Colorimetric device and method for performing analyte sensing

Abstract

According to embodiments, a colorimetric device including a detector unit and a control unit is provided. The detector unit includes a first chemical responsive layer configured to change colour and / or transmissivity in presence of an analyte of interest; and a first photodetector configured to detect light filtered through the first chemical responsive layer to obtain a first signal measurable by a first electrode pair. The control unit includes a second chemical responsive layer configured to remain unchanged in absence of the analyte; and a second photodetector configured to detect the light passing through the second chemical responsive layer to obtain a second signal measurable by a second electrode pair. The colorimetric device is configured to facilitate a real-time readout based on a ratio of the first and second signals. According to further embodiments, a method for performing analyte sensing is also provided.

Description

COLORIMETRIC DEVICE AND METHOD FOR PERFORMING ANALYTE SENSINGCross-Reference To Related Application

[0001] This application claims the benefit of priority of Singapore patent application No. 10202403547Y, filed 14 November 2024, the content of it being hereby incorporated by reference in its entirety for all purposes.Technical Field

[0002] Various embodiments relate to a colorimetric device for analyte sensing and a method for performing analyte sensing.Background

[0003] Active healthcare monitoring is a pertinent undertaking for understanding one’s own general wellbeing in an ageing population. Wearable and point-of-care devices are gaining traction due to their potential as tools for personalized healthcare assistants in an increasingly health-conscious population This is especially important given the ageing population in developed nations such as Japan and Singapore.

[0004] The advent of wearables such as Fitbit and Samsung Gear Fit is synonymous with everyday wellbeing. However, such devices monitor physical (e.g. heart rate and blood pressure) and electrophysiological (e.g. ECG) vital signs. Non- invasive biochemical information is a desired and practical dimension as it provides complementary and supplementary feedback on a user’s health. Apart from lifestyle healthcare, medically and even diagnostically relevant information may be obtained from such non-invasive biochemical monitoring.

[0005] Biomarkers are physiological indicators that hold a trove of information, which may be used to detect diseases and monitor health conditions. Through quantitative or qualitative information about biological processes, biomarkers are useful in medical diagnosis, prognosis and personalised medicine. Biomarkers may include proteins, hormones, enzymes, and molecular and ionic metabolites. For instance, molecularmetabolite lactate indicates inadequate tissue oxygenation while increased glucose levels may be linked to diabetic conditions. Knowing such information allows for early intervention and preventive measures. Non-invasive and real-time monitoring may occur via electrochemical, electrochemiluminescence and colorimetric means.

[0006] Colorimetric sensing approach is widely used and studied for health monitoring. Existing colorimetric wearable or point-of-care biosensors either rely on subjective colour chart comparison, an external device for manual, indirect data quantification, or an inbuilt spectrophotometer that adds to cost and bulk of the device. Direct quantified readout of colorimetric responses in wearables is rare but desired. Colorimetric sensing approach is cost-effective and easy to fabricate, but its data readout may be disadvantageous. For example, conventional colour chart comparison may be subjective; having an external image scanner may be cumbersome, manual and inconvenient; and / or interfacing with a built-in spectrophotometer is a bulky and expensive solution. Hence, there is lack of automatic, digitalized and quantifiable interpretation of existing colorimetric sensors. A colour-electrical signal conversion, that is automatic, real-time, reliable against different environmental lighting, digital and quantifiable, is highly critical, especially for wearable or point-of-care applications.

[0007] A smartwatch for real-time monitoring of sweat glucose was developed by allowing the user to directly assess his health status on an E-ink display. However, it relied on electrochemical sensors to achieve its outcome. Another existing wearable, which directly images biometric data and physical vitals but not physiological biomarkers, was also explored. A photoconductivity method for pH detection arising from an imbalanced voltage was introduced. However, the outcome was mathematically derived rather than experimentally verified. Despite the limitations mentioned, the investigations made to at least these existing devices have provided an enticing proposition for the development of a colorimetric wearable sensor for direct readout.

[0008] Thus, there is a need for wearable sensors using photoconductivity or other signal types for biomarker sensing that address at least the problems mentioned above. More specifically, a sensor where a colorimetric output is quantified directly to analyte concentration, allowing the user to ascertain his / her physiological status through a direct readout, is provided.Summary

[0009] According to an embodiment, a colorimetric device for analyte sensing is provided. The colorimetric device includes a detector unit configured to detect an analyte of interest to produce a first signal; and a control unit configured to produce a second signal in absence of the analyte of interest. The detector unit includes a first chemical responsive layer configured to change colour and / or transmissivity in response to a presence of the analyte of interest; a first photodetector configured to detect light filtered through the first chemical responsive layer and convert the detected filtered light into the first signal; and a first pair of electrodes configured to measure the first signal, the first photodetector including an active material being sandwiched between the first pair of electrodes. The control unit includes a second chemical responsive layer configured to remain unchanged in terms of colour and transmissivity in absence of the analyte of interest; a second photodetector configured to detect the light passing through the second chemical responsive layer and convert the detected light into the second signal, the first photodetector and the second photodetector being substantially identical, and a second pair of electrodes configured to measure the second signal, the second photodetector including the active material being sandwiched between the second pair of electrodes. The colorimetric device is configured to facilitate a real-time readout from the first pair of electrodes and the second pair of electrodes, the real-time readout being based on a ratio of the first signal and the second signal.

[0010] According to an embodiment, a method for performing analyte sensing is provided. The method includes in response to a presence of an analyte of interest, changing colour and / or transmissivity of a first chemical responsive layer; by a first photodetector, detecting light filtered through the first chemical responsive layer and converting the detected filtered light into a first signal; measuring the first signal. The method further includes substantially simultaneously in absence of the analyte of interest, allowing a second chemical responsive layer to remain unchanged in terms of colour and transmissivity; by a second photodetector, detecting the light passing through the second chemical responsive layer and converting the detected light into a second signal, wherein the first photodetector and the second photodetector are substantially identical; measuring the second signal. The method alsoincludes facilitating a real-time readout based on a ratio of the first signal and the second signal.Brief Description of the Drawings

[0011] In the drawings, like reference characters generally refer to like parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the invention are described with reference to the following drawings, in which:

[0012] FIG. 1 A shows a schematic representative view of a colorimetric device for analyte sensing, according to various embodiments.

[0013] FIG. IB shows a flow chart illustrating a method for performing analyte sensing, according to various embodiments.

[0014] FIG. 2 shows a schematic cross-sectional view of a colorimetric device, according to one example.

[0015] FIG. 3 shows a schematic cross-sectional view of another exemplary colorimetric device, with a different configuration as compared to FIG. 2.

[0016] FIG. 4 shows a photograph depicting changes in the colour intensity of a chemical responsive layer (CRL) being an indication of glucose concentration, according to various example.

[0017] FIG. 5 shows a schematic perspective (exploded) view illustrating an architecture of a PM6:Y6-based organic photodetector (OPD), according to one example.

[0018] FIGS. 6A and 6B illustrate schematic representations of the enzymatic reactions of glucose and the accompanying coloration effects in the presence of ODA and ABTS, respectively.

[0019] FIG. 7 shows a graph illustrating the normalised absorbance spectra of PM6:Y6, F8T2:PCBM, and the activated CRLs (based on ODA and ABTS) in the presence of glucose, according to various examples.

[0020] FIGS. 8A and 8B illustrate schematic representations of the enzymatic reactions of lactate and the accompanying coloration effects in the presence of ODA and ABTS, respectively.

