Chondroitin sulfate fluorescence biosensor based on graphere quantum dots aggregating on CMC/CS polyelectrolyte microspheres

Here, we report an efficient fluorescence biosensor for chondroitin sulfate (CHS) based on polyelectrolyte microspheres of carboxymethyl cellulose (CMC) and chitosan (CS) composites inducing the aggregation of graphene quantum dots (GQDs), calling CMC/CS-GQDs. The polyelectrolyte microspheres (CMC/CS microspheres) were fabricated by using anionic-cationic electrostatic attraction between CMC and CS by high voltage electrostatic spray technology. The aggregating process of GQDs wasbased on the anionic-cationic electrostatic attraction as well. After combing with the polyelectrolyte microspheres, the fluorescence of GQDs disappeared. CHS, which widely consistsin the cell surface of human beings and animals, carries a large number of negative charges on the surface. The addition of CHS enabled CHS and GQDs to compete with each other to composite with the CMC/CS microshpheres. As a result of the higher surface charge density of CHS, CMC/CS-CHS formed accompanied by the release of GQDs, and the fluorescence of the system recovered. The CHS content was detected by analyzing the system's fluorescence recovery, which suggested that the obtained fluorescence biosensor can accuratelydetectthe concentration of CHS. The test results showed that the linear range of the fluorescence recovery for this biosensor with respect to CHS was 0∼12.00mg/mL, and the detection limitwas 10^-8 M. Besides, to test the stability of the biosensor, the CMC/CS-GQDs micropsheres persisted for one month, with a low fluorescence quenching of 9.48%. These results suggested that CMC/CS-GQDs can be utilized as efficient fluorescence biosensor for the detection of CHS. Moreover, the detection method was simple and efficient, and could be widely popularized.