Seed-Mediated Synthesis of Gold Nanorods with Variation of Silver Nitrate (AgNO3) Concentration

Abstract

Gold nanostructures, such as gold nanorods (AuNRs) had been widely used in variety of utilization including disease detection, drug delivery, biomedical imaging, biosensing and many more. Many studies have been done by researchers due to its unique plasmon resonance properties as well as this research. This paper reports an investigation on the effects of Silver Nitrate (AgNO3) concentration in producing AuNRs. In this study, AuNRs were synthesized using Seed Mediated Growth Method (SMGM) where the concentration of AgNO3 was varied with 0.5 mM, 1.0 mM, 2.0 mM, 3.0 mM, 4.0 mM, 5.0 mM and 6.0 mM to optimize the aspect ratio, density and homogeneity of AuNRs using physical and optical characterization. The color changed from pale yellow to brownish when iced cold freshly prepared Sodium Tetraborohydride (NaBH4) added to the seed solution. In addition, the color of solution changed from pale yellow to colorless as ascorbic acid added to growth solution. The final color of growth solution varied from pale blue to light violet as the concentrations of AgNO3 used were different. Two parameters namely peak position and intensity obtained from transverse surface plasmon resonance (t-SPR) and longitudinal surface plasmon resonance (l-SPR) were analyzed. The optical spectra for all samples show two peaks. The first peaks in the range of 500 nm to 600 nm which are correspond to t-SPR and the second peaks are located in the range of 630 nm to 730 nm which correspond to l-SPR. The results show that the aspect ratio and the size of AuNRs increased as the concentration of AgNO3 increased while the homogeneity decreased as the concentration of AgNO3 increased. It was also found that the concentration of AgNO3 affected the growth of gold nanostructures. Higher concentration of AgNO3 resulted in larger size, higher aspects ratios and thus red shifted the surface plasmon resonance. Hence, the two peaks AuNRs is very suitable to be used in sensing application with the peak position as its sensing parameter.