科创中国

Microfluidics is a promising system for the manipulation of micro-nano particles and fluids.In this platform,alternating current(AC)electric field is usual an effective tool for the general particles control.However,traditional work paid more attention on the regular spherical particles with no obvious distinction when rotating,resulting in imprecise rotation speed calculation.In essence,non-spherical especially biocompatible particles are not only important for biology application but also significant for obtaining accurate rotating results.Hence,in this paper,SU-8,one of the most biocompatible materials was selected as the manipulation object.AC electric field is employed to rotate SU-8 microrods,in order to obtain a controllable rotation angle for both the accurate experimental results and biosensor applications.Firstly,Clausius-Mossotti(CM)factors frequency spectra with different surface conductance and medium conductivities are presented,thereby the theoretical formula is carried out,including both the torque and rotation velocity expressions of SU-8 microrods.Moreover,simulations for the electric field distribution are developed,indicating the rotating direction.Secondly,the quadrupole electrodes are used to generate rotating electric field,and the electrorotation of SU-8 microrods in different medium is carried out,showing that the particles rotate in the opposite direction of the electric field,meanwhile,the peak frequency increases with the conductivity increases.Finally,the experimental results are discussed and compared with theoretical analysis,and the comparison result shows that they have a good agreement.This work proposes an effective and controllable method to rotate microrods,showing extend application potentials in microelectronics and biosensors.

The electric fields employed for such work are generated using chips,such as planar linear interdigitated arrays or two parallel arrays.However,chip geometries usually affect the investigation of dielectrophoresis(DEP)and electrorotation(ER)significantly,and even may misdirect the theoretical prediction.In order to understand the electrodes geometries effect and provide a suitable range of parameters,three-dimensional simulations for the DEP and ER characterizations on the quadrupolar hyperbolical electrodes are carried out.Influences of the electrodes gaps,cell height,work region,energized voltage and frequencies for the DEP and ER manipulations are analyzed,and the analysis results show that the gaps of the electrodes and the cell height have enormous effects,but the work region is not so important.Moreover,depending on the theoretical analysis,ER experiments for polystyrene microspheres with the diameter of 20 m are carried out on two kinds of chips.The experimental results show that the microspheres rotate in the counter-field direction and the maximum rotation speed appears in the megahertz range.In addition,the experimental results are compared with the simulation results,showing that the three-dimensional simulations considering the chip geometries are more accurate than the two-dimensional predictions.This paper provides a new understanding for the theoretical predictions of DEP and ER manipulations,which decreases the difference of the theoretical and experimental results significantly,and will be significant for the lab chip research.