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

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