Surface Modifications Of Gold Nanorods And Studies Of Biorecognition

Integrated biomolecule-spherical gold nanoparticle hybrid systems are widely used in bioanalysis and biotechnological applications. Spherical gold nanoparticles functionalized with biomolecules such as DNA or antigens (or antibodies) were employed as active units in many different biosensing systems. Because the surfaces of gold nanoparticles are easily and efficiently modified,as well as further conjugation with biomolecules.Recently, anisotropic gold nanoparticles (non-spherical shape) such as gold nanorods have attracted much attention. Because of the tunable optical properties and geometry, gold nanorods have promising potentialities in bioanalytical applications. However, in fact, the use of integrated biomolecule-gold nanorods hybrid system in bioaapplications has not been widely pursued. The main reasons exist as follows:(1) The presence of cetyltrimethylammonium bromide (CTAB) molecules adsorbed on the gold nanorod surface in addition to its use as a directing agent for gold nanorod synthesis. CTAB molecules are obstructive for displacing by the interest of biomolecules, which limit the further bioapplications;(2) The large amount of free CTAB molecules dispersed in the solution displays significant cytotoxicity for proteins.On the basis of the above facts, surface modification of gold nanorods is a key in order to label the biomolecules. In addition, gold nanorods can act as good template to construct various shapes of gold nanostructure. All the relative studies are outline as follows.(1) Fine control of gold nanoparticle shape can be achieved by varying the pH of the reaction medium in the presence of gold nanorods with different aspect ratio, which acted as seeds. Under various pH (3.6–9.6) values of the reaction medium, different shapes of gold nanostructural architectures, from rectangle-,"dogbone"- and peanut-like outlines to branched multipods with corrugated surface, can be fabricated in high yield. These shape changes of gold nanorods directly influence their opticalproperties.(2) Silica-coated anisotropic gold nanoparticles (Au@SiO₂), including rod- and"dogbone"-like outlines with different aspect ratios, have been prepared using an improved St?ber method. The obtained Au@SiO₂ have a pure silica surface for straightforward and rapid self-assembly onto poly(4-vinylpyridine) (PVP) functionalized quartz substrates. The assemblies exhibit highly reversible optical changes that can be observed spectroscopically or with the naked eye when repeatedly cycled between a dry and wet process.(3) The colorimetric detection of protein has been achieved based on Au@SiO₂ film.(4) The surface of gold nanorods with functionalized by poly(styrenesulfonate) (PSS) for the attachment of protein yielded gold nanorod molecular probes, which exhibited the rapid and sensitive detection of protein by localized surface plasmon absorption (LSPR).(5) Gold nanorods embedded into silica paricles (SiO₂@Au_rod@SiO₂) have been prepared. We used the comnbination the SERS active molecules, p-aminothiophenol, and SiO₂@Au_rod@SiO₂ to prepare a novel immunotag and propose an immunoassay detection method based on the combination of surface-enhanced Raman scattering (SERS) and the nnaoparticle labeling. Antibody immobilized on a glass slide/antigen/reporter-labeled SiO₂@Au_rod@SiO₂ sandwich assay was build for SERS measurements by SERS signal of p-aminothiophenol for detection of the single type biospecific species.