doi:10.1038/nindia.2014.49 Published online 16 April 2014
Researchers have developed a sensitive sensor that can detect extremely low concentrations of polyphenols — a major source of dietary antioxidants . They made the biosensor from cadmium–telluride quantum dots and a copper-containing enzyme (laccase).
The researchers wanted to devise a simple, sensitive and cost-effective technique to measure polyphenols, the most abundant antioxidants in human diet. Polyphenols have anticancer properties and provide protection against DNA damage. They fabricated the biosensor by smearing the enzyme laccase on cadmium-telluride quantum dots. They tested the sensor's efficacy in detecting dietary polyphenols such as catechin, epicatechin and epigallocatechin gallate.
On exposure to polyphenols, the enzyme attached to the biosensor converts polyphenols to mono- or polyquinones. This reaction transfers electrons from quantum dots to quinone molecules, turning off the fluorescence of the quantum dots — a process known as fluorescence quenching. Quenching of quantum dots increased with increasing polyphenol concentration.
The biosensor could measure polyphenol levels between 1 and 100 nanogram/millilitre (ng/ml). The tested polyphenols had different fluorescence quenching profiles, enabling selective detection of individual polyphenols down to 1 ng/ml.
The human diet also contains metal ions, which can interfere with the detection of polyphenols. The biosensor was able to detect polyphenols even in the presence of metal ions. "The biosensor could be used for monitoring antioxidants at cellular levels," says M. S. Thakur, a senior co-author of the study.