WO2019010530A1

WO2019010530A1 - Chemical responsive compositions

Info

Publication number: WO2019010530A1
Application number: PCT/AU2018/050714
Authority: WO
Inventors: Wei Shen; Liyuan Zhang; Weirui Tan
Original assignee: Monash University
Priority date: 2017-07-11
Filing date: 2018-07-11
Publication date: 2019-01-17

Abstract

Disclosed herein is a chemical-responsive composition including: a non-Newtonian carrier; and a chemical indicator for sensing a chemical analyte; wherein the chemical indicator is retained by the carrier, and the chemical indicator exhibits a chemical response when exposed to the chemical analyte. Also disclosed herein are chemical- responsive tapes including: a film of a backing material with a chemical-responsive adhesive disposed on a surface of the backing material, the chemical-responsive adhesive including: an adhesive carrier, and at least one chemical indicator for a chemical analyte; wherein the chemical indicator is retained by the adhesive carrier, and the chemical indicator exhibits a chemical response when exposed to the chemical analyte. Further disclosed herein are methods for forming such chemical-responsive tape.

Description

Chemical responsive compositions

Field of the invention

The present invention relates to chemical-responsive compositions, and particularly to chemical-responsive adhesive tapes that are used to detect the presence of a chemical analyte on a substrate surface.

Background of the invention

Detection methods based on chemical responsiveness have progressed significantly over the preceding decades. This is largely driven by improvements in analytic instruments, which allow for the sampling and identification of complex substances with a high degree of detection accuracy and with reduced detection limit. For instance, the analysis of single analyte specimens that once took several hours can now be achieved in mere minutes.

Despite these technological advances in analytical instruments, there remains a need for a low-cost and easy-to-use device that can be used for point-of-use diagnostic testing. While such devices are less sensitive and accurate to an analyte than an analytical instrument, such devices also have a number of advantages over analytical instruments. They are easy to use (such as without professional training), are portable, and ideally can be implemented without aid of auxiliary lab equipment (e.g. pipettes).

Current point-of-use devices include paper- and thread-based analytical microfluidic devices. However, these devices have a number of shortcomings. These devices are only suitable for direct measurement of liquid samples. For solid or particulate analytes, complex pre-treatment to convert them to liquid form under laboratory conditions is normally required. Furthermore, for paper-based analytic devices, testing of aqueous liquid samples can give rise to a phenomenon that is termed "coffee staining" whereby differential evaporation of water from the central and edge detection portions of the paper-based device results in a coffee shaped ring on the paper. This can result in displacement of the analyte (and even the chemical indicator) causing an uneven distribution of the analyte which, in turn, can result in the paper- based analytic device exhibiting an uneven colour distribution or hue. As a result, in sensors which include a colourimetric indicator (exhibiting different coloured hues or intensities as a function of analyte concentration), it becomes difficult or impossible to accurately determine analyte concentration.

To address this problem, some researchers have investigated integrating various polymers into the paper substrate of the device to stabilize the reaction product and prevent it from flowing within hydrophilic channels of the paper. However, the selection of a suitable polymer species is highly dependent on the natures of sample, analyte, indicators, and reaction system. This makes paper microfluidic design increasingly complicated.

In one or more forms, it is desirable to provide an alternate or improved composition for detection of a chemical analyte species.

Reference to any prior art in the specification is not an acknowledgment or suggestion that this prior art forms part of the common general knowledge in any jurisdiction or that this prior art could reasonably be expected to be understood, regarded as relevant, and/or combined with other pieces of prior art by a skilled person in the art.

Summary of the invention

In a first aspect of the invention there is provided a chemical-responsive composition including: a non-Newtonian fluid carrier; and a chemical indicator for sensing a chemical analyte; wherein the chemical indicator is retained by the carrier, and the chemical indicator exhibits a chemical response when exposed to the chemical analyte.

The term "non-Newtonian fluid carrier" is intended to refer to any fluid that does not adhere to Newton's law of viscosity, and includes materials that are: viscoelastic, exhibit time-dependent viscosity (e.g. are rheopectic or thixotropic), shear thinning, shear thickening, Bingham plastics, Bingham pseudoplastics, pseudo-plastics, generalised Newtonian fluids. A non-limiting disclosure of such materials includes: fluids, slurries, suspensions, emulsions, gels (such as hydrogels), and pastes. In one or more forms, the non-Newtonian fluid carrier is a gel (for example, a hydrogel formed using nano-cellulose particles), wax, clay, adhesive, or polymeric carrier. In an embodiment, the non-Newtonian fluid carrier is liquid glue. Liquid glues are typically formulated with water and one or more polymeric components to provide bonding. The typical rheological behaviour of liquid glues is pseudo-plastic, with viscosity values at room temperature of 10 cP to 10000 cP. In an embodiment, the non-Newtonian fluid carrier is "solid glue". Solid glues are typically formulated with water, humectant and one or more polymeric components to provide bonding. The typical rheological behaviour of solid glues is pseudo-plastic and Bingham pseudo-plastic, with viscosity values at room temperature of 1 0000 to 250000 cP. In an embodiment, the non-Newtonian fluid carrier is a hydrogel. Hydrogels are typically formulated crosslinking water-soluble polymers; they can also be formulated by colloidal suspensions of polymeric and inorganic particles, and cellulose nanofibres. The typical rheological behaviour of gels is pseudo plastic, with viscosity values at room temperature of 1000 - 5000 cP. Hydrogels made of cellulose nano fibres have pseudo plastic rheological behaviour, with the viscosity value at room temperature of <600 cP. The typically rheological behaviour of the basic elastomers of pressure sensitive glues is pseudo plastic and shear-thinning, with the viscosity values at room temperature of 5000-1 0000 cP.

In an embodiment, the non-Newtonian fluid carrier is a pseudo-plastic or Bingham pseudo-plastic carrier. Preferably, the pseudo-plastic or Bingham pseudo- plastic carrier has a viscosity of from about 10 cP to about 250,000 cP at room temperature (about 20°C). In one form of this embodiment, the viscosity is from about 10 cP to about 1 0,000 cP. In another form of this embodiment, the viscosity is from 10,000 cP to 250,000 cP. In yet another form of this embodiment, the viscosity is from about 1 ,000 cP to about 5,000 cP. In a further form of this embodiment, the viscosity is from about 5,000 cP to about 1 0,000 cP. In still another form of this embodiment, the viscosity is from about 10 cP to about 600 cP. The pseudo-plastic or Bingham pseudo- plastic carrier may be shear thinning.

