Applicability of Surface Enhanced Raman Spectroscopy for Determining the Concentration of Adenine and S-Adenosyl Homocysteine in a Microfluidic System

摘要

Surface-enhanced Raman spectroscopy (SERS) has shown great potential as a highly sensitive detection technique for biologically relevant compounds in small volume scenarios. The applicability of using SERS to differentiate between enzymatic reaction products and their precursors to determine their relative concentrations is investigated here. The enzyme Pfs, important for bacterial quorum sensing, converts S-adenosyl-L-homocysteine (SAH) to adenine by means of a hydrolysis reaction. This leads to the substrate and product having very similar structures. Solutions containing SAH and adenine in ratios ranging from 0:1 to 1:0 at a total concentration of 1 mM were investigated by Raman spectroscopy on a silver SERS substrate. The results show that peaks at 530, 560, 733, and 860 cm~(-1) all increased in relative intensity as the ratio of adenine to SAH grew larger. While the relative increases were different for these peaks, these differences are not yet sufficient to consistently distinguish and quantify the relative amounts of adenine and SAH in a system. Since the SERS phenomenon is highly dependent on molecular proximity to silver nanostructures, these results suggest that the predominant binding mode of adenine and SAH are similar; for example, the adenine moiety present in both molecules is responsible for their binding to the silver surface.