Sulforhodamine 101 is widely used as a fluorescent dye in biological and biomedical research. It is particularly valuable in fluorescence microscopy due to its high photostability and strong emission in the red region of the spectrum, allowing for clear visualization of cellular structures with minimal background interference. The dye is often used to label proteins, antibodies, or nucleic acids for detection and imaging applications. It serves as a tracer in neuronal pathway studies, where it is applied in retrograde labeling to map connections between different regions of the nervous system. Due to its positive charge, it is also employed in mitochondrial staining, accumulating in the mitochondria of live cells for functional and morphological assessment. In addition, Sulforhodamine 101 is used in flow cytometry and fluorescence-activated cell sorting (FACS) to identify and separate specific cell populations. Its compatibility with common laser lines and filter sets makes it a practical choice in multi-color labeling experiments. The dye is also utilized in material science, such as in the development and testing of fluorescent sensors and optoelectronic devices.