Our research was aimed at differentiating between healthy (normal) and cancerous urinary bladder urothelial cells. We developed a fluorescence derivative of fluorescein, sodium disulfonate (SUF), which is an organic compound and emits intense fluorescence. We analysed if SUF can be used in cancer cell diagnostic and examined its potential for targeted therapy as an alternative to the currently used fluorescent dyes, which are more expensive and harder to obtain, and with this approach make such research more accessible. The results of the study have shown that SUF is not toxic to urothelial cells of the urinary bladder and that it may be used to distinguish between healthy and cancerous urothelial cells, based on the way of labelling. SUF was proven to be a useful fluorescent marker.