A Low-Cost Microfluidic Device For the On-Line Counting of Microparticle/Bacteria

On-line counting of the microparticle/bacteria in the liquid medium has great potential in the food safety and biomedical fields. A new low-cost microfluidic device is proposed for the on-line counting of the microparticles/bacteria in the liquid medium. The gradually contracted microchannel and the viscoelastic fluid are combined to achieve the efficient elastic focusing of the particle/bacteria, which significantly improves the counting accuracy by aligning all particles/bacteria in a single position at the center of the microchannel. A simple light resistance-based counting method is designed and integrated with the microchannel, where the low-cost elements including the laser pointer, convex lens, diaphragm, and photodiode, are used to build the optical path of detection. The influence of the flow rate, the particle size, the property of fluid, and the channel structure on the focusing of the particle/bacteria are investigated by the experiment, and the counting ability of the integrated microfluidic device is validated by using different-sized microparticles and the bifidobacterium. With its simple structure, low cost, easy operation, and high efficiency, this microfluidic device is suitable for the commercial applications, such as the on-line counting of the plastic microparticle in water or the colony-forming units (CFU) of bacteria in food.