In one or more forms, the non-Newtonian fluid carrier is non-fibrous. The term "chemical indicator", as used herein, is intended to refer to a substance that provides a visible indication (such as one which can be seen with the naked-eye) of the presence (or possibly absence) of a threshold concentration of a chemical analyte. Preferably, the chemical indicator is a colour change chemical indicator, a colourimetric chemical indicator, or a fluorescent chemical indicator. More preferably, the chemical indicator is a colour change chemical indicator or a colorimetric chemical indicator. A colour change chemical indicator is broadly any indicator which undergoes a change in colouration (including a change in colour and/or colour intensity) on detection of a chemical analyte. A colorimetric chemical indicator is similar to a colour change indicator, but further exhibits a variation in colour or colour intensity as a function of chemical analyte concentration. Thus, it is preferred that the chemical response is a visual response that is visible to the naked eye. More preferably the visual response is a change in colour and/or colour intensity. The skilled addressee will appreciate that the concentration or quantity of the chemical indicator is dependent on the type of indicator, the intended use of the chemical indicator, and the nature of the chemical analyte. Notwithstanding this, the chemical indicator is present in an amount of at least 0.1 % (w/v).

A non-limiting disclosure of suitable chemical indicators include: Horseradish peroxidase and corresponding substrates; Alkaline phosphatase and corresponding substrates; Sulfanilic diazonium salt which react with analytes such as bilirubin, and amino acids; Griess reagent for analysis of NO^2" and/or NO^3"; indicators for metal ion analysis (e.g. bathocuproine, dimethylglyoxime, 1 ,5-diphenylcarbazide) for detection of Cr⁶⁺, Cu²⁺, Ni²⁺, Zn²⁺, Fe³⁺, Pb²⁺, etc.; tetrabromophenol blue for bovine serum albumin, other proteins; and purpald for formaldehyde.

The term "chemical analyte", as used herein, is intended to refer to any chemical compound for which detection is desirable. There are a large range of potential chemical analytes, and a non-limiting disclosure of potential chemical analytes includes: chemical moieties, acids, bases, proteins, metal ions, organic compounds etc.

A non-limiting disclosure of suitable chemical analytes include: acids such as mineral acids (e.g. HCI, HF, HBr, HI, HCIO₄, HNO₃, H₃PO₄, H₃BO₃, H₂SO₄, H₂CO₃ etc.) organic acids (fatty acids, acetic acid, citric acid (in solution or solid states), formic acid, wherein the acids may be in solution, solid state, present as a component of for example insects (e.g. in the case of formic acid in particular) or in foods; bases such as alkali hydroxides, (e.g. NaOH, KOH, etc.) carbonates or bicarbonates (e.g. Na₂CO₃, K₂CO3, NaHC03, KHCO3 etc.); ammonia (such as in solution or gas states); amines; metal ions, including but not limited to, Cu²⁺, Ni²⁺, Cr⁶⁺, Zn²⁺, Pb²⁺, etc.; organic and biochemical compounds, include but not limited to, formaldehyde, NO^2", uric acid, glucose, bilirubin, Gluten (for example in wheat flour). In one form of the invention, the non-Newtonian fluid carrier is chemically inert to the chemical analyte. In an alternative form of the invention, the non-Newtonian fluid carrier is the chemical indicator. By chemically inert it is meant that the carrier does not undergo chemical reaction with the chemical analyte on exposure to the chemical analyte (for example during use). In an embodiment, the non-Newtonian fluid carrier is chemically inert to the chemical indicator (i.e. the carrier does not undergo chemical reaction with the chemical indicator).

In an embodiment, the non-Newtonian fluid carrier is an adhesive. The use of an adhesive is advantageous as this can improve retention of the chemical analyte into the carrier and/or improve retention of the chemical indicator into the carrier. In such cases, the mode of adhesion is by chemisorption (chemical bonding between the carrier and the adhesive) and/or physisorption (physical bonding between the carrier and the adhesive). Chemisorption includes the formation of covalent, ionic, or hydrogen bonds between the carrier and the chemical analyte. In contrast, physisorption includes attraction between the carrier and the chemical analyte as a result of dispersive forces (such as Van der Waals forces), diffusion, and/or electrostatic attraction. A wide range of different adhesives may be used. Preferred adhesives include polymers or elastomers. Particularly preferred adhesives are acrylate polymers (which may also be referred to as acrylics or polyacrylates). In one form of the invention, the adhesive is chemically inert to the chemical analyte, and operates via physisorption. In one form of the invention, the adhesive is chemically inert to the chemical indicator and retains the chemical indicator via physisorption.

In an alternative embodiment, the non-Newtonian fluid carrier is a gel. Preferably the gel is a hydrogel. In an alternative embodiment, the non-Newtonian fluid carrier is a wax. In a further alternative embodiment, the non-Newtonian fluid carrier is a polymeric carrier. It will be appreciated that the chemical indicator may be dispersed within the non- Newtonian fluid carrier and/or on a surface of the non-Newtonian fluid carrier. In a first arrangement, the non-Newtonian fluid carrier is a matrix phase that includes the chemical indicator dispersed therein. In a second arrangement, the non-Newtonian fluid carrier is provided as a layer having a surface with the chemical indicator disposed thereon. In the second arrangement, the chemical indicator may be disposed on the surface of the non-Newtonian fluid carrier as a separate cohesive layer, or may be disposed on the surface in a random or patterned arrangement. It is preferred that the chemical indicator is disposed on the surface of the non-Newtonian fluid carrier in a patterned arrangement, such as in the form of a pattern, shape, symbol, or combination thereof.

In an embodiment, the non-Newtonian fluid carrier includes a plurality of indicators, each indicator sensitive to a different chemical analyte to each other indicator. In an embodiment, the chemical-responsive composition further includes a humectant. The humectant may be disposed within or on a surface of the non- Newtonian carrier. For example, where the non-Newtonian fluid carrier is a matrix phase the humectant is disposed within the non-Newtonian fluid carrier. Alternatively, where the chemical indicator is disposed on the surface of the non-Newtonian fluid carrier as a separate layer, the separate layer includes the humectant. Preferred humectants include glycerol; glycol; polyglycol; metal salts, such as magnesium salts, lithium salts, aluminium salts; and/or sugar.

In an embodiment, the chemical-responsive composition further includes a masking reagent. The masking reagent may be disposed within or on a surface of the non-Newtonian carrier. For example, where the non-Newtonian fluid carrier is a matrix phase the masking reagent is disposed within the non-Newtonian fluid carrier. Alternatively, where the chemical indicator is disposed on the surface of the non- Newtonian fluid carrier as a separate layer, the separate layer includes the masking reagent. The term "masking reagent" is intended to refer to an additives that undergoes reaction with potential interference elements in a sample to convert the interference element to a form that does not interfere with analyte detection. For example, the masking reagent may react with an interference element to form a complex or precipitate.

In a second aspect of the invention, there is provided a chemical-responsive tape including: a film of a backing material having a layer of the chemical-responsive composition as defined above applied to a surface thereof.

The term "backing material" as used herein, is intended to generally refer to any flexible material that may be used to form a tape and retain the layer of the chemical- responsive composition thereon. The skilled addressee is familiar with such materials, and the selection of a specific backing material may be dependent on the intended use of the tape or the environment in which the tape is used. However, a non-limiting disclosure includes polymers, paper, fibres and fabrics. It is preferred that the backing material is transparent. This enables visual observation of a change in the appearance (such as colour) of the chemical indicator.

