A low cost, label-free biosensor based on a novel double-sided grating waveguide coupler with sub-surface cavities

This study proposes a low cost, label-free biosensor based on a novel double-sided grating waveguide coupler with sub-surface cavities. The feasibility of this biosensor is demonstrated by measuring the refractive index resolution (5.13 x 10(-6) RIU) and the limit of detection (7.81 x 10(-8) g/ml) for dinitrophenyl (DNP)/anti-DNP interaction. The results indicate that this biosensor possesses different sensing characteristics from those of its single-sided grating counterpart. The coupling angle and position of the proposed biosensor have their respective effective ranges, any arbitrarily selected incident angle and position within these ranges will not affect the detection sensitivity of the biosensor, which dramatically reduces the precision requirements of external optical equipments. Furthermore, this biosensor uses an injection molded polymer grating chip and a sputtered titanium dioxide waveguide to form a double-sided grating waveguide, providing such advantages as lowered cost, increased reproducibility and reduced production time. In addition, by adjusting the sputtering parameters, we are able to create sub-surface cavities at the interface between the waveguide layer and cyclic olefin copolymer (COC) grating substrate to improve the refractive index sensitivity by 35%. The biosensor discussed in this study is the first to use a double-sided grating waveguide structure with sub-surface cavities in the biosensing applications. (C) 2014 Elsevier B.V. All rights reserved.