Sensor for oxidising agents

• US 20040258562A1
• Filed: 08/12/2004
• Published: 12/23/2004
• Est. Priority Date: 09/05/2001
• Status: Active Grant

• Current Assignee: University of Strathclyde
• Original Assignee: University of Strathclyde
• Inventors: Lee, Soo-Keun, Mills, Andrew
• Granted Patent: US 8,114,673 B2
• Time in Patent Office: Days
• US Class Current: 422/57
• CPC Class Codes: G01J 1/429 applied to measurement of ultraviolet light using counting tubes G01T
• CPC Class Codes: G01J 1/50 using change in colour of an indicator, e.g. actinometer
• CPC Class Codes: G01N 31/225 for oxygen, e.g. including dissolved oxygen
• CPC Class Codes: Y10T 436/207497 Molecular oxygen

Abstract

This invention relates to an irreversible indicator for detecting oxidising agents, or in particular an oxygen indicator, comprising at least one redox-sensitive dyestuff, at least one semiconductor material and at least one electron donor. This indicator is activated by exposure to light of about 200-400 nm. The invention also relates to UV light detector.

Claims

1. An indicator for detecting oxidising agents comprising:

at least one redox sensitive material which displays different visible properties in the oxidised and reduced forms;

at least one electron donor wherein the at least one electron donor is a mild reducing agent; and

at least one semiconductor material specifically sensitive to light of about 200-400 nm, and wherein upon irradiation of said semiconductor material by light of about 200-400 nm an electron is donated by the electron donor to the semiconductor material which in turn provides an electron to the redox sensitive material causing the redox sensitive material to become reduced.

2. An indicator according to claim 1 wherein the oxidising agent is gaseous.

3. An indicator according to claim 1 wherein the oxidising agent is oxygen and the indicator is therefore an oxygen indicator.

4. An indicator according to claim 1 wherein the indicator is in the form of a tablet or pellet in which the components are, for example, pressed together, or as a plastic film in which the components are encapsulated in some medium, such as a polymer.

5. An indicator according to claim 1 wherein the indicator is in the form of an ink which may form a label, LOGO or text i.e. writing.

6. An indicator according to claim 1 wherein the redox sensitive material is a dye such as a thiazine dyestuff, an oxazine dyestuff, an azine dyestuff, a triphenylmethane dyestuff, an indophenol dyestuff, an indigo dyestuff, viologen and/or mixtures thereof.

7. An indicator according to claim 1 wherein the electron donor is selected from any of an amine (e.g. NaEDTA and TEOA), a reducing saccharide (such as glucose and fructose), a readily oxidisable polymer (such as polyvinyl alcohol), and any other general anti-oxidant (such as ascorbic and citric acid).

8. An indicator according to claim 1 wherein the semiconductor material is an oxide of titanium (such as titanium (IV) oxide;

TiO₂, and strontium tiatanate;

SrTiO₃), tin (such as tin (IV) oxide;

SnO₂), tungsten (such as tungsten (VI) oxide;

WO₃) and zinc (such as zinc (II) oxide;

ZnO) and mixtures thereof.

9. An indicator according to claim 1 wherein the indicator comprises a binder such as a polymeric material of gelatin, hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), ethyl cellulose (EC), cellulose acetate (CEA), polypyrolidone (PVP), polyethylene oxide, and polymethylmethacrylate (PMMA).

10. An indicator according to claim 1 wherein the indicator is supported on at least one inert material, such as glass, paper, fabric, ceramic or metal.

11. An indicator according to claim 1 wherein the indicator is in the form of an ink and printed on a substrate.

12. An indicator according to claim 1 wherein the indicator comprises a cover having a very low oxidizing agent permeability which has the effect of preventing the colour change of the UV-light activated indicator upon exposure to an oxidizing agent.

13. An indicator according to claim 12 wherein the cover comprises any of the following:

PET, EVOH, PVDC or regenerated cellulose.

18. A modified atmosphere package having an oxidising agent indicator according to claim 1 wherein upon irradiation of light of about 200-400 nm an electron is donated by the electron donor to the semiconductor material which in turn provides an electron to the redox sensitive material causing the redox sensitive material to become reduced which displays different visible properties in the oxidised and reduced forms.

19. A modified atmospheric package according to claim 18 wherein the modified atmosphere packaging comprises food, beverages, works of art, pharmaceuticals, medical diagnostic kits and sterilised packages.

20. A modified atmosphere package according to claim 18, wherein the indicator is used to determine how long the package, with its contents originally stored in the absence of oxygen, has been opened.

14. A method of detecting oxidising agents, comprising the steps of:

a) providing an oxidising agent indicator comprising;

at least one redox sensitive material which displays different visible properties in the oxidised and reduced forms;

at least one electron donor wherein the at least one electron donor is a mild reducing agent; and

at least one semiconductor material specifically sensitive to light of about 200-400 nm;

b) activating the oxidising agent indicator by irradiating with light of about 200-400 nm so as to convert the redox material into its reduced form which is stable under non-oxidising conditions; and

c) upon exposure of the indicator to an oxidising agent the redox material is oxidised resulting in a visible change of the indicator.

15. A method according to claim 14 wherein the oxidising agent to be detected is oxygen.

16. A method according to claim 14 wherein the activated oxidising agent indicator once exposed to an oxidising agent changes colour and/or fluorescence.

17. A method according to claim 16 wherein the change in colour, and/or fluorescence, is irreversible and persists indefinitely under either oxidising or non-oxidising conditions (provided the indicator is not exposed to another burst of UV light) so that the colour, and/or fluorescence, change cannot be reversed simply by changing the atmosphere from oxidising to non-oxidising.

21. A method of detecting oxidising agents in modified atmosphere packaging using an oxidising agent indicator, comprising the steps of:

a) providing an oxidizing agent indicator comprising;

at least one redox sensitive material which displays different visible properties in the oxidised and reduced forms;

at least one electron donor wherein the at least one electron donor is a mild reducing agent; and

at least one semiconductor material specifically sensitive to light of about 200-400 nm;

b) activating the indicator by irradiating with light of about 200-400 nm so as to convert the redox material into its reduced form which is stable under non-oxidising conditions, until such time as the indicator is exposed to an oxidising agent whereupon the redox material is oxidised resulting in a visible change in the indicator.

22. A method of detecting oxidizing agents in modified atmosphere packages according to claim 21, wherein the indicator is used to determine how long the package, with its contents originally stored in the absence of oxygen, has been opened.

23. A detector for indicating exposure to light of about 200-400 nm comprising an oxidising agent indicator comprising:

at least one redox sensitive material which displays different visible properties in the oxidised and reduced forms;

at least one electron donor wherein the at least one electron donor is a mild reducing agent;

at least one semiconductor material specifically sensitive to light of about 200-400 nm, capable of being activated upon irradiation of light of about 200-400 nm wherein a colour change indicates exposure to light of about 200-400 nm; and

wherein the indicator is covered with an oxygen impermeable film.

24. A detector according to claim 23 wherein the colour change is a progressive change and therefore forms a graduated scale to indicate how much UV light the indicator has been exposed to.

25. A method for indicating exposure to air using an oxidising agent comprising:

at least one redox sensitive material which displays different visible properties in the oxidised and reduced forms;

at least one electron donor wherein the at least one electron donor is a mild reducing agent; and

at least one semiconductor material specifically sensitive to light of about 200-400 nm,

wherein a colour change in the indicator indicates exposure to light of about 200-400 nm.