Design and fabrication of integrated organic thin-film transistor-based sensor on flexible substrate for glucose monitoring / Fazliyatul Azwa Md Rezali

Fazliyatul Azwa , Md Rezali (2025) Design and fabrication of integrated organic thin-film transistor-based sensor on flexible substrate for glucose monitoring / Fazliyatul Azwa Md Rezali. PhD thesis, Universiti Malaya.

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Abstract

With the rising cases of diabetes over the years, there is a growing demand for smart glucose wearables for early diagnosis and routine care. The current advancement in glucose sensors, while generally effective, has lacked system integration for wearability and real-time continuous monitoring in interstitial fluid. Herein, a novel integration of an organic thin-film transistor (OTFT) with a hollow microneedle (HMN) and an interfacing circuit has been proposed by adapting facile printing and flexible technology for minimally invasive sampling and sensitive glucose analysis. For a comparative study, interdigitated electrode (IDE) and organic electrochemical transistor (OECT) structures, a subtype of OTFT, are designed and fabricated on a flexible polyethylene terephthalate (PET) film as an electrochemical sensor. The dispense-printed IDE, modified with a reduced graphene oxide/titanium dioxide nanohybrid and glucose oxidase (GOx), operates at 0.5 V. The device demonstrates fair reproducibility (Coefficient of Variance, CV = 12.2%) and repeatability (CV = 3.3%) within 60 s measurement, with excellent stability for 7 days on a curvature surface (normalized resistance, NR = 7%). The IDE-based sensor has a good linear response to glucose ranging from 0.05 to 30 mM (r2 = 0.988) with a sensitivity of 3.17 μA mM-1cm-2. Meanwhile, the screen-printed OECT, with a PEDOT:PSS channel functionalized by a chitosan-titanium dioxide nanocomposite and GOx, operates at a gate voltage of -0.5 V. In comparison to IDE devices, the OECT devices have better reproducibility (CV = 4.9%) and repeatability within 60 s measurement (CV = 0.3%), although it shows moderate stability when bent for 7 days (NR = 11.9%). The OECT-based sensor has an excellent linear response at glucose concentrations ranging from 0.01 to 30 mM (r2 = 0.993) with a sensitivity of 6.01 μA mM-1cm2. Both devices have good selectivity for glucose over ascorbic acid and uric acid. Subsequently, the OECT is selected for integration with an interfacing circuit since it outperforms the IDE in terms of sensitivity, where the response time of the fully integrated device with the application of a 3D-printed 3x3 HMN array is within 20 s using an agar gel-based skin model. The output signals are calibrated with a glucose concentration of 1–10 mM (r2 = 0.999) at a reading time of below 110 s. As a result, the glucose readings are comparable to those of a commercial glucose meter, and the maximum variation for low glucose levels (< 5.5 mmol/L) is within 0.4 mmol/L, while the maximum variation at high glucose levels (> 5.5 mmol/L) is 9.43%, indicating acceptable accuracy according to the ISO standard. Overall, the current prototype of the fully integrated glucose sensor shows great potential as a viable solution for glucose monitoring wearables.

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