Highly sensitive SERS substrates based on MoS2-Au nanocomposites for detection of hazardous dyes and infectious bacteria.

Surface functionalization of two-dimensional materials with noble metal nanoparticles has unlocked new possibilities in Raman-based sensing by leveraging both chemical and electromagnetic enhancement effects. In this work, the optimized morphology of nanosheets of MoS2 adorned with Au NPs has been utilized for sensing of hazardous molecules Rhodamine B, N719 dye, and S. aureus, E. coli bacteria samples. MoS2 nanosheets were prepared by facile hydrothermal method and Au NPs were decorated onto the nanosheets' surface by reducing chloroauric acid solution. The Au nanoparticles concentration was optimized by altering the concentration of chloroauric acid solution. Rhodamine B and N719 dyes are known to be toxic and carcinogenic, if inhaled or indigested, whereas S. aureus and E. coli bacteria can cause skin infections, sepsis, food poisoning and severe diarrhoea. Therefore, detecting even trace concentrations of these molecules in the environment is critically important. The prepared SERS substrate successfully detects the Rhodamine B and N719 dyes up to 10-15 and 10-9 M concentrations. The highest enhancement factor obtained for Rhodamine B and N719 dyes are 5.2 × 107 and 2.1 × 107, respectively. The nanocomposite SERS substrate exhibits excellent signal uniformity and reproducibility with relative standard deviation value of around 10 %. Further, the nanocomposite substrate was employed for the sensing of infectious S. aureus and E. coli bacteria down to 102 cfu/mL. A charge transfer mechanism is also proposed between N719 dye and MoS2, along with the role of Au NPs, which produces the synergistic enhancement of the SERS signal.