AbstractSensing of neurotransmitters (NTs) down to nm concentrations is demonstrated by utilizing self‐assembled monolayers of plasmonic 60 nm Au nanoparticles in close‐packed arrays immobilized onto glass substrates. Multiplicative surface‐enhanced Raman spectroscopy enhancements are achieved by integrating Fe(III) sensitizers into the precisely‐defined <1 nm nanogaps, to target dopamine (DA) sensing. The transparent glass substrates allow for efficient access from both sides of the monolayer aggregate films by fluid and light, allowing repeated sensing in different analytes. Repeated reusability after analyte sensing is shown through oxygen plasma cleaning protocols, which restore pristine conditions for the nanogaps. Examining binding competition in multiplexed sensing of two catecholamine NTs, DA and epinephrine, reveals their bidentate binding and their interactions. These systems are promising for widespread microfluidic integration enabling a wide range of continuous biofluid monitoring for applications in precision health.