Probing chemical induced cellular stress by non-Faradaic electrochemical impedance spectroscopy using an Escherichia coli capacitive biochip

Abstract

A new capacitive biochip was developed using carboxy-CNT activated gold interdigitated (GID) capacitors immobilized with E. colicells for the detection of cellular stress caused by chemicals. Here, acetic acid, H₂O₂ and NaCl were employed as model chemicals to test the biochip and monitored the responses under AC electrical field by non-Faradaic electrochemical impedance spectroscopy (nFEIS). The electrical properties of E. colicells under different stresses were studied based on the change in surface capacitance as a function of applied frequency (300–600 MHz) in a label-free and noninvasive manner. The capacitive response of the E. coli biochip under normal conditions exhibited characteristic dispersion peaks at 463 and 582 MHz frequencies. Deformation of these signature peaks determined the toxicity of chemicals to E. coli on the capacitive biochip. The E. colicells were sensitive to, and severely affected by 166–498 mM (1–3%) acetic acid with declined capacitance responses. The E. coli biochip exposed to H₂O₂ exhibited adaptive responses at lower concentrations (<2%), while at a higher level (882 mM, 3%), the capacitance response declined due to oxidative toxicity in cells. However, E. colicells were not severely affected by high NaCl levels (513–684 mM, 3–4%) as the cells tend to resist the salt stress. Our results demonstrated that the biochip response at a particular frequency enabled the determination of the severity of the stress imposed by chemicals and it can be potentially applied for monitoring unknown chemicals as an indicator of cytotoxicity.