Fabrication Of Two-dimensional Ordered Au/Ag Composite Nanoparticle Arrays And Their Optical Sensing

Compared with the single metal nanoparticles,bimetallic composite nanoparticles have been a research hotspot in the field of nanotechnology due to their unique physical and chemical properties.In particular,duo to surface plasmon resonance（SPR）properties,Au/Ag composite nanoparticles can form new optical properties via the synergistic effect between the two metals.And they are widely applied in different fields,such as biochemical sensing,surface-enhanced Raman spectroscopy（SERS）and catalysis.However,most of the Au/Ag composite nanoparticles show disordered distribution,which leads to poor signal uniformity and repeatability in practical applications.In this paper,two-dimensional Au@Ag and Au@porous Au-Ag nanoparticles orderly array were prepared.Furthermore,optical sensor with high stability was constrcted based on the two-dimensional Au@Ag nanoparticle arrays through the localized surface plasmon resonance（LSPR）of Au,Ag nanoparticles and diffraction originated from periodic nanostructure arrays.The main contents of this paper are as follows:1.The two-dimensional Au@Ag nanoparticle ordered arrays were fabricated by using the two-dimensional ordered Au nanoparticle arrays as templates,followed by a chemical reduction to coat a layer of Ag shell on the Au nanoparticles surface.The templates of the two-dimensional ordered Au nanoparticle arrays were prepared by deposited Au film on colloidal crystals and subsequent high temperature annealing.The results showed that with the increase of the thickness of Ag shells,the LSPR peak of Ag gradually increased and red shifted;The LSPR peak of the Au nanoparticles blue-shifted caused by the shielding effect of Ag shell.The array diffraction peaks red-shifted due to the change of dielectric constant of the surrounding environment of the Au nanoparticles.2.The two-dimensional ordered array of Au@Ag nanoparticles prepared above was used to detect iodine in liquid phase and gas phase at room temperature,and the effects of iodine concentration and induction time on its morphology and optical properties were explored.After sensitve iodine,the morphology of nanoparticles appeared an obvious change,accompanied a series of color variations due to the form of Ag I.Besides,with the increase of iodine concentration and detecting time,the LSPR peak and the array diffraction peak of the Au@Ag nanoparticle arrays have a significant red shift.Therefore,the concentration of I₂ can be detected qualitatively by the change of color,and quantitatively via the shift of peak position.Additioanlly,the Au@Ag nanoparticle ordered arrays as sensor revealed good uniformity and stability.Importantly,it is found that Au@Ag nanoparticle arrays can detect gaseous I₂ at trace level.3.A two-dimensional ordered array of Au@porous Au-Ag nanoparticles was prepared by template method combined with chemical replacement method.The effects of the thickness of the Ag shell and the replacement time on the surface morphology of Au@porous Au-Ag nanoparticles were explored.Firstly,the prepared two-dimensional Au nanoparticle ordered array was used as a template to obtain Au@Ag nanoparticle array by chemical reduction method.Then,the obtained Au@Ag nanoparticle array was immersed in HAu Cl₄ solution for replacement reaction.After removing the Ag Cl generated in the reaction process by ammonia water,the two-dimensional ordered Au@porous Au-Ag nanoparticle array was obtained.The results showed that when the thickness of the Ag shell was same,with the increase of replacement time,the ordering of the array was decline.The optimum time was about 1 min.Under the same displacement time,with the increase of the thickness of the Ag shell,the porous Au-Ag network structure gradually appeared.The thicker the Ag shell is,the more obvious the porous network structure is.