Self-carbonization synthesis of highly-bright red/near-infrared carbon dots by solvent-free method

Abstract

In biosensing and biophotonics, red/near-infrared fluorescent carbon dots (R-CDs) are attractive and deserve more attention. However, the synthesis and purification of R-CDs are time-consuming, impeding their industrial production and application on a large scale. We proposed a solvent-free method for reducing the number of raw materials used in the R-CD synthesis by utilizing the dehydration self-carbonation effect of the-HSO₃ group in the precursor. The synthesized R-CDs exhibit a quantum yield of 59% and an emission wavelength of 600–800 nm with only one raw material (3,4-diaminobenzenesulfonic acid) and without the addition of any extra precursors, solvents, catalysts, dehydration agent, or other additives. We hypothesized that the red/near-infrared emission was caused by carbon-nucleus conjugated structures formed during the dissociation of the –HSO₃ group at high temperatures. Additionally, the prepared R-CDs demonstrated a good response to the products of glucose oxidation, indicating glucose's sensing capability. Additionally, the synthesized R-CDs demonstrated excellent single-photon imaging of cells while being non-toxic, demonstrating their enormous potential in biophotonics. We believe that this simple and environmentally friendly R-CD synthesis can significantly accelerate industrialization and application.