Label-Free Evaluation of Chromatin Condensation in Human Normal Morphology Sperm Using Raman Spectroscopy

Chromatin condensation is one of the main factors essential for sperm function. Evaluation of chromatin condensation by current methods render the assessed sperm unsuitable for assisted reproduction. We examined the Raman spectra of normal morphology sperm to determine whether a non-invasive confocal Raman spectroscopy can detect spectral differences between groups having different levels of chromatin condensation. Semen samples from 85 donors who underwent ICSI were obtained. Chromomycin A3, aniline blue and acridine orange staining were performed to evaluate the protamine deficiency, histone retention and DNA fragmentation respectively. Raman spectra were obtained from 50 normal morphology sperm for each donor. Spectral analysis was performed using home written programs in LabVIEW software and samples were grouped based on chromomycin A3 staining. Raman peaks intensities at 670 cm^-1, 731 cm^-1, 785 cm^-1, 858 cm^-1, 1062 cm^-1, 1098 cm^-1, 1185 cm^-1, 1372 cm^-1, 1424 cm^-1, 1450 cm^-1, 1532 cm^-1, 1618 cm^-1 and 1673 cm^-1 were significantly correlated with at least one of the sperm staining methods. The median intensity of the Raman peaks at 670 cm^-1, 731 cm^-1, 785 cm^-1, 1062 cm^-1, 1098 cm^-1, 1185 cm^-1, 1372 cm^-1, 1424 cm^-1, 1450 cm^-1, 1532 cm^-1, 1618 cm^-1 and 1673 cm^-1 show a significant difference between the CMA3≤41 and CMA3>41groups. The Raman spectroscopic measurements represent a promising diagnostic tool that has the ability to label-free detect sperm with chromatin abnormalities, such as improper chromatin condensation and DNA fragmentation to a certain degree similar to that of the existing staining techniques at the individual cell level.