[0021] FIG. 9 shows the calibration curve of the ABTS-based CRL in the presence of different glucose concentrations, according to one example.

[0022] FIG. 10 shows a graph illustrating plots of photocurrent ratio versus glucose concentration for various light sources, encompassing AM1.5G solar simulator, red light emitting diode (LED 655 nm), halogen lamp and white LED, according to an example.

[0023] FIGS. 11 A, 1 IB, 11C and 1 ID show graphs, depicting plots of photocurrent ratio versus glucose concentration for AM1.5G solar simulator, red LED (655 nm), halogen lamp and white LED under different light intensities, respectively, according to one example.

[0024] FIG. 12 shows a graph illustrating the calibration curve of the o-PD-based CRL due to different lactate concentrations, according to one example.

[0025] FIG. 13 shows a summary of the possible combinations that are feasible with the colorimetric devices.Detailed Description

[0026] The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the invention. The various embodiments are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.

[0027] Embodiments described in the context of one of the methods or devices are analogously valid for the other methods or devices. Similarly, embodiments described in the context of a method are analogously valid for a device, and vice versa.

[0028] Features that are described in the context of an embodiment may correspondingly be applicable to the same or similar features in the other embodiments. Features that are described in the context of an embodiment may correspondingly be applicable to the other embodiments, even if not explicitly described in these other embodiments. Furthermore, additions and / or combinations and / or alternatives as described for a feature in the contextof an embodiment may correspondingly be applicable to the same or similar feature in the other embodiments.

[0029] In the context of various embodiments, the articles “a”, “an” and “the” as used with regard to a feature or element include a reference to one or more of the features or elements.

[0030] In the context of various embodiments, the phrase “at least substantially” may include “exactly” and a reasonable variance.

[0031] In the context of various embodiments, the term “about” as applied to a numeric value encompasses the exact value and a reasonable variance.

[0032] As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0033] As used herein, the phrase of the form of “at least one of A or B” may include A or B or both A and B. Correspondingly, the phrase of the form of “at least one of A or B or C”, or including further listed items, may include any and all combinations of one or more of the associated listed items.

[0034] As used herein, the expression “configured to” may mean “constructed to” or “arranged to”.

[0035] Various embodiments provide an organic optoelectronic approach for quantifying wearable colorimetric biosensors Such wearable colorimetric biosensors are point of care devices for at least one of the following applications: health or nutritional monitoring, medical diagnostics, or bioreactor monitoring. The organic optoelectronic approach may also be applicable for environmental monitoring for health and safety.

[0036] FIG. 1A shows a schematic representative view of a colorimetric device 100 for analyte sensing, according to various embodiments. The colorimetric device 100 includes a detector unit 102 configured to detect an analyte of interest to produce a first signal; and a control unit 112 configured to produce a second signal in absence of the analyte of interest.

[0037] The detector unit 102 includes a first chemical responsive layer 104 configured to change colour and / or transmissivity in response to a presence of the analyte of interest; a first photodetector 106 configured to detect light filtered through the first chemical responsive layer 104 (as denoted by a dotted line 101) and convert the detected filtered light into the first signal; and a first pair of electrodes 108 configured to measure the firstsignal. The first photodetector 106 includes an active material being sandwiched between the first pair of electrodes 108, as denoted by lines 103. The first photodetector 106 may be orientated in a manner such that one of the first pair of electrodes 108 may be a first top electrode, the other of the first pair of electrodes 108 may be a first bottom electrode and the active material may be arranged across the first top and bottom electrodes, the first top electrode being opposite the first bottom electrode. The first top electrode may be arranged between the first chemical responsive layer 104 and the active material.

[0038] The control unit 112 includes a second chemical responsive layer 114 configured to remain unchanged in terms of colour and transmissivity in absence of the analyte of interest; a second photodetector 116 configured to detect the light passing through the second chemical responsive layer 114 (as denoted by a dotted line 111) and convert the detected light into the second signal; and a second pair of electrodes 118 configured to measure the second signal. The first photodetector 106 and the second photodetector 116 are identical or substantially identical. The second photodetector 116 includes the active material being sandwiched between the second pair of electrodes 118, as denoted by lines 113. The second photodetector 116 may be orientated in a manner such that one of the second pair of electrodes 118 may be a second top electrode, the other of the second pair of electrodes 118 may be a second bottom electrode and the active material may be arranged across the second top and bottom electrodes, the second top electrode being opposite the second bottom electrode. The second top electrode may be arranged between the second chemical responsive layer 114 and the active material.

[0039] The colorimetric device 100 is configured to facilitate a real-time readout from the first pair of electrodes 108 and the second pair of electrodes 118. The real-time readout is based on a ratio of the first signal and the second signal. In one example, the colorimetric device 100 may be configured to operate with a bias. In another example, the colorimetric device 100 may be configured to operate without a bias (i.e. at zero bias).

[0040] In other words, a direct readout or direct digital readout may be obtained from a colorimetric response through a simple optoelectronic approach. This direct readout on biomarker concentration may be performed without the need for interfacing with an external device or with a complex built-in spectrophotometer. By relying on the paired photodetector approach (i.e. the first photodetector 106 and the second photodetector 116)of measuring photovoltage, photocurrent, photoresistivity, photoconductivity or other types of signals of the photodetector in response to changes in the colour intensity / transmittance of a colorimetric device, an automatic, direct, real-time, quantifiable digital signal / readout of the biomarker concentration allows immediate access to physiological status. The colorimetric device 100 may be able to operate with and without bias. The colorimetric device 100 may eliminate subjective bias. The chemical responsive layer changes its colour intensity in accordance with biomarker concentration. The photodetectors and the chemical responsive layers are solution processed. Such colorimetric device 100 is also easily made flexible and thin (for wearable purposes) and printable (for scale-up fabrication), thereby having a small footprint.

[0041] Tn the context of various embodiments, the term “facilitate” may mean provide, generate, calculate, determine or evaluate.

[0042] The colorimetric device 100 may further include a display unit configured to display the real-time readout.

[0043] In various embodiments, the first chemical responsive layer 104 and the second chemical responsive layer 114 each may include a chromogenic agent, and an enzyme reactive to the analyte of interest. For example, the chromogenic agent may include o- dianisidine (ODA) or 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), or o- Phenylenediamine (o-PD), or 3,3',5,5'-Tetramethylbenzidine (TMB).

[0044] The first chemical responsive layer 104 and the second chemical responsive layer 114 each may further include a heme-containing enzyme reactive to the chromogenic agent.

[0045] In various embodiments, the active material may include but is not restricted to a polymer / fullerene blend, polymer / non-fullerene acceptors, small molecules, perovskites, perovskite / organic hybrids, or any combinations thereof. The first photodetector 106 and the second photodetector 116 may be a first organic photodetector and a second organic photodetector, respectively. In one embodiment, the first photodetector 106 and the second photodetector 116 each may include a wideband photodetector configured to sense a wide spectrum of the light. The wide spectrum of the light may be anywhere between ultraviolet

[0046] In other embodiments, the first photodetector 106 and the second photodetector 116 each may include a narrowband photodetector configured to detect a narrow range of the light. For example, the bandwidth of a narrowband photodetector may have its response centered around a peak wavelength in the 300-500 nm region or in the 600-800 nm range.

