Ultrasensitive electrochemiluminescence detection of mercury ions based on DNA oligonucleotides and cysteamine modified gold nanoparticles probes

A simple and ultrasensitive biosensor for the determination of mercuric ions was developed based on an electrochemiluminescence (ECL) nanoprobe combined with DNA oligonucleotides and cysteamine-gold nanoparticle (AuNP) conjugates. In this work, we designed a rapid and simple assay by using a magnetic platform and avoiding a long and complicated electrode-modifying procedure. Moreover, we greatly improved the assay sensitivity by the employment of AuNPs labelled with a high concentration of ECL signal probes carried by cysteamine. Two types of thymine-enriched single-strand DNA (ssDNA) probes were labelled onto magnetic bead (MB) and AuNP, respectively. Upon addition of mercury ions, the thymine–Hg2+–thymine (T–Hg2+–T) interaction between two ssDNA probes directed the coordination between the AuNPs and MBs and yielded the MB–ECL nanoprobe complexes. These complexes were then captured on an unmodified electrode by magnetic separation and enrichment. Via our custom-built ECL system, a detection limit of 50 pM was achieved. This novel ECL biosensor also exhibited excellent selectivity over a series of interference metal ions, even for an ion concentration 1000 times higher than that of the mercury ions. Given the excellent sensitivity and selectivity of our biosensor, it provides great potential for future applications of mercury ion monitoring.