Mechanical valve design goes nano

Building nanoscale devices is tricky because they straddle two worlds, the molecular and the bulk material.

Designing objects on the molecular scale requires mathematical models of the interactions of individual atoms, but even nanoscale devices typically contain thousands of atoms, and modeling that many atoms in detail is mathematically difficult and requires a lot of computing power.

California Institute of Technology researchers used a combination of molecular modeling and classical engineering techniques to design a nanomechanical fluid valve. The device could be used for drug delivery, biological and chemical testing, and fuel delivery for microscale and nanoscale engines.

The valve consists of a single-walled carbon nanotube connected at one end to a fluid reservoir. A silicon cantilever is fixed to the middle of the nanotube and the free end of the cantilever is positioned above the free end of the tube. When the cantilever is deflected, it presses on the nanotube, pinching it closed. A single layer of acrylic acid molecules is affixed to the surface of the cantilever and causes the cantilever to deflect when the pH level of the surrounding environment is high, or basic.

The researchers used classical engineering techniques to approximate the design, and molecular modeling to determine precise values for pinching the nanotube. The prototype designs range from 34.5 to 70 nanometers in length and contain about 75,000 atoms.

High-resolution inkjet printers could be design using the system in about three years, but it is likely to be closer to 10 years before drug delivery applications are practical, according to the researchers.

The work is scheduled to appear in the November issue of Nanotechnology.