Mercury Ion Detection based-on Organic-Inorganic or Bio-Inorganic Hybrid Nanomaterials

Abstract

We have developed simple mercury sensor systems based-on organic-inorganic hybrid nanomaterials, and bio-inorganic hybrid nanomaterials. First method is a heterogeneous colorimetric sensor based on azo-coupled macrocyclic receptor grafted onto the surface of silica nanotube (SNT-1). Upon the addition of Hg2+ in suspension SNT-1 resulted in a color change from yellow to violet. On the other hand, no significant changes in color were observed in the parallel experiments with other metal ions. More interestingly, after addition of NO3– and ClO4– SNT-1 was observed to change color from yellow to violet and pink, respectively. However, no color changes were observed upon addition of Cl–, Br–, I–, SCN–, or SO4 2–. Second method is a homogeneous fluorescence sensor based on the Hg2+ induced conformational change of a thymine (T)-rich ssDNA. QDs conjugated ssDNA was adsorbed on AuNP surface by electrostatic interaction, subsequently the fluorescence of QDs was quenched by AuNPs due to close proximity of QDs to AuNPs. In the presence of Hg2+, the QDs conjugated ssDNA was detached from AuNPs by Hg2+ induced conformational change of ssDNA consequently the fluorescence of QDs was recovered. In this study, some parameters (i.e. molar ratio of QDs to AuNPs and spacer size of ssDNA) were optimized to increase the quenching effect of QDs by the strong interaction of QDs conjugated ssDNA to AuNPs. The fluorescent intensity of QDs was proportional to the concentration of Hg2+ in a range of 5 to 75 μM, and the limit of detection was about 5 μM (1 ppm). In control experiment, the increasing of fluorescence in the presence of other metal ions was not observed.