Gold Nanorod Surface-Enhanced Raman Spectroscopy Substrate for l-DOPA Detection: Experimental and Theoretical...

Area of Science:

• Nanotechnology
• Spectroscopy
• Biochemistry

Background:

• Surface-enhanced Raman scattering (SERS) is a sensitive technique for molecule detection.
• Detecting negatively charged molecules like levodopa (l-DOPA) using SERS with negatively charged nanoparticles presents challenges due to electrostatic repulsion.
• Understanding adsorption mechanisms is crucial for optimizing SERS-based detection.

Purpose of the Study:

• To investigate the adsorption mechanism of levodopa (l-DOPA) on gold nanorods (AuNRs) with a cetrimonium bromide (CTAB) bilayer.
• To elucidate the factors influencing the SERS signal of l-DOPA.
• To correlate experimental SERS findings with theoretical calculations.

Main Methods:

• Preparation of gold nanorods (AuNRs) coated with a cetrimonium bromide (CTAB) bilayer.
• Adsorption of l-DOPA onto AuNRs in colloidal solution and after drying on solid substrates (glass, silicon, Au).
• Surface-enhanced Raman scattering (SERS) measurements.
• Density functional theory (DFT) calculations to model adsorption.

Main Results:

• The SERS signal of l-DOPA is dependent on time and concentration, influenced by electrostatic interactions.
• l-DOPA adsorbs onto the CTAB-coated AuNRs primarily through its catechol ring.
• Experimental and theoretical results indicate the formation of anionic and dianionic l-DOPA species upon adsorption.
• The SERS profile is directly linked to the adsorption mode and the resulting charge states of l-DOPA.

Conclusions:

• The catechol ring of l-DOPA is the key functional group for adsorption onto CTAB-modified AuNRs.
• The formation of anionic and dianionic species of l-DOPA is essential for achieving a detectable SERS signal.
• This study provides a mechanistic understanding for optimizing SERS-based detection of l-DOPA and similar molecules.