NANOSTRUCTURED SURFACE ENHANCED RAMAN SPECTROSCOPY SENSOR FOR MARINE POLLUTANTS

Abstract

Excess concentrations of nitrate and phosphate in seawater can lead to harmful algae blooms that damage coastal ecosystems, pose health risks and adversely impact commercial activity. Early in situ detection of over-nutrification is necessary for rapid response and mitigation plans. Commercial nitrate and phosphate sensors utilize UV-Vis spectroscopy methods. Those sensors show interference with ions present in seawater and are prone to biofouling, necessitating new approaches for in situ monitoring. Surface enhanced Raman spectroscopy (SERS) is a technique theoretically capable of single molecule detection, and therefore may be a promising approach for nitrate and phosphate detection. However, there are clear challenges as SERS sensing is negatively affected by interference in complex media and in situ sensing in a solution phase reduces accuracy and resolution. It is because of these challenges, in part, why much of the data reported in the literature are taken for purified samples that are then dried on a SERS substrate. Our goal is to address the engineering challenges for a SERS in situ seawater nutrient concentration measurement system. Batch and flow-through devices have been designed to incorporate commercially available, nanostructured gold SERS substrates. By benchmarking against 4-nitrobenzenethiol/ethanol solutions and ultrapure water spiked with nitrate and phosphate, our results show that our SERS devices can be used as a development platform for a seawater nutrient sensor, showing a route for a commercializable product that will greatly benefit scientific operations.