Response characteristics of single-cell impedance sensors employed with surface-modified microelectrodes.

The underlying sensing mechanism of single-cell-based integrated microelectrode array (IMA) biosensors was investigated via experimental and modeling studies. IMA chips were microfabricated and single-cell-level manipulation was achieved through surface chemistry modification of IMA chips. Individual fibroblast cells (NIH3T3) were immobilized on either lysine-arginine-glycine-aspartic acid (KRGD) short peptide-modified or fibronectin extracellular-cell-adhesion-molecule-modified microelectrodes to record the impedance variations of cell-electrode heterostructure over a frequency range of 1-10 kHz. By fitting experimental data to an application-specific single-cell-level equivalent circuit model, important sensing parameters, including specific cell membrane capacity, cell membrane resistivity, and averaged cell-to-substrate separation, were determined. It was demonstrated that biofunctionalization of planar microelectrode surface by covalently linking short peptides or fibronectin molecules could achieve strong or tight cell adhesion (with an estimated averaged cell-to-substrate separation distance of 11-16 nm), which, in turn, improves the transduced electrical signal from IMA chips. Analyses on frequency-dependent characteristics of single-cell-covered microelectrode impedance and of IMA sensor circuitry response have revealed an addressable frequency band wherein electrical properties of single cells can be distinctively determined and monitored for cellular biosensing applications. The presented work addresses some major limitations in single-cell-based biosensing schemes, i.e., the manipulation of a single cell, the transduction of weak biological signals, and the implementation of a proper model for data analysis, and demonstrates the potential of IMA devices as single-cell biosensors.