[0047] The first pair of electrodes 108 may include a first electrode and a second electrode. The first photodetector 106 may be orientated in a manner such that first electrode may be referenced as a top electrode of the first pair of electrodes 108 that may be positioned above the active material, and the second electrode is opposite to the first electrode and may be referenced as a bottom electrode of the first pair of electrodes 108 that may be positioned below the active material. In other words, the active material may be arranged across or between these top and bottom electrodes The first electrode may be positioned in close proximity to the first chemical responsive layer 104. More specifically, the top electrode of the first pair of electrodes 108 may be arranged between the first chemical responsive layer 104 and the active material. The first electrode may be a top transparent electrode and the second electrode may be a bottom opaque electrode. The detector unit 102 may further include a first substrate coupled to the first electrode. The first substrate may comprises a transparent material.

[0048] The second pair of electrodes 118 may include a third electrode and a fourth electrode. The second photodetector 116 may be orientated in a manner such that third electrode may be referenced as a top electrode of the second pair of electrodes 118 that may be positioned above the active material, and the fourth electrode is opposite to the third electrode and may be referenced as a bottom electrode of the second pair of electrodes 118 that may be positioned below the active material. In other words, the active material may be arranged across or between these top and bottom electrodes. The third electrode may be positioned in close proximity to the second chemical responsive layer 114 More specifically, the top electrode of the second pair of electrodes 118 may be arranged between the second chemical responsive layer 114 and the active material. The third electrode may be a top transparent electrode and the fourth electrode may be a bottom opaque electrode. The control unit 112 may further include a second substrate coupled to the third electrode. The second substrate may comprises a transparent material.

[0049] The first substrate and the second substrate each may include a glass substrate, or a polymer substrate. For example, the polymer substrate may include a flexible polymer substrate.

[0050] The first electrode and the third electrode may include a first material, and the second electrode and the fourth electrode may include a second material different from the first material. For example, the first material and the second material may include: different (types of) conducting polymers, or different (types of) metals, or different (types of) metal oxides. Alternatively, the first material and the second material may include a metal and a metal oxide, respectively.

[0051] In various embodiments, colorimetric device 100 may include a wearable colorimetric device.

[0052] FIG. IB shows a flow chart illustrating a method for performing analyte sensing 120, according to various embodiments. As seen in FIG. IB, at Step 122, in response to a presence of an analyte of interest, (at sub-Step 122a) colour and / or transmissivity of a first chemical responsive layer (e.g. 104 of FIG. 1 A) is changed; (at sub-Step 122b) light filtered through the first chemical responsive layer 104 is detected by a first photodetector (e.g.106) and the detected filtered light is converted into a first signal by the first photodetector 106; and (at sub-Step 122c) the first signal is measured.

[0053] At Step 124, substantially simultaneously in absence of the analyte of interest, (at sub-Step 124a) a second chemical responsive layer (e.g. 114) is allowed to remain unchanged in terms of colour and transmissivity; (at sub-Step 124b) the light passing through the second chemical responsive layer 114 is detected by a second photodetector (e.g. 116) and the detected light is converted into a second signal by the second photodetector 116; and (at sub-Step 124c) the second signal is measured. The first photodetector 106 and the second photodetector 116 are identical or substantially identical.

[0054] At Step 126, a real-time readout is facilitated based on a ratio of the first signal and the second signal.

[0055] In other words, a colorimetry method 100 is provided to quantify biomarkers based on optoelectronic response such as photocurrent, photoconductivity, photoresistivity, photovoltametry, using two photodetectors (e.g. 106, 116), complemented with a pair of chemical responsive layer (e.g. 104, 114). One photodetector (e.g. 116) measures lightfiltered through the chemical responsive layer (e g. 114) that remains unchanged in terms of colour and transmissivity in absence of the analyte of interest, while the other photodetector (e.g. 106) measures changes in transmittance intensity of the chemical responsive layer (e.g. 104).

[0056] For example, the first signal may include a first photocurrent signal and the second signal may include a second photocurrent signal. The first photodetector 106 and the second photodetector 116 used in the method 120 may include the same or like elements or components as those of the first photodetector 106 and the second photodetector 116 of FIG. 1A, and as such, the same numerals are assigned and the like elements may be as described in the context of the first photodetector 106 and the second photodetector 116 of FIG. 1 A, and therefore the corresponding descriptions are omitted here

[0057] In one embodiment, the first photodetector 106 and the second photodetector 116 each may be optimized with an absorption sensitivity of wideband photodetector. The first photodetector 106 and the second photodetector 116 each may include a wideband photodetector including but not restricted to a polymer / fullerene blend, polymer / non-fullerene acceptors, small molecules, perovskites, perovskite / orgamc hybrids, or any combinations thereof, and may sense a wide spectrum of the light. In another embodiment, the first photodetector 106 and the second photodetector 116 each may include a narrowband photodetector engineered to match an absorption spectrum of the first chemical responsive layer 104 and the second chemical responsive layer 114. The narrowband photodetector may include but is not restricted to a polymer / fullerene blend, polymer / non-fullerene acceptors, small molecules, perovskites, perovskite / orgamc hybrids, or any combinations thereof, and may detect a narrow range of the light.

[0058] In various embodiments, facilitating the real-time readout at Step 126 may include providing a concentration of the analyte of interest based on the ratio of magnitude of the first signal and magnitude of the second signal.

[0059] The light may be ambient light or may be transmitted from a light source. The realtime readout may be independent from the types of light used.

[0060] In various embodiments, in response to presence of multiple analytes of interest, detecting the light at sub- Step 122b may include detecting, by the first photodetector 106 being the narrowband photodetector, the light filtered through the first chemical responsivelayer 104 and converting the detected filtered light into a plurality of first signals; and measuring the first signal at sub-Step 122c may include measuring the plurality of first signals.

[0061] Substantially simultaneously in absence of the multiple analytes of interest, detecting the light at sub-Step 124b may include detecting, by the second photodetector 116 being the narrowband photodetector, the light passing through the second chemical responsive layer 114 and converting the detected light into a plurality of second signals; and measuring the second signal at sub-Step 124c may include measuring the plurality of second signals.

[0062] Facilitating the real-time readout at Step 126 may include providing a plurality of real-time readouts according to the multiple analytes of interest, each readout being based on a ratio of magnitude of a first signal from the plurality of first signals and magnitude of a corresponding second signal from the plurality of second signals, according to an analyte from the multiple analytes of interest. In other words, multiple real-time readouts may be provided simultaneously or at least substantially about the same time.

[0063] The first chemical responsive layer 104 and the second chemical responsive layer 114 used in the method 120 may include the same or like elements or components as those of the first chemical responsive layer 104 and the second chemical responsive layer 114 of FIG. 1A, and as such, the same numerals are assigned and the like elements may be as described in the context of the first chemical responsive layer 104 and the second chemical responsive layer 114 of FIG. 1 A, and therefore the corresponding descriptions are omitted here.

[0064] The chromogenic agent, the enzyme reactive to the analyte of interest, and the heme-containing enzyme reactive to the chromogenic agent may be mixed and provided in a form of a scaffold, preferably a hydrogel. For example, the heme-containing enzyme may include horseradish peroxidase (HRP).

