Application Of Localized Surface Plasmons In Dipole Radiation Regulation And Hydrogen Sulfide Sensing

Localized surface plasmon resonance(LSPR)is the collective free electron oscillation confined in nanostructures.On the one hand,LSPR can break the optical diffraction limit and focus electromagnetic field within nanoscale,thus it can be used as nanoantennas.However,the plasmonic resonances in most nanostructures are electric resonances,which can produce very strong electric field enhancement but cannot create magnetic field enhancement in the region near the nanostructure surface.As a result,electric plasmons can enhance and control the spontaneous emission from electric dipole emitters but cannot tune the emission from magnetic dipole emitters.On the other hand,the plasmonic nanoparticles show relatively large optical cross-section,which leads to obvious resonance peaks on the extinction spectra.The peak wavelength and intensity are highly dependent on the surrounding dielectric environment.For Au@Ag nanoparticles,since the silver shell is readily to react with sulfidion to produce silver sulfide,the conversion of silver to silver sulfide accompanies with the changes of dielectric function which produces the variation of plasmon resonance wavelength and intensity.Therefore,Au@Ag plasmonic nanostructures can be utilized for H2S sensing.In this dissertation,the application of noble metal nanoparticles in nanoantennas and sensor application fields have been exploited.The specific contents of this dissertation are as follows:1.The special structure of Au nanocup endows it with relatively strong electric and magnetic field enhancement.Because both electric and magnetic plasmons can be supported in Au nanocup,the effect of Au nanocup on the emission of electric and magnetic dipoles are studied.I first studied the far-field and near-field plasmonic properties of Au nanocup.It is confirmed that the Au nanocup can supports strong electric and magnetic field enhancement simultaneously,and it shows two different scattering peaks.Then,the influence of Au nanocup on emission enhancement electric and magnetic dipoles with different polarizations is studied.It is found that the emissions of electric and magnetic dipoles can be enhanced by the Au nanocup.The enhancement is dependent on the plasmonic electric and magnetic resonance wavelength and the distribution of the electromagnetic field enhancement.The enhancement exhibits peaks at the wavelength very close to the electric and magnetic modes.The largest Purcell factor of electric dipole can reach 280.Finally,the strong magnetic mode not only can enhance the emission of the magnetic dipole but also can make the emission of the magnetic dipole unidirectional.2.Since the plasmon resonance of Au triangular nanoplates is highly sensitive to the change of refractive index of surrounding environment,it can be expected that Au TNP@Ag nanostructures will have excellent performance for H2S sensing.Firstly,Au TNP@Ag nanocrystals were prepared by seed-mediated growth method and overgrowth method.Then,the sensing performance of Au TNP@Ag nanoprobes for Na2S solution and H2S gas were studied.For detecting Na2S solution,the response concentration can be as low as 1 μM.When nanoprobes are dispersed 10 μM and 100μMNa2S,a typical concentration range for H2S in vivo,the resonance wavelength shift of nanoprobe is between 66 nm and 480 nm.Meanwhile,the extinction peak showed a 16-nm-shift and obvious intensity reduction when 1 ppm hydrogen sulfide was flowed in the Au TNP@Ag solution,which confirms the highly sensitive property of Au TNP@Ag nanoprobe to H2S.In addition,the Au TNP@Ag nanoprobe also shows great selectivity for detecting H2S.