Femtoampere integrated current preamplifier for low noise and wide bandwidth electrochemistry with nanoelectrodes

Abstract

The direct tracking of the potential-induced modulation of the double layer capacitance (100mV bias steps resulting in 1.2fF variations) of Pt nanoelectrodes (100nm diameter) in physiological solution with sub-fF resolution and 10ms response time is reported. This result is an example of the enhanced performance achieved thanks to an integrated CMOS current preamplifier used as an add-on for standard bench-top electrochemical instrumentation. The chip provides a current amplification of 103 over the wide frequency range DC-2MHz and can be placed at the input of a current-to-voltage converter to reach higher gains. Thanks to its millimetric size it drastically reduces the input stray capacitance of the connection cables to the electrode, offering superior noise performance such as 0.55fA (rms) current resolution with 1Hz bandwidth demonstrated in the detection of 1.5fA current steps. The improvement in performance of state-of-art commercial potentiostats is also reported: the largest measurable impedance is increased by two orders of magnitude (up to 100GΩ with only 10mV applied and 0.125s averaging time) and the impedance noise in time tracking is reduced 35 times. This module has been developed for nano-electrochemical and bio-sensing applications but can be profitably used in all the situations in which few electrons are exchanged at the interface, either since the electrode area is nanometric or since the concentration of the redox species is extremely low.