Fig. 6: Identification and digital counting of bacterial species using SERS.

a Raman spectra of various bacterial species highlighting key peaks: E. coli 25922 (1567 cm⁻¹), S. aureus 25923 (2413 cm⁻¹), E. coli 1655 (1494 cm⁻¹), S. mutans 3065 (1241 cm⁻¹), and Lactobacillus brevis (2579 cm⁻¹). b SERS intensity maps for the respective bacterial species at the indicated Raman shifts. The color scale indicates Raman intensity, with warmer colors representing higher intensities. c Digital counting maps showing the binary presence (1) or absence (0) of Raman signals for each bacterial species. The total count of positive detections is listed for each species. d Calibration curves showing the correlation between Raman counts and bacterial concentration for each species: E. coli 25922, S. aureus 25923, E. coli 1665, S. mutans 3065, and Lactobacillus brevis. The R² values indicate the linearity of the response. Data represent mean ± s.d.; n = 3 independent experiments. e SERS intensity maps of urine samples spiked with Lactobacillus brevis and E. coli 25922. The leftmost map shows a blank urine sample. The middle maps show the detection of Lactobacillus brevis (2579 cm⁻¹) and E. coli 25922 (1567 cm⁻¹) individually, while the rightmost map shows the merged detection of both bacteria in the same sample