Lateral flow test for visual detection of silver(I) based on cytosine-Ag(I)-cytosine interaction in C-rich oligonucleotides

The authors describe an oligonucleotide-based lateral flow test for visual detection of Ag(I). The assay is based on cytosine-Ag(I)-cytosine [C-Ag(I)-C] coordination chemistry to capture gold nanoparticle (AuNP) tags in the test zone. A thiolated C-rich oligonucleotide probe was immobilized on the AuNPs via gold-thiol chemistry, and a biotinylated C-rich oligonucleotide probe was immobilized on the test zone. The AuNPs labelled with C-rich oligonucleotides are captured by Ag(I) ions in the test zone through the C-Ag(I)-C coordination. The resulting accumulation of AuNPs produces a readily visible red band in the test zone. Under optimized conditions, the test is capable of visually detecting 1.0 ppb of Ag(I) which is 50 times lower than the maximum allowable concentration as defined by the US Environmental Protection Agency for drinking water. Hence, the test is inexpensive and highly sensitive. It was applied to the detection of Ag(I) in spiked samples of tap water and river water. In our perception, the test is a particularly valuable tool in limited resource settings.