Fluorescein-derived carbon dots with chitin-targeting for ultrafast and superstable fluorescent imaging of fungi

Fluorescence microscopy based on fluorochrome has been rapidly developed as the candidate for morphological identification of pathogenic fungi over recent years, offering superior rapidity and efficacy over traditional culture methods. However, the intrinsic quenching properties of fluorescein limit the clinical application of fluorescence imaging. Herein, we report a nano-strategy by converting a commercial fluorescein dye, fluorescent brightener-33 (FB-33), into carbon dots (FB-CDs) through a one-pot hydrothermal method. FB-CDs exhibit a chitin-targeting capacity allowing the selective recognition and ultrafast imaging of fungi within 30 s. The fluorescence quantum yield of FB-CDs is 51.6% which is 8.6-fold higher than that of commercial dye, FB-33. Moreover, FB-CDs also display superstable fluorescence signals under continuous intense light irradiation for 2 h and long-term storage for more than 2 months. The significantly improved photobleaching resistance meets the prolonged fluorescence observation and quantitative analysis of microbial samples. This work offers a novel nanoconversion strategy of commercial dyes for point-of-care testing of pathogenic organisms.