Particle detection on microfluidic chips by differential resistive pulse sensing (RPS) method.

The resistive pulse sensing (RPS) method has been widely used for characterization of particles, cells, and biomolecules due to its merits of high sensitivity and resolution. This paper investigates working parameters involved in detecting submicron and micron-sized particles by the differential RPS method on microfluidic chips. Effects of particle-to-sensor size ratio, ionic concentration and pH of the electrolyte solution, and applied electric field are studied systematically by using polystyrene particles with a size range from 140 nm to 5 µm. The results show that both the amplitude and the signal-to-noise ratio (SNR) of the RPS signals increase with the particle-to-sensor size ratio as well as the ionic concentration of the electrolyte media. The amplitude of the RPS signals also increases with increasing applied voltage, while the SNR experiences an upslope at low voltages and a decline under the condition of high voltages. pH has little effect on the background noise of the differential RPS signals but reduces the amplitude of the RPS signals at high pH. Grouping of RPS signals is considered to be caused by interactions between the sensor walls and the particles. Nanoparticle detection by the differential RPS method can be enhanced by optimizing these working parameters.