Fluorescent disease sniffers
doi:10.1038/nindia.2012.121 Published online 23 August 2012
Researchers have designed a new kind of fluorescent nanosensor that could help detect minute traces of formaldehyde, a colourless but harmful gas. The fluorescence from these nanosensors is enhanced when the enzyme formaldehyde dehydrogenase breaks down formaldehyde in the presence of nicotinamide adenine dinucleotide (NAD), a co-enzyme involved in metabolic pathways.
Besides detecting formaldehyde, these nanosensors could be new diagnostic tools since dehydrogenases are clinically important signature enzymes for diseases such as myocardial infarction, cancer, and malaria.
Formaldehyde is reported to be carcinogenic and is a potent neurotoxin. Formaldehyde releasers are frequently added to consumable items, and may contribute to growth disorders, blindness, and respiratory diseases. Organic fluorescent agents used as sensors are expensive and time-consuming. To devise a cheap and easy technique to detect formaldehyde, the researchers produced cadmium telluride (CdTe) quantum dots (QDs).
Studies have shown that during dehydrogenase-based reactions, NAD is reduced to NADH, with the fluorescence energy transferred to the dots through non-radiative energy transfer. Taking clues from these studies, the researchers studied the efficacy of the quantum dots to detect formaldehyde in the presence of formaldehyde dehydrogenase and NAD. For this, they irradiated the experimental solution with near-ultraviolet light.
They found that the fluorescence intensity of NADH decreased in the presence of the dots, showing efficient energy transfer from NADH. This energy transfer was observed by fluorescence enhancement of the QDs during formation of NADH. The QDs gave off a yellow fluorescence.
The QDs could detect formaldehyde in the range of 1000-0.01 ng/ml, with a detection limit of 0.01 ng/ml.
"These QDs can detect dehydrogenase-dependent analytes more sensitively than existing detection techniques, making them potential candidate for designing ultrasensitive optical probes," says lead researcher M. S. Thakur, from the Central Food Technological Research Institute, Mysore.