Development of a label-free dual-grating waveguide coupler biosensor

This study developed a novel dual-grating waveguide coupler biosensor (DGB) which comprised two optical gratings and a waveguide layer, wherein the first grating coupled light into the waveguide layer, and the second grating coupled light out of the waveguide layer. The DGB used the combined light input and output coupling effects of the first and second gratings of the biosensor to improve the normalized refractive index sensitivity and detection capability. In addition, the double-sided grating waveguide (DSG) structure was used to increase the biosensor coupling angle range and coupling position range, improving device setup error tolerance and reducing detection device cost. The results showed that the DGB had a refractive index resolution of 1.82 x 10(-6) RIU and a normalized refractive index sensitivity of 48.55 RIU-1, which was twice that of a single-grating waveguide coupler biosensor (SGB). N-(2,4-dinitrophenyl)-epsilon-amino-n-caproic acid (DNP) and anti-DNP immunoassay results showed that the limit of detection (LOD) was 2.73 x 10-8 g/ml. Compared with other biosensors, the dual grating waveguide coupler biosensor proposed in this study has a better optimal refractive index resolution and an excellent LOD.