[0065] In various embodiments, the analyte of interest may include a biomarker / analyte. The biomarker / analyte may include a molecular metabolite or a salt or an ion or pH or a synthetic / pharmaceutical drug or a protein or a macromolecule or a neurotransmitter or a

[0066] In one example, the analyte of interest may include glucose, the enzyme reactive to the analyte of interest may include glucose oxidase (GOx), and the method may further include introducing the glucose to the first chemical response layer 104 to catalyze conversion of the glucose to hydrogen peroxide (H2O2), which reacts with the chromogenic agent in the presence of a horseradish peroxidase enzyme, thereby facilitating oxidation of the chromogenic agent and in turn, resulting in a colorimetric change, which leads to a measurable alteration in light absorption properties of the first chemical response layer 104.

[0067] In another example, the analyte of interest may include lactate, the enzyme reactive to the analyte of interest may include L-lactate oxidase (LOx), and the method may further include introducing the lactate to the first chemical response layer 104 to catalyze conversion of the lactate to hydrogen peroxide (H2O2), which reacts with the chromogenic agent in the presence of a horseradish peroxidase enzyme, thereby facilitating oxidation of the chromogenic agent and in turn, resulting in a colorimetric change, which leads to a measurable alteration in light absorption properties of the first chemical response layer 104.

[0068] The method 120 may be performed by a colorimetric device 100, according to various embodiments. The method 120 may also be performed in absence of an external digital image analysis, or a spectrophotometer, or a naked-eye quantification.

[0069] While the method described above is illustrated and described as a series of steps (sub-steps) or events, it will be appreciated that any ordering of such steps (sub-steps) or events are not to be interpreted in a limiting sense. For example, some steps (sub-steps) may occur in different orders and / or concurrently with other steps (sub-steps) or events apart from those illustrated and / or described herein. In addition, not all illustrated steps may be required to implement one or more aspects or embodiments described herein. Also, one or more of the steps (sub-steps) depicted herein may be carried out in one or more separate acts and / or phases.

[0070] Examples of a colorimetric device and method for analyte sensing will be described in details below.

[0071] FIG. 2 shows a schematic cross-sectional view of a colorimetric device 200, according to one example. The colorimetric device 200 may include the same or like elements or components as those of the colorimetric device 100 of FIG. 1 A, and as such, the same ending numerals are assigned and the like elements may be as described in thecontext of the colorimetric device 100 of FIG. 1A, and therefore the corresponding descriptions are omitted here.

[0072] As shown in FIG. 2, to measure colorimetric response based on optoelectronic approach, two identical photodetectors 206a, 206b, 216a, 216b are paired, with a chemical responsive layer (CRL) 204, 214 placed on top of each photodetector 206a, 206b, 216a, 216b. The CRL 204 and the CRL 214 are identical. Each photodetector 206a, 206b, 216a, 216b may have a multilayer structure possessing the function of converting light of specific wavelength into electron-hole pairs and transporting the electrons and holes to an electrode pair 208a, 208b, 218a, 218b that generates the response measurable from the the electrode pair 208a, 208b, 218a, 218b. While the schematic views of the photodetector 206a, 206b and the photodetector 216a, 216b in FIG 2 are each denoted with two layers, it should be appreciated that each of the photodetector 206a, 206b and the photodetector 216a, 216b is not limited to just two layers. In other words, the photodetector 206a, 206b may have more than two layers, and similarly, the photodetector 216a, 216b may have more than two layers. The CRL 204, 214 functions as a biorecognition site. One photodetector 206a, 206b function as the “detector” unit 202 to detect the analyte of interest 205 while the other 216a, 216b acts as a “control” unit 212. In the absence of an analyte, both CRLs 204, 214 allow the same amount of light L to irradiate each corresponding photodetector 206a, 206b, 216a, 216b. Dotted lines represent the light L that passes through the CRLs 204, 214 towards the photodetectors 206a, 206b, 216a, 216b, respectively.

[0073] In absence of a target biomarker at the colorimetric device 200, both photodetectors 206a, 206b, 216a, 216b produce a current output of Ao. When the target biomarker (e.g. analyte 205) triggers the CRL 204 at the “detector” unit 202 to change colour, a change in absorption of the CRL 204 at the “detector” unit 202 occurs while no absorption change manifests at the “control” unit 212. A current output of Ai is registered across the electrode pair (i.e. two electrodes) 208a, 208b at the “detector” unit 202, while it remains unchanged at Ao across the electrode pair (i.e. two other electrodes) 218a, 218b at the “control” unit 212. By taking the ratio of the measured signals (e.g. photocurrents) at both the “detector” unit 202 and the “control” unit 212, that is (Ai / Ao), the corresponding analyte concentration is ascertained.

[0074] At the “detector” unit 202, one electrode 208a (e.g. made of indium tin oxide, ITO or a suitable transparent material) of the electrode pair is disposed (deposited) on a substrate 207, and at the “control” unit 212, one electrode 218a (e.g. made of ITO) of the electrode pair is disposed on a substrate 217. The substrate 207 and the substrate 217 may be separate substrates. In another example (not shown in FIG. 2), the substrate 207 and the substrate 217 may form a unitary substrate. The other electrode 208b, 218b of each electrode pair may be made of an opaque material, e.g. aluminium, Al.

[0075] The use of the photodetectors 206a, 206b, 216a, 216b may be broadly classified into two categories, namely, a material system with a narrow bandgap absorption strategy and a material system with a broadband absorption approach. A wideband photodetector is useful for a single biomarker while a narrowband photodetector is practical for both single biomarker and multi-biomarker detection. For example, supposing a CRL changes colour in the presence of glucose in 350-500 nm range while another CRL changes colour in the presence of lactate in 600-750 nm range. To detect both biomarkers simultaneously, two separate narrowband photodetectors are required to match both ranges. This ensures that the device (e.g. 200) operates with high accuracy due to its selectivity. A narrowband photodetector is also useful for a single biomarker if the colour change in the CRL matches that with the absorption of the photodetector.

[0076] FIG. 3 shows a schematic cross-sectional view of another exemplary colorimetric device 300, with a different configuration as compared to FIG. 2. The colorimetric device 300 may include the same or like elements or components as those of the colorimetric device 100 of FIG. 1A, and as such, the same ending numerals are assigned and the like elements may be as described in the context of the colorimetric device 100 of FIG. 1 A, and therefore the corresponding descriptions are omitted here

[0077] Turning briefly to FIG. 2 for comparison with FIG 3, the substrate 207 and the substrate 217 are arranged adjacent in close proximity to and facing towards the respective CRLs 204, 214. In other words, in a stacked manner, at the “detector” unit 202, the substrate 207 is arranged between the CRL 204 and the photodetector 206a, 206b, wherein the photodetector 206a, 206b is sandwiched between the electrode pair 208a, 208b, while at “control” unit 212, the substrate 217 is arranged between the CRL 214 and the photodetector 216a, 216b, wherein the photodetector 216a, 216b is sandwiched betweenthe electrode pair 218a, 218b. For the colorimetric device 200, the light L travels through the CRLs 204, 214 and reaches the substrates 207, 217, and then propagates through the photodetectors 206a, 206b, 216a, 216b.

