Researchers have designed a novel biosensor from cells of onion scales. The biosensor could be useful for detecting methyl parathion, a harmful pesticide widely used in agriculture1.
Organophosphorous pesticides such as methyl parathion degrade into products that are harmful to mammals. Such pesticides are usually detected using biosensors made by smearing enzymes or microbial cells on porous surfaces of a glass fibre or synthetic membrane.
Unfortunately, enzymes or microbial cells are only weakly adsorbed to such synthetic surfaces. Dipping the sensor in a pesticide-containing solution washes out the enzymes or microbial cells, making the device unfit for reuse.
To overcome this drawback, the researchers identified a host of new polymers in the cell walls of the inner epidermis of onion scales. They found polymers such as polygalacturonic acid, hemicelluloses, proteins and phenolics, including lignin. The researchers smeared cells of Sphingomonas sp. , a naturally occurring aerobic bacteria, onto the inner epidermis of onion scales. The natural polymers of onion then adsorbed and cross-linked with the bacterial cells.
A microplate with 96 reaction vessels containing samples of methyl parathion was connected to an optical transducer linked to a computer for monitoring and detecting multiple pesticide samples. The bacterial cells secreted an enzyme that converted methyl parathion into para-nitrophenol, which, through the optical transducer, yielded a detectable signal on the computer.
The biosensor could be reused reliably up to 52 times. The researchers say that this is the first report of exploiting onion scales as a reusable biocomponent in a biosensor application.