A facile and sensitive electrochemiluminescence biosensor for Hg2+ analysis based on a dual-function oligonucleotide probe

In this study, a sensitive electrochemiluminescent (ECL) biosensor for the detection of Hg2+ was easily prepared by self-assembling mercury-specific oligonucleotide on the surface of gold nanoparticles (AuNPs) modified indium tin oxide (ITO) electrode. A conformation change of the oligonucleotide from linear chain to hairpin occurs upon the binding of Hg2+ through thymine-Hg2+-thymine coordination. The dual-function oligonucleotide serves as the probe to Hg2+ but also a carrier of signal-generating molecules, [Ru(bpy)2(dppz)](BF4)2. It was estimated that one oligonucleotide was able to load with eight ECL signal molecules; a ratio of four or five oligonucleotides per gold nanoparticle was obtained basing on the calculation with surface density. Without tedious multiple-labeling procedures and special modification of oligonucleotide probe for signal transduction/amplification, a detection limit of 5.1 pM Hg2+ was outstanding from the interference of other ten metal ions. Results of spiked water samples were in good agreement with that obtained by atomic fluorescent spectrometry.