This paper presents a novel impedance-sensing device and its related microfluidics system developed to characterize the macroscopical properties of bacteria and microparticles. The system is based on a phase-sensitive detector with square-waves excitation voltage ranging from 20 kHz to 40 MHz as inputs to characterize microparticles in situ using impedance spectroscopy and impedance flow cytometry. The particles pass through a 100 mu m by 120 mu m polydimethylsiloxane microchannel bonded on a printed circuit board etched with 200 mu m wide electrodes. The measured data show an error of less than 7% for the impedance magnitude and of less than 3 degrees for the phase, over the whole frequency range. It adequately measures the three zones of the impedance of saline water usually associated to the electrical double-layer, liquid bulk-resistance, and electrode shape.