Abstract
A novel colorimetric assay employing oligonucleotide-conjugated gold nanoparticle (AuNP probes) and rolling circle amplification (RCA) was developed for simple detection of mercuric ions (Hg2+). The thymine-Hg2+-thymine (T-Hg2+-T) coordination chemistry makes our detection system selective for Hg2+. In the presence of Hg2+, the thymine 12-mer oligonucleotide is unable to act as a primer for RCA due to the formation of T-Hg2+-T before the RCA reaction. However, in the absence of Hg2+, DNA coils as RCA products are generated during the RCA reaction, and is further labeled with AuNP probes. Colorimetric signals that depend on the amount of DNA coil-AuNP probe complexes were generated by drop-drying the reaction solution on nitrocellulose-based paper. As the reaction solution spread radially because of capillary action, the complexes formed a concentric red spot on the paper. The colorimetric signals of the red spots were rapidly measured with a portable spectrophotometer and determined as the ΔE value, which indicates the calculated color intensity. Our assay displays great linearity (detection limit: 22.4 nM), precision, and reproducibility, thus demonstrating its utility for Hg2+ quantification in real samples. We suggest that our simple, portable, and cost-effective method could be used for on-site Hg2+ detections.
Highlights
Mercury is one of the most toxic heavy metals, representing a severe threat to the global environment and human health [1]
The strategy of the radial flow assay for sensing Hg2+ is shown in Figure 1 and is based on the assembly of AuNPs bound with DNA coils, which are generated by rolling circle amplification (RCA)
Detection sensors, the RCA reaction is driven by the linking of a padlock probe that is dependent on the presence of a detection target [37,38,39,40]
Summary
Mercury is one of the most toxic heavy metals, representing a severe threat to the global environment and human health [1]. The most common methods currently used for mercury detection include inductively coupled plasma–mass spectrometry (ICP-MS) [5], atomic absorption spectroscopy (AAS) [6], and gas chromatography (GC) [7] These methods can detect a wide range of metal ions with high sensitivity and selectivity, they require expensive and sophisticated equipment, trained personnel, and time-consuming and labor-intensive procedures. To overcome these drawbacks, a variety of sensor approaches using nanomaterials for fluorescent detection of Hg2+ [8,9,10,11] have emerged due to its capabilities for sensitivity, selectivity, reproducibility, and rapid real-time monitoring [12]. Guidelines for Drinking-Water Quality; World Health Organization: Geneva, Switzerland, 2005.
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