[0078] Tn the different configuration of the colorimetric device 300, the substrate 307 and the substrate 317 are arranged away from (at a distal end to) the CRLs 304, 314, as shown in FIG. 3. In other words, in a stacked manner, at the “detector” unit 302 to detect the analyte of interest 305, the photodetector 306a, 306b is arranged between the CRL 304 and the substrate 307, wherein the photodetector 306a, 306b is sandwiched between the electrode pair 308a, 308b, while at the “control” unit 312, the photodetector 316a, 316b is arranged between the CRL 314 and the substrate 317, wherein the photodetector 316a, 316b is sandwiched between the electrode pair 318a, 318b. Here, the light L travels through the CRLs 304, 314 and propagates through the photodetectors 306a, 306b, 316a, 316b to reach the substrates 307, 317. The electrode 308a at the “detector” unit 302 and the electrode 318a at the “control” unit 312 are transparent or at least sufficiently translucent to minimize losses of the filtered light entering the photodetectors 306a, 306b, 316a, 316b.Materials

[0079] In photoconductivity, an optical excitation leads to changes in electrical conductivity (or resistance) in a photosensitive material. To illustrate as proof-of-concept, a donor-acceptor system including poly[(2,6-(4,8-bis(5-(2-ethylhexyl-3-fluoro)thiophen-2-yl)-benzo[l,2-b:4,5-b’]dithiophene))-alt-(5,5-(r,3’-di-2-thienyl-5’,7’-bis(2-ethylhexyl)benzo[r,2’-c:4’,5’-c’]dithiophene-4, 8-dione)] and 2,2'-((2Z,2'Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[l,2,5]thiadiazolo[3,4-e]thieno[2",3”:4’,5']thieno[2',3':4,5]pyrrolo[3,2-g]thieno[2',3':4,5]thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-lH-indene-2,l-diylidene))dimalononitrile (also known as PM6: Y6) is used.

[0080] PM6:Y6 is a common material system for organic photovoltaic technology. As a bulk heterojunction solar cell, it has a remarkably high power conversion efficiency (PCE) of 15.7%. However, the real motivation for using PM6:Y6 is its broadband absorption in the visible range, which easily detects the signal change without considering the colour of the CRL. Hence, the material system is suitably improvised as a photodetector, or morespecifically, organic photodetector (OPD). In solar cells, organic materials have higher absorption coefficient than inorganic counterparts. Hence, the former works better in low light conditions as compared to the latter. The use of organic materials in the photodetector is crucial as it allows the colorimetric device to function in low light conditions without compromising performance. The OPD may include the first photodetector 106 and the second photodetector 116 used in the colorimetric device 100 (FIG. 1A), or the photodetectors 206a, 206b, 216a, 216b used in the colorimetric device 200 (FIG. 2), or the photodetectors 306a, 306b, 316a, 316b used in the colorimetric device 300 (FIG. 3).[0081J For example, the CRL (e.g. the first and second chemical responsive layers 104, 114 of FIG. 1A; the CRLs 204, 214 of FIG. 2; and the CRLs 304, 314 of FIG. 3) is prepared by mixing a concoction of glucose oxidase (GOx), horseradish peroxidase (HRP) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) in agarose-based hydrogel. Different glucose concentrations may be introduced to the CRL. This activates the CRL and causes the colour of the CRL to change into a bluish-green hue. FIG. 4 shows a photograph 450 depicting changes in the colour intensity of the CRL being an indication of glucose concentration. As observed from FIG. 4, the higher the glucose concentration, the darker the colour intensity. It should be appreciated that different combinations apart from the concoction of GOx, HRP and ABTS are possible in other examples not discussed here.Fabrication of OPD

[0082] The colorimetric setup includes a pair of PM6:Y6-based OPDs. One OPD functions as the “detector” unit (e g. 102 of FIG. 1A, 202 of FIG. 2, 302 of FIG. 3) to detect the analyte of interest while the other acts as a “control” unit (e.g. 112 of FIG. 1 A, 212 of FIG.2, 312 of FIG 3)

[0083] FIG. 5 shows a schematic perspective view illustrating an architecture of a PM6:Y6-based OPD 502, according to one example.

[0084] To fabricate each OPD 502, an indium tin oxide (ITO) glass substrate (e g. a conducting oxide 508b on a transparent substrate 507) was first sequentially cleaned in Hellmanex detergent, distilled (DI) water, acetone and isopropanol alcohol (IP A). The ITO glass substrate was blown dry before placing in a 60°C oven for at least an hour. Next, theITO surface was rendered hydrophilic in an UV-ozone environment, before spin-coating a layer of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) 506b. After annealing the PEDOT:PSS layer 506b at about 120°C for about 10 min, PM6:Y6 solution was spin-coated on top. PM6:Y6 was prepared in a chloroform medium at a ratio of 1:1.2, mixed together with 0.5 vol% of 1-chloronaphtalene. The spin-coated PM6:Y6 layer 506a was annealed at about 120°C for about 10 min before thermally depositing a 100 nm layer of aluminium electrode 508a on top.

[0085] Although for the experiment process, the OPD 502 was fabricated on a rigid glass substrate for simplicity purposes, the OPD 502 has also been well studied to be fabricated flexible, making it highly suitable for integration into wearable devices. This characteristic is particularly beneficial for applications requiring on-body monitoring of physiological parameters. Additionally, the OPD 502 may be printed using scalable fabrication techniques, facilitating large-scale production and reducing manufacturing costs.Analyses

[0086] The design of the colorimetric device (e g. 200, 300 of FIGS. 2 and 3, respectively) includes a CRL (e.g. 204, 214, 304, 314) placed on top of each photodetector (206a, 206b, 216a, 216b, 306a, 306b, 316a, 316b). The CRL acts as a biorecognition site, whose colour intensity changes in the presence of an analyte.

[0087] Taking glucose as an example, the enzymatic reaction of this metabolite is illustrated by the following:GOxGlucose + 02— > Gluconic acid + H2O2- Equation (1)[ 00881 As shown in Equation (1), glucose is converted into gluconic acid and hydrogen peroxide (H2O2) in the presence of oxygen and glucose oxidase (GOx). The evolution of H2O2 is a direct indication of glucose concentration However, as H2O2 is transparent, chromogenic substrates are used to taint H2O2 to allow ease of quantification. Two possible chromogenic chemicals are o-dianisidine (ODA) or 2,2'-azino-bis(3-ethylbenzothiazoline- 6-sulfomc acid) (ABTS).

[0089] According to Equation (2):GOx HRP+ODA> >2O + ODA* - Equation (2)H2O2, in the presence of horseradish peroxidase (HRP), oxidises the colourless ODA to become light orange. The darker (higher intensity) the colours, the higher the glucose concentration.

[0090] According to Equation (3):GOx HRP+ABTSGlucose + O2— > H2O2- > H2O + ABTS* - Equation (3) H2O2, in the presence of horseradish peroxidase (HRP), oxidises the colourless ABTS to become blue. Similarly, the darker (higher intensity) the colours, the higher the glucose concentration.[00911 FIGS. 6A and 6B illustrate schematic representations of the enzymatic reactions of glucose and the accompanying coloration effects in the presence of ODA and ABTS, respectively.

[0092] FIG. 7 shows a graph 750 illustrating the normalised absorbance spectra of PM6: Y6 750a, F8T2:PCBM 750b, and the activated CRLs (based on ODA 750d and ABTS 750c) in the presence of glucose. F8T2:PCBM is a blend of poly [9, 9’- dioctyl-fluorene-alt-bithiophene] and [6,6]-phenyl-C61-butyric acid methyl ester. The insets in FIG. 7 shows photographs depicting changes in the colour intensity of the activated ODA-based CRL 750d (left) and the activated ABTS-based CRL 750c (right) being an indication of glucose concentration.

