US scientists have developed a new sensor capable of detecting trace levels of a lethal neurotoxin. The sensor is quicker and more sensitive than the mouse bioassay currently used for detecting the toxin and, unlike the bioassay, does not require animal sacrifice.

David Beebe and colleagues at the University of Wisconsin-Madison designed a portable microfluidic device that can detect botulinum toxin A (BoNT/A). Although known for its use in Botox cosmetic treatments, BoNT/A is one of the most poisonous naturally occurring substances - eating around 70 micrograms can kill the average person. It causes the muscle paralysis illness botulism, which poses a serious bioterrorism threat. Many people can be affected by a single contaminated food source so a quick and effective detection method is required.

The toxin-specific beads in the botulinum sensor react with a BoNT/A solution to release fluorescently labelled fragments

Beebe's sensor contains toxin-specific beads, which react with a BoNT/A solution to release fluorescently labelled fragments. The solution then flows down a microfluidic channel to a detection port, where evaporation of the solution concentrates the fluorescent fragments and amplifies the signal.

Hugh Fan, an expert in microfluidics from the University of Florida, Gainesville, US, appreciates the clever design of the sensor. 'It exploits unique features of enzymatic cleavage on the bead surface and an evaporation-induced flow in a microchannel,' he says. 'The technique can also be extended to other biological assays,' Fan adds, and Megan Frisk from the Beebe group agrees. 'I'm hoping that we can simplify our current microfluidic systems to meet the needs of developing countries, particularly in the area of rapid and reliable tests for tuberculosis and HIV,' she says.

Roxane Owen

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