Fig. 1. Process of on-site bacterial SERS detection on different surfaces with anisotropic morphologies, including instant-ready SERS substrates preparation, SERS screening, and chemometric analysis.

Fig. 2. (a) Schematic diagram of the preparation of MCDs and Au@MCDs. (b) Fermi energy level of CDs and MCDs. (c) SERS spectra of MB on Au@MCDs synthesized with MCDs in different volume. (d) TEM and (e) HRTEM images of MCDs with the size distribution curve in (d). (f) TEM and (g), (h) HRTEM images of Au@MCDs with the size distribution curve in (f).

Fig. 3. (a) UV-Vis spectra, (b) FTIR spectra, and (c) XPS profiles of MCDs and Au@MCDs. High resolution XPS profiles of Mo 3D in (d) MCDs, (e) Au@MCDs, and (f) Au 4f in Au@MCDs.

Fig. 4. (a) Scheme for SERS experiments using the Au@MCD devices. (b) SERS activity of the Au@MCDs at various organic pollutants (MB, CV, R6G, and MG) under 785 nm. (c) 3D score plots for organic pollutants spectral datasets based on PCA.

Fig. 5. (a) SERS spectra of MB at different concentrations induced by Au@MCDs. (b) Enhancement factors of typical Raman peaks of the MB. (c) Repeatability of SERS detection of MB absorbed on the same SERS sensor at twenty different sample spots. (d) Uniformity of SERS intensity of seven characterized peaks of MB.

Fig. 6. (a) Reproducibility of SERS signals of ten sample spots on prepared Au@MCDs in six batches. (b) Plot of SERS signal intensities at 1624  cm−1. (c) SERS spectra and (d) changes of SERS intensity of MB (10−5  M) induced by Au@MCDs after 7 weeks.

Fig. 7. (a) SERS spectra of MB on Au@MCDs and control Au NPs. (b) Hydrodynamic diameter distribution and zeta potentials of Au NPs and Au@MCDs. (c) Schematic model and electric field simulation of single Au NPs and Au@MCDs of varying thicknesses of MCDs layers.

Fig. 8. (a) Schematic diagram of CT process induced by metal surface plasmon resonance in the Au@MCD-MB system. (b) UPS spectrum of MCDs. (c) Band gap spectrum and (d) valence band spectrum of MCDs. (e) Degree of CT varies with MCD thickness.

Fig. 9. SERS spectra of (a) R6G, (b) MG, and (c) CV irritated by Au NPs and Au@MCDs, and the normal Raman spectra of dyes. (d) Diagram of the PICTT process between Au@MCDs and dye molecules.

Fig. 10. SERS spectra of four common foodborne pathogens (Listeria, Salmonella, S. aureus and E. coli) on the surfaces of (a) facecloth, (b) paper, (c) mask, (d) cotton pad, and (e) stainless steel. (f) LDA score plot of E. coli, S. aureus, Salmonella, and Listeria on the paper.

Fig. 11. SERS spectra of (a) E. coli, (b) S. aureus, (c) Salmonella, and (d) Listeria at different concentrations (from 10 to 108  CFU/mL) using instantly prepared Au@MCDs on the surfaces of the paper with foodborne pathogen in 108  CFU/mL as the control group.