Detection of the Quorum Sensing Signal Molecule N-Dodecanoyl-DLHomoserine Lactone Below 1 Nanomolar Concentrations using Surface Enhanced Raman Spectroscopy

To the best of our knowledge we here for the first time demonstrate surface enhanced Raman spectroscopy (SERS) to detect a quorum sensing (QS) signal molecule below 1 nM concentration in both ultrapure water and under physiological conditions. Based on our results, SERS shows promise as a highly suitable tool for in situ measurements of low Acyl-Homoserine Lactone (AHL) concentrations in biofilms containing QS bacteria. Signal molecules communicate information about their environment and coordinate certain physiological activities in QS systems that exist in many bacteria. SERS enables detection of different AHLs at low concentrations due to structural differences observed in the corresponding SERS spectra. Ag colloidal nanoparticles, produced by the hydroxylamine reducing method, were used for the SERS measurements. SERS spectra of C12-HSL suspended in ultrapure water and in supplemented minimal medium were collected for 5 concentrations ranging from 2 μM to 0.2 nM, and a comparison between the spectra from these two media is also presented. We have been able to detect biologically relevant concentrations of AHL molecules ranging from 1 nM to 1 μM using SERS.