Determination of ascorbic acid using electrochemiluminescence sensor based on nitrogen and sulfur doping graphene quantum dots with luminol as internal standard

A novel internal standard electrochemiluminescence (ECL) sensor has been designed for the detection of ascorbic acid (AA). The adopted dual-emission luminophore (NSGQDs-PEI-luminol-Pt) is composed of nitrogen and sulfur double-doped graphene quantum dots (NSGQDs, as the main luminophore), luminol (as the auxiliary luminophore and internal standard), platinum nanoparticles (Pt NPs, as the co-reaction accelerator), and polyetherimide (PEI, as the linker of NSGQDs and luminol). The results suggest obviously enhanced  ECL intensities by the Forster resonance energy transfer (FRET) between luminol (donor) and NSGQDs (acceptor). In this sensing system, the cathodic ECL intensities of NSGQDs (ECL-1, −1.8 V vs. Ag/AgCl) gradually decrease with increasing concentration of AA, while the anodic ECL intensities of luminol (ECL-2, 0.3 V vs. Ag/AgCl) almost remain essentially constant at a potential window from −2.0 to 0.4 V. The natural logarithm of the ratio between ECL-1 and ECL-2 (ln I (ECL-1/ECL-2)) shows a good linear relationship with AA concentration ranging from 10 to 360 nM. The regression equation is ln I (ECL-1/ECL-2) = − 0.0059 cAA + 3.55 (R2 = 0.992) with a limit of detection of 3.3 nM. Such sensor has also been applied for monitoring AA in human serum. The recovery range was 96.5–105.3% and the relative standard deviation was  1.3–3.3%.