doi:10.1038/nindia.2009.14 Published online 29 January 2009
An organic layer smeared upon a field effect transistor can help sniff explosives1. Known as organic field effect transistor (OFET), it can detect vapours of explosives like TNT and RDX. The research could help develop a prototype for explosive detection.
Field effect transistors modified with organic molecules and polymers have gained importance for sensing gases. Driven by this trend, the researchers made a composite of poly (3- hexylthiophene) (P3HT) and copper-tetraphenylporphyrin (CuTPP). The composite of these compounds was dissolved in chloroform and spin coated to form a thin layer of semiconducting organic material. This was laid on the transistor.
The modified transistors were exposed to saturated vapours of RDX (1,3,5-trinitro-1,3,5-triazacyclohexane) and TNT (2,4,6-trinitrotoluene). Current and conductance were measured for each sensor before and after exposure to explosive vapours. For transistors, appreciable changes in current and conductance were observed on exposure to TNT as well as RDX vapours.
The study found that P3HT alone does not have enough sensitivity for use with explosives. It needs to be mixed with compounds like CuTPP. Superior sensor response in this case could be due to the well-known strong tendency to form bonding between the metalloporphyrin molecule and the nitro group of the explosives.
"As it will be small in size and easy to process, it is easy to electrically network such sensors," says lead researcher V. Ramgopal Rao.