Wettability tunable surfaces: Naked-eye detection of Hg2+ based on contact angle variation and colorimetric change

[Display omitted] •Contact angle was introduced as visual signal to detect Hg2+ ions.•Colorimetric change as a second visual signal was used to realize on-site detection of Hg2+ ions.•Silver nanoparticles modified hydrophobic nanopin surfaces were constructed for naked-eye detection of Hg2+ ions. Developing multiple visual signals to reveal comprehensive information of metal ions with simplest operations is attractive and significant for on-site detection. In this paper, wettability tunable surfaces were fabricated to selectively detect Hg2+ ions based on contact angle (CA) variation and colorimetric change. Firstly, hydrophobic nanopin surfaces were fabricated through a chemical bath deposition method and fully characterized by FTIR, XRD, SEM and TEM. Then chitosan stabilized silver nanoparticles (AgNPs) were deposited onto the hydrophobic surfaces to introduce reactants for detecting metal ions. By varying the concentration of AgNPs, the surface wettability can be regulated and the CA are tuned ranging from 152.1 ± 1.0° to 128.9 ± 0.6°. As addition of Hg2+ ions, the CA of AgNPs modified hydrophobic surfaces decrease obviously and surface color changes from brown to white, which are attributed to the vanishment of AgNPs based on the redox reaction between AgNPs and Hg2+ ions and the simultaneously destruction of the nanopin surface structure. A linear relationship between the CA changes and Hg2+ concentration was achieved over the range of 10−6 M–10−2 M and the limit of detection (LOD) is calculated to be 2.6 × 10−7 M. In addition, this strategy was also applied to detect Hg2+ in the real water samples with recoveries ranged from 98.0% to 107.0%. This method introducing both CA variation and colorimetric change as signals provides a new avenue for developing multiple on-site detection signals of metal ions by naked-eye.