doi:10.1038/nindia.2013.144 Published online 28 October 2013
Researchers have developed a biosensor capable of simultaneously detecting very low concentrations of nitrate and nitrite ions (nitric oxide metabolites) in human plasma, blood and saliva samples, making it potentially useful for diagnosing various diseases .
Nitric oxide regulates various biological processes, including blood vessel relaxation, communication between nerve cells and immune cell function. As it is readily oxidized to nitrate and nitrite ions in the body, nitric oxide levels are generally assessed by measuring the plasma concentrations of nitrate and nitrite ions.
The researchers fabricated an effective and sensitive biosensor for nitrite and nitrate ions by smearing copper, zinc superoxide dismutase and sodium reductase enzymes on a nanocomposite consisting of carbon nanotubes and a polymer called polypyrrole. This nanocomposite was then deposited on a platinum electrode.
The researchers tested the efficacy of the biosensor in measuring the concentrations of nitrate and nitrite ions. They found that the current from the nanocomposite-containing biosensor increased significantly on adding nitrite ions as a result of the nitrite ions being oxidized to nitrate ions. The addition of nitrate ions caused a similar increase in the current of the biosensor through the reduction of the nitrate ions to nitrite ions.
The nanocomposite-containing biosensor showed a much higher current response than a biosensor without the nanocomposite. To test its ability to measure nitrate and nitrite ions in clinical samples, the researchers coated the biosensor with cellulose acetate. The coated biosensor successfully detected nitrate and nitrite ions in human plasma, blood and saliva samples even in the presence of interfering proteins and other biological molecules.
The nanocomposite-containing biosensor retained its activity and stability over a period of four weeks. "Besides measuring nitrate and nitrite ions in clinical samples, the biosensor can also be used for detecting such ions in environmental and agricultural samples," says Chandran Karunakaran, a co-author of the study.