Particle Detection In A Microfluidic Resistive Pulse Sensor With A Side Sensing Gate

Portable particle detection and counting technology has a wide application prospect in many fields,such as on-site rapid detection of harmful microorganisms in ship ballast water.Microfluidic chip is the most advanced means to realize portable analysis at present,and the research of microfluidic resistive pulse sensor can meet the demand of on-site detection for portable rapid detection while realizing particle detection and counting.In this paper,the microfluidic resistive pulse sensor with a side sensing gate was studied to avoid two main shortages existed in tradition microfluidic resistive pulse sensor-sample clogging and limited range of particle size.The main research contents are as follows:(1)Firstly,the microfluidic resistive pulse sensor with a side sensing gate was designed,the corresponding equivalent circuit diagram was established,the formula embodying the relationship between the amplitude of the detection signal and the resistance of each part of the system were deduced and followed by numerical simulations carried out according to the formula.The results showed that the amplitude of the pulse signal varies with ratio of the external resistor,the main channel resistance,the detection channel resistance,the resistance change caused by particle,and the sensing gate resistance.In addition,the circuit voltage can also influence the pulse signal amplitude.These theoretical analysis results provide a basis for the design and optimization of chip structure.(2)On the basis of theoretical research,a microfluidic resistive pulse sensor with a side sensing gate for micron particle detection experiment was designed,and the influence of external resistor,channel paralleling,electric field intensity and particle size on the amplitude of detecting signal were verified by experiments.The experiment results showed that the amplitude of the detection signal will reach its peak value when the external resistor and the whole channel shares equal voltage drop,and it will increase significantly if the main channels are parallel connected,it will also increase when the increase of electric field intensity and particle size,these relevant experimental results are consistent with the theoretical analysis.Then,the differentiation detection ability of different size samples of this novel sensor was tested by the individual and mixed detection experiments of 3?m and 5?m sample particles.(3)On the basis of the micron particle detection system,the law of flow resistance and pressure drop in microchannel applying pressure driving and focusing is numerically analyzed,a microfluidic resistive pulse sensor for nanometer particle detection was designed and manufactured after the optimization of chip structure.Then the detecting performance of this nanoparticle detecting chip was compared with the chip used for micro size particle detection,and nanoparticles with 500nm size and E.coli cells were successfully detected.In addition,the signals of E.coli cells and nanoparticles were distinguished by their different dwelling time.And finally,detecting signals of chlorella cells and Dicrateria sp cells were distinguished according to their waveforms of pulse signals and the detecting result showed chlorella cells and Dicrateria sp cells can be well distinguished according to their different range of pulse signal magnitude and dwelling time.The research in this paper has developed a novel method to overcome the two major shortages in traditional resistive pulse sensors-sample clogging and range limit of particle size,which provides a means for the development of portable marine ballast water harmful organisms detection technology and has certain reference significance for widening the application range of resistive pulse sensor.