Scientists from Cornell and Tel Aviv universities have created a nanoelectromechanical system (NEMS) that can be used to sense the presence of very small concentrations of chemicals and microorganisms. Using an oscillating cantilever that wobbles at predictable frequencies depending on what is placed on it, the researchers are able to detect the nature of the object in the sensor. By generalizing the process and grouping large numbers of these cantilever systems together, they should be able to create a multipurpose sensor that can detect a wide range of pathogens and varying chemicals.
In past research, the team has demonstrated that by treating the cantilever with different substances, they can tell what other substances are present. For example, E. coli antibodies attached to the cantilever can detect the presence of E. coli in water.
The researchers have perfected the oscillators’ design, Ilic [Rob Ilic, research associate at the Cornell NanoScale Science and Technology Facility] said, by laying their device on top of a layer of silicon dioxide, all of which rest on a silicon substrate. A pad with holes connects pegs of silicon dioxide, lined up like telephone poles, which eventually end at the cantilever.
A laser beam, switched on at the far end from the cantilever, travels down the device and causes the oscillator to wobble. The frequency is then measured by shining another laser on the oscillator and noting patterns in the reflected light.
The “telephone poles” allow the energy to move efficiently across the device by preventing it from buckling or sagging. The design makes it easy to read the resonant frequency of the cantilever.
In this process, the researchers discovered that over short distances, the energy from the laser came in the form of heat, which quickly dissipates. But when the laser was parked hundreds of microns away from the cantilever, the energy came in the form of acoustical waves that traveled through the device, dissipated more slowly, and allowed them to make their device longer.
Image: The nanoelectromechanical oscillator with the cantilever on the far right. The inset is a tilted 3-D profile of the structure, which shows the silicon dioxide posts.
Abstract in Journal of Applied Physics: Theoretical and experimental investigation of optically driven nanoelectromechanical oscillators
Press release: Nanoelectromechanical oscillators could lead to detection of harmful molecules, bacteria …