Raman computational and experimental studies of dopamine molecules on silver nanocolloids

Combined theoretical and experimental analysis of dopamine is presented in this work to better understand phenomena related to this neurotransmitter's detection and monitoring at very low concentrations specific to physiological levels. Surface-enhanced Raman spectroscopy (SERS) on silver nanoparticles was employed for recording dopamine concentrations as low as 10−11 molar. Quantum chemical density functional calculations were carried out using Gaussian-09 analytical suite software. Relatively good agreement between the simulated and experimentally determined results indicates the presence of all dopamine molecular forms, such as neutral DA0, ionic DA− and DA+, and of dopaminequinone as well. Disappearance of the strongest bands of dopamine at 750 cm−1 and 795 cm−1, which suggests its adsorption onto the metallic surface, is consistent with the appearance of the latter molecular configuration. Thus, through coordinated experiment and theory, valuable insights into changes observed in the vibrational signatures of this important neurotransmitter can be analyzed and comprehended.