Carbon dots as Reactive Nitrogen Species nanosensors

Three sets of Carbon Dots (Cdots) were produced through the carbohydrates acid thermal decomposition method. These nanoparticles were functionalized with a polymer, known for its biological compatibility: polyethylene glycol, PEG₂₀₀, and folic acid, FA, a biomolecule associated with the reactive oxygen and nitrogen (ROS/RNS) savaging process, thus resulting CdotsPEG₂₀₀, CdotsPEG₂₀₀FA and CdotsFA. These nanoparticles were tested as nitric oxide radical (NO·) sensors and it was determined that CdotsPEG₂₀₀FA and CdotsFA fluorescence intensity was quenched by the presence of this radical specie. Moreover, according to the Benesi-Hilderbrand plot, the nanoparticles have a high affinity towards the analyte and this interaction is consistent with a 1:1 stoichiometry, through an independent mechanism. The Stern-Volmer constant, obtained for both sensing systems, is compatible with the formation of stable complexes (static quenching) between the Folic Acid residues on the Cdots surface and NO·. The detection and quantification limits along with the sensitivity were calculated for both nanoparticles: DL (31.7 ± 0.02) x 10^-9, QL (96.29 ± 0.01) x 10^-9, Sensitivity (5.2 ± 0.5) x 10⁹ M for CdotsFA and DL (83 ± 3) x 10^-10, QL (251 ± 2) x 10^-10, Sensitivity (8.4 ± 0.3) x 10¹⁰ M. These values are adequate for biological sensing and are quite competitive with other reported nanosensors for NO· detection and quantification.