Fluorescent brightener-mimetic carbon dots with microbe-targeted capability for bacterial Gram typing and...

The fluorescent brighteners (FBs) utilized in microscopic morphological examination of clinical microorganism exhibit suboptimal performance due to fluorescence instability and unfavorable chromatic properties. Here we provide an alternative strategy by one-pot hydrothermal synthesis of green fluorescent carbon dots (G-CDs) using the structural components of FB molecule as precursors. G-CDs display microbe-targeted capability similar to FB dye, while more friendly fluorescent color (Em: 523 nm) with ultra-stable fluorescence under continuous intense illumination (2 h), wide pH range from 3 to 11 and long storage (>2 months). G-CDs can efficiently attach to the peptidoglycan layers of Gram-positive bacteria while excluded by the outer membrane lipopolysaccharide barrier of Gram-negative bacteria, enabling wash-free, single-step Gram typing within 1 min. This property also endows G-CDs with live/dead identification of bacteria, which can serve as novel fluorescence nanosensor to quantify the antibacterial efficacies of multiple disinfection methods. Therefore, G-CDs offer a feasible alternative to FB dyes for clinical bacterial visualization and evaluation of bactericidal efficacy.