Optimization of an electrical impedance flow cytometry system and analysis of submicron particles and bacteria

Electrical impedance flow cytometry (EIFC) based on microfluidic chips has be en applied to particle and bacterial cell analysis, but detection of submicron particles is limited by the sensitivity of the existing microfluidic systems. Our objective was to increase the sensitivity of a coplanar electrode EIFC system and fulfill the increasing demand of analyzing submicron-organisms such as bacteria, apoptotic bodies, extracellular vesicles, exosomes and viruses. To this end, we optimized a series of parameters, including the width of the electrodes (We) of the microfluidic chip, the width (Wc) and height (Hc) of the channel’s sensing zone, and the buffer conductivity. The results indicated that 10 µm and 5 µm are the optimal We and Wc values, respectively, for microparticle detection. Based on these results, we developed an EIFC chip to test the detection of ⌀ 3.0 µm microspheres and yeast cells suspended in buffers of different conductivity. The optimal conductivities for microsphere and yeast cell detection were approximately 1.6 S/m and 6.4 S/m, respectively. Moreover, submicrospheres of ⌀ 0.2–0.6 µm and bacterial cells of species such as Serratia marcescens (with a cell size of 0.5 × (0.5–1.0) µm) were detected using the optimized EIFC system with a wide channel (Wc = 5 µm). In conclusion, our results demonstrate that the optimized EIFC system can be used to detect almost all types of bacteria in a high-throughput approach, allowing an effective and accurate enumeration of bacteria or other submicron-organisms in liquid samples in the future.