Planar photonic crystal waveguide biosensor

We present protein detection using a planar photonic crystal waveguide sensor. Experimental results of refractive index measurements show good agreement with simulations. The sensor has been used for protein detection and showed successful detection with excellent signal to noise ratio of proteins with concentrations around 10 μg/ml (0.15μMolar). Introduction In the past 20 years, the research within biosensing has experienced increased intrest. Biosensing is a wide term that includes areas like fast and effective recognition of DNA/RNA, proteins or other biological molecules, recognition of chemical reactions for diagnoses of diseases, discovery of new drugs, and environmental control. In connection with biosensing, increased focus has been on the development of integrated optical biosensors, as they have the potential to be made compact with high sensitivity, and to be easily fabricated and integrated with other optical or electrical components. The research in integrated optical biosensors has resulted in a wide range of devices and still new ones are suggested, especially those requiring easier fabrication methods. Amongst the well-proven methods suggested for biosensors, a few wide-known methods can be mentioned: optical waveguides, SPR-devices, resonant mirrors, interferometers, cantilevers and optical fiber-based devices. We present a biosensor based on a planar photonic crystal. The advantages of the device we suggest are that it is realized in silicon and can be integrated on a SOI-wafer (silicon-on-insulator) along with other electronic and optical devices. Thus, the fabrication technology used for the sensor is the same used for CMOS electronic devices. The suggested planar photonic crystal waveguide (PC-WG) sensor has been tested for both refractive index (RI) measurements and protein detection. The PC-WG can be made very compact and the sample volume to be analyzed can also be reduced considerably compared to the earlier suggested devices mentioned above. Photonic crystal waveguide sensor The basic property of a PC-WG is that a given bandwidth of light can be guided in the waveguide as the light is confined laterally by the band-gap of the photonic crystal (PhC) and vertically by total internal reflection (TIR), akin to conventional waveguide structures. Fig. 1(A) shows the experimental setup and a top-view of the configuration of the PC-WG sensor is illustrated in Fig. 1(B). Fig. 1: A) Experimental setup. B) Top-view of the photonic-crystal waveguide configuration. The properties of the PC-WG are highly influenced by changes in RI at the silicon surface, both on the top of the layered structure but also at the sidewalls of the holes due to the field distribution, which is decaying fast into the cover medium. This can be an advantage in biosensing as it will typically involve an aqueous cover medium containing biological molecules. The detection of specific biological molecules ThG02