A fluorescent turn-off/on method based on carbon dots as fluorescent probes for the sensitive determination of Pb2+ and pyrophosphate in an aqueous solution

Unmodified carbon dots (CDs) were demonstrated as novel and environmentally friendly fluorescent probes for sensing Pb2+ and pyrophosphate (PPi) in an aqueous solution. The prepared CDs had an average diameter of 50 nm, and the fluorescence intensity of the CD solution was sensitive to the pH and exhibited a yellow-green color under UV light (365 nm). The approach relied on the fact that the fluorescence intensity of CDs was effectively quenched by Pb2+ (turn-off), and the resulting CD-Pb2+ system was observed to be sensitive to PPi. Due to the ability of PPi to coordinate with Pb2+, the fluorescence intensity of the CDs was effectively protected and reversibly restored by the addition of PPi (turn-on). Good linearity for detecting Pb2+ was attained over the concentration range from 5.0 x 10(-7) to 1.1 x 10(-5) mol/L. The binding constant between Pb2+ and CDs was 5.0 x 10(4) L/mol with a detection limit of 2.0 x 10(-9) mol/L. The optimized conditions for detecting PPi, such as the incubation time, pH of the CD solution and CD concentration, were 3.0 min, and 7.0 and 0.07 mg/mL, respectively. Under the optimized conditions, the concentrations of PPi ranging from 1.0 x 10(-5) to 1.7 x 10(-3) mol/L exhibited a linear relationship with the relative fluorescence intensity with a correlation coefficient of R-2 = 0.9948. The detection limit for PPi was 5.0 x 10(-7) mol/L. The fluorescent turn-off/on method offered good selectivity for detecting PPi in the presence of 18 different types of ions. (C) 2014 Elsevier B.V. All rights reserved.