<i>In situ</i> monitoring of quorum sensing signalling molecules using a SERS chip with a micro -chamber array

The <i>in situ</i> 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 <i>in situ</i> SERS detection is proposed for the monitoring of pyocyanine, an important signal molecule and biomarker secreted by <i>Pseudomonas aeruginosa</i>. 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 <i>Pseudomonas aeruginosa</i> biofilms with and without the treatment of different types of antibacterial drugs. Furthermore, pyocyanine secreted by <i>Pseudomonas aeruginosa</i> was confirmed using mass spectrometry (MS), and the concentration relationship obtained <i>via</i> MS/MS was consistent with that obtained <i>via</i> SERS detection. The proposed method based on the SERS chip for monitoring QS in bacterial biofilms offers the advantages of <i>in situ</i> detection, flexibility and efficiency.