In one or more forms, the backing material is non-fibrous. The backing material may be porous or non-porous. However, in one or more forms, the backing material is non-porous.

In a third aspect of the invention, there is provided a chemical-responsive tape including: a film of a backing material with a chemical-responsive adhesive disposed on a surface of the backing material, the chemical-responsive adhesive including: an adhesive carrier, and at least one chemical indicator for a chemical analyte; wherein the chemical indicator is retained by the adhesive carrier, and the chemical indicator exhibits a chemical response when exposed to the chemical analyte.

In one or more forms, the backing material is non-fibrous.

In one or more forms, the backing material is non-porous. In an embodiment, the adhesive carrier includes a pressure-sensitive adhesive. A pressure-sensitive adhesive is one which forms a bond with a surface when the adhesive is placed onto the surface with pressure. In an embodiment, the adhesive carrier includes a plurality of indicators, each indicator sensitive to a different chemical analyte to each other indicator.

In an embodiment, the adhesive carrier further includes a humectant.

In an embodiment, the adhesive carrier further includes a masking reagent. In an embodiment, the chemical indicator is disposed on the surface of the carrier in the form of a pattern, shape, symbol, or combination thereof.

In an embodiment, the indicator is a colorimetric indicator or a fluorescent indicator.

In a fourth aspect of the invention, there is provided a method for forming a chemical-responsive tape, the method including: depositing a chemical-responsive composition onto a surface of a tape to form the chemical-responsive tape, wherein the chemical-responsive composition includes: a non-Newtonian fluid carrier; and a chemical indicator for a chemical analyte; wherein the chemical indicator is retained by the chemical-responsive composition on the surface of the tape, and the chemical indicator exhibits a chemical response when exposed to the chemical analyte.

In one or more forms, the tape is non-fibrous.

The backing material may be porous or non-porous. However, in one or more forms, the tape is non-porous.

In an embodiment, the carrier further includes a humectant. In an embodiment, the carrier further includes a masking reagent.

In a fifth aspect of the invention, there is provided a method for forming a chemical-responsive tape, the method including: depositing a chemical indicator composition including a chemical indicator for a chemical analyte onto an adhesive surface of an adhesive tape, to form the chemical-responsive tape; wherein the chemical indicator composition is retained by the adhesive, and the chemical indicator exhibits a chemical response when exposed to the chemical analyte.

In one or more forms, the adhesive tape is non-fibrous. In one or more forms, the adhesive tape is non-porous.

In an embodiment, the chemical indicator composition further includes a humectant.

In an embodiment, the chemical indicator composition further includes a masking reagent.

In an embodiment of the fourth and fifth aspects, the indicator is deposited on the surface of the carrier in the form of a pattern, shape, symbol, or combination thereof.

In a sixth aspect of the invention, there is provided the use of a chemical- responsive composition or a chemical-responsive tape as defined previously to test for the presence of a chemical analyte.

Further aspects of the present invention and further embodiments of the aspects described in the preceding paragraphs will become apparent from the following description, given by way of example and with reference to the accompanying drawings.

Brief description of the drawings

Figure 1 : Illustration of an embodiment of a chemical-responsive adhesive tape in accordance with the present invention.

Figure 2: Schematic diagram of tape-based adhesive sensor detection and reporting of metal ions in their chemical symbols.

Figure 3: Schematic diagram of tape-based adhesive sensor detection and reporting of multi-metal ions in bar-code style.

Figure 4: (A) The detection process for Cr⁶⁺ with tape-sensor; (B) Tape- sensor detects alkaline and acid liquid samples on paper; (C) Tape-sensor detects bovine serum albumin (BSA) sample on paper; (D) Tape-sensor detects Cu²⁺, Ni²⁺, Cr⁶⁺ in text reporting manner on paper; (E) Tape-sensor detects metal ions in bar-code shaped style (left: sample contains Ni⁺² only; middle: sample contains Cu⁺² only; right: sample contains Cr⁺⁶ only. Figure 5: Schematic diagram of tape-based adhesive sensor detection of target chemical analytes in dry powder.

Figure 6: Comparison of powder detection on glass- and paper-based substrates by chemical-responsive adhesive tape. Figure 7: Colorimetric assay of heavy metal salts powder in text-on chemical- responsive adhesive tape

Figure 8: Calibration curves fitted by the measured colour intensity versus the molar ratio of each kind of metal powder with Si0₂ powder: a) CuS0₄, molar ratio from 1 :30000 to 1 :100; b) NiCI₂, from 1 :20000 to 1 :400 mg/L; c) K₂Cr₂0₇, from 1 :50000 to 1 :400.

Figure 9: Comparison of control group and impurity group. Impurities tolerant studies of the CAT device for three kinds of target heavy metal salt Si0₂ powders (with molar ratio of 1 :1000) in the presence of NiCI₂-6H₂0/Si0₂, CuSCySi0₂, K₂Cr₂0₇/Si0₂, ZnS0₄-7H₂0/Si0₂, and CoCI₂-6H₂0/Si0₂ powders (with molar ratio 1 :1000, respectively) as impurities with the mass ratio of 1 :1 :1 :1 :1 (5 parallel tests for each assay).

Figure 10: Calibration curves fitted by the measured colour intensity versus the concentration of each ion: a) Cu(ll), 0 to 1 0 mg/L; b) Cr(VI), from 0 to 4mg/L ; (c) Ni(ll), from 0 to 1 0mg/L. Figure 11 : Colorimetric text-reporting assays by CAT depicting different concentrations of: (a) Cu(ll), (b) Cr(VI), (c) Ni(ll) and (d) BSA solution.

Figure 12: Interference tolerant studies of the paper devices for the three target heavy metal ions in the presence of 20mg/L Cu(ll), Cr(VI), Co(ll), Fe(lll), Zn(ll), Mn(ll) for 2mg/L Ni(ll) assay ; 20mg/L Ni(ll), Cr(VI), Co(ll), Fe(lll), Zn(ll), Mn(ll) for 2mg/L Cu(ll) assay ; 20mg/L Ni(ll), Cu(ll), Co(ll), Fe(lll), Zn(ll), Mn(ll) for 2mg/L Cr(ll) assay, and 400mg/L Na(l) and K(l), 200mg/L Ca(ll) and Mg(ll) for all the three assays. Five parallel tests for each target metal ion assay.

Figure 13: Calibration curves fitted by the measured colour intensity versus the natural logarithm of gluten content percentage from 0.1 % to 5% in flour. Figure 14: Detection of wheat flour with different gluten contents.

Figure 15: Calibration curve of BSA solution with concentration from 0 to 6mg/ml_.

Figure 16: Chemical-responsive adhesive paper chip for NiCl₂/SiC>₂ powder (with molar ratio of 1 :5000, 1 :2000, 1 :1 000, respectively) detection.

