Optofluidics-based DNA structure-competitive aptasensor for rapid on-site detection of lead(II) in an aquatic environment

Lead ions (Pb²⁺), ubiquitous and one of the most toxic metallic pollutants, have attracted increasing attentions because of their various neurotoxic effects. Pb²⁺ has been proven to induce a conformational change in G-quadruplex (G4) aptamers to form a stabilizing G4/Pb²⁺ complex. Based on this principle, an innovative optofluidics-based DNA structure-competitive aptasensor was developed for Pb²⁺ detection in an actual aquatic environment. The proposed sensing system has good characteristics, such as high sensitivity and selectivity, reusability, easy operation, rapidity, robustness, portability, use of a small sample volume, and cost effectiveness. A fluorescence-labeled G4 aptamer was utilized as a molecular probe. A DNA probe, a complementary strand of G4 aptamer, was immobilized onto the sensor surface. When the mixture of Pb²⁺ solution and G4 aptamer was introduced into the optofluidic cell, Pb²⁺ and the DNA probe bound competitively with the G4 aptamer. A high Pb²⁺ concentration reduced the binding of the aptamer and the DNA probe; thus, a low-fluorescence signal was detected. A sensitive sensing response to Pb²⁺ in the range of 1.0–300.0 nM with a low detection limit of 0.22 nM was exhibited under optimal conditions. The potential interference of the environmental sample matrix was assessed with spiked samples, and the recovery of Pb²⁺ ranged from 80 to 105% with a relative standard deviation value of <8.5%. These observations clearly illustrate that with the use of different DNA or aptamer probes, the sensing strategy presented can be easily extended to the rapid on-site monitoring of other trace analytes.