[0093] Both spectra of the activated ODA-based CRL 750d and the activated ABTS-based CRL 750c are overlaid (or overlapped) with the active component of the OPD, i.e. PM6: Y6 750a. The photoactive layer (206a, 206b, 216a, 216b, 306a, 306b, 316a, 316b, 506a) has a strong absorption between 450 nm and 800 nm, with a peak at about 625 nm (see spectrum 750a). The peak absorption of the ODA-based CRL 750d in the presence of glucose is within the 400-500 nm range. This spectral alignment is suboptimal, as it coincides with a less absorbing region of the PM6:Y6 spectrum, specifically a dip around 420 nm. In contrast, the peak absorption of the ABTS-based CRL 750c in the presence of glucose lies within the 600-800 nm range. This range aligns well with the strong absorption region of PM6:Y6, despite a minor dip around 675 nm. This alignment optimizes the sensitivity of the colorimetric device to changes in colour intensity in the CRL, when the ABTS-based CRL 750c is paired with a PM6:Y6 OPD. Consequently, a prototype is fabricated using this combination. This band matching strategy is essential for optimizing the colorimetricdevice. This allows for the use of the OPD in ambient conditions, regardless of indoors or outdoors. As it has a wide visible range absorption, it permits great flexibility in adjusting a colorimetric response that corresponds to the absorption sensitivity of PM6:Y6.

[0094] To further refine this approach, it is evident that narrowband OPDs which are specifically engineered to match the absorption spectrum of the CRL may be utilized to further enhance the sensitivity. For example, the absorption of an ODA-based CRL matches well with that of a narrowband F8T2:PCBM 750b. This combination makes it superior for high accuracy detection.

[0095] Similarly, lactate may be detected using the chromogenic approach. The enzymatic reaction of lactate is as shown in Equation (4):LOxLactate + O2— > Pyruvate + H2O2- Equation (4)

[0096] In the presence of oxygen and L-lactate oxidase (LOx), lactate is broken down into pyruvate and H2O2. The chromogenic reactions arising from the use of ODA takes on Equation (5), as follow:> > - Equation (5)

[0097] The chromogenic reactions arising from the use of ABTS takes on Equation (6), as follow:> > - Equation (6)

[0098] Since ODA and ABTS are used as the chromogenic agents, the colour change here are the same as for Equations (2) and (3). FIGS. 8A and 8B illustrate schematic representations of the enzymatic reactions of lactate and the accompanying coloration effects in the presence of ODA and ABTS, respectively.

[0099] It should be noted that the present design is not restricted to testing glucose and lactate. There is a flexibility to expand to other biomarkers such as uric acid, creatinine, cholesterol, pH and any colorimetric techniques for sensing concentrations of (bio)chemicals.

[0100] As a demonstration, only glucose reactions (Equations (1), (2) and (3)) will be discussed further below. Details for fabricating the CRL are expanded from the Materials section above, as follow. An agarose hydrogel is first prepared by mixing agarose powder in phosphate buffered saline (PBS) solution (0.01 M, pH 7.4) with a concentration of about 20 mg / ml. The hydrogel functions as a scaffold for the enzymatic and chromogenicreactions to take place. Separately, about 20 mg of GOx and about 1.5 mg of HRP are mixed in about 2 ml of DI water each. Both solutions are blended before adding about 20 mg of ABTS into the 4 ml mixture. Next, about 720 pl of agarose hydrogel and about 320 pl of the enzyme / chromogenic mixture are aliquoted into a microwell A series of glucose concentrations are prepared: 0 mM, 0.06 mM, 0.07 mM, 0.08 mM, 0.09 mM, 0.1 mM and 0.2 mM. This series is selected as the physiological level of sweat glucose in a healthy individual is 0.06 - 0.1 mM. The glucose concentrations are prepared in PBS solution. Thereafter, about 320 pl of each corresponding glucose concentration is introduced into the agarose hydrogel and enzyme / chromogenic mixture. Depending on the glucose concentration, a blue hue with varying intensity is formed. The higher the concentration, the darker the hue.

[0101] A PM6:Y6-based material system is a wideband OPD, which is useful for a single biomarker detection. Narrowband OPDs are more practical if multiple biomarkers are involved. This strategy is necessary for selectivity. Supposing a CRL changes into light orange in the presence of lactate while another CRL changes into light blue in the presence of glucose (analogous to FIG. 7). This necessitates two separate OPDs, each with its distinct narrowband absorption. Both OPDs may be stacked in a tandem configuration, with each OPD having its absorption that aligns with the absorption of the corresponding CRL.

[0102] FIG. 9 shows the calibration curve 950 of the ABTS-based CRL in the presence of different glucose concentrations. Absorbance was plotted against glucose concentration. Absorbance data was obtained at a wavelength of 740 nm as this is the peak absorption of the activated CRL. The mset of FIG. 9 shows photographs depicting the activated CRLs for a glucose concentration ranging from 0 mM to 0.1 mM. The R-square of the calibration curve is 0.992, which represents excellent linearity. In other words, the absorbance of the activated ABTS-based CRL follows a linear relationship with glucose concentration.

[0103] As the colorimetric device is envisioned to be worn for daily activities monitoring, it is important that the readout works in different lighting conditions, including outdoor and indoor environments. Regardless of different light source and lighting intensity, the colorimetric device ought to elucidate the same biomarker concentration reading (e g., if it reads 0.08 mM under white LED lighting, it should also read 0.08 mM under sunlightillumination; and if it reads 0.1 mM under 250 W / m2, it should also read 0.1 mM under 750 W / m2). By plotting signal ratio (e.g. photocurrent ratio) against glucose concentration, similar slope values are to be expected. To reinforce this, the colorimetric device (based on the example of FIG. 2) was tested under various light sources: Air Mass 1.5 Global (AMI ,5G) solar simulator, red LED (peak wavelength of 655 nm), halogen lamp and white LED.

[0104] Different light sources were firstly analysed. FIG. 10 shows a graph 1050 illustrating plots of photocurrent ratio versus glucose concentration for various light sources, encompassing AM1.5G solar simulator 1050a, red light emitting diode (LED 655 nm) 1050b, halogen lamp 1050c and white LED 1050d. The points are the measured values while the lines represent the lines of best fit. The slope corresponds to the calibrated gradient, which allows for interpolating glucose concentration within this range. The values of the gradient are similar, lying between -1.047 to -1.103. This is a value of -1.075+0.028, which represents a standard deviation of 2.60%. This result indicates the preliminary capability of the device to operate under different light sources. However, the photocurrent ratio varies under different lighting conditions at the same glucose concentration, which limits reading accuracy. It may be anticipated that by switching to a narrowband OPD, this reading discrepancy may be resolved, thereby enhancing the practicality and accuracy of the colorimetric device.

[0105] Different light intensities were subsequently examined. The same set of experiments were repeated but under varying light intensities for each light source. For each light source, different light intensities were investigated. FIGS. 11 A, 11 B, 11C and 1 ID show graphs, depicting plots of photocurrent ratio versus glucose concentration for AM1.5G solar simulator 1150-1, red LED (655 nm) 1150-2, halogen lamp 1152-3 and white LED 1150-4, respectively, under different light intensities. The points are measured values while the lines represent the lines of best fit. Each slope is synonymous with the calibrated gradient, allowing for interpolating glucose concentration within this range.

