doi:10.1038/nindia.2013.101 Published online 26 July 2013
Researchers have designed a new kind of biosensor that can detect minute traces of bisphenol-A (BPA), a harmful chemical known to disrupt the human endocrine system . They made the sensor with modified synthetic single-stranded nucleic acid known as aptamer. This sensor will be very useful for detecting BPA and other harmful small molecules in biological and environmental samples.
Aptamers can recognize a wide range of compounds from ions to cells. Aptamers undergo structural changes on binding with target molecules, resulting in a visible colour change. Unlike antibodies, aptamers are highly selective and are stable over a wide range of temperatures. They are economical and can be stored for long periods. Previous studies used nanocomposites of aptamer and gold nanoparticles (GNPs), but making such aptamer–GNP-based sensors requires complex chemical processes.
The researchers developed a simple technique for fabricating aptamer-based sensors by modifying a DNA aptamer with two different dye molecules. One of these dyes emits fluorescence, whereas the other quenches fluorescence. To test the efficacy of this sensor, they exposed it to solutions containing varying concentrations of BPA.
They found a gradual reduction in the emission with increasing BPA concentration of the solution. Binding of BPA with the modified aptamer reduced the fluorescence emission ('turn-off') of the solution. The new sensor had a detection limit of 0.01 picogram/millilitre, which is better than that (0.01 nanogram/millilitre) of aptamer–GNP-based sensors.
"These aptamers can be generated without performing animal-based experiments and can replace the generation of antibodies using animals," says M. S. Thakur, a co-author of the study.