Control Of Gold Nanoparticles By Double Optical Tweezers And Its Applications

The local electric field induced by the surface plasmonic resonance arising from metal nanostructures greatly enhances optical force,realizes optical manipulation at sub-wavelength scale,and generates a very attractive research area focusing on the surface plasmonic optical force.Experimentally,researchers mainly use micro-nano processing technology to prepare metal nanostructures,including nano films,nanoparticles,nanostripes,chiral nanostructures,etc.Different types of lasers are considered to excite the surface plasmonic and to achieve optical trapping and manipulation.However,these methods are often complex,expensive and time consuming.Some of them even have permanent fixed structures which is lack of the tunability of gap sizes on small scales.The controlled aggregation of colloidal metal nanoparticles provides a convenient and less demanding alternative.The key spirit of this method is to realize the dynamic assembly of plasmonic nanoparticles with controllable nanometer gaps in these nanostructures,especially in fluid media.Previously,the most common aggregation method used in related studies is to add sodium chloride or pyridine to silver or gold nanoparticles stabilized by negatively charged citrate ions.These chemicals cause the nanoparticles to accumulate irreversibly,and they cannot be re-dispersed in the liquid for further use.Here,for the first time,we proposed a new type of double optical tweezers technology,which greatly enhances the near-field optical interaction force between the nanoparticles experimentally.On this basis,we break through the limit of nanoscale particle trapping in the existing commercial optical tweezers system.The effective optical tweezers for nanoscale biological structure and micro-nano materials are realized.Unlike previous studies,the average spacing between nanoparticles is entirely dependent on the power of the trapping laser,which eliminates the need for chemical polymerizers.Using commercially available metallic nanoparticles as a reference,manipulation and testing can be done in free solution.This thesis focuses on the all optical tuning of metal nano-aggregates and their applications in biological and chemical fields.The main contents are as follows:Double laser optical tweezers.A new type of double laser tweezers system is proposed and independently built.Two laser sources are combined to coordinate the process of metal nanoparticles.The main idea lies in the use of long wavelength laser(1064 nm)to achieve wide range constraint of gold nanoparticles aggregates near the focus,and cooperate with short wave laser(532 nm)manipulation of the nanometer level spacing between particles.Here 532 nm laser is mainly used to enhance the attraction between the nanoparticles,bring particles in free solution closer,so as to shorten the particle spacing,thus to achieve the goal of “nano optical tweezers”,preparing to trap small molecules or irregular biological molecules.Surface plasmonic enhanced optical force between metal nanoparticles.The distribution of electric and magnetic fields in the system is numerically calculated by using the finite element software COMSOL of multi-physical field,and the optical interaction between gold nanoparticles is studied theoretically by means of maxwell stress tensor.The results show that the force depends on the polarization direction,spacing,particle shape and other factors.According to the above experimental needs,we can select the appropriate size of nano-metal particles and the corresponding dual laser wavelength through simulation calculation.Single molecule detection based on surface-enhanced Raman spectroscopy.Based on the above double laser optical tweezers platform and different reactions of laser polarization and power on nanoparticles,we effectively control particle spacing in the far field,which results in a different intensity of Raman spectrum signal.We detect the subresolution spacing of trapped nanoparticles aggregates by measuring the surface enhanced Raman scattering(SERS).In addition,we also confirm the ability of the single molecule sensitivity of this kind of nanostructure in SERS applications according to the method of bianalytes.This new technology provides new possibilities for all optical manipulation of nanomaterials and the application of super-sensitive biochemical sensing.Trapping of DNA molecule based on double optical tweezers system.The optical trapping of a single ?-DNA and the detection of surface-enhanced Raman spectroscopy are achieved by using a double laser-induced gold nanoaggregates as a “nanoclamp”.This subresolution interparticle forces are studied by tracking the motion of GNPs in solution.