Caspofungin-Based Red-Emissive Probes for Fluorescent Imaging of Pathogenic Fungi

Fungal infections are an often-neglected cause of morbidity worldwide, while their inaccurate and often inconclusive diagnosis indirectly promotes high morbidity and the development of antimicrobial resistance. Here, the clinically used semisynthetic echinocandin antifungal caspofungin was selectively conjugated to red-emitting fluorescent dyes to develop new optical imaging probes for fungal detection. The probes were characterized using established 2D NMR techniques to determine the specific position of the fluorophore on the peptide backbone, and both isomers demonstrated selective labeling of pathogenic fungal strains with similar efficacy. Selective multiplexed imaging of target species was achieved in a co-culture of fungi and bacteria, including when using benchtop imaging platforms.