Figure 17: Formulation of acid-base responsive liquid adhesive tape, (a) Methyl orange is mixed and dissolved in liquid glue (Stuk); (b) a drop of acid-base responsive glue is transferred onto a 3M magic tape; (c) the glue is spread evenly on the tape, forming an acid-base responsive tape; (d) the acid-base responsive tape detect low pH on an acid treated paper.

Figure 18: Chemical responsive hydrogel (demonstration 3). (a) A transparent hydrogel of cellulose nano-fibres; (b) methyl orange is mixed with the hydrogel, forming an indicator hydrogel, which can be shaped and can adhere to other surfaces; (c) hydrogel indicator can be transferred onto a substrate (in the demonstration we used glass) to form a chemical responsive hydrogel sensor; (d) the application of the chemical responsive hydrogel sensor to an acid- and base- treated papers caused instant colour change of the hydrogel indicator, leading to instant identification of acid and base sample. Photos in (d) were taken from the front surface of acid (base) modified paper (left) and the back surface of the paper (right). Figure 19: Photograph showing colour intensity difference and absence of

"coffee staining" in analytical paper modified with chemical-responsive glue composition in comparison with an analytical paper without chemical-responsive glue.

Figure 20: Photograph showing colourimetric result from experiment to detect presence of total serum bilirubin. Figure 21 : Photograph showing droplets of Ni²⁺ solution on standard office A4 paper, and subsequent detection of trace amounts of Ni²⁺ using a chemical-responsive adhesive tape. Figure 22: Photograph showing droplet of HRP solution on a hydrophobic plastic surface, and subsequent detection of trace amounts of HRP using a chemical- responsive adhesive tape.

Figure 23: Photograph showing droplets of HRP solution on a hydrophobic paper surface, and subsequent detection of trace amounts of HRP using a chemical- responsive adhesive tape.

Detailed description of the embodiments

In preferred forms, the invention provides a platform (adhesive tapes, adhesives formulated with chemicals, solid gels formulated with chemicals) for a new class of analytical sensors that can directly analyse and report analytical results by contact. This platform can be easily used to test whether a substrate (for example a surface) includes chemical analyte(s) of interests. If the substrate includes the chemical analyte(s), then the platform can rapidly provide a visual output (such as a colour change) indicating the presence of the chemical analyte(s). The invention is broadly described in relation to two forms. The first form is a chemical-responsive adhesive tape. The second embodiment is a chemical-responsive composition.

A chemical-responsive adhesive tape is an adhesive tape that has been modified with a chemical indicator composition that includes a chemical indicator (e.g. a colour, colourimetric, fluorescent, or biological sensing chemical indicator) to enable the tape to detect and report the presence of target chemical analytes (e.g. heavy metal ions; salts; biomolecules such as proteins, biofilms, blood antigen-antibody identifications, and bio- contaminants). Chemical indicators can be introduced onto or into the adhesive surface of the tape using a variety of different mechanisms available to the skilled person, for example, by deposition or printing. The chemical indicators may be patterned onto or into the adhesive surface, for example in the form of a dot pattern, symbols, or text. Alternatively, the chemical indicators may be directly formulated into the adhesive component of the tape.

One embodiment of the invention is illustrated in Figure 1 . Figure 1 shows a chemical-responsive adhesive tape that is formed from a film of a backing material 100 having first and second opposite facing surfaces. An adhesive composition 102 is applied to the first surface of the backing material 100, such as by patterning 104 or coating 106 the first surface 100 with the adhesive composition 102. The adhesive composition 102 includes a chemical indicator composition having at least a chemical indicator for a chemical analyte, the chemical indicator undergoing a change that is visible to the naked-eye on contact with the chemical analyte (such as due to a chemical reaction between the indicator and the chemical analyte). To use the chemical-responsive tape, a user places a portion of the tape first side down (i.e. the side that is coated with the adhesive) onto a substrate surface 108 to be tested for the chemical analyte 1 1 0. The user may apply pressure to the second side to flatten the chemical responsive adhesive tape against the substrate 1 12 so that a sample is transferred into the adhesive from the substrate surface. The chemical responsive adhesive tape may then be removed from the substrate surface 1 14. If the chemical analyte is present in the sample then this can interact with the chemical indicator to provide a visually observable change in the chemical-responsive adhesive tape indicating the presence of the chemical analyte in the sample 1 1 6.

Chemical-responsive adhesive tapes have a number of advantages over traditional paper based chemical responsive sensors. Traditional paper based chemical responsive sensors rely are those that include a chemical indicator embedded within a paper carrier. However, these paper based sensors are limited to sensing and measurement of a chemical analyte in liquid samples. This is because paper based sensors rely on liquid absorption or wicking to bring the chemical sensor and the chemical analyte into contact. Reliance on liquid absorption or wicking creates a number of problems. Traditional paper sensors cannot be applied to dry surfaces as they are unable to detect the presence of a chemical analyte in a dry state. Instead a dry surface needs to be washed with a solvent carrier for the chemical analyte, and then that solvent carrier is applied to the paper based sensor to test for the presence of the chemical analyte. Further, the reliance on a solvent carrier for the chemical analyte places restrictions on the type of indicator composition that can be used. The indicator composition ideally needs to be insoluble in the solvent carrier otherwise the indicator composition may be leached or washed from the paper sensor by the solvent carrier. This has been an issue with the development of paper based sensor for detection of chromium (VI) ion, since when an indicator-loaded paper is dipped in an aqueous sample containing Cr(VI), the indicator is washed off the paper.

In contrast, the chemical responsive adhesive tapes of the present invention may advantageously be applied to detect the presence of a chemical analyte in solid surfaces, particulate materials, materials that have physical properties of putties (e.g. dough, cheese, fruit flesh, plant matter, some building materials, etc.) and liquid samples to obtain a rapid analytical appraisal of the presence of target chemicals and biological substances while avoiding many of the issues of paper sensors. Use of chemical-responsive adhesive tapes is not restricted by the wettability of a surface or substrate, and as such, chemical responsive adhesive tape can be applied to both hydrophilic and hydrophobic surfaces for chemical analysis.

By way of non-limiting example, the chemical responsive adhesive tapes of the present invention are capable of analysing: solid powder samples that contain heavy metal ions; biofilms formed on walls of industrial reactors for biological, pharmaceutical and food processing; biological contaminations of solid surfaces, such as lab benches, commercial or home kitchen equipment for hygiene assurance, testing surfaces for the presence of organic contaminants etc.

In another example, chemical responsive adhesive tape can be used with single- direction-liquid-transport-fabrics such as in wound-dressing products. These products can be applied to wounds; the single direction fabrics will allow body fluid to transport across the fabric in one direction to reach the chemical indicator on the chemical responsive adhesive tape while preventing transport of the indicator in the reverse direction across the fabric to reach the wound.

