Electrochemiluminescent detection of Hg(II) by exploiting the differences in the adsorption of free T-rich oligomers and Hg(II) loaded T-rich oligomers on silica nanoparticles doped with Ru(bpy)₃²⁺

The detection scheme for Hg(II) ions described here is based on the finding that nanoparticles (NPs) prepared from silica and chitosan, and doped with the ruthenium(II) bipyridyl complex [Ru(bpy)₃²⁺] display large differences in their affinity for T-rich oligomers and Hg(II)-loaded T-rich oligomers. The effect was exploited to design a sensitive electrochemiluminescence (ECL) based assay for Hg(II). In the absence of Hg(II), the oligomers (with 40 bases) strongly bind to the surface of the NPs. Such oligomer-loaded NPs do not bind to a glass carbon electrode (GCE) modified with carbon nanotubes (CNT) in a nafion host matrix. If, however, Hg(II) is present, it will cause the formation of Hg(II)-loaded double-stranded oligomers via T-Hg-T duplexes which are not easily adsorbed on the doped silica NPs. Such NPs are readily assembled on the GCE and this will result in strong ECL. The increase in ECL intensity is a viable parameter for detection of Hg(II) with a detection limit as low as 0.3 pM. Such as sensitivity has not been accomplished in previously reported ECL based methods for detecting Hg(II). In our perception, the method based on differential adsorption presented here is not limited to the detection of Hg(II) but represents a method of wider scope in that other analytes may be detected by this method if respective oligomer probes are available. (author)