A one-step, magnetically-activated biosensor has been developed by scientists in the Netherlands. It could be used to rapidly screen motorists for drug abuse, they claim. 

The device, designed by Menno Prins and colleagues from Philips Corporate Technologies, Eindhoven, is based on an immunoassay - it uses antibodies to detect analyte molecules of interest. Most immunoassays require the sample fluid - often saliva or blood serum - to be manipulated or replaced. But Prins' device uses a stationary fluid sample, which makes it easier to use at the point-of-care.

The team coated magnetic nanoparticles with antibodies and added them to the sample fluid in a cheap, disposable cartridge, which had electromagnets positioned above and below it and a sensing surface on its base. The nanoparticles bound to complementary analyte molecules in the fluid. The team then used the lower electromagnet to move the particles through the fluid to the sensor surface, where only the nanoparticle-analyte conjugates bound to the sensor. They removed the unbound particles by switching on the upper magnet and then worked out the concentration of analyte by measuring the intensity of reflected light from the nanoparticles.       

The sensor could be used to detect disease-related molecules accurately and quickly, says Prins. 'Doctors frequently have to make crucial decisions in a short space of time,' he comments. 'Often they don't have the benefit of lab-based tests of the patient's samples simply because these tests take too long.'  

Prins suggests that the sensor is also ideal for the roadside drugs screening of motorists - the group showed can detect sub-nanogram per millilitre levels of morphine in saliva within one minute. It can also detect several drugs in a single test.  

Ljiljana Fruk, a biosensor expert at the KarlsruheInstitute of Technology, Germany, envisages that the 'principle will find its way into clinical use'. '[The work] has many possible applications and it will be interesting to see the future developments,' she says. 

The team now intend to improve the technique's speed, precision and sensitivity and use it with novel capture molecules and biological analytes.  

Ben Merison