Effect of gap size of gold interdigitated electrodes on the electrochemical immunosensing of cardiac troponin-I for point-of-care applications

This work describes the effect of electrode geometry on the sensor's performance, towards the fabrication of impedimetric bio-sensor for cardiac troponin-I (CTnI) detection. Herein, development of a novel, Electrochemical Impedance Spectroscopy (EIS) based immunosensor for point-of-care applications is explored using gold coated Interdigitated Electrodes (IDEs). The effect of sensor's geometry and its effect on sensor's performance has not been well characterised in the available literature; the understanding of which would significantly advance bio-sensor design and its performance. Greater control of electrode geometries and inter-electrode spacing will increase the electrode surface area, consequently increasing the charge-transfer resistance and reduce the double-layer capacitance. These, in turn, give rise to improved signal-to-noise ratios, thereby affording greater sensitivity, lower detection limits and faster detection times. IDEs of various gap sizes (5 µm, 10 µm, 50 µm and 75 µm) were investigated for sensing of CTnI within 2 ng/mL-12 ng/mL concentration range. The sensitivity is found to be largely dependent on IDE's gap size: ∼ 50% enhancement is achieved upon decreasing the spacing from 75 µm to 5 µm. The response time of the developed immunosensor was found to be ∼ 10 s with excellent selectivity and performance in spiked serum, which makes it an ideal candidate for point of care applications.