Multiple fluorescence response behaviours to proteins/bacteria and selective antibacterial activity of cetylpyridinium chloride (CPC)-based cationic carbon dots

Direct interaction between carbon dots (CDs) and biomolecules leads to changes in the chemical and physical status as well as properties of CDs, which can have various biological and biomedical applications. In this work, the surface of CDs was modified with cetylpyridinium chloride (CPC) to facilitate interactions between CDs and biomolecules. Multiple fluorescence response behaviours of CPC-based CDs were observed towards several proteins (bovine serum albumin, lysozyme, protamine, and hemoglobin) and bacterial cells (Escherichia coli and Staphylococcus aureus). Electrostatic attraction and hydrogen bonding were involved in inducing aggregation of CDs and fluorence enhancement. An inner filter effect might also occur to reduce fluorescence of CDs when interacting with proteins. Selective antibacterial activity of CPC-based CDs was observed towards Gram positive bacterium Staphylococcus aureus. This work provides potential to develop CD-based techniques for detecting and visualizing proteins/bacteria as well as selective antibacterial agents towards Gram-positive bacteria.