Novel fixative solutions with superior preservation of structure and antigenicity are suitable for optical clearing, tissue staining, and flow cytometry.

Fixation of tissues and cells is an essential step in histological analysis; however, structural deformation and fluorescence signal attenuation caused by fixatives often pose challenges. This study aimed to evaluate the performance of a newly developed fixative, the FM Fix, by comparing it with conventional fixation methods in tissue staining, optical clearing, and flow cytometry analysis. FM Fix demonstrated staining properties comparable to those of standard fixatives and showed superiority with respect to tissue structure retention. Optical clearing allowed the visualization of fluorescent signals at greater depths. In flow cytometry using green fluorescent protein (GFP)-expressing cells, FM Fix minimized the loss of GFP fluorescence, preserved cell membrane integrity, and maintained cell size. Furthermore, the staining quality of human renal biopsy samples was equivalent to that of 10% neutral buffered formalin (NBF). These findings suggest that FM Fix has excellent structural preservation, fluorescence retention, and antigen preservation properties, making it broadly applicable for histological evaluation and quantitative cellular analysis.