Multi-Variable Biosensing Platform Based on Aerosol Jet Printed Organic Electrochemical Transistors (OECTs) for Diabetic Wound Care

Diabetic patients have an increased risk of developing chronic foot ulcers/wounds that may lead to severe consequences, including lower-extremity amputation and mortality. Studies have shown that specific parameters, such as pH, pressure, moisture, and temperature, are related to wound infection and healing phases [1]. However, in conventional wound management physicians have limited access to the real-time monitoring of these parameters and can only assess wound status by removing the dressing, which often leads to patient discomfort and may disrupt the healing process [1]. Continuous monitoring of the wound environment with embedded wound dressing biosensors provides real-time wound status to physicians, which can aid wound care decision-making to reduce severe outcomes.<br/><br/>Here, we have developed a multi-variable biosensing platform to achieve <i>in situ</i> continuous monitoring of glucose and temperature levels on chronic diabetic mice wounds. Organic electrochemical transistors (OECTs) were selected for enzymatic glucose sensor development due to their high intrinsic signal amplification, low operation voltages, and compatibility with aqueous environments. We have previously reported functionalization optimization of aerosol jet printed glucose sensors[2]. In this work, the OECTs were fabricated using an Optomec Aerosol Jet 5X printer on flexible Kapton substrates with Au nanoparticle ink for the source and drain electrodes, Pt nanoparticle ink for the gate electrode, a PEDOT:PSS channel, and polyimide as the insulator. Glucose sensing was achieved by functionalizing the printed Pt gate with glucose oxidase, chitosan, and Nafion. The glucose sensor was first optimized in simulated wound fluid to achieve a desired detection range of 0.1mM – 50 mM with an average sensitivity of 0.17NR/dec.<br/><br/>The resistive temperature sensor was developed from a thermoplastic and carbon nanotube nanocomposite mixture. The nanocomposite was drop casted and annealed on printed Au traces and demonstrated a high linearity in its resistance change for the temperature range of 20°C to 55°C. Currently, the sensitivity is approximately 20 Ω/°C with an average negative temperature coefficient of -0.001 K^-1. The ease of fabrication coupled with extremely high linearity (R² &gt; 0.999) makes this an ideal candidate for temperature detection to include with our OECT devices on one substrate.<br/><br/>We developed a custom-designed circuit with signal processing hardware for data collection during <i>in vivo</i> wound monitoring. It includes low-noise biasing circuitry to enable OECT operation as well as a multi-channel analog to digital converter for the measurement of OECT voltage and current characteristics. Raw 32-bit data is logged to an on-board high-capacity SD card for long-term operation and further data processing is done off-board using a custom MATLAB program. Preliminary results of our glucose and temperature level measurements using our biosensing platform on healthy and diabetic mice animal model wounds will be presented.<br/><br/>Reference<br/>[1] Salvo, P., Calisi, N., Melai, B., Dini, V., Paoletti, C., Lomonaco, T., Pucci, A., di Francesco, F., Piaggesi, A., & Romanelli, M, <i>Temperature- and pH-sensitive wearable materials for monitoring foot ulcers.</i> International Journal of Nanomedicine, 2017. 12: p. 949.<br/>[2] Fan, J., A.A. Forero Pico, and M. Gupta, <i>A functionalization study of aerosol jet printed organic electrochemical transistors (OECTs) for glucose detection.</i> Materials Advances, 2021. <b>2</b>(22): p. 7445-7455.