Wafer level fabrication of single cell dispenser chips with integrated electrodes for particle detection

This work presents the microfabrication and experimental evaluation of a dispenser chip, designed for isolation and printing of single cells by combining impedance sensing and drop-on-demand dispensing. The dispenser chip features 50 x 55 mu m (width x height) microchannels, a droplet generator and microelectrodes for impedance measurements. The chip is fabricated by sandwiching a dry film photopolymer (TMMF) between a silicon and a Pyrex wafer. TMMF has been used to define microfluidic channels, to serve as low temperature (75 degrees C) bonding adhesive and as etch mask during 300 mu m deep HF etching of the Pyrex wafer. Due to the novel fabrication technology involving the dry film resist, it became possible to fabricate facing electrodes at the top and bottom of the channel and to apply electrical impedance sensing for particle detection with improved performance. The presented microchip is capable of dispensing liquid and detecting microparticles via impedance measurement. Single polystyrene particles of 10 mu m size could be detected with a mean signal amplitude of 0.39 +/- 0.13 V (n = 439) at particle velocities of up to 9.6 mm s(-1) inside the chip.