Microfluidic Biochip for Impedance Spectroscopy of Biological Species

This paper describes the fabrication and characterization of a microelectronic device for the electrical interrogation and impedance spectroscopy of biological species. Key features of the device include an all top-side processing for the formation of fluidic channels, planar fluidic interface ports, integrated metal electrodes for impedance measurements, and a glass cover sealing the non-planar topography of the chip using spin-on-glass as an intermediate bonding layer. The total fluidic path volume in the device is on the order of 30 nl. Flow fields in the closed chip were mapped by particle image velocimetry. Electrical impedance measurements of suspensions of the live microorganism Listeria innocua injected into the chip demonstrate an easy method for detecting the viability of a few bacterial cells. By-products of the bacterial metabolism modify the ionic strength of a low conductivity suspension medium, significantly altering its electrical characteristics.