Synchronous Fe3+-Enhanced Colorimetric and Liquid SERS-Based Detection of Dopamine Using Core-Shell Plasmonic Nanoparticles

Reliable and direct detection of dopamine (DA), which is a crucial neurotransmitter, is required to diagnose dopamine-related diseases. However, the plasmonic colloidal sensing systems without prefunctionalization (e.g., aptamer, receptor, antibody, etc.) have not been well-established for trace DA detection yet. Herein, we develop a synchronous colorimetric and liquid-surface-enhanced Raman scattering (SERS) sensing system for the sensitive and selective detection of DA neurotransmitters using Au-Ag core-shell nanoparticles (Au@Ag CSNPs). The DA-mediated aggregation of Au@Ag CSNPs changed their plasmon resonance, leading to a distinct color change of the CSNP dispersion and generation of strong electromagnetic "hot spots" in the clustered CSNPs. Notably, the addition of Fe3+ ions to the CSNP dispersion intensified the DA-mediated aggregation of CSNPs, which significantly improved the colorimetric response and liquid-SERS detection of DA in the nanomolar range. Notably, the dual-mode sensing system without prefunctionalization demonstrated highly selective detection of the DA analyte against similar catecholamines (such as norepinephrine and epinephrine), which can be potentially applied to the selective discrimination of trace DA in real samples.