Minimizing the effect of near-distance dielectric sensitivity on retrieving average aspect ratio of gold nanorod by optical extinction spectroscopy: in the case of CTAB adsorption

The aspect ratio (AR) is one of the most intriguing parameters of gold nanorods (GNRs), which plays an important role in determining localized surface plasmon (LSPR) properties. Instead of conventional imaging techniques, the optical extinction spectroscopy (OES) method has been developed for allowing fast statistically measuring the average AR under static approximation. In this work, combining with the previous achievements in spectroscopic technique, we further analyze the effects of gold dielectric function and near distance dielectric sensitivity. The former may reflect possible dielectric loss of real Au samples from ideal single crystalline. The latter reflects the cetyltrimethylammonium bromide (CTAB) adsorption on the surface of GNR induces different LSPR shifts below and above critical micelle concentration (CMC). However, their effect on the determination of AR has not been evaluated in OES method. The average AR measurements as a function of absorbance of CTAB-GNRs and LSPR maximum below the CMC were studied. Our results indicate that after considering these factors, the mean ARs obtained from spectroscopic techniques are closer to those obtained from imaging techniques.