A magnetic relaxation switching and visual dual-mode sensor for selective detection of Hg2+ based on aptamers modified Au@Fe3O4 nanoparticles.

The solvated mercuric ion (Hg2+) from industrial pollutants are highly toxic to the ecological environment and human health. Driven by urgent need for the selective and sensitive detection of Hg2+, a magnetic relaxation switching (MRS) based on Fe3O4 nanoparticles (NPs) was designed. Practically, the concentrations of Hg2+ in industrial pollutant is usually much higher than the detection range. Thus, gold nanoparticles (AuNPs) were synthesized on the surface of Fe3O4 NPs to enable the visual detection of Au@Fe3O4 NPs. The presence of Hg2+ in sample can specifically cause the aggregation of Au@Fe3O4-aptamers NPs through T-Hg2+-T base pairs, leading to the change in transverse relaxation time T2 value of detection solution. The MRS sensor showed excellent response for Hg2+ ions in the range of 10 nM-100 nM and 100 nM to 5 μM. A highly sensitive and selective measurement of Hg2+ was obtained with a limit of detection of 2.7 nM. Noticeably, the visual detection can qualitatively analyze the Hg2+ beyond 5 μM by naked eye without advanced instrumentation and skilled operators.