Chemical and functional inheritance of carbon quantum dots hydrothermally-derived from chitosan

Owing to their extremely small size, carbon-quantum-dots (CQDs) can cross biological barriers, which makes them attractive for many biomedical and other applications. CQDs can retain key-chemical features and associated functionalities of the molecular sources they are derived from, provided a suitable synthesis method is used at relative mild carbonization temperatures. Here we demonstrate that CQDs hydrothermally-derived from chitosan or 2-hydroxypropyltrimethyl ammonium-chloride (HAC)-chitosan under pressurized conditions at 180 °C have a comparable elemental and molecular composition, as determined using X-ray photoelectron spectroscopy and Fourier-transform-infrared spectroscopy. In addition, both types of CQDs generated reactive-oxygen-species as an added functionality alien to their molecular carbon sources. As a result, CQDs exhibited stronger antibacterial properties against a Gram-positive Staphylococcus aureus and a Gram-negative Escherichia coli strain, while both molecular HAC-chitosan as well as CQDs derived from it had stronger antibacterial properties than molecular chitosan and chitosan CQDs due to the possession of quaternary ammonium groups in HAC-chitosan. Therewith, carbonization of chitosan and HAC-chitosan yields enhanced properties that can be beneficial in a high variety of different applications, including promotion of healing and bacterial infection control, preservation of food and beverages, pesticide control in agriculture and horticulture, water treatment and in many cosmetics and personal care products.