Chemical Transistor

A new device, the chemical equivalent of a transistor, might make possible ultrasensitive bio-medical single-antigen detection.

The things we associate with transistors, the closing or opening of a switch or the amplification of a signal, are normally carried out by injecting a tiny electric signal into a gate electrode which then changes the environment of a nearby channel region. This allows a current to be shut off or to be amplified. In an experiment carried out by physicists at the University of California at Irvine, the same things are done through chemical reactions.

Philip Collins (collinsp@uci.edu, 949-824-9961) and his colleagues use carbon nanotubes as the central working substance of their device. The nanotubes, immersed in a liquid, can be switched from a conducting state to an insulating state by oxidizing them -- that is, by chemically removing the free electrons. The chemical reactions are triggered by an electrical potential applied across the interaction area (figure at Physics News Graphics).

What the Irvine researchers show is that this process can be performed reversibly and over short periods of time, as fast as 10 microseconds. This is quite slow by today's transistor standards; the more important promise for prospective chemical field effect transistors (or ChemFETs) is the potentially large amplifications. It looks as if only a few electrons' worth of oxidation can be used to switch currents as large as microamps.

In a future bio-detector the switching would be provided not by an applied electrochemical signal but by the trace presence of antigens docking with antibodies attached to the nanotubes. In previous detectors, chemical actuation has required the presence of tens of antigens; here, a single antigen might be enough to change the state of the nanotube.

Mannik et al., Physical Review Letters, 7 July 2006
Contact Philip Collins, University of California at Irvine
collinsp@uci.edu
Tel: 949-824-9961
Image at Physics News Graphics
Philip Collins' Research Group