This paper presents a novel impedance-sensing device and its related microfluidics system developed to characterize the macroscopical properties of bacteria and microparticles using impedance flow cytometry. 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. The measured data show an error of less than 7% for the impedance magnitude and of less than 3 degrees for the phase, and adequately measures the three zones of the impedance of saline water usually associated to the electrical double-layer, liquid bulk-resistance, and electrode shape.