In-situ monitoring of Quorum Sensing signalling molecules by a SERS chip with array micro-chambers

The in-situ monitoring of quorum sensing (QS) signal molecules in bacterial biofilms was 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 biofilm cultivation and in-situ SERS detection was 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 array micro-chambers and a bottom quartz layer. The Nano-silver SERS substrate showed good homogeneity and stability with the enhancement factor up to 1.84×108 for pyocyanine, and the design of SERS substrate located at the top layer of chip effectively attenuated the interference of complex matrix. In merit of the SERS chip, the detection limit for pyocyanine was as low as 1nM with a wide detection range of 1 nM~100 μM. The proposed SERS chip could achieve the monitoring of pyocyanine during the growth of Pseudomonas aeruginosa biofilms with and without treatment of different types anti-bacterial drugs. Furthermore, pyocyanine secreted by Pseudomonas aeruginosa were confirmed by mass spectrometry (MS) and the concentration relationship obtained by MS/MS was consistent with the SERS detection. The proposed method based on the SERS chip for monitoring QS in bacterial biofilms had advantages of in-situ detection, flexibility and efficiency.