Investigation Of The Optical Properities Of Cysteine-modificated Gold Nanorods

Gold nanometerials have unique optical, electro and magnetic properties, and they were more and more widely used in the field of biomedicine, energy and environmental protection, electronics and so on. In recent years, to design and development of new metal nanomaterials have aroused keen interest of many scholars and researchers. Especially, gold nanorods have stable optical properties, biocompatibility and easy-preparation, which become a research hotspot. During synthetic process of gold nanorod will inevitably use a large number of surfactant CTAB, which attach onto the gold nanorod surface, in this case biomolecules is difficult to couple with the gold nanorods. Thereby it limits the application of gold nanorods in bioanalysis. This paper focus on the optical properties of gold nanorods coated with biocompatible cysteine molecules. The main work of this paper is shown as following:1、Using seed mediated growth preparation, we have prepared gold nanorods with different aspect ratios and morphologies. With the help of ultraviolet-visible absorption spectroscopy (UV-Vis), scanning electron microscopy instruments (SEM), we characterized gold nanorods. Experimental results show that our prepared gold nanorods have length between40nm-60nm. The different aspect ratio of gold nanorod can be prepared through controlling the experimental reaction conditions (reaction temperature, the amount of the silver nitrate solution). With the increase of silver nitrate added in the growth solution, the length of gold rod increases. The lateral absorption peak of the gold nanorod absorption spectrum locates at520nm, the longitudinal absorption peak of UV-Vis absorption spectrum along has a redshift with an increasing length of the gold nanorods. We also prepared the bone shape of the gold nanorod particles by reducing the seed solution.2、Optical properties of cysteine-coated gold nanorods with different aspect ratios were studied. Cysteine molecule has a special nature, which is ubiquitous in living organisms. Cysteine molecules has a sulfhydryl group, which can bond to the metallic surface, making the gold nanorods and cysteine molecules have a strong interaction. We prepared three different aspect ratios of cysteine-coated gold nanorods solution, and then measure the absorption spectroscopy and Raman spectroscopy have been tested. Experimental results show that the longitudinal absorption peak of the gold nanorod solution with modified cysteine molecules has a8nm-15nm blue shift, which indicate better dispersion of gold nanorod was achieved when they were surface-modified with cysteine molecules. Taking CV as a probe molecule, we analysised Raman scattering enhancement of different aspect ratio of the surface-modified cysteine gold nanorods, and results show that the cysteine-modified gold nanorods having a good surface Raman increasing effect and it can be a good candidate of SERS substrute. With the increased length of the gold nanorods (from40nm to60nm) enhanced Raman effect was obtained. Through the analysis of the experimental results, we concluded that:within the limits of a certain length(40nm-60nm), the longer length of a gold nanorod, the better effect of Raman enhancement. With the modified Cysteine molecules on gold nanorod surface by a simple and efficient method, it not only improved the biocompatibility of the gold nanorods and but also it can be used as an active substrate for SERS scattering.