Dual-Functional Janus Electrode for Enhanced Sensitivity in Enzymatic Electrochemical Biosensors

Abstract

This study introduces a Janus electrode geometry for enzymatic glucose biosensors, designed to enhance sensitivity by minimizing the distance between the enzyme immobilization site and the signal- sensing region. The Janus electrode separates two functions: gold interdigitated electrodes (IDE) for selective enzyme immobilization and a carbon electrode for electrochemical signal detection. Glucose oxidase (GOx) is immobilized on the gold IDE, while reaction byproducts from glucose oxidation are detected at the underlying carbon electrode. Because the electrodes are closely spaced, the by-products are more efficiently collected due to the close electrode proximity, enabling efficient local signal collection. This geometry leads to high current response and sensitive glucose detection. The carbon component of the Janus electrode was fabricated using a simple and cost-effective carbon microelectromechanical systems (C-MEMS) process. SU-8 polymer was first patterned and then converted into carbon through vacuum pyrolysis. Au IDEs were subsequently patterned on the carbon surface by metal evaporation and lift-off, forming the Janus electrode structure. To immobilize GOx, carboxyl functional groups were introduced onto the gold electrode surface using self-assembled monolayers. Covalent enzyme immobilization was achieved through zero-length crosslinking chemistry. Glucose sensing performance was evaluated using chronoamperometry over a glucose concentration range of 0–5,000 µM. Since physiological glucose levels in blood range from ~3 to 10 mM, the selected 0–5 mM range covers clinically relevant values. Sensor sensitivity was defined as the change in current response per unit change in glucose concentration, normalized by the active sensor area. The Janus electrode exhibited linear response from 0–5 mM, with sensitivities of 6.06 µA·mM⁻¹·cm⁻² in the glucose concentration range.