| The optical signals changes of gold nanoparticles(Au-NPs)owing to morphological transformation have opened up fascinating applications in medical determination,gene detection,immune analysis and biomolecule detection,and so on.In this paper,many techniques such as UV-Vis absorption spectra and plasmon resonance light scattering (PRLS),electron microscopes and dark-field image are used to further study Au-NPs. We investigated the morphological transformation of gold nanorods(Au-NRs)induced by iodine,and the application of Au-NPs in cysteine and prion proteins analysis.The mian content is as follows:Firstly,The morphological transformation process resulting from the reaction between Au-NRs and iodine in situ produced from the redox between KI and CuCl2, was monitored by virtue of the plasmon resonance absorption(PRA)spectra and the scanning electron microscope images(SEM).It was found that the presence of KI or CuCl2 could make the longitudinal PRA band of Au-NRs shift without any change of morphological transformation,which is due to the change of the refractive index of the medium.Different from that,iodine,which was in situ produced from the redox of KI and CuCl2,could fuse Au-NRs with the side-by-side mode,resulting in morphological transformation from Au-NRs to sphericity with the decrease of Au-NRs aspect ratio, blue-shift of the longitudinal PAR band,red-shift of transverse PRA band,broadening of both longitudinal and transverse PRA bands of Au-NRs,and the fall of Au-NRs PRA intensity.The blue-shifted wavelength of longitudinal PRA band was found to be in proportion to the concentration of copper chloride or iodide,supplying the possibility to detect copper and iodine element in samples with spectrophotometry.The above theory also can be exploited to detect reducing agent—tetracycline hydrochloride acid.Tetracycline can deoxidize I2,resulting in the decrease of I2 effective concentration and the fusion rule to gold nanorods.As a result,the longitudinal PRA of gold nanorods shifted to longer wavelength linearly as increase the concentration of tetracycline.Based on which,tetracycline can be detected in the range of 5.0×10-5mol L-1-5.0×10-4mol L-1,with a LOD of 2.4×10-6mol L-1(3σ).Most foreign substances in the samples did not interfere in the detection,and tetracycline in the synthetic samples could be detected with the recovery between 92.8%and 107.2%, and R.S.D.is less than 4.3%.It is found that concebtration of tetracycline in milk detected with standard addition method was so low that accord with the safety regulation.A rapid method for cysteine detection is developed using the positively charged spherical Au-NPs as a light sacattering probe.In aqueous medium of pH 4.2,the CTAB-capped Au-NPs could react with cysteine though Au-S covalent bond.The cysteine-induced aggregates of Au-NPs display strong PRLS signals characterized at 566.0 nm,and the PRLS intensities of the aggregates are in proportion to the concentration of cysteine in the range of 25-400ng mL-1with the limit of detection (LOD)being 2.9 ng mL-1(3σ).No amino acids in the samples interfere in the detection, and cysteine in synthetic samples could be detected with the recovery between 95.3% and 105.9%,and R.S.D.is less than 3.6%.Furthermore,the prion proteins of different configurations have distinct responses to positively charged Au-NPs.PrPSccould induce the aggregation of Au-NPs,resulting in the enhancement of PRLS singals,the shift of UV-Vis spectra and the color change of Au-NPs.Besides,the enhanced PRLS singals were in proportion to the concentration of PrPSc,which supplied the theoretical base for PrPScdetection.However,PrPC can stablize Au-NPs,without the increase of PRLS or change of UV-Vis spectra.Then,the configurations of prion protein can be distinguished.
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