A Sensitive Fluorescence Biosensor for Silver Ions (Ag⁺) Detection Based on C-Ag⁺-C Structure and Exonuclease III-Assisted Dual-Recycling Amplification

Abstract

A C-Ag+-C structure-based fluorescence biosensor with novel combination design of exonuclease III (Exo III) dual-recycling amplification is proposed for the application of silver ions (Ag+) detection. Since oligo-1 involves C-C mismatches, the presence of Ag+ can be captured to form C-Ag+-C base pairs, which results in a double-helix structure with a blunt terminus. The double-helix structure can be cleaved by EXO III to release short mononucleotide fragments (trigger DNA) and Ag+. Released Ag+ can form new bindings with oligo-1, and other trigger DNA can be produced in the digestion cycles. Hybridization with the signal DNA (oligo-2) transforms a trigger DNA into double-stranded DNA with blunt terminus which can be cleaved by Exo III to reproduce the trigger DNA and form guanine- (G-) quadruplex DNA. The trigger DNA returns free to the solution and hybridizes with another signal DNA, which realizes the dual-recycling amplification. The G-quadruplex DNA can be reported by N-methylmesoporphyrin IX (NMM), a specific G-quadruplex DNA fluorochrome. This method allows Ag+ to be determined in the 5 to 1500 pmol/L concentration range, with a 2 pmol/L detection limit, and it has been successfully applied to the detection of Ag+ in real samples.

Short DNA Oligonucleotide as a Ag+ Binding Detector

“…For our designed sequences, all of the binding constants at different temperatures are in the 30–190 nM range. Our method allows Ag + to be detected in 5–500 nM, while the detection range of a newly reported fluorescence biosensor based on exonuclease III enzymatic amplification is 5–1500 pM . However, compared to our simple and rapid detection method, the Ag + analysis based on enzymatic amplification is more time consuming, expensive, and requires more skilled technicians.…”

“…Silver ions (Ag + ) have been known as one of the most hazardous metal pollutants that can be widely distributed in air, water, soil, and even food. − The interaction of Ag + with various metabolites and inactivating sulfhydryl enzymes can cause cytopathic effects in many types of cells including keratinocytes, human tissue mast cells, human gingival fibroblasts, and endothelial cells. − Therefore, developing a sensitive and specific method to detect Ag + is important. Traditional methods for the detection of Ag + such as atomic absorption spectrometry (AAS), , inductively coupled plasma-mass spectrometry (ICP-MS), − and ionic selective electrode (ISE) are expensive and complex . Hence, the need for a rapid and simple method for the detection of Ag + is significant.…”

FRET-Based Genetically Encoded Sensor to Monitor Silver Ions

“…A range of fluorescence-based biosensors has been developed for monitoring silver ions in real samples. A C–Ag + –C structure-based fluorescence biosensor has been developed by Li et al (2019) for the detection of Ag + ions in real samples of lake water and human sera. They used a C–Ag + –C structure with signal amplification using an Exo III-assisted dual-recycling process for the synthesis of the biosensor.…”

Silver–Cytidine Coordination Polymer: Electrical Properties, Modulating Intrachain Ag···Ag Distance, and MOF–Nanosheet Transformation

“…There is renewed interest in the interaction of silver ions with DNA and its components, , primarily due to an emergence of novel analytical and nanotechnological applications. These include quantum-confined optoelectronic materials − and sensors, − plasmonic materials, and thermal stabilization of DNA-based nanostructures. , An important aspect for many of these is the ability to assemble clusters or contiguous arrays of metal ions. High-resolution X-ray crystallography of Ag-bound oligonucleotides ,− as well as small-molecule complexes ,, has shown this is possible through the formation of metal-mediated base pairs.…”