Sulfur-doped carbon quantum dots and derived 3D carbon nanoflowers are effective visible to near infrared fluorescent probes for hydrogen peroxide

Near-infrared photoluminescence is intrinsic only to a minority of carbonaceous nanomaterials. Longwave fluorescence is, however, well suited for bio-sensing and bio-imaging owing to the low autofluorescence and low absorbance by biomatter. The authors describe here sulfur doped carbon quantum dots (S-CQDs) and their derivatives (referred to as 3D carbon nanoflowers; S-CNFs). Their average diameters are 2 and 28.5 nm, respectively. They display two emission peaks, one being purple and peaking at 407 nm, the other in the near-infrared and peaking at 780 nm. Quantum yields are 4% for S-CQDs and 6.4% for S-CNFs. The nanoparticles are shown to be viable fluorescent probes for hydrogen peroxide which acts as a quencher. The 3D structure of the S-CNFs and near-infrared detection result in a better linear relationship and lower detection limits. The detection limits for H2O2 are 1.1 μM for S-CQDs, and 0.6 μM for S-CNFs. The results presented here contribute to an improved understanding on how the nanostructure and selection of wavelengths affect the sensitivity and detection limits of such probes.