Fig. 1. Schematic of the fabrication process of Cu₂O-Ag SERS substrate by in-situ growth

Fig. 2. SEM pictures of Cu₂O particles at different sintering temperatures

Fig. 3. Characterization results of Cu₂O-Ag substrate. SEM pictures of Ag NPs on the Cu₂O-Ag surface, when the reaction time is (a) 10 s, (b) 60 s, and (c) 120 s, respectively; substrate (d) Cu and (e) Ag element distribution maps, and (f) element content map, when the reaction time is 60 s; (g) picture of water droplets on the surface of the Cu₂O-Ag substrate

Fig. 4. Results of R6G detection on Cu₂O-Ag substate. (a) Raman spectra of 2 μM R6G at different substrates; (b) Raman spectra of R6G at different concentrations on Cu₂O-Ag substate; (c) relationship between peak intensity and concentration logarithm of R6G at 615 cm^-1

Fig. 5. Uniformity, reproducibility, and stability of Cu₂O-Ag substrate. (a) Raman spectra of R6G from 15 points randomly selected on Cu₂O-Ag substrate; (b) peak intensity of R6G at 615 cm^-1 on the 6 batches of Cu₂O-Ag substrates; (c) change of peak intensity of R6G at 615 cm^-1 after the substrate was fabricated for different time

Fig. 6. Results of three banned drugs and their mixtures tested on Cu₂O-Ag substrate. (a) Malachite Green; (b) enrofloxacin; (c) nitrofurazon; (d) Raman spectra of three drug mixtures in different water bodies