DNA sniffs pesticides
doi:10.1038/nindia.2008.213 Published online 29 May 2008
A new sensor that can detect minute amounts of toxic organophosphate insecticides promises to be a boon for screening of environmental samples such as drinking water, wastewater and industrial effluents. The sensor that can track chlorpyrifos and malathion has been developed using a conducting polymer and nucleic acid.
There are a host of enzyme-based biosensors to detect chemical toxins including organophosphates. These biosensors have longer response time, poor stability and low sensitivity. But to get easy-to-craft and selective biosensors with faster response time, researchers turned to DNA biosensors.
The researchers made a composite film mixing polyaniline (PANI), a conducting polymer, and poly vinyl sulfonate (PVS) with indium-tin-oxide. They electrochemically trapped double-stranded calf thymus DNA on the composite film. This worked as a bioelectrode to detect chlorpyrifos and malathion.
The detection limit of these DNA entrapped bioelectrodes was studied in different concentrations of chorphyrifos (0.5-200 ppb) and malathion (0.005-10 ppm). The study found decrease in DNA oxidation peak current with increasing chlorpyrifos concentrations. The oxidation current of the DNA (guanine) decreased as malathion concentration increased.
"The uniqueness of this biosensor is that it responds in about 30 seconds," says lead researcher Bansi Dhar Malhotra. The biosensor has been found to be stable for six months with low detection limit for chlorpyrifos (upto 0.5 ppb) and malathion (0.01 ppm), he added.
- Prabhakar, N. et al. Improved electrochemical nucleic acid biosensor based on polyaniline-polyvinyl sulphonate. Electrochim. Acta. 53, 4344-4350, (2008)