Influence of amount of CTAB and ascorbic acid concentration on localized surface plasmon resonance property of gold nanorod

Gold nanorods (AuNRs) are prepared through seeded growth approach. Synthesis parameters of the amount of cetyltrimethylammonium bromide (CTAB), and concentration of ascorbic acid (AA) were studied. We were aiming for an aspect ratio of 3 which could be achieved by a nanorod feature in the range of 45 nm length and 15 nm width. The absorption spectra are observed with an UV–visible NIR spectrophotometer and analysed theoretically. It is known that there are two plasmon resonance peaks for gold nanorod corresponding to transverse surface plasmon resonance (TSPR) and longitudinal surface plasmon resonance (LSPR), respectively. It is found that as the concentration of CTAB increases, the yield of NRs increases. As the concentration of AA increased from 0.05 to 0.2 M, LSP shifts to longer wavelength but upon further increasing the concentration, LSP shifts back to shorter wavelength. A linear relationship between LSPR wavelength and surrounding medium dielectric constant is obtained, which is in good agreement with the theoretical results.