Interferometer approach improves bio-sensor sensitivity

March 03, 2014 // By Christoph Hammerschmidt
A research team of the Toyohashi University of Technology has developed a label-free biosensor that overcomes the weakness of conventional MEMS-based biosensors for medical and pharmaceutical applications. Utilizing a Fabry-Perot interferometer, the researchers succeeded in raising the sensor's sensitivity by a factor of 100.

Label-free biosensors are used in many laboratory applications including rapid diagnosis, tailor-made medication and drug discovery. Label-free MEMS-based sensors detect molecules by measuring the deflection of cantilevers caused by biomolecular adsorption. This approach however suffers from poor sensitivity because of low conversion efficiency of linear transducing from the mechanical deflection to the readout signal.

The research team around Kazuhiro Takahashi from the Toyohashi University has developed a biosensor based on MEMS Fabry-Perot interferometer integrated with a photodiode which utilises the non-linear optical transmittance change in the Fabry-Perot interference to enhance the sensitivity. The theoretical minimum detectable surface stress of the proposed sensor was predicted to be -1 µN/m, which is two orders of magnitude greater than that of the conventional MEMS sensor.

The sensor was fabricated using a 4-inch p-type silicon wafer. The photodiode was integrated into the silicon substrate using ion implantation of phosphorus. Sacrificial polysilicon was isotropically etched to form a freestanding membrane. Amino-methyl-functionalized parylene was coated on the membrane for immobilization of the biomolecules via electrostatic coupling.

The MEMS Fabry–Perot interferometric sensor allows the use of a universal biochemical sensing platform in a label-free manner, the research team claims.