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

Area of Science:

• Electrochemistry
• Biosensor Technology
• Instrumentation

Background:

• Electrochemical impedance spectroscopy (EIS) is crucial for characterizing biosensors like field-effect transistor-based biosensors (BioFETs).
• Current limitations include the lack of portable impedance spectroscopes, restricting EIS use to laboratory settings.
• This hinders the application-oriented deployment of biosensors in field environments.

Purpose of the Study:

• To develop a portable impedance analyzer (PIA) for 4-channel EIS measurements of BioFETs.
• To implement a power-saving algorithm for determining charge transfer resistance (Rct) from EIS spectra.
• To validate the system's performance with simulated data and electrochemical sensors.

Main Methods:

• A portable impedance analyzer (PIA) was designed for 4-channel EIS measurements.
• A power-saving algorithm was developed to determine Rct by fitting a circle to the Nyquist representation of the Randles circuit.
• The system was evaluated using simulated Randles circuit spectra and measurements from pH-sensitive ion-sensitive field-effect transistors (ISFETs).

Main Results:

• The circular fitting algorithm achieved a median accuracy of 1.2% for Rct detection on simulated spectra with low power consumption (40 mW) and fast computation (3054 µs).
• The PIA system demonstrated a median Rct error of 4.2% when using a custom Randles circuit simulator.
• Measurements with ISFETs showed a deviation of 6.5 ± 2.8% compared to complex non-linear least squares (CNLS), offering significant speed and efficiency gains.

Conclusions:

• The developed portable impedance analyzer enables power-saving, field-deployable EIS measurements for biosensors.
• The system provides accurate Rct determination, outperforming traditional methods in speed and efficiency.
• This technology paves the way for novel, low-power, automated, and portable biosensor measurements outside the laboratory.