Multi-positively charged dendrimeric nanoparticles induced fluorescence quenching of graphene quantum dots for heparin and chondroitin sulfate detection

A label-free fluorescence assay for rapid and sensitive detection of heparin (Hep) or chondroitin sulfate (CS) was developed by guanidine-terminated poly (amidoanime) (PAMAM-Gu+) dendrimers induced aggregation of graphene quantum dots (GQDs). The fluorescence of GQDs was obviously quenched after mixing with PAMAM-Gu+. However, the addition of highly negatively charged Hep or CS into the fluorescence sensing system resulted in the fluorescence recovery. Because the multi-positively charged PAMAM-Gu+ would prefer to bind with highly negatively charged Hep or CS, resulting in the deaggregation of GQDs. Under the optimized experimental conditions, the recovery of fluorescence intensity ratio I/I0 (I0 and I were the fluorescence intensity of the sensing system in the absence or presence of target analytes, respectively) was proportional to the concentration of target analytes in the range of 0.04-1.6 μg mL−1 for Hep and 0.1-2.5 μg mL−1 for CS. In addition, this method afforded high sensitivity with the detection limit as low as 0.02 μg mL−1 and 0.05 μg mL−1 for Hep and CS, respectively. All results suggested that the fluorescence turn-on method could be successfully employed for sensitive and selective detection of heparin analogs.