Development of novel sensors for the detection of lead ions (Pb2+) has attracted increasing interest due to their inherent toxic effects on human health and the environment. In this study, we describe two new polydiacetylene (PDA)-based liposome sensors for the colorimetric and fluorometric recognition of Pb2+ in aqueous solution. In the sensor system, a thymine-1-acetic acid (TAA) or orotic acid (OA) group was reasonably introduced into the diacetylene monomer to work as a strong binding site for Pb2+. The TAA- or OA-functionalized monomer and 10,12-pentacosadiynoic acid (PCDA) were incorporated into PDA liposomes in aqueous solution. After UV light-induced polymerization, deep blue colored liposome solutions were obtained. Upon the addition of a series of transition metal cations into the liposome solutions, only Pb2+ could induce a color change from blue to red observable by the naked eye and a large fluorescence enhancement. The results clearly showed that the PDA-EDEA-TAA and PDA-EDEA-OA liposomes could act as highly selective and sensitive probes to detect Pb2+ in aqueous solution. The detection limits of PDA-EDEA-TAA and PDA-EDEA-OA systems are 38 nM and 25 nM, respectively. The excellent selectivity of PDA liposomes could be attributed to the stronger complexation behavior of Pb2+ with TAA (or OA) and the carboxylic acid at the lipid-solution interface which could perturb the PDA conjugated backbone. In addition, the proposed sensors were successfully applied to detect trace amounts of Pb2+ in real water samples with excellent recovery, indicating that the developed method had a good accuracy and precision for the analysis of trace Pb2+ in practical samples.
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