Antibacterial Nitrogen-doped Carbon Dots as a Reversible "Fluorescent Nanoswitch" and Fluorescent Ink

The present finding describes an efficient facile approach for the fabrication of nitrogen-doped carbon dots (N-CDs) as a "fluorescent nanoswitch". Highly fluorescent blue-light-emitting N-CDs have been synthesized via a simpler hydrothermal method using 2,2'-(ethylenedioxy)-bis(ethylamine) and malic acid as the precursors. N-CDs showed excitation-dependent and pH-independent emission along with a quantum yield of similar to 25%. The blue fluorescent emission of N-CDs has been selectively "turned off" (quenching of fluorescence (FL)) during the sensing of Cr(VI) with 0.02 mu M limit of detection and further been selectively "turned on" (restoration of FL) on sensing ascorbic acid, compared with other metal cations and biomolecules tested. For testing the practical applicability of N-CDs, the switchable reversibility of the fluorescent nanoswitch has been tested for up to four cycles on the basis of FL "on-off-on". Furthermore, the toxicological test showed the antibacterial effect of the N-CDs on the tested Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli cells. Additionally, these N-CDs can also be used as a fluorescent ink for imaging purposes.