[0106] In the case of a solar simulator illumination using AML 5G solar simulator 1150-1 (FIG. 11 A), the colorimetric devices were measured under intensities of 600 W / m21150- lc. The slope values lie between -0.989 to -

[0107] Four intensities of 10W / m21150-2a, 50 W / nr 1150-2b, 80W / m21150-2c and 100 W / m21150-2d were utilised for red LED (FIG. 1 IB). Slope values range from -1.077 to -1.083. Three different intensities were looked into for halogen lamp, namely 100 W / m21150-3a, 200 W / m21150-3b and 400 W / m21150-3c, each with slope values ranging from -0.947 to -1.196 (FIG. 11C).

[0108] Only two intensities were conducted for white LED illumination (200 W / m21150-4a and 250 W / m21150-4b), with each slope registering at -0.963 and -1.047 (FIG. HD).

[0109] For ease of referencing, Table 1 below summarises the slope values for the various light sources together with the corresponding standard deviation.

[0110] Table 1 : The average slope values and the corresponding standard deviation for all the light sources.

[0111] Considering the collective average of slope values, the resultant calculation equates to -1.048 ± 0.043, exhibiting a standard deviation of 4.10%. The congruity among these slope values bolsters our anticipation that the concentration readings of a biomarker are barely affected by variations in light intensity. Moreover, this observation aligns closely with a slope value of -1.075 ± 0.028 (with a standard deviation of 2.60%) derived from diverse light sources. The similarity in slope values between both experiments substantiates the efficacy of the colorimetric sensor across varying light sources and intensities.

[0112] For ease of data interpretation, an algorithmic coding may be developed to offer a direct biomarker readout by efficiently computing photocurrent ratio. This eliminates the need for interfacing with an external device (e.g., mobile phone app) and eradicates subjective bias arising from colour chart comparison (by naked-eye quantification). Hence, the design of the colorimetric device offers an attractive solution for users who yearn for convenience and simplicity while monitoring their health status on the go.

[0113] It should be acknowledged that the above discussed design permits other combinations of OPD and CRL complementation. The simple CRL structure reserves the potential of detecting other biomarkers apart from glucose by changing the glucose oxidase to other enzymes such as lactate oxidase and uricase. The utilisation of chromogenic agent in the CRL may be extended beyond ABTS and ODA to o-Phenylenediamine (o-PD) and 3,3',5,5'-Tetramethylbenzidine (TMB). To illustrate an example, a CRL may be redesigned to detect lactate based on Equation (5) or (6). Rather than relying on ABTS or ODA, o-PD may be used as the chromogenic agent. Hence, Equation (5) or (6) may be rewritten as> > - Equation (7)

[0114] The replacement of the chromogenic component changes colourless o-PD to a yellowish-orange tinge in the presence of lactate. FIG. 12 shows a graph 1250 illustrating the calibration curve of the o-PD-based CRL due to different lactate concentrations. Absorbance was plotted against lactate concentration. Absorbance data was obtained at a wavelength of 450 nm as this is the peak absorption of the activated CRL. The inset of FIG.12 shows the activated CRL for a lactate concentration ranging from 0.1 tnM to 20 mM. The R2of the calibration curve is 0.960, which represents good linearity. In other words, the absorbance of the activated oPD-based CRL follows a linear relationship with lactate concentration.

[0115] Besides optimising the CRL, the sensitivity of our colorimetric sensor may be further maximised by utilizing novel narrow band photodetectors which match with the CRL absorption. In further pursuit of enhancing performance, the employment of PM6: Y6 as an OPD confronts constraints due to its classification as a broad-band OPD material.

[0116] Colorimetric devices (or similarly referred to as colorimetric sensors or colorimetric biosensors) are highly adaptable to various permutations. Testing of biomarkers may include but not restricted to molecular metabolites, salts, proteins, hormones, etc. It accommodates any biomarkers detected by colorimetric means. To measure these biomarkers, the use of photodetectors may include but not restricted to polymer / fullerene blend, polymer / non-fullerene acceptors, small molecules, perovskites, perovskite / orgamc hybrids, and so on. Adopting such material systems permit for fabricating flexible devices using solution processed printing techniques. The use ofchromogenic agents may include but not restricted to o-PD, ODA, ABTS, TMB, and so on. Through a careful selection of photodetectors and chromogenic agents, the sensors may be adjusted to measure different types of biomarkers. FIG. 13 shows a summary of the possible combinations that are feasible with the colorimetric devices

[0117] The colorimetric device may include or may be incoporated into a sweat-channel device. As a sweat wearable for healthcare monitoring, the use of the correct material for use in the photodetector is very important. In this aspect, existing methods and device are not ideal, given the use of an inorganic photodetector in those designs. While an organic photodetector may have been previously explored, the inclusion of a complex hierarchical micro / nanostructures as the scaffold is not synonymous with scalable production as provided by the colorimetric device here, according to various embodiments and examples, with the introduction of aqueous-based hydrogel. The chromogenic film in some existing devices was irreversible, rendering disposability as a necessity. It would be impractical for a disposable component of a sensor to undergo complex lithographic steps when it would be more prudent to execute a technique which may be easily mass produced.

[0118] While the invention has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.

Claims

CLAIMS1. A colorimetric device for analyte sensing, the colorimetric device comprising: a detector unit configured to detect an analyte of interest to produce a first signal; anda control unit configured to produce a second signal in absence of the analyte of interest,wherein the detector unit comprises:a first chemical responsive layer configured to change colour and / or transmissivity in response to a presence of the analyte of interest;a first photodetector configured to detect light filtered through the first chemical responsive layer and convert the detected filtered light into the first signal; anda first pair of electrodes configured to measure the first signal, the first photodetector comprising an active material being sandwiched between the first pair of electrodes,wherein the control unit comprises:a second chemical responsive layer configured to remain unchanged in terms of colour and transmissivity in absence of the analyte of interest; a second photodetector configured to detect the light passing through the second chemical responsive layer and convert the detected light into the second signal, the first photodetector and the second photodetector being substantially identical; anda second pair of electrodes configured to measure the second signal, the second photodetector comprising the active material being sandwiched between the second pair of electrodes, andwherein the colorimetric device is configured to facilitate a real-time readout from the first pair of electrodes and the second pair of electrodes, the real-time readout being based on a ratio of the first signal and the second signal.

2. The colorimetric device as claimed in Claim 1 further comprising a display unit configured to display the real-time readout.

3. The colorimetric device as claimed in Claim 1 or 2, wherein the first chemical responsive layer and the second chemical responsive layer each comprises a chromogenic agent, and an enzyme reactive to the analyte of interest.

4. The colorimetric device as claimed in Claim 3, wherein the chromogenic agent comprises o-dianisidine (ODA) or 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), or o-Phenylenediamine (o-PD), or 3,3',5,5'-Tetramethylbenzidme (TMB).

5. The colorimetric device as claimed in Claim 3 or 4, wherein the first chemical responsive layer and the second chemical responsive layer each further comprises a hemecontaining enzyme reactive to the chromogenic agent.

6. The colorimetric device as claimed in any one of Claims 1 to 5, wherein the active material comprises a polymer / fullerene blend, polymer / non-fullerene acceptors, small molecules, perovskites, perovskite / organic hybrids, or any combinations thereof.

7. The colorimetric device as claimed in any one of Claims 1 to 6, wherein the first photodetector and the second photodetector each comprises a wideband photodetector configured to sense a wide spectrum of the light.

8. The colorimetric device as claimed in any one of Claims 1 to 6, wherein the first photodetector and the second photodetector each comprises a narrowband photodetector configured to detect a narrow range of the light.

