Biosensor for drug detection

Philips has developed a novel biosensor that uses nanomagnetic particles and optical technology to detect disease, diagnose clinical conditions and test for illegal drugs.

Lab-on-a-chip technology to allow rapid, single-step in-vitro testing away from the laboratory has been available for about 20 years. Traditionally, it replicates the pipette fluid exchange steps carried out manually or by robots in the laboratory, but on a miniaturised scale: introducing a sample, incubation, washing step, adding a reagent and so on.

In Philips' Magnotech device (pictured below) the sample is added to a cartridge containing magnetic nanoparticles chemically bonded to a ligand — a substance such as an antibody designed to attach to the target protein.

The cartridge is inserted into a hand-held analyser, which applies a magnetic field attracting the molecules to the active surface of the sensor, where more ligands attached to the surface bind them in place. Another magnet then draws the unbound molecules away.

A visualisation technique called frustrated total internal reflection (FTIR) then gives an accurate reading of the amount of analyte present.

In FTIR, light shines onto an optically flat plastic surface in the cartridge and bounces off into an imaging sensor in what is known as the condition of internal reflection.

It is caused by the fact that the optical refractive index of the plastic is higher than the optical refractive index of the material in the chamber — initially air then the biological sample.

Where the magnetic particles bind to the surface, they scatter and absorb the light. The grey value, or darkness, of the spots where they gather is a measure of the amount of magnetic particles on the surface, which in turn is a measure of the concentration of the original target molecules.