Fig. 1. Energy level diagram for Raman scattering process

Fig. 2. Bright-field optical image of human sperm cells (A) and chemical mapping constructed from sperm Raman spectra (B)^[35]

Fig. 3. Averaged spectra and wavelet coefficient distributions^[36]. (a) Average spectra showing the distinct difference at 1042 cm^-1 (arrow) in spectra of UVB irradiated (red) and untreated (green) sperms; (b) wavelet coefficient distribution of UVB irradiated sperm

Fig. 4. Raman spectra^[38]. (a) Raman spectra comparison of untreated sperm (27% DFI, black) and the sperm induced with oxidative nDNA damage (92% DFI, red); (b) Raman spectra in the region corresponding to the DNA PO₄ backbone indicating different levels of oxidative damage

Fig. 5. Typical Raman spectra obtained from different shapes of sperms and the vertical shaded areas show the spectral regions where the main differences among different spectra are located^[36]

Fig. 6. Bright-field image of stained sperms on glass substrate and Raman spectra of sperms head^[40]. (a) Bright-field image of stained sperms; (b) Raman spectra obtained from DNA-intact sperm (blue line), DNA-damaged sperm (red) and their difference spectra (black)

Fig. 7. Receiver operating characteristic (ROC) curves for PCA-LDA and PLS-DA for intact and damaged sperm groups^［40］

Fig. 8. Outline of sperm head and acrosome area, as well as Raman spectrum of high-quality sperm^[41]. (a) A typical white light image of sperm cell; (b)(c) outline of sperm head and acrosome area; (d) Raman spectra of high-quality sperm from 600 to 1800 cm^-1

Fig. 9. Holographic image of sperm and its spectra of under different laser powers^[42]. ^{(a) Acquired hologram of the sperm out of focus; (b) reconstructed amplitude map at the plane of acquisition; (c) reconstructed amplitude map of the interest region at the focus plane; (d) 3D phase map of interest region at the focal plane; (e) Raman spectra acquired at laser powers of 0, 30, 61 and 107 MJ/cm2 in various spectral regions}

Fig. 10. Raman spectral comparison of acrosome and equatorial region of ZP-bound versus ZP-unbound sperm, as well as spectral comparison between various regions of the sperm^[43]. (a) Raman spectral responses of sperm acrosome region for ZP-bound and ZP-unbound sperm (red arrow indicates ZP-bound sperm and blue arrow indicates ZP-unbound sperm); (b) Raman spectral responses of equatorial region for ZP-bound and ZP-unbound sperm; (c) spectral comparison between various regions of the sperm

Fig. 11. Biochemical mapping of individual living sperm reconstructed from hyperspectral datasets^[44]

Fig. 12. White light image and Raman spectra of motile sperm head attached to the substrate^[45]. (a) White light image; (b) Raman spectra