Influence of L-Dopa adsorption time and concentration on Au nanorods aggregation for SERS quantitative analysis

Levodopa (L-Dopa) is an important neurotransmitter from the amino acid family and is also associated with the treatment of Parkinson's disease. The obtention of the L-Dopa SERS signal in colloid is a challenge due to the zwitterionic charge promoting repulsion from nanoparticle surface and leading to poor or not active SERS signal. In this work, SERS signal of L-Dopa was successfully obtained using Au nanorods (AuNRs) covered with a cationic lipid bilayer and using the 785 nm laser line. The UV–Vis extinction, dynamic light scattering, and zeta potential results indicated an influence of L-Dopa adsorption time and L-Dopa concentration on AuNRs aggregation. The SERS signal followed this time dependence, being the characteristic L-Dopa band observed only after 30 min. The L-Dopa quantitative analysis using the standard addition method presented a linear SERS signal at 439 cm−1 with a limit of detection of 6.7 × 10−7 mol L−1 for peak intensity, and 7.9 × 10−7 mol L−1 for band integrated area.