Colorimetric and fluorescence detection of Pb²⁺ by fluorescein derivative

A simple and low cost method for rapid detection of Pb²⁺ was developed in this study using a simple fluorescent probe, biotin-4-fluorescein. The presence of Pb²⁺ induced the color change of fluorescein from yellow to pink which can be detected visually by naked eyes. The color change of biotin-4-fluorescein was not observed while testing with other metal ions, such as Fe³⁺, Cu²⁺, Ca²⁺, Co²⁺ and Cd²⁺, indicating the selectivity of fluorescein derivative with Pb²⁺. Moreover, the color change was observed at pH above 7.0, and the pink color got more intense when increasing pH. Adding EDTA, a chelating reagent, into the solution of biotin-4-fluorescein/Pb²⁺ resulted to the rebound of the color to the original color of free biotin-4-fluorescein. The fluorescence spectra of fluorescein decreased with increasing Pb²⁺concentration, and the quenching was enhanced at higher pH. The association constant (K_a) of 2.00 × 10⁴ M^-1 was calculated from the fluorescence spectra with the limit of detection (LOD) and the limit of quantitation (LOQ) of 1.38 × 10^-5 M (2.86 ppm) and 4.61 × 10^-5 M (9.55 ppm), respectively. Job's plot analysis indicated 2:1 ratio of binding interaction. Pb²⁺ in untreated wastewater was quantified for 24.99 ppm using this method. This quick analysis can be beneficial for the application of lead detection in real sample solutions, such as wastewater from industrial factories.