Getting the lead out
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
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.
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