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

4-(Triethoxysilyl)butanoic acid as a self-assembled monolayer for surface modification of titanium dioxide

“…As the dual-grating waveguide coupler biosensor (DGB) simultaneously considers the additive effects of the coupled-in and coupled-out effects to enhance sensitivity, this biosensor was employed in this study. 3 A schematic diagram of the DGB developed in this study is shown in Fig. 1(a).…”

“…A steel dual-grating mold for injection molding was fabricated using nanoimprinting and lithography. 3 A steel microfluidic channel mold for injection molding was fabricated using a numerical control (CNC) machine. The DGC and MFC were fabricated via injection molding, which can result in the production of chips of uniform quality.…”

“…1 According to the evanescent wave intensity equation 2 and the law of conservation of energy, the propagation depth and evanescent wave field strength increase as the refractive index of the solution or the concentration of the analyte increases, thereby reducing the coupling intensity. 3 The GWB is one of the most widely used optical biosensors for measuring changes in coupling optical properties, such as angle, 1 wavelength, 4 and intensity. 5 The signals change with changes in the refractive index of the solution or the concentration of the analyte.…”

“…SiO x N y , Si 3 N 4 , and SiO 2 must be treated with oxygen (O 2 ) plasma or a piranha solution to generate hydroxyl groups (–OH) on the surface. However, titanium (Ti) is cheap, and TiO 2 can generate –OH groups on its surface through a photocatalyst reaction, 3,5 which can reduce the cost and simplify the experimental steps. Therefore, TiO 2 was selected as the waveguide-layer material for this study.…”