Liquid crystal-based sensing platform for detection of Pb²⁺ assisted by DNAzyme and rolling circle amplification

Lead ions (Pb²⁺) are one of the most widespread heavy metal contaminants that pose detrimental impact on environment and human health. We demonstrate a highly sensitive and specific liquid crystal (LC)-based sensing platform for detecting Pb²⁺ assisted by DNAzyme and rolling circle amplification (RCA). Magnetic beads (MBs) are functionalized with DNA duplexes of the catalytic strands (DNAzymes) and the substrate strands. In the presence of Pb²⁺, the substrate strands are disassembled due to activation of the DNAzyme, which allows initiation of DNA RCA on MBs. The amplified DNA strands can disrupt arrangement of octadecy trimethyl ammonium bromide monolayers (OTAB), thereby inducing planar orientation of LC molecules at the interface of aqueous and LCs. Thus, LCs exhibit bright appearance. In contrast, RCA cannot be triggered in the absence of Pb²⁺. Therefore, LC molecules adopt perpendicular orientation at the interface, which induces the dark morphology of LCs. The limit of detection reaches as low as 16.7 pM. It is an improvement of more than two orders of magnitude compared to that of previously reported LC-based sensing approaches. This approach also shows excellent performance in monitoring Pb²⁺ in tap water and lake water.