Capacitive Particle Detection In A Microfluidic Chip

It has a huge demand for rapid and accurate detection of the number and sizes of particles in the sample in areas of ship safety and ship pollution prevention. For example, ship machinery system fault diagnosis based on oil performance analysis requires to determine the number, sizes and types of the abrasive particles in lubricating oil. In marine pollution zones caused by ships, port states need to count the number of surviving organisms of different sizes in ballast water after treatment when ships arrive at port.A as a highly integrated and miniaturized total analysis system, microfluidic chip is suitable as portable detection equipment. This paper studied particle capacitive detection technology on microfluidic chips, and applied this technology in distinguishing the types and measuring the sizes of the abrasive particles in lubricating oil and microalgae in ship ballast water. The main research contents of this paper are:(1) Established theory model of abrasive particle capacitance detection in oil, and numerically simulated the influence of the abrasive particles of different sizes and dielectric constants on the value of the capacitance detection when passing capacitance detection zone. The study showed that, for abrasive particles of the same material, the capacitance change value increased with the size of the abrasive particle; The capacitance change value increased rapidly with dielectric constant of the particles when the sizes of the abrasive particles were the same; Whereas, the capacitance change value increased slowly with dielectric constant of the particles when the dielectric constant of the particles was higher than50, and gradually approached the final stable value, which meant, it was nearly impossible to distinguish the material of metal with capacitive sensor.(2) Processed capacitive sensor on microfluidic chips with a relatively simple way, and build the3D capacitance detection system to achieve the detection and size determination of8μm aluminum particles in lubricant oil, the distinction and count of metallic and non-metallic abrasive particles.(3) Deduced the theoretical formula of capacitance value change with cell parameters, capacitive sensor parameters and excitation frequency according to Maxwell mixture theory and cellular model. Analysis showed that the for one cell, the capacitance detection value decreased with excitation frequency; however, for living and dead cells of the same size, the capacitance detection value of living cells is higher in the same excitation frequency comparatively.(4) Tested the relationship between capacitance change caused by microalgae in ballast water of different activities and the excitation frequency using capacitive detection system, and the experimental results and theoretical analysis were in good agreement. Experimental results showed that, in the range of200kHz-500kHz, there was significant difference between capacitance value of living microalgae and that death microalgae. And this frequency had guiding significance on the distinction of the survival status of microalgae in ballast water based on capacitance method afterwards.This study has certain value for the development of the abrasive particles counting and distinguishing technology and device of harmful organisms in ballast water based on microfluidics chips.