Para-formaldehyde in phosphate buffer is widely used in biological and medical research for tissue fixation. It helps preserve cellular structures by cross-linking proteins, ensuring minimal distortion during microscopic examination. This solution is particularly essential in immunohistochemistry, where it maintains antigen integrity for accurate antibody binding. It is also employed in cell biology studies to stabilize samples for flow cytometry and fluorescence microscopy. Additionally, it serves as a disinfectant and sterilizing agent in laboratory settings due to its ability to inactivate microorganisms. Proper handling is crucial, as it releases formaldehyde, which can be hazardous.