An impedance microsensor with coplanar electrodes and vertical sensing apertures

An impedance microsensor with coplanar electrodes and a vertical sensing aperture is presented for detecting single particles/cells. The sensing mechanism utilizes gating electrodes patterned in a plane perpendicular to the fluidic flow to minimize coincidence due to multiple particles. The design was implemented by integrating gating microelectrodes across the entrance of an orifice anisotropically etched into a silicon substrate. Through holes in diameters of 20, 60, and 100 μm were made on a single device. The microsensor was tested by detecting microbeads 45 μm in diameter suspended in 0.9% saline solution using AC excitation of 500 kHz. For comparison, a larger version made on a printed circuit board was also tested on microbeads 367 and 867 μm in diameter using an excitation frequency of 50 KHz. The impedance change across the gating electrodes due to passage of particles through the sensing apertures was converted into electrical pulses using an interfacing system including demodulation and signal processing circuitry and acquired into a LabView program for automatic pulse detection and analysis. Preliminary results on detection of microbeads indicate that the sensing mechanism is capable of detecting passing particles, and the pulse amplitude distribution correlates with the size of beads.