A new molecular "fishing" technique developed by researchers at Duke University and Duke's Pratt School of Engineering lays the groundwork for future advances in hand-held sensing devices.
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The new technique uses an atomic force microscope (AFM), a device for observing the surface of individual molecules and measuring the force of interactions among them. The AFM includes a tiny cantilever arm with a sharp tip that scans the surface of atomic specimens, and monitoring the deflection of the cantilever provides information about the force of molecular interactions.
The researchers use the AFM's cantilever as a fishing rod, which they bait with a sample of the chemical to be measured in order to catch "fish," actually proteins known to specifically bind the target chemical. They dangle the chemical "worm" in a solution that contains the target chemical and also is stocked with the protein fish. Because the fish are easier to catch with the baited cantilever when there are fewer free worms to compete with, the researchers can quantify the amount of chemical in solution by tallying the number of successful catches.
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In demonstrating the new method using lactose molecules as the worms and a protein called galectin 3 as the fish, the researchers relied on computerized AFM controls to lower the baited cantilever toward the solution a billionth of a meter at a time.
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When galectin 3 fish bound the lactose bait, withdrawal of the cantilever registered a greater force. They repeated the process until the bait had made some form of contact at least 350 times.
They found, as expected, that the probability of binding varied with the concentration of lactose in the solution. At low concentrations, binding occurred with the greatest frequency. As the concentration rose, the likelihood of binding declined. The researchers used that probability of binding to calculate the chemical concentration.
Good news. I think.
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