Graphene-enhanced Raman spectroscopy in ultra-low concentrations of pharmaceuticals

Abstract

In this work, we provide a novel metrology method to detect the presence of ultra-low concentrations of ibuprofen and paracetamol dissolved in water by Raman spectroscopy. We have deposited a single microdrop of the contaminated water solution onto a graphene substrate. We found that low concentrations of pharmaceuticals trigger a Graphene Surface Enhanced Raman Spectroscopy response allowing for the detection of pharmaceuticals in the low concentration limit of $100\mu g$/mL. The enhancement factor observed for GERS in the G- and 2D lines reached up to 48 times derived from the molecular interaction of both molecules (graphene and the pharmaceutical), and 200 times for the D-line. Thus, we observed that the graphene monolayer enhances the pharmaceutical bands and quenches its fluorescence, allowing the identification of the pharmaceutical characteristic spectrum, which can be employed as a bio-marker of the pharmaceutical molecular presence. Finally, we performed a high-temperature treatment in vacuum conditions to study the recovery of graphene. After the thermal treatment, no contributions from ibuprofen were evident by Raman spectroscopy, but a high functionalization/oxidation stage. The conductivity of the graphene surface was also analyzed and it showed: (I) a decrease in the conductivity after the deposition of the pharmaceutical, and (II) a recovered conductance after the thermal treatment, which indicates a partial recovery of the substrate’s properties. This project brings an innovative tool for the detection of ultra-low concentrated pharmaceuticals when deposited on graphene. This discovery opens doors to a better understanding of the pollutant sources that will potentially contribute to the preservation of public sanity, pharmaceutical pollution research, and water quality monitoring in developing countries like Ecuador.