An efficient "off-on" carbon nanoparticle-based fluorescent sensor for recognition of chromium(vi) and ascorbic acid based on the inner filter effect.

A simple approach based on calcination treatment of diethylenetriaminepentaacetic acid (DTPA) was developed to prepare water-soluble nitrogen doped carbon nanoparticles (N-CNPs) with a high quantum yield of approximately 53.7%. The fluorescence of N-CNPs could be quickly and efficiently quenched by Cr(vi) rather than Cr(iii) based on an inner filter effect (IFE) process. The addition of ascorbic acid (AA) can recover the intensity of fluorescence of the N-CNP-Cr(vi) system through the reduction of Cr(vi) to Cr(iii) and inhibit the IFE process between N-CNPs and Cr(vi) (turn-on). Accordingly, an efficient N-CNP based fluorescent probe for sensitive and selective sensing of Cr(vi) ions and l-ascorbic acid (AA) has been established. The proposed fluorescence sensor displays excellent performance for Cr(vi) determination in the range from 0.5 to 160 μmol L-1 (R2 = 0.998) with a detection limit down to 0.15 μmol L-1. Moreover, the observed linear response concentration range was from 1 to 400 μmol L-1 for AA with a detection limit as low as 0.13 μmol L-1. The fluorescent probe was successfully applied to detect Cr(vi) concentration in different water samples and AA concentration in human serum samples.