Spectroscopic identification of bacterial source molecules yielding ROS-generating nitrogen-species in bacteria-derived carbon quantum dots with anti-biofilm properties

• Bacterial proteins can be hydrothermally converted into carbon quantum dots (CQDs) • Such conversion of bacterial proteins yields pyrrolic and graphitic nitrogen. • Pyrrolic and graphitic nitrogen in CQDs are responsible for ROS generation. • Carbonization of protein-rich bacteria yield CQDs with strong antibiofilm activity. Bacteria-derived carbon-quantum-dots (CQDs) have been proposed for different applications, amongst which biofilm control. Anti-biofilm activities of bacteria-derived CQDs result from generation of reactive-oxygen-species (ROS), but the key-chemical pathways of carbonization of bacterial components and ROS-generation by bacteria-derived CQDs are unknown. Formation of low-yield, bacteria-derived CQDs (diameter 2–3 nm) upon hydrothermal-carbonization was confirmed using UV–vis absorption and fluorescence-emission spectroscopy. Amide-bands characteristic in FTIR spectra of source-bacteria remained visible in bacteria-derived CQDs. XPS indicated an N 1s photo-electron binding energy peak at 399.5 eV in source-bacteria due to amines that were converted upon carbonization into pyrrolic (400.5 eV) and graphitic (401.8 eV) nitrogen in bacteria-derived CQDs. A C 1s peak at 288.4 eV in source-bacteria due to carboxyl-groups related with the occurrence of amines in bacteria, but disappeared upon carbonization. Relations between the occurrence of amine nitrogen in source-bacteria with pyrrolic and graphitic nitrogen in bacteria-derived CQDs confirm that bacterial proteins are converted into pyrrolic and graphitic nitrogen-species upon hydrothermal carbonization. Relations between ROS-generation with the occurrence of pyrrolic and graphitic nitrogen-species identified these nitrogen-species in bacteria-derived CQDs as being responsible for enhanced ROS-generation and accompanying anti-biofilm activity. These findings enable selection of source-bacteria for preparing bacteria-derived CQDs with optimized ROS-generation and anti-biofilm activity.