A cytosine-rich DNA decorated gold nanoparticles surface enhanced Raman-scattering platform for sensitive and selective detection of silver ions.

In this work, we developed a label-free, homogeneous surface-enhanced Raman-scattering (SERS) platform for the rapid, simple and sensitive detection of Ag(+) by using the unmodified gold nanoparticles (AuNPs). It utilizes the different absorption properties of single-strand DNA (ssDNA) and double-strand DNA (dsDNA) on citrate-coated AuNPs and specific interactions between Ag(+) and cytosine-cytosine pairs. In the presence of Ag(+), the structure of ssDNA containing rich cytosine will form a duplex, resulting in the salt-induced aggregation of gold nanoparticles; the corresponding SERS signal transduction can be observed due to the plasmonic coupling of metallic nanoparticles. The assay possesses a superior signal-to-background ratio as high as ∼35.8 with a detection limit of 15 nM. This approach is not only rapid and convenient in operation, but also shows excellent selectivity, which makes it possible to detect Ag(+) in actual samples.

Highly sensitive fluorescent immunoassay of human immunoglobulin G based on PbS nanoparticles and DNAzyme.

This paper reports a highly sensitive fluorescent immunoassay for the detection of human immunoglobulin G based on PbS nanoparticles and DNAzyme. A sandwich immunoassay format was performed on a microtiter plate. Goat anti-human IgG was coated onto the polystyrene microtiter plate. The human IgG analyte was first captured by the goat anti-human IgG, and then sandwiched by a goat anti-human IgG antibody labeled with PbS nanoparticles. After being dissolved with HNO3, the released Pb(2+) made the substrate chain of the DNAzyme labeled with the fluorophore dissociate from the enzyme strand of the DNAzyme labeled with the quencher, which resulted in fluorescence recovery. Then, the human IgG could be detected indirectly from the fluorescent signals. Under the optimized conditions, the linear range of the developed immunosensor was from 1 ng mL(-1) to 10 µg mL(-1) with a detection limit of 0.8 ng mL(-1). This immunosensor could be used to detect the amount of human IgG in human serum samples.