Label-free detection of biomolecules using LED technology

Abstract

This paper presents a label-free biosensor using two Light Emitting Diodes (LEDs) as light sources and a photo detector as a receiver. The sensor uses a silica-on-silicon wafer with PMMA [Poly(methyl methacrylate)] as the functional layer. The principle of this biosensor is based on the Fabry Perot (FP) interferometer. A thickness of a 100 nm PMMA layer is spin-coated on the silicon wafer, which has a thin thermal oxide layer of 500 nm. In such a configuration, the PMMA layer and silica layer function as an FP cavity. When a light illuminates the surface of the sensor, the reflections from the PMMA-air and silica-silicon interfaces will interfere with each other. Consequently, the change of the cavity length, which is caused by biomaterial binding on the PMMA layer, will result in a red shift in the reflection spectrum. An intensity change of the reflection light will be observed on an individual wavelength. In order to eliminate environment noise and to enhance the sensitivity of the sensor, two LEDs, whose center wavelength is chosen on either side of the spectrum notch, are introduced in the system. A photo detector will alternatively obtain the intensities of the two individual reflected lights, and collect the signal via a data acquisition system. Long-term tests have shown that the sensor is resistant to environmental fluctuation. Biolinker Protein G' was used for binding tests. The sensor shows great potential in biosensor applications due to its compact size and low cost.