Although multiple methods have been developed to detect metal cations, only a few offer sensitivities below 1â €‰pM, and many require complicated procedures and sophisticated equipment. Here, we describe a class of simple solid-state sensors for the ultrasensitive detection of heavy-metal cations (notably, an unprecedented attomolar limit for the detection of CH 3 Hg + in both standardized solutions and environmental samples) through changes in the tunnelling current across films of nanoparticles (NPs) protected with striped monolayers of organic ligands. The sensors are also highly selective because of the ligand-shell organization of the NPs. On binding of metal cations, the electronic structure of the molecular bridges between proximal NPs changes, the tunnelling current increases and highly conductive paths ultimately percolate the entire film. The nanoscale heterogeneity of the structure of the film broadens the range of the cation-binding constants, which leads to wide sensitivity ranges (remarkably, over 18 orders of magnitude in CH 3 Hg + concentration).
Bibliographical noteFunding Information:
This work was supported by the Non-equilibrium Energy Research Center, which is an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences under grant number DE-SC0000989. E.S.C. and F.S. acknowledge the support of ENI within the MIT Energy initiative for their work. E.S.C. is supported by a Samsung Scholarship from the Samsung Foundation of Culture. H.J., S.C.G. and F.S. acknowledge support from the Defense Threat Reduction Agency under Grant No. HDTRA1-09-1-0012. T.M.H. is financially supported by the Human Frontier Science Program. We acknowledge L. Meda for her X-ray photoelectron spectroscopy measurements, and R. Borrelli and P. Cesti for helpful discussions. We also thank the USGS for providing fish samples and for helpful discussions.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering