Amplifier spurious input current components in electrode-electrolyte interface impedance measurements

Abstract

Background: In Impedance Microbiology, the time during which the measuring equipment is connected to the bipolar cells is rather long, usually between 6 to 24 hrs for microorganisms with duplication times in the order of less than one hour and concentrations ranging from 10 1 to 10 7 [CFU/ml]. Under these conditions, the electrode-electrolyte interface impedance may show a slow drift of about 2%/hr. By and large, growth curves superimposed on such drift do not stabilize, are less reproducible, and keep on distorting all over the measurement of the temporal reactive or resistive records due to interface changes, in turn originated in bacterial activity. This problem has been found when growth curves were obtained by means of impedance analyzers or with impedance bridges using different types of operational amplifiers.

An embedded portable biosensor system for bacterial concentration detection

“…The test signal is applied to the electrodes only when the electrical characteristics are measured, while between inter-measurements time (5 minutes) the electrodes are disconnected from the system by a couple of relais G6J-2FS-Y (Omron, Japan) to prevent charging of the sample-electrode interface resulting in parameter drift, long time for baseline stabilization and, in general, difficult DT calculation (Felice et al, 2005). The current resulted from the application of V in is measured by means of the I-V converter, providing an output (V out ) proportional to the input current (I in ).…”