Portable Impedance Analyzer for FET-Based Biosensors with Embedded Analysis of Randles Circuits’ Spectra

Pfeiffer N, Bach M, Steiner A, Gerhardt AE, Bausells J, Errachid A, Heuberger A (2025)

Publication Type: Journal article

Publication year: 2025

Journal

Sensors MDPI

Book Volume: 25

Article Number: 3497

Journal Issue: 11

DOI: 10.3390/s25113497

Abstract

The electrochemical impedance spectroscopy (EIS) is a measurement method for characterizing bio-recognition events of a sensor, such as field-effect transistor-based biosensors (BioFETs). Due to the lack of portable impedance spectroscopes, EIS applies mainly in laboratories preventing application-oriented use in the field. This work presents a portable impedance analyzer (PIA) providing a 4-channel EIS of BioFETs. It performs the analysis of the recorded spectra by determining the charge transfer resistance (Formula presented.) with a power-saving algorithm. Therefore, a circle is fitted into the Nyquist representation of the Randles circuit, from whose zero crossings (Formula presented.) can be determined. The introduced algorithm was evaluated on 100 simulated spectra of Randles circuits. To analyze the overall system, an adjustable reference circuit was developed that simulates configurable Randles circuits. Additional measurements with pH-sensitive ion-sensitive field-effect transistors (ISFETs) demonstrate the application of the measurement system with electrochemical sensors. Using simulated spectra, the circular fitting is able to detect (Formula presented.) with a median accuracy of (Formula presented.) at an average nominal power of 40 mW and 3054 µs computing time. The PIA with the embedded implementation of the circuit fitting achieves a median error for Rct of 4.2% using the introduced Randles circuit simulator (RCS). Measurements with ISFETs show deviations of 6.5 ± 2.8% compared to the complex non-linear least squares (CNLS), but is significantly faster and more efficient. The presented system allows a portable, power-saving performance of EIS. Future optimizations for a specific applications can improve the presented system and enable novel low-power and automated measurements of biosensors outside the laboratory.

Involved external institutions

Institute of Analytical Sciences / Institut des Sciences Analytiques (ISA) FR France (FR) Fraunhofer-Institut für Integrierte Schaltungen (IIS) DE Germany (DE) Institut de Microelectrònica de Barcelona (IMB-CNM) ES Spain (ES)

How to cite

APA:

Pfeiffer, N., Bach, M., Steiner, A., Gerhardt, A.E., Bausells, J., Errachid, A., & Heuberger, A. (2025). Portable Impedance Analyzer for FET-Based Biosensors with Embedded Analysis of Randles Circuits’ Spectra. Sensors, 25(11). https://doi.org/10.3390/s25113497

MLA:

Pfeiffer, Norman, et al. "Portable Impedance Analyzer for FET-Based Biosensors with Embedded Analysis of Randles Circuits’ Spectra." Sensors 25.11 (2025).

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