Detection of p-coumaric acid from cell supernatant using surface enhanced Raman scattering

A standard protocol for analysis of microbial factories requires the screening of several populations in order to find the bestperforming ones. Standard analytical methods usually include high performance liquid chromatography (HPLC), thin layerchromatography (TLC) or spectrophotometry, which are expensive and time-consuming processes. Surface Enhanced Raman Spectroscopy (SERS), instead, is a highly sensitive spectroscopic technique for specific, fast and real-time sensing of biologicalsamples. Here we demonstrate the use of SERS to discriminate between two different bacterial populations based on detection ofp-coumaric acid (pHCA) in cell supernatant.SERS active substrates, based on leaning gold-capped silicon nanopillars, were used for detection. They were successfullyused to detect culture medium spiked with pHCA, and the effect of medium dilution was studied. For analysis of biologicalproduction of pHCA, triplicate cultures of E. coli strains expressing a pHCA-forming enzyme (P) as well as of a non-producingstrain (C) were grown. Then, supernatant samples were collected and their pHCA content was measured using SERS and HPLCfor comparison. The intensity of the pHCA Raman mode at 1169 cm^-1 (CH-rocking motion) showed different trends for P and Cstrains, similar to the results obtained using the HPLC method. Results illustrate that SERS can be used for quick and semiquantitativediscrimination of pHCA concentrations in cell supernatant medium.