Roles of Interdigitated Electrode Geometry in Non-Faradaic Impedimetric Biosensors

In this work, we investigate the effect of interdigitated electrode fingers width and gap on the performance of biosensors. Two different configurations of interdigitated electrodes were utilized; one consists of 50 mu m wide fingers with a gap of 50 mu m, and the other consists of 100 mu m wide fingers with a 100 mu m gap. First, the active surface area of both interdigitated electrodes was investigated. Then, the surface electronic parameters were investigated using faradaic and non-faradaic electrochemical impedance spectroscopy modes. Both interdigitated electrodes were then functionalized with LDL-antibodies through a standard chemical functionalization route and were utilized for the detection of LDL-antigen of cholesterol. The biosensor with 50 mu m width and gap demonstrated better sensitivity and limit of detection of 6.08 nF/log(ng/ml) and 40 pg ml-1, respectively. Biosensors with 100 mu m finger width and gap sensitivity and detection limit are 5.16 nF/log(ng/ml) and 300 pg ml-1, respectively. The enhanced sensitivity and limit of detection for the first biosensor is due to the increased surface area, enhanced electric field, and less diffusion of ions onto the biosensor surface. The study reported here suggests room for improving the geometry of many interdigitated electrodes for enhanced non-faradaic biosensing performances.