Mussel inspired redox surface for one step visual and colorimetric detection of Hg2+ during the formation of Ag@DOPA@Hg nanoparticles

Abstract

Inspired by the bioadhesive and redox properties of the 3,4-dihydroxy-phenylalanine (DOPA) contained in marine mussels, a facile, rapid and economic colorimetric strategy for Hg²⁺ detection was developed. The abundant catechol chains on the surface of Ag@DOPA can reduce Hg²⁺ to Hg⁰ and form a Ag@DOPA@Hg nanostructure with the deposition of Hg⁰. The nanostructures of Ag@DOPA and Ag@DOPA@Hg were confirmed by X-ray photoelectron spectroscopy, transmission electron microscopy, elemental mapping and Fourier transform infrared spectroscopy. The formation of the Ag@DOPA@Hg nanostructure causes a change in the color of the Ag@DOPA colloids from golden yellow to purple blue, making it directly possible to detect Hg²⁺ using a colorimetric strategy within 5 minutes. With increasing concentrations of Hg²⁺ from 10 nM to 4 μM, the surface plasmon resonance absorbance peak of the Ag@DOPA colloids decreased in intensity and exhibited a good linear relationship with the Hg²⁺ concentration. The limit of detection was determined as 5 nM. Furthermore, this response was found to be highly selective for Hg²⁺ as the absorption spectrum was not affected by other metal ions such as Pb²⁺, Cr³⁺, Cu²⁺, Al³⁺, Ni²⁺, Co²⁺, etc. The excellent stability, selectivity and sensitivity of this strategy offer analytical practicability for Hg²⁺ detection in real water samples with recoveries in the range of 104–105% and cosmetic samples with recoveries in the range of 85–103%.