Multicolor Luminescent Carbon Nanoparticles: Synthesis, Supramolecular Assembly with Porphyrin, Intrinsic Peroxidase-Like Catalytic Activity and Applications

Luminescent carbon nanoparticles (CNPs) are newcomers to the world of nanomaterials and have shown great impact in health and environmental applications as well as being promising building blocks for future nanodevices because of their fascinating photoluminescence and potential to serve as nontoxic replacements for traditional heavy-metals-based quantum dots. Herein, fluorescent CNPs have been prepared from candle soot by refluxing with HNO₃ and subsequently separated by a single centrifugation. The CNPs can be represented by the empirical formula C₁H_0.677O_0.586N_0.015Na_0.069, and have a size of 20–100 nm, height of 3.0 nm, lifetime of 7.31 ns ± 0.06 ns and quantum yield of ~1.7%. Further studies demonstrate that: (1) the as-prepared CNPs exhibit excellent stability in biological media and their luminescence intensity does not change with ionic strength or pH in the physiological and pathological range of pH 4.5–8.8; (2) CNPs can act as electron donors and transporters and porphyrin can assemble onto CNPs through electrostatic and π-stacking interactions to form porphyrin–CNPs supramolecular composites; (3) CNPs have strong intrinsic peroxidase-like activity. Based on this intrinsic peroxidase activity, a simple, cheap, and highly selective and sensitive colorimetric and quantitative assay has been developed for the detection of glucose levels. This assay has been used to analyze real samples, such as diluted blood and fruit juice.