In still another example, chemical responsive adhesive tape can be designed to detect the emission of vapours of certain harmful compounds from a solid surface (potentially capable of detecting formaldehyde and amine emission from building materials, painted surfaces and textiles). In this example, the chemical responsive adhesive tape may be adhered to a surface to detect gaseous chemical analyte species that are evolved over time (such as compounds that are emitted from painted surfaces as the paint ages). Another advantage over traditional paper sensors is that chemical responsive adhesive tape can be used to detect and report the distribution of chemical analyte on a substrate. This is in part because, the chemical indicator is immobilized by application to, or formulation within, the adhesive of the tape; and the application of the indicator is through direct physical contact and does not require the chemical analyte to be washed from the surface for testing as with a paper sensor which relies on absorption or wicking for detection. In an exemplary embodiment, a chemical-responsive adhesive tape includes a chemical indicator that exhibits a visual response that is proportional to the concentration of a chemical analyte (such as an intensity or variation in colour). A portion of this chemical-responsive tape may be applied over a length of a surface of the substrate. If one part of the substrate includes a higher concentration of the chemical analyte than the rest of the substrate, then the portion of the chemical- responsive tape overlying this portion will exhibit a visual response indicative of this higher concentration (such as a colour change of higher intensity, or by exhibiting a different colour). In this way, a chemical-responsive provides a mechanism for quickly determining the distribution of a chemical analyte over the surface of a substrate.

The second form of the invention is broadly described as a chemical-responsive composition. A chemical-responsive includes a non-Newtonian fluid carrier (such as a gel, wax, clay, adhesive, or polymeric carrier) that has been modified to include a chemical indicator composition. Chemical-responsive compositions can be used to detect target chemical analytes in samples of different physical forms, e.g. solid, solid particles, putties, vapours. It is difficult to analyse samples of such physical forms using microfluidic sensors, since extra steps of sample preparation are required, which can make the microfluidic sensing too difficult for those samples. The platform of chemical- responsive compositions delivers a class of convenient contact sensing, which significantly reduces difficulty.

Many materials can be used to form gels which become the carrying phase of the chemical indicators, these materials include (but are not limited to) starch, gelatine, cellulosic materials, polar wax, adhesives on adhesive tapes, pencils with "white lead" (e.g. clay filler containing indicators), Blu Tack, Glue Stick, liquid glue, hydrogels, etc.

The gel or solid indicators can be designed to (a) transfer the indicator to the substrate and cause colorimetric change for detection, (b) back-transfer chemical analytes from a given surface to the gel indicator, which displays colorimetric sensing results. The gel indicators can be formed using the same or different base materials and can be combined by kneading to form new indicators for multiple chemical analyte sensing, without interference. Examples

Materials and equipment

Copper(ll) sulfate (CuS0₄), nickel(ll) chloride hexahydrate (NiCI₂-6H₂O), potassium dichromate (K₂Cr₂07), bathocuproine, chloroform, hydroxylamine hydrochloride (NH₂OH HCI), glacial acetic acid (CH₃COOH), dimethylglyoxime (DMG), ethanol, sodium fluoride (NaF), sodium thiosulfate (Na₂S₂0₃), 1 ,5-diphenylcarbazide (DPC), acetone, sulfuric acid (H₂S0₄), bovine serum albumin (BSA), tetrabromophenol blue, citrate acid, glycerol, zinc sulfate heptahydate (ZnS0₄-7H₂0), cobalt(ll) chloride hexahydrate (CoCI₂-6H₂0), silica (Si0₂), and Whatman 1 # quantitative-grade filter paper were purchased from Sigma Aldrich (St. Louis, MO, USA). Scotch magic tape and glue stick were from Monash University (Melbourne, AU). Flour with different contents of gluten (0, 20%) was purchased from Coles supermarket (Melbourne, AU). Colour intensity recording was conducted with a colour scanner (EPSON Perfection V370).

Device fabrication and operation Chemical-responsive adhesives were fabricated using two primary methods. In the first method, a chemical indicator composition was applied to the adhesive surface of an adhesive tape (such as scotch tape which includes an acrylate polymer adhesive). The chemical indicator compositions were either applied in a dot pattern or in text pattern. Figure 2 and Figure 3 illustrate the application of the chemical indicator composition in text and barcode pattern to form the chemical-responsive adhesive tape.

In order to test these devices (as will be described in more detail below) the chemical-responsive adhesive tapes are brought into contact with a filter paper that has been soaked in a solution containing the chemical analyte and subsequently dried. On detection of the chemical analyte a chemical symbol indicating the chemical analyte becomes visible (see Figure 2) or a coloured bar corresponding to the chemical analyte becomes visible (see Figure 3).

Figure 4 shows the results from testing chemical-responsive adhesive tapes configured to detect (a) Cr⁶⁺, (b) acid and base, (c) bovine serum albumin (BSA), (d) Cu²⁺, Ni²⁺, Cr⁶⁺ in text reporting manner on paper, (e) metal ions in bar-code style shapes (left: sample contains Ni²⁺ only; middle: sample contains Cu²⁺ only; right: sample contains Cr⁶⁺ only). This will be discussed in more detail below. In Figure 4(A), Cr6+ indicator is applied to the adhesive layer of an adhesive tape in a r' pattern, the presence of the indicator on the adhesive tape is not visible. The tape is then applied to a paper including Cr⁶⁺. The chemical indicator reacts with the Cr⁶⁺ exhibiting a colour change, resulting in the letters r' becoming visible. Similar results are reported in Figure 4(B) which shows a colour change revealing the letters OH and H+; Figure 4(c) revealing the letters BSA; Figure 4(D) revealing orange letters for Cu, and pink letters for Ni and Cr respectively; and Figure 4(E) revealing different coloured bars indicating the detection of Ni²⁺, Cu²⁺, and Cr⁶⁺ respectively.

In the second method, adhesive obtained from a glue stick was blended with a chemical indicator composition and then applied to a film of a backing material (such as paper, plastic film, etc.) (see Figure 5). The glue stick used in this method was a solid glue stick sold by Office Works with the brand name Glue Stick produced by Staples. The primary components are water 60%, polyvinyl pyrrolidine 22%, glycerol 10%, sodium stearate 8%. To test the operation of the device, the adhesive surface was brought into contact with a dry substrate including the chemical analyte. A visible colour change occurs (discernible via the naked-eye) indicating the presence of the chemical analyte. Example 1 : Metal ion detection and quantification in dry metal salt powder

This example reports the use of chemical responsive adhesive tapes for a one- step detection of metal ions in a dry metal salt powder. In this example, different chemical indicator compositions were prepared and applied to the adhesive surface of an adhesive tape for detecting the presence of Cu ⁺, Ni ⁺, and Cr⁶⁺ in dry metal salt samples of CuS0₄, NiCI₂, K₂Cr₂07 respectively. In each case, the chemical indicator composition included: an indicator reagent specific to the metal ion analyte, a masking reagent to mitigate to mask chemical species which may interfere with the analysis, and a humectant. In this example, the presence of the humectant is important. This is because the humectant retains moisture, which on contact with the dry metal salt powder, dissolves a portion of the dry metal powder releasing the metal ions for reaction with the indicator reagent. The specific chemical indicator compositions for detection of Cu²⁺, Ni²⁺, and Cr⁶⁺ in dry salt samples are provided below.

