturally occurring compound or its synthetic analogue is selected from diarylheptane compounds or flavonols.

4. The colorimetric oxygen sensor according to any of the preceding claims further comprises an antioxidant.

5. The colorimetric oxygen sensor according to claim 4, wherein the antioxidant is a carotenoid, a phenolic compound, or a vitamin.

6. The colorimetric oxygen sensor according to claim 5, wherein the antioxidant is annatto, quercetin, or DL-α-tocopherol.

7. The colorimetric oxygen sensor according to any of the preceding claims, wherein the second luminescent element is complexed with aluminum, boron, or zinc.

8. The colorimetric oxygen sensor according to any of the preceding claims, wherein the polymer is selected from polystyrene, polyvinyl alcohol, polyamide, polyurethane, acrylate, shellac, rosin, rosin ester, cellulose and cellulose derivatives; and mixtures thereof.

9. The colorimetric oxygen sensor according to any of the preceding claims, wherein the first luminescent element and the second luminescent element are dispersed in the same polymer.

10. The colorimetric oxygen sensor according to any one of claims 1 to 8, wherein the first luminescent element and the second luminescent element are dispersed in different polymers.

11. The colorimetric oxygen sensor according to any of the preceding claims, wherein the second luminescent material is curcumin or fisetinone.

12. The colorimetric oxygen sensor according to any of the preceding claims, wherein the first luminescent element is 4,7-diphenyl-1,10'-phenanthroline ruthenium(II)[Ru(dpp)3] 2+ Or octaethylporphyrin platinum (PtOEP).

13. The colorimetric oxygen sensor according to claim 12, wherein the first luminescent element is 4,7-diphenyl-1,10'-phenanthroline ruthenium(II)[Ru(dpp)3] 2+ Furthermore, the second luminescent substance is curcumin.

14. The colorimetric oxygen sensor according to claim 12, wherein the first luminescent element is 4,7-diphenyl-1,10'-phenanthroline ruthenium(II)[Ru(dpp)3] 2+ Furthermore, the second luminescent body is fisetin.

15. The colorimetric oxygen sensor according to claim 13 or claim 14, further comprising an antioxidant.

16. The colorimetric oxygen sensor according to claim 15, wherein the antioxidant is DL-α-tocopherol.

17. The colorimetric oxygen sensor according to any one of claims 13 to 16, wherein the polymer is ethyl cellulose.

18. The colorimetric oxygen sensor according to any of the preceding claims, wherein the molar ratio of luminescent body 1 to luminescent body 2 is from 1:1.9 to 1:

10.

19. The colorimetric oxygen sensor according to any of the preceding claims, wherein the sensor is in the form of one or more inks.

20. A method for determining the oxygen content of an atmosphere, the method comprising exposing a colorimetric sensor according to any one of claims 1 to 19 to the atmosphere; applying a UV excitation source or a UV-visible light excitation source to the colorimetric sensor; and observing the color of the sensor.

21. The method for determining the oxygen content of an atmosphere according to claim 20, wherein the method further comprises comparing the color of the sensor with a reference color or calibration curve to assess the oxygen content.

22. The method for determining the oxygen content of an atmosphere according to claim 20 or claim 21, wherein the color of the preparation is observed by the naked eye, by using a spectroscopic method, or by using a digital imaging device.

23. The method according to any one of claims 20 to 22, wherein the atmosphere is a food packaging atmosphere.

24. The method of claim 23, wherein the sensor is positioned within the top space of the modified atmosphere packaged food.

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