Monitoring anionic pollutants such as nitrate and phosphate in marine environments is essential to maintain water quality at acceptable levels and prevent eutrophication and algae blooms from occurring. Current methods to conduct this monitoring have major sensitivity and selectivity issues that limit their effectiveness or prevent the detection of real-time changes in pollutant levels. Surface Enhanced Raman Spectroscopy (SERS) works by enhancing the Raman scattering emitted by target analytes using nanostructured plasmonic materials excited by a laser in the near infrared regime. The resulting spectra consists of energy shifts specific to target analytes that can be used to detect its presence. The functionalization of the gold-plated Silmeco substrates functionalized with cationic cysteamine can be used as a pre-concentration step to increase the total number of target molecules within the SERS active region and boost the selectivity and analyte capture.
We have previously shown that cysteamine self-assembled monolayers (SAMs) can be used to capture and detect anionic analytes like nitrate. Detection arises from interactions between the SAM and the nitrate anions and changes in the conformational state of the SAM, which can be examined by changing the SAM protonation state. In this work, we extend the SAM capture+reporter approach to include analytes of different charge and size, and SAM ligands with varying degrees of polarizability to identify parameters that result in the most sensitive SERS detection. These studies are achieved using a continuous flow channel device to simulate in situ measurements with dynamic changes in analyte concentration. Environmental parameters such as pH and concentration are varied to analyze sensor specificity. Our findings provide deeper insights into in situanionic analyte detection such as nutrients, aiding efforts to mitigate marine pollution.
