Biosensor for rapid detection of organophosphate insecticides
A potentially portable and simple way to detect compounds such as parathion.
A simple, reusable, and portable biosensor with a fast response that can detect less than 1 part per billion (ppb) of some commonly used organophosphate insecticides could ease the task of detecting such pesticides. The biosensor, which is described in research posted to ES&T’s Research ASAP website (es050720B), can selectively detect organophosphate insecticides, such as parathion, methyl parathion, and ethyl parathion, which are widely used both legally and illegally throughout the world.
Although methyl parathion is regulated in the U.S., its illegal use led to a series of poisonings in the 1990s. Even today, methyl parathion use is often not well controlled in the developing nations, and this leads to recurrent poisonings. A biosensor “that is potentially inexpensive to produce and can be formatted for a very easy yes/no answer at certain threshold limits can be very easily and conveniently adapted to measure these insecticides in third-world countries,” says Kim Rogers, a biosensor expert with the U.S. EPA.
Current analysis methods for these organophosphates are less selective, less sensitive, or require extensive sample preparation, according to corresponding author Ashok Mulchandani of the University of California, Riverside.
The new biosensor uses whole-cell Pseudomonas putida, engineered to produce on its surface a key enzyme that breaks down organophosphates. Along with another naturally-occurring enzyme on the surface, these organophosphates are converted into a detectable, electrochemically active intermediate.
“Because of its use of genetically engineered organisms, this is an incremental but significant advance in microbial biosensors for organophosphate compounds,” says Rogers. He adds that having the two enzymes expressed extracellularly decreases the response time and increases sensitivity.
Each analysis takes less than 5 minutes, and the same sensor can be used up to 20 times by merely rinsing it in between measurements, according to the authors. It is a one-step assay system that is “small [and] potentially portable, and the detection element can either be reused a number of times or it can be built in a disposable fashion so that you can throw it away and clip a new one on,” adds Rogers.
Because the biosensor only measures one class of organophosphate insecticides, Mulchandani and Rogers both think that the sensor will be most effective when combined with an initial screening assay. “My feeling is that this assay should be used in combination with cholinesterase inhibition assays,” says Rogers. Multistep cholinesterase inhibition assays are used to screen for a broad spectrum of agents that damage the nervous system but cannot identify specific chemicals.
