Abstract
In this article, the influence of the medium refractive index on optical properties of gold nanorods (GNRs) and their surface enhanced Raman spectroscopy application were studied. In particular, GNRs have been applied in biomedical sensors to detect diseases by monitoring the changes in the environment. In this study, the changes in optical properties of GNRs were investigated according to the medium refractive index changes in the cationic surfactant cetyltrimethylammonium bromide (CTAB) during synthesis processes as well as GNR dispersion in different medium refractive indices. For instance, in the solutions with different concentrations of CTAB, GNRs were coated by biomolecules [such as PEG, bovine serum albumin (BSA), and glutathione (GSH)], which have different refractive indices. The fundamental reason for the change in optical properties of GNRs is also elucidated. GNRs have been used to enhance surface Raman scattering to detect indigo molecules. The results showed that due to the surface plasmon resonance effect, the GNRs could strongly enhance the scattering signal of indigo dyes, with the lowest detectable concentration of up to 10−8 M and with an enhancement coefficient of over 2000 times.
Highlights
Gold nanorods (GNRs) have been known for their typical outstanding optical properties such as having two surface plasmon resonant peaks corresponding to the transverse and long dipole oscillations of the rod
To study the dependence of optical properties of gold nanorods (GNRs) on the medium refractive index, we investigated the formation of GNRs in different refractive indices by changing the concentration of cetyltrimethylammonium bromide (CTAB) and studied optical properties of these nanorods when they were dispersed into different medium refractive indices as well
The optical properties of GNRs were strongly dependent on the refractive index of the surrounding medium
Summary
Gold nanorods (GNRs) have been known for their typical outstanding optical properties such as having two surface plasmon resonant peaks corresponding to the transverse and long dipole oscillations of the rod. Long surface plasmon resonance (LSPR) can be controlled in a wide range—from visible to near infrared—by varying the aspect ratio.. Long surface plasmon resonance (LSPR) can be controlled in a wide range—from visible to near infrared—by varying the aspect ratio.1–4 This makes GNRs more widely used in applications.. One remarkable feature of GNRs is that their LSPR properties are very sensitive to the changes in the dielectric constant or the refractive index of environmental surroundings.11–13 These phenomena have been applied to a biosensor to record the changes in plasmonic resonance wavelength while a new bond is added or removed on the surface of gold and silver nanoparticles.. It will be necessary to study the effect of enhancing surface Raman scattering of GNRs for indigo dye detection. To the best of our knowledge, this is one of the few works in which GNRs have been used as in SERS to detect indigo
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