Nanoparticles Sense Ultralow Levels Of Toxic Ions

An electronic sensor coated with patterned nanoparticles can detect concentrations of the toxic ion methylmercury down to attomolar (10^–18 M) levels in water (Nat. Mater., DOI: 10.1038/nmat3406). This detection limit—about 600 methylmercury cations per mL of solution—is far below what other analytical methods, such as atomic fluorescence spectroscopy, can achieve, according to the research team that designed the sensor. To fabricate the device, Bartosz A. Grzybowski of Northwestern University; Francesco Stellacci of the Swiss Federal Institute of Technology, Lausanne; and colleagues produced gold nanoparticles covered with alternating rows of short and long molecular bristles: n-hexanethiols and n-hexanethiols tipped with polyethylene glycol units. The team cast a film of the particles onto a glass substrate between two electrodes. When dipped into water containing methyl­mercury, the particles selectively trap the cations among their bristles. After the sensors are dried, the researchers measure this capture via an increase in conductance across the films. The researchers tested their sensors on water from Lake Michigan and on fish collected in Everglades National Park. The methylmercury levels determined from the sensor data agreed within error to published values for the lake and values measured by the U.S. Geological Survey for the fish.