Target-Responsive DNAzyme Cross-Linked Hydrogel for Visual Quantitative Detection of Lead

Abstract

Because of the severe health risks associated with lead pollution, rapid, sensitive, and portable detection of low levels of Pb(2+) in biological and environmental samples is of great importance. In this work, a Pb(2+)-responsive hydrogel was prepared using a DNAzyme and its substrate as cross-linker for rapid, sensitive, portable, and quantitative detection of Pb(2+). Gold nanoparticles (AuNPs) were first encapsulated in the hydrogel as an indicator for colorimetric analysis. In the absence of lead, the DNAzyme is inactive, and the substrate cross-linker maintains the hydrogel in the gel form. In contrast, the presence of lead activates the DNAzyme to cleave the substrate, decreasing the cross-linking density of the hydrogel and resulting in dissolution of the hydrogel and release of AuNPs for visual detection. As low as 10 nM Pb(2+) can be detected by the naked eye. Furthermore, to realize quantitative visual detection, a volumetric bar-chart chip (V-chip) was used for quantitative readout of the hydrogel system by replacing AuNPs with gold-platinum core-shell nanoparticles (Au@PtNPs). The Au@PtNPs released from the hydrogel upon target activation can efficiently catalyze the decomposition of H2O2 to generate a large volume of O2. The gas pressure moves an ink bar in the V-chip for portable visual quantitative detection of lead with a detection limit less than 5 nM. The device was able to detect lead in digested blood with excellent accuracy. The method developed can be used for portable lead quantitation in many applications. Furthermore, the method can be further extended to portable visual quantitative detection of a variety of targets by replacing the lead-responsive DNAzyme with other DNAzymes.

Functional nucleic acid-based hydrogels for bioanalytical and biomedical applications

“…181-183 These nucleic acids have catalytic capability similar to that of protein enzymes and possess the advantages of thermostability, low-cost synthesis and easy modification, making DNAzymes attractive elements for biosensing and biotechnological applications, such as biosensors for metal ions and other molecules, 184-186 components for DNA-based logic gates, 187, 188 components for nanomotors, 189, 190 and building units for nanomaterial assembly, including hydrogels. 191-196 …”

DNAzymes: Selected for Applications

“…In the presence of Pb 2+ , the DNAzyme cleaves the substrate, resulting in disassembly of AuNPs, accompanied by a color change from purple to red. Another interesting example of a colorimetric sensor is based on DNA‐crosslinked hydrogel networks . As shown in Figure B, a special hydrogel is designed to contain the complex of Pb 2+ ‐activated RNA‐cleaving DNAzyme and its substrate as the crosslinker, as well as caged AuNPs.…”

DNAzyme sensors for detection of metal ions in the environment and imaging them in living cells

“…The subsequent release of the embedded gold nanoparticles resulting in a similar change in color, based on detection of the desired metal ion. This hydrogel-DNAzyme-based colorimetric biosensor was demonstrated effectively for sensing lead [82], lanthanide [76] and uranyl ions [73] (Fig. 2B) with 20 and 37 nM LOD values, respectively.…”