Dogs are often used to sniff out the presence of explosives and drugs by the police. Now, at the Electrical Engineering department of Indian Institute of Technology, Bombay, research is on to develop an “electronic nose” which can avoid this altogether. Based on the process of inelastic quantum tunneling, the “nose” can differentiate between molecules based on their vibrational energies.
There are two competing theories that try to explain factional, or the action of smelling – the shape theory and the vibration theory. According to the shape theory, the shape of a particular molecule acts as a “key” and fits into the “lock” in the nose, thereby stimulating it to perceive a smell.
The nose they have proposed is actually a one-dimensional “resonant tunneling diode” – a quantum device that conducts only when it is excited by special discrete values of electrical energy. Essentially this is a modification of a quantum wire a linear array in which the electrons can move in one dimension only.
Making the device involves fabricating a one-dimensional semiconductor device with a double barrier, using standard semiconductor fabrication technology. Normally such vibrational signatures are washed out at higher temperatures, but the paper shows that for the proposed device they would persist at room temperature.