Label-free refractive index mapping of human sperm cells

Area of Science:

• Biomedical Optics
• Reproductive Biology
• Microscopy Techniques

Background:

• Intracytoplasmic sperm injection (ICSI) relies on subjective sperm selection using standard microscopy.
• Current methods lack detailed visualization of sperm internal morphology due to cell transparency.
• Staining is not feasible during ICSI, limiting contrast enhancement.

Purpose of the Study:

• To develop a label-free method for quantitative refractometry of individual human sperm cells.
• To enable automated identification of subcellular structures within sperm for improved selection.
• To overcome limitations of subjective morphological evaluation in ICSI.

Main Methods:

• Utilized interferometric phase microscopy (IPM) for quantitative phase imaging in media with varying refractive indices.
• Combined IPM with fluorescence microscopy to localize sperm structures and enable refractometry.
• Developed a machine learning model trained on label-free phase images for automated classification.

Main Results:

• Successfully performed refractometry of individual human sperm cells, distinguishing nucleus and acrosome based on refractive index differences.
• The machine learning model achieved 89% sensitivity and 94% specificity in identifying subcellular structures.
• Demonstrated the potential of IPM for label-free, quantitative morphological characterization.

Conclusions:

• Label-free interferometric phase microscopy provides essential quantitative information for human sperm analysis.
• This approach can significantly improve the accuracy and objectivity of sperm selection for ICSI.
• The developed method holds promise for enhancing assisted reproductive technologies.