Two Indians discover ultra-small pathogen detectors

By agencies   |   Wednesday, 06 September 2006, 19:30 IST
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WEST LAFAYETTE: Amit K. Gupta, a former Purdue doctoral student and presently a postdoctoral researcher at Harvard University and Pradeep R. Nair, a doctoral student in electrical and computer engineering, are among the group of researchers at Purdue University who have discovered the behaviour of tiny structures called ‘nanocantilevers’ that may prove crucial to design a new class of ultra-small sensors for detecting viruses, bacteria and other pathogens. These nanocantilevers, which resemble tiny diving boards made of silicon, have been found to vibrate at different frequencies when contaminants stick to them, thus detecting the presence of dangerous substances. The minute size of the cantilevers is found to be more sensitive than larger devices and promises the development of advanced sensors that detect minute quantities of a contaminant to provide early warnings of the presence of dangerous pathogens. The researchers were surprised to find that different sized cantilevers, when coated with antibodies to detect certain viruses, attracted different densities or quantity of antibodies per area. The devices were immersed into a liquid containing antibodies to allow proteins to stick to its surface. Rashid Bashir, a researcher at the Birck Nanotechnology Center and a professor of electrical and computer engineering and biomedical engineering at Purdue University said that, “Instead of simply attracting more antibodies because they are longer, the longer cantilevers also contained a greater density of antibodies, which was very unexpected.” Engineers discovered the cantilevers to vibrate faster after the antibody attachment when devices had about the same nanometer-range thickness as the protein layer. The longer the protein-coated cantilever, the faster was the vibration, which could be explained only when the density of antibodies were to increase with increasing lengths. Gupta measured the cantilever’s vibration frequency using an instrument named laser Doppler vibrometer. The researchers then treated the antibodies with a fluorescent dye and took images of the proteins on the cantilever’s surface, thus proving that the density increases with longer cantilevers. Nair then teamed up with Ashraf Alam, a researcher at the Birck Nanotechnology Center and professor of electrical and computer engineering, developed a mathematical model to explain why the density increases as the area of the cantilever rises. The model uses a “diffusion reaction equation” to simulate antibodies sticking to the cantilever’s surface. The cantilevers that were used in the studies in the work range in length from a few microns to tens of microns. This would count down to millionths of a meter. They are about 20 nanometers thick that would roughly sum up to the thickness of the antibody coating. The work is being funded by the National Institutes of Health and is aimed at developing advanced sensors capable of detecting minute quantities of viruses, bacteria and other contaminants in the air and fluids by coating cantilevers with proteins, including antibodies that attract the contaminants. Such sensors would have applications in areas including environmental-health monitoring in hospitals and homeland security. Called as the “lab-on-a-chip” technologies, these could possibly replace bulky lab equipment with miniature sensors, saving time, energy and materials. These findings have been detailed in the research paper authored by Gupta, Nair, Bashir, Alam, Demir Akin, research assistant professor of biomedical engineering; Michael Ladisch, Distinguished Professor of Agricultural and Biological Engineering with a joint appointment in the Weldon School of Biomedical Engineering and Steven Broyles, a professor of biochemistry.