9. The colorimetric device as claimed in any one of Claims 1 to 8, whereinthe first pair of electrodes comprises a first electrode and a second electrode opposite to the first electrode,the first photodetector is orientated in a manner such that first electrode is positioned above or on top of the active material and the second electrode is positioned below or under the active material, the first electrode being positioned in close proximity to the first chemical responsive layer,the second pair of electrodes comprises a third electrode and a fourth electrode opposite to the third electrode, andthe second photodetector is orientated in a manner such that third electrode is positioned above or on top of the active material and the fourth electrode is positioned below or under the active material, the third electrode being positioned in close proximity to the second chemical responsive layer.

10. The colorimetric device as claimed in Claim 9, wherein the detector unit further comprises a first substrate coupled to the first electrode, and the control unit further comprises a second substrate coupled to the third electrode.

11. The colorimetric device as claimed in Claim 10, wherein the first substrate and the second substrate each comprises a glass substrate, or a polymer substrate.

12. The colorimetric device as claimed in Claim 11, wherein the polymer substrate comprises a flexible polymer substrate.

13. The colorimetric device as claimed in any one of Claims 9 to 12, wherein the first electrode and the third electrode comprise a first material, and the second electrode and the fourth electrode comprise a second material different from the first material.

14. The colorimetric device as claimed in Claim 13, wherein the first material and the second material comprise:different conducting polymers, ordifferent metals, ordifferent metal oxides, ora metal and a metal oxide, respectively.

15. The colorimetric device as claimed in any one of Claims 1 to 14, comprising a wearable colorimetric device.

16. The colorimetric device as claimed in any one of Claims 1 to 15, configured to operate at zero bias or with bias.

17. A method for performing analyte sensing, the method comprising:in response to a presence of an analyte of interest,changing colour and / or transmissivity of a first chemical responsive layer; by a first photodetector, detecting light filtered through the first chemical responsive layer and converting the detected filtered light into a first signal; measuring the first signal,substantially simultaneously in absence of the analyte of interest,allowing a second chemical responsive layer to remain unchanged in terms of colour and transmissivity;by a second photodetector, detecting the light passing through the second chemical responsive layer and converting the detected light into a second signal, wherein the first photodetector and the second photodetector are substantially identical;measuring the second signal, andfacilitating a real-time readout based on a ratio of the first signal and the second signal.18 The method as claimed in Claim 17, wherein facilitating the real-time readout comprises providing a concentration of the analyte of interest based on the ratio of magnitude of the first signal and magnitude of the second signal.

19. The method as claimed in Claim 17 or 18, wherein the light is ambient light or is transmitted from a light source.

20. The method as claimed in Claim 19, wherein the real-time readout is independent from types of the light used.

21. The method as claimed in any one of Claims 17 to 20, wherein the first photodetector and the second photodetector each comprises a wideband photodetector.

22. The method as claimed in Claim 21 , wherein the wideband photodetector comprises a polymer / fullerene blend, polymer / non-fullerene acceptors, small molecules, perovskites, perovskite / orgamc hybrids, or any combinations thereof, and senses a wide spectrum of the light.

23. The method as claimed in Claim 21 or 22, wherein the first photodetector and the second photodetector each is optimized with an absorption sensitivity of wideband photodetector.

24. The method as claimed in any one of Claims 17 to 20, wherein the first photodetector and the second photodetector each comprises a narrowband photodetector.

25. The method as claimed in Claim 24, wherein the narrowband photodetector comprises a polymer / fullerene blend, polymer / non-fullerene acceptors, small molecules, perovskites, perovskite / organic hybrids, or any combinations thereof, and detects a narrow range of the light.

26. The method as claimed in Claim 24 or 25, wherein the narrowband photodetector is engineered to match an absorption spectrum of the first chemical responsive layer and the second chemical responsive layer.

27. The method as claimed in any one of Claims 24 to 26, whereinin response to presence of multiple analytes of interest, detecting the light comprises detecting, by the first photodetector being the narrowband photodetector, thelight filtered through the first chemical responsive layer and converting the detected filtered light into a plurality of first signals;measuring the first signal comprises measuring the plurality of first signals; substantially simultaneously in absence of the multiple analytes of interest, detecting the light comprises detecting, by the second photodetector being the narrowband photodetector, the light passing through the second chemical responsive layer and converting the detected light into a plurality of second signals;measuring the second signal comprises measuring the plurality of second signals, andfacilitating the real-time readout comprises providing a plurality of real-time readouts according to the multiple analytes of interest, each readout being based on a ratio of magnitude of a first signal from the plurality of first signals and magnitude of a corresponding second signal from the plurality of second signals, according to an analyte from the multiple analytes of interest.

28. The method as claimed in any one of Claims 17 to 27, wherein the first chemical responsive layer and the second chemical responsive layer each comprises a chromogenic agent, and an enzyme reactive to the analyte of interest.

29. The method as claimed in Claim 28, wherein the chromogenic agent comprises o-dianisidine (ODA) or 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), or o-Phenylenediamine (o-PD), or 3,3',5,5'-Tetramethylbenzidine (TMB).

30. The method as claimed in Claim 28 or 29, wherein the first chemical responsive layer and the second chemical responsive layer each further comprises a heme-containing enzyme reactive to the chromogenic agent.

31. The method as claimed in Claim 30, wherein the chromogenic agent, the enzyme reactive to the analyte of interest, and the heme-contaming enzyme reactive to the chromogenic agent are mixed and provided in a form of a scaffold, preferably a hydrogel.

32. The method as claimed in Claim 30 or 31, wherein the heme-containing enzyme comprises horseradish peroxidase (HRP).33 The method as claimed in any one of Claims 17 to 32, wherein the analyte of interest comprises a biomarker / analyte.

34. The method as claimed in Claim 33, wherein the biomarker / analyte comprises a molecular metabolite or a salt or an ion or pH or a synthetic / pharmaceutical drug or a protein or a macromolecule or a neurotransmitter or a hormone.35 The method as claimed in any one of Claims 28 to 31, wherein the analyte of interest comprises glucose, the enzyme reactive to the analyte of interest comprises glucose oxidase (GOx), and wherein the method further comprises introducing the glucose to the first chemical response layer to catalyze conversion of the glucose to hydrogen peroxide (H2O2), which reacts with the chromogenic agent in the presence of a horseradish peroxidase enzyme, thereby facilitating oxidation of the chromogenic agent and in turn, resulting in a colorimetric change, which leads to a measurable alteration in light absorption properties of the first chemical response layer.

36. The method as claimed in any one of Claims 28 to 31 , wherein the analyte of interest comprises lactate, the enzyme reactive to the analyte of interest comprises L- lactate oxidase (LOx), and wherein the method further comprises introducing the lactate to the first chemical response layer to catalyze conversion of the lactate to hydrogen peroxide (H2O2), which reacts with the chromogenic agent in the presence of a horseradish peroxidase enzyme, thereby facilitating oxidation of the chromogenic agent and in turn, resulting in a colorimetric change, which leads to a measurable alteration in light absorption properties of the first chemical response layer.

37. The method as claimed in any one of Claims 17 to 36, being performed by a colorimetric device as claimed in any one of Claims 1 to 16.

38. The method as claimed in any one of Claims 17 to 37, being performed in absence of an external digital image analysis, or a spectrophotometer, or a naked-eye quantification.39 The method as claimed in any one of Claims 17 to 38 or the colorimetric device as claimed in any one of Claims 1 to 16, wherein the first signal comprises a first photocurrent signal and the second signal comprises a second photocurrent signal.

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