For CuS0₄ detection, the chemical indicator composition included: 0.05g/ml_ bathocuproine in chloroform as the indicator reagent, 0.1 g/L hydroxylamine in acetic buffer (6.3M) as the masking reagent, and glycerol as the humectant. The ratio of indicator reagent to masking reagent to humectant was 1 :1 :2 by volume.

For NiCI₂ detection, the chemical indicator composition included: 120mM dimethylglyoxime (DMG) in ethanol as the indicator reagent, a mixture of NaF and Na₂S₂0₃ in solution (20 and 80 mg/mL, respectively) as the masking reagent, and glycerol as the humectant. The ratio of indicator reagent to masking reagent to humectant was 1 :1 :2 by volume.

For Κ₂ΟΓ₂0₇ detection, the chemical indicator composition included 1 ,5- diphenylcarbazide(DPC, 1 mg/mL) in 50% acetone as the indicator regent, 1 % H₂S0₄ as the masking reagent, and glycerol as the humectant. The ratio of indicator reagent to masking reagent to humectant was 1 :1 :2 by volume.

To conduct the tests 0.05g of mixed metal powders was prepared in molar ratios of CuS0₄/Si0₂ of from 1 :30000 to 1 :100, NiCI₂/Si0₂ of from 1 :20000 to 1 :400, and K₂Cr₂0₇/Si0₂ of from 1 :50000 to 1 :400. The silica (Si0₂) acts as a diluent and thus allows for results to be obtained at different metal salt concentrations. Samples of the mixed metal powders were transferred onto both glass and filter paper (Whatman 1 #) platforms, followed by affixing a corresponding chemical adhesive tape to the filter paper over the powder. In all cases, a colour change was observed indicating detection of the chemical analyte. Photographs showing the colour change on glass and paper substrates are shown in Figure 6. Figure 6 generally shows a powder including an analyte on a surface, a tape sensor loaded with an appropriate indicator wherein the indicator is not visible to the human eye, and then the colour change that occurs on application of the adhesive tape to the surface including the analyte containing powder. In the case of Figure 6(B), a different colour change is observed for Cr (pink) and Cu (orange); as such, the chemical-responsive tape can be used to distinguish between analytes by providing visually distinct outputs.

Figure 7 is a photograph of further results where the chemical indicator composition was patterned onto the chemical-responsive adhesive tapes in the form of letters corresponding to the chemical symbols for Cr, Cu, and Ni. Again, this provides a mechanism for the chemical-responsive tape to provide a different output based on the detected analytes.

The limits of detection for Cu-, Ni-, and Cr-powder were found to be 1 :30,000, 1 :20,000, and 1 :50,000 respectively using the naked-eye. Additionally, the intensity of the colour change was found to vary with concentration of the Cu-, Ni-, and Cr-powder. A linear relationship between the natural logarithm of the mixed metal powder molar ratio and the colour intensity was observed. The results are shown in Figure 8. These results can be used as calibration curve to determine the concentration of an unknown sample from colour intensity.

The effect of metal ion impurities on detection of metal ion analytes

A multi-mixed metal salt/Si0₂ powder was prepared by blending NiCI₂/Si0₂, CuSCVSi0₂, K₂Cr₂0₇/Si0₂, CoCI₂/Si0₂ and ZnSO+/Si0₂ (with molar ratio of 1 :1000, respectively) in a mass ratio of 1 :1 :1 :1 :1 . The same chemical responsive adhesive tapes as used above (i.e. for detection of Cu²⁺, Ni²⁺, and Cr⁶⁺ in dry salt samples) were then used to detect the presence of the target metal ion analyte in 0.05g of the multi- mixed metal salt. The results were compared against the results above in respect of the single target metal salt Si0₂ powder with molar ratio of 1 :5000.

Results are shown in Figure 9 illustrating that impurities do not have a significant impact on the performance of the chemical responsive adhesive tape. Thus, chemical responsive adhesive tape may be used for sophisticated metal salt powder mixture detection. Example 2: Metal ion detection and quantification from a metal ion solution This example reports the use of chemical responsive adhesive tapes for the detection of metal ions in samples obtained from a metal ion solution. Metal ions including Cu²⁺, Ni²⁺, and Cr⁶⁺ were tested.

Samples were prepared by immersing filter paper into aqueous solutions of Cu²⁺, Ni²⁺, and Cr⁶⁺ ions. The filter paper was then air dried at room temperature and chemical responsive adhesive tapes were used to test for the presence of these ions. Results, along with device photographs, are shown in Figure 10 and Figure 11. As with Example 1 , the colour intensity was proportional to the concentration of metal ions detected over the range of: 0 to 10ppm for Cu²⁺, 0 to 10ppm for Ni²⁺ and 0 to 4ppm for Cr⁶⁺. This provides a tool that can be used to estimate the metal ion concentration for a specific metal ion analyte in a sample of unknown concentration.

The inventors also envisage using such chemical responsive adhesive tapes as a product that can quickly determine whether a particular metal ion exceeds a threshold concentration for a particular environment. By way of example, drinking water standards apply maximum concentrations for various ions. In Australia, these standards are set by the National Health and Medical Research Council which have set limits as follows: the limit for Cu²⁺ is 1 mg/L, the limit for Cr⁶⁺ is 0.5 mg/L, and the limit for Ni²⁺ is 2 mg/L.

Figure 11 (a) to 11 (c) illustrate an embodiment in which the chemical responsive adhesive tapes have been applied to the filter paper samples (prepared as described above) which adhesive tapes are patterned with chemical indicator compositions in the form of letters denoting "Cu", "Cr", and "Ni". On detection of a threshold level of Cu²⁺, Ni²⁺, and Cr⁶⁺ ions, the "Cu", "Cr", and "Ni" become visible with increasing colour intensity as a function of Cu²⁺, Ni²⁺, and Cr⁶⁺ concentration. The appearance of these symbols informs a user that the concentration of these ions exceeds the threshold limit, and is therefore potentially dangerous.

The effect of metal ion impurities on detection of metal ion analytes

Interference tolerance studies were conducted for the three target heavy metal ions (Cu ⁺, Ni²⁺, and Cr⁶⁺) in the presence of 20mg/L Cu(ll), Cr(VI), Co(ll), Fe(lll), Zn(ll), Mn(ll) for 2mg/L Ni(ll) assay ; 20mg/L Ni(ll), Cr(VI), Co(ll), Fe(lll), Zn(ll), Mn(ll) for 2mg/L Cu(ll) assay ; 20mg/L Ni(ll), Cu(ll), Co(ll), Fe(lll), Zn(ll), Mn(ll) for 2mg/L Cr(ll) assay, and 400mg/L Na(l) and K(l), 200mg/L Ca(ll) and Mg(ll) for all the three assays. Five parallel tests for each target metal ion assay.

