Purdue University researchers have developed a modeling technique to study and design miniature biosensors, which could help industry perfect lab-on-a-chip technology for uses ranging from medical diagnostics to environmental monitoring. Biosensors represent a class of portable sensors designed to

capture and detect specific target molecules, allowing the identification of pathogens, DNA, or other substances.

The technique creates a conceptual framework and computational model to show that smaller, nanometer-scale sensors performed more effectively than larger sensors. "Everyone presumes that nanometer-scale sensors are better simply because they are closer to the size of the target molecules," said Ashraf Alam, professor of electrical and computer engineering at Purdue. "What we found, however, was not that smaller sensors are better able to detect target molecules, but that they are better able to capture target molecules. It's not what happens after the molecule is captured that determines how well the sensor works. It's how fast the sensor actually captures the molecule to begin with that matters most."

The new model explains why a single nanotube performs better than sensors containing several nanotubes or flat planar sensors. That's because the single nanotube sensor eliminates a phenomenon called "diffusion slowdown." As a result, target molecules move faster toward single nanotubes than other structures.

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