Drugs biosensor could save lives

Researchers in the UK are developing a kind of biosensor which can determine in minutes if an overdose patient's blood contains a particular compound, for example paracetamol. Currently, this type of examination needs to be carried out in a laboratory and which is expensive and time-consuming.

The sensor system can return a response in fewer than 10 minutes, compared with the two to three hours required by a routine laboratory, depending on the workload.

"Our sensor is portable and will be easy to use even by unskilled staff," said reserach leader Dr Sub Reddy. "Ideally, the overdose sensor may be located in the ambulance so that a result is available when the patient arrives at hospital."

The paracetamol sensor is the pilot to the development of an array of overdose sensors which will test for alcohol and anti-depressants as well.

The heart of the biosensor consists of a disc-shaped quartz crystal, about a centimetre in diameter and 0.2 mm thick. "When an alternating electric field is applied, the crystal vibrates from side to side, like a nano-scale earthquake," added Dr Reddy. "It shakes ten million times a second with an amplitude of a fraction of a nanometre."

The crystal can continue to oscillate even when immersed in a liquid. Anything which then sticks to the crystal surface or which affects the viscosity or elasticity of any attached film at the surface will affect the frequency at which the crystal vibrates.

The concept of the sensor is to have a small reaction chamber above the surface of the crystal. When a sample - for example, blood - is placed in the chamber a series of carefully designed chemical reactions can be made to occur which result in the molecule of interest - such as cholesterol - contributing to the formation of a solid product. The product then attaches to the surface of the crystal, affecting the frequency of its oscillation.

Because the chemical reaction can be made to be highly specific to the molecule of interest so that only one solid product is formed, other substances in the sample will not interfere with the process or provide spurious readings.