Toward a Practical Impedimetric Biosensor: A Micro-Gap Parallel Plate Electrode Structure That Suppresses Unexpected Device-to-Device Variations

Haruka Honda; Yusuke Kusaka; Haiyun Wu; Hideaki Endo; Daiju Tsuya; Hitoshi Ohnuki

doi:10.1021/acsomega.1c06942

Toward a Practical Impedimetric Biosensor: A Micro-Gap Parallel Plate Electrode Structure That Suppresses Unexpected Device-to-Device Variations

ACS Omega. 2022 Mar 23;7(13):11017-11022. doi: 10.1021/acsomega.1c06942. eCollection 2022 Apr 5.

Authors

Haruka Honda¹, Yusuke Kusaka¹, Haiyun Wu², Hideaki Endo², Daiju Tsuya³, Hitoshi Ohnuki¹

Affiliations

¹ Department of Marine Electronics and Mechanical Engineering, Tokyo University of Marine Science and Technology, 2-1-6 Etchujima, Koto, Tokyo 135-8533, Japan.
² Department of Ocean Sciences, Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato, Tokyo 108-8477, Japan.
³ National Institute for Material Science, 1-21 Sengen, Tsukuba, Ibaraki 305-0047, Japan.

Abstract

We propose a rational electrode design concept for affinity biosensors based on electrochemical impedance spectroscopy to substantially suppress unexpected device-to-device variations. On the basis that the uniformity of the current distribution affects the variation, a novel micro-gap parallel plate electrode (PPE) was developed, where two planar electrodes with edges covered with a SiO₂ layer were placed face to face. The structure provides a uniform current distribution over the planar electrode surface and maximizes the contribution of the planar electrode surface to sensing. For a comparative study, we also fabricated a micro-structured interdigitated electrode (IDE) that has been widely adopted for high-sensitivity measurement, although its current is highly concentrated on the electrode edge corner. Protein G (PrG) molecules were immobilized on both electrodes to prepare an immunoglobulin G (IgG) biosensor on which the specific binding of PrG-IgG can occur. We demonstrated that the IgG sensor with the PPE has small device-to-device variations, in strong contrast to the sensor with the IDE having large device-to-device variations. The results indicate that the current distribution on the electrode surface is important to fabricating electrochemical impedance spectroscopy biosensors with small device-to-device variations. Furthermore, it was found that the PPE allows ultrasensitive detection, that is, the sensor exhibited a linear range from 1 × 10^-13 to 1 × 10^-7 mol/L with a detection limit of 1 × 10^-14 mol/L, which is a record sensitivity at low concentrations for EIS-based IgG sensors.