A novel ultrasensitive carboxymethyl chitosan-quantum dot-based fluorescence “turn on–off” nanosensor for lysozyme detection

In this work, we developed an ultrasensitive “turn on–off” fluorescence nanosensor for lysozyme (Lyz) detection. The novel nanosensor was constructed with the carboxymethyl chitosan modified CdTe quantum dots (CMCS-QDs). Firstly, the CMCS-QDs were fabricated via the electrostatic interaction between amino groups in CMCS polymeric chains and carboxyl groups on the surface of QDs. In the fluorescence “turn-on” step, the strong binding ability between Zn2+ and CMCS on the surface of QDs can enhance the photoluminescence intensity (PL) of QDs. In the following fluorescence “turn-off” step, the N-acetyl-glucosamine (NAG) section along the CMCS chains was hydrolyzed by Lyz. As a result, Zn2+ was released from the surface of QDs, and the Lyz–QDs complexes were formed to quench the QDs PL. Under the optimal conditions, there was a good linear relationship between the PL of QDs and the Lyz concentration (0.1–1.2ng/mL) with the detection limit of 0.031ng/mL. The developed method was ultrasensitive, highly selective and fast. It has been successfully employed in the detection of Lyz in the serum with satisfactory results. •This proposed Zn2+–CMCS-QDs based sensor for lysozyme is ultrasensitive.•The selectivity and stability of the sensing system was improved than before.•The fluorescence “turn on–off” nanosensor is a novel nano-sensing model.