doi:10.1038/nindia.2013.37 Published online 19 March 2013
Researchers have developed a new biosensor that can detect extremely low concentrations of bilirubin, an orange-yellow pigment in blood whose levels increase dramatically in various diseases such as jaundice and sickle-cell anaemia1.
In humans, older red blood cells are continuously destroyed and haemoglobin degrades into heme and globin. The heme part is converted to biliverdin, a green pigment, which is rapidly reduced to bilirubin. This bilirubin is normally excreted in bile and urine. As some diseases shoot up bilirubin levels abnormally, there is a strong need to monitor serum bilirubin. Most current methods for measuring blirubin levels are time-consuming and some devices are not stable.
To design an effective and simple bilirubin sensor, the researchers modified a gold electrode with a nanocomposite film made from zirconium dioxide, silica nanoparticles and chitosan — a biopolymer. They then dipped the electrode in a solution containing the enzyme bilirubin oxidase (BOx). Bilirubin present in clinical samples binds to the bilirubin oxidase, an enzyme that converts bilirubin to biliverdin.
Eletrochemical studies were carried out on blood samples from jaundice patients and healthy individuals. The current increased linearly with the bilirubin concentration. The biosensor responded within 2 seconds and remained stable over a period of four months when stored at 4°C. Furthermore, the biosensor selectively detected bilirubin even in the presence of interfering biological molecules such as uric acid, ascorbic acid, glycine and creatinine.
"This biosensor offers a simple, highly sensitive way to determine bilirubin levels in serum samples in hospital and diagnostic laboratories for diagnosing jaundice," says lead researcher C. S. Pundir.