The interference tolerance shown in Figure 12 illustrates that the presence of other metal ions does not have a significant effect on the detection of Cu²⁺, Ni²⁺, and Cr⁶⁺.

Example 3: Gluten detection and quantification

Gluten is a large protein found in grass grains including wheat, barley and rye. In sensitive people, gluten can damage the intestine, leading to disease. Gluten -related disorders are an umbrella term for all diseases triggered by gluten, which include celiac disease (CD), non-celiac gluten sensitivity (NCGS), wheat allergy, gluten ataxia, and dermatitis herpetiformis (DH). NCGS (or "gluten sensitivity") is a clinical entity induced by the ingestion of gluten leading to intestinal and/or extraintestinal symptoms that resolve once the gluten-containing foodstuff is eliminated from the diet. Thus, the provision of a simple device that can be easily and rapidly used to test a food product for the presence of gluten and provide a simple "yes or no" indication is desirable.

Chemical responsive adhesive tape provides an ideal platform to implement gluten point-of-use assay since gluten source in our daily diet normally originates from grain food like wheat flour, which is a type of powder. In this example, tetrabromophenol blue (TBPB) has been used as the indicator to detect gluten. The flour samples used in this example are those that do not have extra proteins to ensure that the detection result are due to the presence of gluten. The existence of gluten can be quantitatively monitored via observing the colour hue development from yellow to dark green shown in Figure 13 and Figure 14. There is a liner relationship between the natural logarithm of gluten content percentage (from 0.1 % to 5%) and the colour intensity. Example 4: Bovine serum albumin (BSA) detection and quantification

This example reports the use of chemical responsive adhesive tapes for the detection of BSA in a BSA solution.

The BSA indicator composition included 3mM tetrabromophenol blue in 95% ethanol, 250mM citrate buffer and glycerol with the volume ratio of 1 :1 :2. The measurement procedure of BSA solution (from 0.2mg/ml_ to 8mg/ml_) was similar to that for metal ion detection discussed in Example 2.

BSA detection (similar with metal ions in Example 2) can also be reported using a text indicator (see "BSA" in Figure 11 (d)). For this experiment, the limit of detection was found to be 0.5mg/ml_. The result shown in Figure 15 indicates that the colour intensity of the product complex is proportional to the logarithm of the BSA concentration over the range of 0 to 6 img/mL and can be fitted using the function Log (CBSA₊I ) -

Example 5: Gel based glue sensors

This example demonstrates the use of gel or solid indicators. This example demonstrates the formulation of an adhesive indicator using a solid glue (trade name Glue Stick), a liquid paper glue (trade name Stuk), and a cellulose nano-fibre hydrogel.

(a) Glue stick based adhesive sensor

A Chemical-responsive adhesive shows the use of Glue Stick to formulate a Ni²⁺ detecting adhesive by mixing the Ni²⁺ indicator with Glue Stick.

400 μΙ_ of DMG/ethanol solution (120mM) was mixed with 1 .0 g of glue from a Glue stick to form a Ni²⁺ responsive glue. This Ni²⁺ responsive glue is transferred onto a piece of Whatman filter paper to form a Ni²⁺ responsive adhesive paper. Upon contacting Si0₂ powder containing NiCI₂, this Ni²⁺ responsive adhesive paper exhibits an almost instant colour change, indicating the presence of Ni²⁺ (see Figure 16 which demonstrates chemical-responsive adhesive applied to paper to for sampling NiC^/SiC^ powder with molar ratios of 1 :5000, 1 :2000, 1 :1000 respectively) In this demonstration, the metal ion analyte (Ni²⁺) is back transferred from the powder onto the Ni²⁺ responsive adhesive tape. (b) Stuk based adhesive sensor

Another chemical-responsive adhesive shows the use of liquid glue (Stuk) to formulate an acid-base adhesive indicator. Methyl orange (solid), was first mixed with the liquid glue and dissolved in the glue to form an acid-base responsive glue with a methyl orange concentration of about 0.01 wt%. The acid-base responsive glue was then applied directly to a transparent adhesive tape to form an acid-base responsive tape (see Figure 17). An acid treated paper was made by depositing 200μΙ_ of <1 % H₂S0₄ solution on the filter paper which is then allowed to dry at room temperature.

When the acid-base responsive tape is contacted with an acid-treated paper, it exhibits an almost instant colour change (see Figure 17).

(c) Hydrogel based sensor A chemical-responsive hydrogel is prepared via a formulation of gel indicator. A hydrogel is a material that shows solid characteristics, while containing large amount of water (up to >98%). Hydrogel can be shaped and can also adhere to other solid surfaces. While many gels can be used to demonstrate the concept of gel indicator, the present example is based on a transparent gel made of cellulose nano-fibres. This gel consists of 98% water and is able to dissolve water soluble indicators while retaining the gel properties.

A hydrogel acid-base indicator was formulated by mixing methyl orange with cellulose nano-fibre gel in a ratio of 1 :99 (w/w). The gel containing methyl orange retains the gel structure and can be easily shaped. The indicator gel is transferred onto a substrate (in the demonstration as illustrated in Figure 18, a glass substrate is used).

When the indicator gel is brought into contact with an acid-treated paper, it exhibits and almost instant colour change (see Figure 18).

Example 6: Demonstration of improved sample retention with chemical- responsive glue

Figure 19 shows a comparison in the collection and result reporting between analytical paper and an analytical paper including a chemical-responsive glue detecting Ni²⁺, Cu²⁺, and Cr⁶⁺ samples (as per Example 1 ). As can be seen in Figure 19, the analytical paper with the chemical-responsive glue exhibits better sample retention, and reports results with greater colour intensity and without "coffee staining" than in comparison with the analytical paper without the chemical-responsive glue. Example 7: Adhesive tape sensor for total serum bilirubin (TSB) detection

Detection and quantification of serum bilirubin is a critical sensory technology for care of jaundiced infants. Major Children's Hospitals in Australia only take serum bilirubin level as the diagnostic information for decision-making. The disclosed method is a method suitable for developing bilirubin sensor for home-care of jaundiced babies. Materials

Bilirubin (in form of dry powder), human serum, dimethyl sulfoxide (DMSO), hydrochloric acid (HCI), sodium carbonate (Na₂C0₃), a commercial bilirubin assay kit (Reagent A (a mixture of sulfanilic acid and hydrochloric acid), Reagent B (sodium nitrite), Reagent C (caffeine and sodium benzoate)). In preparation of sample of bilirubin/human serum, a known amount of dry bilirubin sample (2.0 mg) was thoroughly dissolved in DMSO (0.3 ml.) and 0.05 mol/L Na₂C0₃ solution (0.6 ml.) in a beaker, and then was fully transferred to a 1 0 mL flask. The beaker was rinsed by human serum and then transferred to the flask. 0.1 mol/L HCI solution (0.6 mL) was then added in the flask to adjust the pH to neutral. Finally, human serum was added to the volumetric flask to obtain the 20 mg/dL TSB solution.

