Study On Behavor Of Micro-scale Particles And Micro-sensor Development Based On Dielectrophoresis

Microfluidic chip technology,developed from analytical chemistry,is mainly used to study the stress of fluids and particles in micro/nano systems.One of the most important applications in microfluidic chips is the separation of microparticles,especially the rapid separation of biological particles.Due to its ability to manipulate particles of various sizes and integrate with micromachining systems efficiently,dielectric mobility is easy to achieve in drug screening.Dielectrophoresis?DEP?forces are flexible and can be modified simply by changing frequencies,which showed some advantages over other methods,i.e.,label-free,ease of handling,high precision and being high speed.DEP has attracted a great deal of attention to control particles due to its high selectivity and rapidity in manipulation.Based on the DEP,a lab-on-a-chip device for separation of non-biological micro-particleS and bacteria mixtures was established.This dissertation addresses series of studies on the DEP behavior of micro-particles and the separation micro-particles mixtures.The DEP separation was achieved by a pair of metal electrodes with the shape of radal-interdigital to generate a localized non-uniform alternating current?AC?electric field.The electric field and DEP force were firstly investigated by finite element methods?FEM?.The mixed microparticles such as different scaled polystyrene?PS?beads,PS beads with inorganic micro-particles?e.g.,ZnO and SiO₂ beads?and non-bioparticles with bacterial Staphylococcus aureus?S.aureus?were successfully separated at DEP-on-a-lab by an AC electric field of 20 kHz,10 kHz and 1 MHz,respectively.The results indicated that DEP trapping can be considered as a potential candidate method for certainly opening an intriguing avenue of investigation in separation of biological mixtures.The investigation of DEP force dependency on bacteria viability of impedance,admittance and capacitance experiments for S.aureus cells were conducted.The limit of detection?LoD?of approximate 10⁵ cells/mL was achieved at the DEP frequency of 500 kHz.In addition,live and dead S.aureus cells were distinguished and characterized at near 20MHz.Additionally,the estimated glial cell properties are value-added to the scarce information currently available about this type of cell.Finally,we integrate our chip with an impedance spectroscope for obtaining rapid,real-time data of antimicrobial action against bacteria.The effects of experimental parameters such as field frequency,voltage and cell concentration are investigated in detail and shown below.In order to improve the efficiency of particle enrichment and screening,biochemical methods can be introduced to enhance its bioselectivity.The IgG molecules were immobilized on a gold electrode via covalent bonding to form SAM as the recognition element of the QCM system to detect S.aureus.By studying the mechanism of the QCM system effect for S.aureus detection,combined with the optimization of detection conditions,such as temperature,time-costs and buffer pH,to lead an optimum condition of 36?,30 min,pH 8.0.Based on optimum condition,the response characteristics for concentration of S.aureus was detected in a linear detection range of 5.8×10⁵⁵.8×10⁷ cells/mL.Further studies on the specific interaction between immobilized S.aureus and five different species of IgG?i.e.rat,rabbit,dog,goat and horse?.IgG were carried out and the marked species-dependent difference was observed.Based on that result,biological selectivity of chip for different bacteria was investigated by using IgG from various species.It was found that different immunoglobulins from different species have obvious bioselectivity to affinity,and the main reason of bioselectivity is that gene affinity and oligosaccharides appear in morphology and structure.