Getting the lead out

David Shenkenberg

Lead can kill people and poison the environment, but existing techniques can measure only total lead content. In principle, fluorescent chemosensors can provide information on exchangeable lead pools with spatial and temporal resolution, but these molecules cannot function in water or in living cells. Assistant professor Christopher J. Chang and colleagues at the University of California, Berkeley, have developed a fluorescent sensor, called Leadfluor-1, that detects lead in water and living cells.

The researchers report in the July 26 issue of the Journal of the American Chemical Society that they combined a fluorescein scaffold with a dicarboxylate pseudocrown receptor to create the sensor. They chose the receptor because it satisfied the size and charge requirements of the lead cation. The Leadfluor-1 emission spectra remained similar to that of fluorescein, which has visible excitation and emission spectra that do not damage cells, as do UV and infrared. Also, certain molecules in cells exhibit autofluorescence upon exposure to the invisible part of the spectrum, and fluorescein’s spectral properties avoid that problem. Furthermore, viewing its fluorescence does not require a special detector.

The fluorescence intensity of Lead-fluor-1 increased by up to 18 times in the presence of lead. The fluorescence rose 15 percent, with an error of 2 percent, upon the addition of 15 parts-per-billion of lead in drinking water, the maximum amount allowed by the FDA. Treatment with the chelator TPEN returned the fluorescence to within 5 percent of baseline levels. The researchers tested the response of the sensor to other biologically relevant ions, and it demonstrated selectivity for lead.

The lab plans to further modify Leadfluor-1 so that it emits more brightly and exhibits a greater dynamic range, so as to increase its sensitivity and selectivity for lead.