Preliminary development of a transistor-based biosensing platform

Abstract

Early detection of osteoarthritis remains challenging, as few diagnostic methods combine accessibility, minimal invasiveness, and sufficient analytical sensitivity. Biosensor-based detection of disease related biomarkers found in saliva represents one promising route toward more practical and sensitive diagnostic tools. Electrochemical biosensors employing Extended-Gate Field-Effect Transistor (EG-FET) designs represent a viable approach due to their compact format and low cost implementation. This project presents the preliminary development of a transistor-based biosensing platform using an EG-FET design coupled to an EmStat Pico potentiostat, representing an early step toward a system capable of detecting osteoarthritis biomarkers in equine saliva. Screen-printed gold electrodes (Au-SPEs) were functionalized using copper free click chemistry, enabling selective surface modification for future attachment of DBCO-coupled Fab’ fragments. The functionalization strategy used in this work employed lipoamido-PEG4-azide as the linker molecule, followed by DBCO-PEG4-alcohol passivation and BSA blocking prior to exposure to equine saliva samples to evaluate non specific binding. Cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry were used to evaluate each functionalization step and to assess the performance of the EG-FET system. Both linker attachment and subsequent DBCO-PEG addition and BSA layers produced clear and reproducible electrochemical signatures when measuring with either cyclic voltammetry or electrochemical impedance spectroscopy, confirming that the functionalization protocol used was effective on the Au-SPE surfaces. Chronoamperometric measurements with the custom EG-FET system responded to surface bound charge variations, demonstrating that the setup successfully enabled detection of electrochemical changes occurring at the gold electrode interface. However, functionalization with molecules carrying a net neutral charge or positioned too far from the surface resulted in no detectable transistor response, this underscores the importance of understanding the system’s sensitivity to Debye screening effects. Both the ionic strength of the surrounding medium and the physical length and net charge of the functionalization molecules influence the effective sensing distance, which in turn affects the transistor’s ability to detect future biomolecular binding events. Further optimization of buffer conditions, molecular architecture, and electrode geometry will therefore be essential to improve sensitivity and robustness. Overall, this work represents a promising first step toward a transistor-based biosensor for osteoarthritis related biomarkers. While the platform shows clear potential, substantial development remains before a fully functional diagnostic device can be achieved.