In situ monitoring of quorum sensing signalling molecules using a SERS chip with a micro -chamber array†

Abstract

The in situ monitoring of quorum sensing (QS) signal molecules in bacterial biofilms is crucial for the diagnosis and treatment of bacterial biofilms. In this work, a surface-enhanced Raman scattering (SERS) chip integrated with functional units of bacterial biofilms and in situ SERS detection is proposed for the monitoring of pyocyanine, an important signal molecule and biomarker secreted by Pseudomonas aeruginosa. The SERS chip was composed of a top self-assembled nano-silver SERS substrate layer, a PDMS layer containing a micro-chamber array and bottom quartz layer. The nano-silver SERS substrate showed good homogeneity and stability with an enhancement factor of up to 1.84 × 10⁸ for pyocyanine, and the design of the SERS substrate located at the top layer of the chip could effectively attenuate interference from complex matrices. Using the SERS chip, a detection limit of as low as 1 nM for pyocyanine with a wide detection range of 1 nM–100 μM was observed. The proposed SERS chip could achieve the monitoring of pyocyanine during the growth of Pseudomonas aeruginosa biofilms with and without the treatment of different types of antibacterial drugs. Furthermore, pyocyanine secreted by Pseudomonas aeruginosa was confirmed using mass spectrometry (MS), and the concentration relationship obtained via MS/MS was consistent with that obtained via SERS detection. The proposed method based on the SERS chip for monitoring QS in bacterial biofilms offers the advantages of in situ detection, flexibility and efficiency.