Experiment

This example demonstrates the use of chemical responsive adhesive tapes for the detection of total serum bilirubin (TSB).

The detection of TSB was demonstrated by using the chemical reagents of the bilirubin assay kit. Firstly, 20 mg/dL TSB was mixed with Reagent C in volume ratio of 1 :3. A filter paper was soaked in the mixture of TSB and Reagent C and then dried under the room temperature. A mixture of Reagent A and Reagent B (volume ratio of 5:2) were applied to a tape to form a tape with an adhesive layer loaded with the mixture of Reagent A and Reagent B. The tape was adhered to the filter paper to conduct the detection of TSB. The colorirmetric result was shown in Figure 20.

Example 8: Detection of precise location of trace amounts of analvtes on random surfaces by tape sensor Non-uniform distribution of a chemical analyte on a random surface represents the majority circumstances of surface contamination. Examples can be listed as follow: the distribution of pesticide on fruit surface, food residue (protein) distribution on cloth surface, dinning-table; bacteria contamination of a kitchen bench surface, etc. Here we demonstrate the detection of surface contamination by (a) Ni⁺² on the surface of office paper and, (b) peroxidase from horseradish plastic and filter paper.

Materials

Peroxidase from horseradish (HRP), 3, 3', 5, 5'-tetramethylbenzidine liquid (TMB), phosphate buffered saline (PBS), plastic bag, NeverWet liquid repelling kit.

HRP solution (0.1 g/L) was prepared by dissolving 2.0 mg HRP powder to 20 ml_ PBS buffer. The hydrophobic paper was made by coating with the NeverWet product.

Experiment

Droplets of an aqueous Ni²⁺ (100 ppm, 2 μΙ_) solution were placed on the surfaces of standard office A4 paper (see Figure 21 ).

A chemical-responsive adhesive tape loaded with a Ni²⁺ indicator ink by applying the Ni²⁺ ink to the adhesive of the tape. The tape was then applied to the surface of the A4 paper to test for the presence of Ni²⁺. A reaction occurred and the chemical- responsive adhesive tape exhibited a colour change in the area corresponding to the distribution of Ni²⁺ on the substrates.

The results are shown in Figure 21 , which illustrates that that the chemical- responsive adhesive tape exhibits a colour change corresponding to the location and pattern of the Ni²⁺ droplets on the paper surface.

A drop of HRP solution (0.1 g/L) was applied to a hydrophobic plastic surface (see Figure 22), and to a paper surface treated with NeverWet to form a hydrophobic paper surface (see Figure 23). Given the hydrophobic nature of these surfaces, the droplets were resident on these surfaces for less than 20 seconds. The surfaces were then dried so that the distribution of analytes could not be visually discerned by the naked eye. A chemical-responsive adhesive tape loaded with an H RP indicator ink was formed by applying the HRP ink to the adhesive. The tape was then adhered to each surface to detect the trace amounts of HRP reside, with a blue colour change observed (see Figure 22 and Figure 23 - colour change circled in broken lines in the Figures).

Despite the hydrophobic surfaces (e.g. the hydrophobic plastic and hydrophobic paper surfaces) having only trace amounts of HRP due to sample run off, the chemical- responsive adhesive tape was still able to detect the presence of the HRP on both surfaces.

It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

Claims

1 . A chemical-responsive composition including:

a non-Newtonian carrier; and

a chemical indicator for sensing a chemical analyte;

wherein the chemical indicator is retained by the carrier, and the chemical indicator exhibits a chemical response when exposed to the chemical analyte.

2. The chemical-responsive composition of claim 1 , wherein the chemical indicator is a colour change chemical indicator, a colourimetric chemical indicator, or a fluorescent chemical indicator, and the chemical response is visible to the naked eye.

3. The chemical-responsive composition of claim 1 or 2, wherein the carrier is chemically inert to the chemical analyte and/or the carrier is chemically inert to the chemical indicator.

4. The chemical-responsive composition of any one of the preceding claims, wherein the carrier is an adhesive.

5. The chemical-responsive composition of any one of claims 1 to 4, wherein the carrier is a matrix phase and the chemical indicator is dispersed within the carrier.

6. The chemical-responsive composition of any one of claims 1 to 4, wherein the chemical indicator is dispersed on a surface of the carrier as a separate cohesive layer, or in a random or patterned arrangement.

7. The chemical-responsive composition of any one of the preceding claims, wherein the carrier includes a plurality of indicators, each indicator sensitive to a different chemical analyte to each other indicator.

8. The chemical-responsive composition of any one of the preceding claims, wherein the carrier further includes a humectant.

9. The chemical-responsive composition of any one of the preceding claims, wherein the carrier further includes a masking reagent.

10. A chemical-responsive tape including:

a film of a backing material having a layer of the chemical-responsive composition of any one of the preceding claims applied to a surface thereof.

1 1 . A chemical-responsive tape including:

a film of a backing material with a chemical-responsive adhesive disposed on a surface of the backing material, the chemical-responsive adhesive including:

an adhesive carrier, and

at least one chemical indicator for a chemical analyte;

wherein the chemical indicator is retained by the adhesive carrier, and the chemical indicator exhibits a chemical response when exposed to the chemical analyte.

12. The chemical-responsive tape of claims 1 1 or 12, wherein the backing material is transparent.

13. The chemical-responsive tape of any one of claims 1 1 to 13, wherein the adhesive carrier includes a pressure-sensitive adhesive.

14. The chemical-responsive tape of any one of claims 1 1 to 13, wherein the adhesive carrier includes a plurality of chemical indicators, each chemical indicator sensitive to a different chemical analyte to each other chemical indicator.

15. The chemical-responsive tape of any one of claims 1 1 to 14, wherein the adhesive carrier further includes a humectant.

16. The chemically-responsive tape of any one of claims 1 1 to 15, wherein the adhesive carrier further includes a masking reagent.

17. The chemical-responsive tape of any one of claims 1 1 to 16, wherein the chemical indicator is disposed on the surface of the carrier in the form of a pattern, shape, symbol, or combination thereof.

18. A method for forming a chemical-responsive tape, the method including:

depositing a chemical-responsive composition onto a surface of a tape to form the chemical-responsive tape, wherein the chemical-responsive composition includes:

a non-Newtonian fluid carrier; and a chemical indicator for a chemical analyte;

wherein the chemical indicator is retained by the non-Newtonian fluid carrier on the surface of the tape, and the chemical indicator exhibits a chemical response when exposed to the chemical analyte.

19. A method for forming a chemical-responsive tape, the method including:

depositing a chemical indicator composition including a chemical indicator for a chemical analyte onto an adhesive surface of an adhesive tape, to form the chemical- responsive tape;

wherein the chemical indicator composition is retained by the adhesive, and the chemical indicator exhibits a chemical response when exposed to the chemical analyte.

20. A use of a chemical-responsive composition of any one of claims 1 to 9 or the use of the chemical-responsive tape of any one of claims 1 1 to 1 7, to test for the presence of a chemical analyte.