A Fluorescence Strategy for Silver Ion Assay via Cation Exchange Reaction and Formation of Poly(thymine)-templated Copper Nanoclusters

Cascade signal amplification using Hg2+-induced oxidation of silver nanoparticles and cation exchange reaction for ICP-MS bioassay

Combining the Hg2+-induced oxidization of silver nanoparticles with the cation exchange reaction between Ag+ and CuS nanoparticles for cascade signal amplification, a sensitive, universal and label-free ICP-MS bioassay for nucleic acids and proteins was developed. By replacing the loop sequence of the T-Hg-T hairpin structure with specific sequences or aptamers to different biomarkers, it has great promise for the early detection of biomarkers potentially for diagnosis of cancerous diseases.

Recyclable fluorescence sensing based on copper clusters for simultaneous determination of copper ions and ammonia

A one-step strategy for synthesizing fluorescent copper clusters stabilized by L-cysteine has been successfully established in aqueous solutions. The direct determination of copper ions was realized by the fluorescence enhancement phenomenon caused by the preparation and aggregation process. At the same time, ammonia treatment can lead to rapid fluorescence quenching, resulting from the influence on the aggregation behavior of Cu clusters, while the fluorescence can be recovered by the continuous addition of copper ions. Therefore, a recyclable fluorescence sensing system is constructed for the simultaneous determination of copper ions and ammonia. This method is simple, anti-interference and has been successfully applied to the determination of environmental samples.

Detection of silver through amplified quenching of fluorescence from polyvinyl pyrrolidone-stabilized copper nanoclusters

Silver ion detection with ultra-high sensitivity was established. We synthesized copper nanoclusters (CuNCs) with blue fluorescence through a one-pot process. Instead of a direct quencher toward the CuNCs, silver ions activated the strong oxidation from persulfate and subsequently converted divalent manganese ion into manganese dioxide (MnO₂). The surface charges of MnO₂ and the CuNCs brought them together and quenched the fluorescence from the latter. Due to silver ions' role as the catalyst in the process, it cycled and even a small amount leads to a significant fluorescence change. This signaling provided the determination of  silver ions in the range 5 pM~1 nM, with a detection limit of  1.2 pM. The method is selective, and its applicability was validated through practical water sample analyses.

Bright fluorescent nucleic acid detection with CRISPR-Cas12a and poly(thymine) templated copper nanoparticles

Fluorescence-based diagnostic tools are attractive and versatile tests with multiple advantages: ease of use, sensitivity and rapid results. The advent of CRISPR-Cas technology has created new avenues for the development of diagnostic testing tools. In this study, by effectively combining the specific functions of two enzymes, CRISPR-Cas12a and terminal deoxynucleotidyl transferase (TdT), we developed a DNA detection assay that generates copper nanoparticles (CuNPs) that are easily visible to the naked eye under UV-light; we named this detection assay Cas12a Activated Nuclease poly-T Reporter Illuminating Particles (CANTRIP). Upon specific target DNA recognition by Cas12a, single-stranded DNA (ssDNA) reporter oligos with blocked 3'-ends are cut into smaller ssDNA fragments, thereby generating neo 3'-hydroxyl moieties. TdT subsequently elongates these newly formed ssDNA fragments, incorporating only dTTP nucleotides, and these poly(thymine)-tails subsequently function as scaffolds for the formation of CuNPs. These CuNPs produce a bright fluorescent signal upon UV excitation, and thus, this bright orange signal indicates the presence of target DNA, which in this proof-of-concept study consisted of anthrax lethal factor plasmid DNA. CANTRIP, which combines two detection platforms consisting of CRISPR-Cas12a and fluorescent CuNPs into a single reaction, appears to be a robust, low-cost and simple diagnostic tool.