Ultra-Small Sensors Detect Microorganisms

Tiny structures called nanocantilevers could be used in detectors of bacteria, viruses, and other pathogens, because they vibrate at different frequencies when contaminants stick to them.

Because of the minute size of the nanocantilever, it is more sensitive than larger devices, and could be incorporated in detectors of contaminants that provide early warning of the presence of dangerous pathogens. Scientists at the Birck Nanotechnology Center at Discovery Park, Purdue University (West Lafayette, IN, USA), found that the cantilevers, coated with antibodies to detect certain viruses, attract different densities--or quantity of antibodies per area--depending on the size of the cantilever. The devices were immersed into a liquid containing the antibodies to allow the proteins to stick to the cantilever surface.

"Instead of simply attracting more antibodies because they are longer, the longer cantilevers also contained a greater density of antibodies, which was very unexpected,” said Rashid Bashir, professor of electrical and computer engineering as well as biomedical engineering at Purdue University. The density was greater toward the free end of the cantilevers. The engineers found that the cantilevers vibrate faster after the antibody attachment if the devices have about the same nanometer-range thickness as the protein layer. Moreover, the longer the protein-coated nanocantilever, the faster the vibration, which could only be explained if the density of antibodies were to increase with increasing lengths, said Prof. Bashir.

Thousands of the cantilevers can be fabricated on a one square-centimeter chip, noted Prof. Bashir. The cantilevers studied ranged in length from a few microns to tens of microns, or millionths of a meter, and were about 20 nm thick, which is also roughly the thickness of the antibody coating. A nanometer is a billionth of a meter, or approximately the length of 10 hydrogen atoms strung together.

The findings were described in the August 28, 2006, online issue of the Proceedings of the [U.S.] National Academy of Sciences (PNAS). The scientists intend to develop advanced sensors capable of detecting minute quantities of viruses, bacteria, and other contaminants in air and fluids. These sensors will have applications in areas such as environmental-health monitoring in hospitals and homeland security. So-called "lab-on-a-chip” technologies could make it possible to replace bulky lab equipment with miniature sensors, saving time, energy and materials.



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Birck Nanotechnology Center