A convenient and label-free fluorescence turn off-on nanosensor with high sensitivity and selectivity for acid phosphatase

In this study, we reported a convenient label-free fluorescence nanosensor for rapid detection of acid phosphatase on the basis of aggregation-caused quenching (ACQ) and enzymolysis approach. The selectivity nanosensor was based on the fluorescence turn off-on mode, which possessed high sensitivity features. The original strong fluorescence intensity of CuInS2 QDs was quenched by sodium hexametaphosphate (NaPO3)(6). The high efficiency of the quenching was caused by the non-covalent binding of positively charged CuInS2 QDs to the negatively charged (NaPO3)(6) through electrostatic interactions, aggregating to form a CuInS2 QDs/(NaPO3)(6) complex. Adding acid phosphatase caused intense fluorescence of CuInS2 QDs/(NaPO3)(6) to be recovered, and this was because of enzymolysis. (NaPO3)(6) was hydrolyzed into small fragments and the high negative charge density decreased, which would weaken the strong electrostatic interactions. As a result, the quenched fluorescence turned on. Under the optimum conditions, there was a good linear relationship between I/I-0 (I and I-0 were the fluorescence intensity of CuInS2 QDs/(NaPO3)(6) system in the presence and absence of acid phosphatase, respectively) and acid phosphatase concentration in the range of 75-1500 nU mL(-1) with the detection limit of 9.02 nU mL(-1). The proposed nanosensor had been utilized to detect and accurately quantify acid phosphatase in human serum samples with satisfactory results. (C) 2015 Elsevier B.V. All rights reserved.