A Fluorescence Sensor for Pb²⁺ Detection Based on Liquid Crystals and Aggregation-Induced Emission Luminogens

Abstract

Heavy metals, such as lead ions, are regarded as the main environmental contaminants and have a negative impact on human bodies, making detection technologies of lead ions critical. However, most existing detection methods suffer from time consumption, complicated sample pretreatment, and expensive equipment, which hinder their broad use in real-time detection. Herein, we show a new fluorescence sensor for detecting lead ions derived from liquid crystals doped with an aggregation-induced emission luminogen. The mechanism is based on the variation of fluorescence intensity caused by the disturbance of an ordered liquid crystal configuration in the presence of Pb 2+ , induced by DNAzyme and its catalytic cleavage. The proposed fluorescence sensor exhibits a low detection limit of 0.65 nM, which is 2 orders of magnitude lower than that previously reported in an optical sensor based on liquid crystals. The detection range of the Pb 2+ fluorescence sensor is broad, from 20 nM to 100 μM, and it also selects lead ions from numerous metal ions exactly, resulting in a highly sensitive, highly selective, simple, and low-cost detection strategy of Pb 2+ with potential applications in chemical and biological fields. This approach to designing a liquid crystal fluorescence sensor offers an inspiring stage for detecting biomacromolecules or other heavy metal ions by varying decorated molecules.

State-of-the-Art Development in Liquid Crystal Biochemical Sensors

“…In the appearance of Pb 2+ , the catalytic hydrolysis of DNAzyme changed the alignment of LC and AIEgen, inducing the fluorescence signal change. This method resulted in better signal contrast and improvement in LOD at 0.65 nM compared to the traditional optical method [ 48 ].…”

Design and Applications of Liquid Crystal Biophotonic Sensors for Ion Detection

“…Aiming at solving the problem of time consumption, a new LC Pb 2+ sensor composed of the LCs and an aggregation‐induced emission (AIE) luminogen has been developed recently (Figure 3c–e). [ 116 ] The sensor shows fluorescence property as the aggregated AIE fluorogens are highly emissive due to the restricted molecule rotation. TPE–PPE is utilized as the AIE material, in which the emission dipole moment along the short‐axis direction is greater than that along the long‐axis direction.…”

“…c-e) The fluorescence signals and molecular arrangements of the LC Pb 2þ sensor based on AIE with and without Pb 2þ . Reproduced with permission [116]. Copyright 2018, Wiley.…”

A highly sensitive fluorescent sensor for ammonia detection based on aggregation-induced emission luminogen-doped liquid crystals

“…Recently, a fluorescent sensor based on LC and AIEgen has been demonstrated by Du et al for lead ion detection with a low detection limit at 0.65 nM. 40 It is expected that by combining the AIEgen with LC, the sensitivity of polarized optical sensors could be greatly improved through the fluorescence signal.…”