Fig. 1. Raman scattering process^[11]. (a) Spontaneous Raman scattering; (b) coherent Raman scattering

Fig. 2. Research of molecular markers of atherosclerosis, liver disease, and neurodegenerative disease based on SRS. (a) Representative SRS images of cholesterol crystal (yellow), lipid droplet (green), and protein (cyan) in atherosclerotic artery and their superimposed image (scale bar is 20 µm)^[67]; (b) hematoxylin-eosin staining and representative SRS images of saturated (magenta) /unsaturated (green) triglycerides and collagen fibers (yellow) in different areas of fibrotic liver tissue slices (scale bar is 20 µm)^[71]; (c) representative single-color SRS images of 1 mm thick fresh Alzheimer’s disease mouse brain section at 1658, 1670, and 1680 cm^-1 and superimposed image of lipid (green), normal protein (blue), and amyloid plaque (magenta) (scale bar is 30 µm)^[72]; (d) SRS spectral curves of amyloid plaque and normal tissue^[72]

Fig. 3. Research of molecular markers of infectious diseases based on SRS. (a) Representative SRS images of C-D and C-H signals in fluconazole-susceptible and -resistant Candida albicans, where C-D imaging represents newly synthesized lipids and C-H imaging represents total lipid accumulation^[91]; (b) C-D signal intensity in fluconazole-susceptible and -resistant Candida albicans in Fig. (a); (c) representative SRS images of C-D signals in vancomycin-susceptible and -resistant enterococci cultured in the presence and absence of vancomycin for 0.5, 1.0, and 3.0 h using hyperspectral SRS microscopy; (d) average change in C-D signal intensity of vancomycin-susceptible and -resistant enterococci in Fig. (c) ^[93]; (e) representative SRS images of Pseudomonas aeruginosa cultured in media containing deuterium oxide (D₂O) for 0 h, 10 min, 30 min, 45 min, 1 h, 2 h, and 3 h; (f) average change in C-D signal intensity of Pseudomonas aeruginosa in Fig. (e) ^[94]

Fig. 4. Research on cancer molecular markers based on SRS. (a) Representative SRS (grey) images of lipid droplets and two-photon fluorescence (green) images of fluorescent particles in normal prostate and prostate cancer tissue; (b) Raman spectra of fluorescent particles in normal prostate, lipid droplets in prostate cancer tissues, and pure cholesterol ester standard in Fig. (a), with black arrows indicating characteristic peak of cholesterol ring at 702 cm^-1[102]; (c) large-scale (∼500 μm) hyperspectral SRS images of saturated fats (yellow), unsaturated fats (green), lipofuscin granules (cyan), and proteins (magenta) in liver cancer and normal liver tissues; (d) MCR decomposition of saturated fat, unsaturated fat, and protein in liver cancer tissue^[107]; (e) representative SRS images that reflect C-D signals (representing newly synthesized protein), total proteins, total lipids, and C-D/CH₃ ratio in mice xenografted with colon tumor 2.5 days after injection of deuterated amino acid (dAA) into carotid artery ,where boundaries between tumors and surrounding tissues are highlighted with white dashed lines and blood vessels containing red blood cells are highlighted with white dashed circles^[120]; (f) representative SRS images of C-D signal (2199 cm^-1), non-resonant background (2000 cm^-1), and protein (1655 cm^-1) in proliferative or necrosis zones of U-87 MG tumor xenograft mice cultured in 3-O-Propargyl-D-Glucose (3-OPG) medium^[99]; (g) representative DO-SRS images of distribution of lipid (CD_L and CH_L), protein (CD_P and CH_P), and ratio (CD_L/CH_L and CD_P/CH_P) in tissues of glioblastoma and colon cancer xenografts after 15 days of drinking D₂O at mole fraction of 25%, with tumor boundaries highlighted with white dashed line (scale bar is 20 µm)^[121]