Phosphonic Acid Fluorescent Organic Nanoparticles for High-Contrast and Selective Staining of Gram-Positive Bacteria

Fast and selective detection of pathogens represents high challenges given the considerably high proliferation rate and mutation potential of bacteria against antibiotics. With this aim, anionic red-orange-emitting fluorescent organic nanoparticles (FONs), characterized by high brightness and photostability, are developed to selectively stain Staphylococcus aureus after only 5 min of exposure. No cytotoxicity effects are observed as a result of the negatively charge surface of the employed FONs. By contrast, no staining can be observed with Pseudomonas aeruginosa strains. The exclusive labeling of Gram-positive bacteria is ascribed to originate from the phosphonic acid moieties incorporated in the FON-constituting fluorophores because model FONs, devoid of phosphonic acids, show no adhesion under the same experimental conditions. Tight hydrogen bonding between the FON acidic units and the peptidoglycan (PG) layers comprising the outer wall of S. aureus is suspected to be the prevailing factor for the enco...