Study On The Assembly Of The Intelligent Microgels To Form Monolayer Film

Gold nanorods (AuNRs) have many features, such as photothermal effect, localized surfaceplasmon resonance (LSPR) optical property, surface electric field enhancement effect, etc. If theyare loaded into temperature stimulus responsive poly (N-isopropylacrylamide)(PNIPAM)microgels, the formed hybrid microgels have light stimuli responsive property. If the intelligentmicrogels are assembled to produce the intelligent materials of macroscopic size and orderedstructure, their applications will be further increased. In this paper, the PNIPAM microgels werefirstly assembled to generate monolayer film, and the main factors influencing the monolayer filmwere investigated. Then, the core-shell structured AuNR@PNIPAM hybrid microgels using AuNRas core are synthesized, and their adsorption behavior for protein in response to light stimulus wasstudied. Finally, AuNR@PNIPAM hybrid microgels were assembled to prepare monolayer filmand it was used as surface enhanced Raman scattering (SERS) substrate to detect trace amounts of1-naphthol in aqueous solution. The detailed research work and the obtained results of the thesisare as follows:(1) The PNIPAM microgels with amidine groups on their surfaces are synthesized bysoap-free emulsion polymerization, and their shape, volume phase transition temperature, particlesize and zeta potential are characterized by transmission electron microscopy, ultraviolet-visiblespectroscopy, particle size and zeta potential analyzer, respectively. The synthesized PNIPAMmicrogels have good monodispersity which undergo volume phase transition at around35℃,along with their zeta potential increasing significantly. The PNIPAM microgels are assembled toprepare monolayer film on the hydrophilic glass substrate by dip coating method. The effect oftemperature, pH value, KCl concentration, PNIPAM concentration of the dipping solution on themonolayer film was investigated.The obtained results show that, the increase of temperature pHvalue or KCl concentration is beneficial to improve the compactness of the monolayer film. Toincrease the concentration of PNIPAM microgels is also helpful to increase the compactness of themonolayer film. After the prepared monolayer film was oscillated for a certain period of time byoscillators, it was characterized by atomic force microscopy and the result demonstrates that themonolayer film has good stability.(2) After the surfaces of the synthesized AuNRs were modified by3-butenoic acid,AuNR@PNIPAM hybrid microgels with core-shell structure were prepared by coating PNIPAMhydrogel on the surface of AuNR by seed precipitation polymerization. The preparedAuNR@PNIPAM hybrid microgels have light stimuli responsiveness. Upon exposure ofnear-infrared light irradiation, the longitudinal LSPR wavelength of the AuNR inside the hybridmicrogel is red-shifted.When the near-infrared light irradiation is turned off, the longitudinalLSPR peak can be returned to its original position. Under near-infrared light irradiation,AuNR@PNIPAM hybrid microgels can adsorb the protein (bovine serum albumin) in aqueous solution during their volume phase transition, and the adsorption capacity can reach375mg/g.(3) In the dipping solution of the temperature of50℃and KCl concentration of10mM,AuNR@PNIPAM hybrid microgels were assembled on the hydrophilic silicon wafer by dipcoating method to produce dense monolayer film. The AuNRs in the monolayer film still hasLSPR optical property, and its longitudinal LSPR wavelength is obviously red-shifted comparedwith the one of AuNR@PNIPAM hybrid microgels. When the monolayer film is used as SERSsubstrate, the Raman signal of trace amounts of1-naphthol in aqueous solution can be detected,with the detection limit being1×10-4M. The SERS signals measured at different positions on themonolayer film are great reproducible.