Cultural and built heritage are continuously exposed to physical, chemical, and biological agents that cause deleterious effects. Among the biological agents that cause deterioration, microorganisms are of critical importance, due to their metabolic versatility and flexibility, and their ability to tolerate unfavorable extreme conditions. Therefore, microorganisms can cause damage in cultural and built heritage surfaces through a variety of mechanisms, including biofilm formation, chemical reactions, physical penetration into the substrate and production of pigments [1-3]. The development of new strategies to detect microbial contamination is imperative, in order to plan effective remediation strategies. The aim of this work is to develop an alternative method for the detection of microbial proliferation. This method involves the development of a new fluorescent water-soluble coumarin derivative (1) for labeling biomolecules to the characterization and quantification of microbial populations.