Carbon dots as fluorescent sensor for detection of explosive nitrocompounds

Highly and stable fluorescent carbon dots (CQDs), with λex/λem = 350/465 nm were obtained using a strong acid oxidation of activated carbon in aqueous suspension. The nanoparticles had a mean size of 12 nm and quantum yield of 3.94%. After functionalization with amine groups by PAMAM-NH2 dendrimer (CQDs@PAMAM-NH2), the size of particles increased and aggregates of 65 nm were formed. Quantum yield also increased to 6.33%. CQDs were characterized by various analytical techniques including ATR-FTIR, Raman, XPS and fluorescence spectroscopies. The prepared CQDs@PAMAM-NH2 were used as fluorescent ratiometric nanosensor of 4-chloro-2,6-dinitroaniline, which is a constituent of explosives. As a result of interactions, the fluorescence at 465 nm was quenched. Moreover, a new band at 507 nm emerged and it is linked to a charge transfer and the formation of a Meisenheimer complex. A ratio of fluorescence intensities at 465 and 507 nm (I465/I507) is used for a ratiometric fluorescence sensing. A linear detection ranges from 1.0 × 10−5 to 6.0 × 10−4 M with a detection limit of 2 μM and accuracy of 0.85% as standard relative deviation (RSD, n = 10). The detection accuracy in the presence of other nitrocompounds was 2.80% as RSD.