A turn-on near-infrared fluorescent chemosensor for selective detection of lead ions based on a fluorophore–gold nanoparticle assembly

Abstract

A turn-on fluorescent chemosensor of Pb²⁺ in the near-infrared (NIR) region, which is based on the Pb²⁺-tuned restored fluorescence of a weakly fluorescent fluorophore–gold nanoparticle (AuNPs) assembly, has been reported. In this fluorophore–AuNP assembly, NIR fluorescent dye brilliant cresyl blue (BCB) molecules act as fluorophores and are used for signal transduction of fluorescence, while AuNPs act as quenchers to quench the nearby fluorescent BCB molecules via electron transfer. In the presence of Pb²⁺, fluorescent BCB molecules detached from AuNPs and restored their fluorescence due to the formation of a chelating complex between Pb²⁺ and glutathione confined on AuNPs. Under the optimal conditions, the present BCB–AuNP assembly is capable of detecting Pb²⁺ with a concentration ranging from 7.5 × 10⁻¹⁰ to 1 × 10⁻⁸ mol L⁻¹ (0.16–2.1 ng mL⁻¹) and a detection limit of 0.51 nM (0.11 ng mL⁻¹). The present BCB–AuNP assembly can be used in aqueous media for the determination of Pb²⁺ unlike common organic fluorescent reagents, and also shows advantages of NIR fluorescence spectrophotometry such as less interference, lower detection limit, and higher sensitivity. Moreover, the present method was successfully applied for the detection of Pb²⁺ in water samples with satisfactory results.