Signal Improvement by Dielectric Focusing in Microfluidic Impedance Cytometers

We report the design and the electrical and microfluidic characterization of a device that improves signal strength and increases the detection levels in microfluidic impedance cytometry. Low-conductivity aqueous and two-phase dielectric sheathing allows the use of wider, more easily fabricated channels, increases the precision of celland particle-size measurements, and decreases the smallest detectable object size. For aqueous dielectric sheathing with a fixed excitation voltage of 400 mVrms, the highest relative signal strength measured was 1.4 ± 0.6% for a 27-μm core. The use of a twophase system and a core width of 33 μm resulted in a signal strength of 5.1 ± 0.5%. This two-phase system increases SNR by 23 dB compared to the aqueous system.