Research On The Trapping Of Single Sphere Probe Based On Microfluidic Chip

Biosensing is to convert target recognition into measurable photoelectric enhancement signal through specific biomolecular recognition and signal conversion elements,achieving high-sensitivity analysis and detection at molecular level,and to promote the development of biochemical detection technology based on the change of molecular characteristics.Among many biosensing methods,the single sphere probe as a platform to achieve fixed-point detection has attracted much attention of researchers.The precise control of single sphere probe and the effective mixing with the sample waiting measured are the key to realize fixed-point detection.Although the traditional method can achieve effective mixing of fluids,the single sphere probe is very small and hard to achieve accurate control.Microfluidic chip is very suitable for single-particle manipulation because of their compatible length-to-volume ratio.With the help of micromixer,the disadvantages of slow and inefficient mixing of microfluids in laminar flow can be overcome,so that the fluid flowing through the micromixer can achieve rapid and efficient mixing that cannot be achieved by traditional methods.Combining microfluidic technology with dielectrophoresis technology can precisely control the trajectory of micro-nanoparticles to achieve precise manipulation of single particles.In this paper,the motion state of fluid and the force acting on particle in the microfluidic chip were analyzed,and a microfluidic chip with mixing and trapping functions was designed to realize the precise control of single-sphere probe and lay the foundation for the fixed-point detection of sample.The mechanism of single particle trapping based on dielectrophoresis force was discussed firstly.Based on the single induced dipole model,the expression of dielectrophoresis force of spherical particles was deduced.The frequency response characteristics of polystyrene microspheres were studied by homogeneous model.The relationship between the type of dielectrophoresis force acting on particles and frequency,particle size and the conductivity of suspension medium was analyzed.The force acted on the particles was analyzed and neglecting the force that has little effect on particle traces which provided a theoretical basis for simplifying the numerical model.Secondly,based on the microfluidic technology,dielectrophoresis principle and passive micromixer design rules,a microfluidic chip could be designed for single sphere probe trapping.On the one hand,three-dimensional Navier-Stokes equation and convection-diffusion equation were solved by numerical simulation.The flow pattern and concentration distribution characteristics of the fluid in the microchannel were analyzed.By evaluating the mixing efficiency index and pressure drop at different flow velocities,the optimal structure design of the micromixer was determined.On the other hand,by solving Maxwell equation,the electric field distribution characteristics were analyzed.By changing the resistivity and dielectric constant around the electrode,the electric field is distorted,so that the electric field was mainly distributed in the preset region to achieve the fixed-point trapping of single particle.The 3D numerical simulation results theoretically verified that the chip could not only achieve efficient and rapid mixing between fluids,but also changed the distribution of electric field through the structure of insulators,The single particle fixed-point trapped could be achieved by adjusting the injection speed of fluids,the magnitude and frequency of the applied electric field,which provided reference data for subsequent experimental research.Finally,the prepared microfluidic chip was used as the experimental operation platform.The injection speed of the syringe was controlled by the syringe pump,and the deionized water and the dyed anhydrous ethanol were simultaneously injected into the microchannel through different inlets,the effectiveness of the microfluidic chip for rapid mixing of laminar fluids was verified.Then,the polystyrene microsphere suspension is injected into the microchannel by using a syringe pump,and the dielectrophoretic force acting on the microsphere is controlled by adjusting the output voltage and frequency of the function signal generator,which also verified the feasibility of the microfluidic chip for directional trapping of single particle.