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Fabrication of Orderly Porous Anodic Alumina Optical Waveguide Sensor via Interface Hydrophilic Treatment for the Detection of Small and Large Molecules

In this paper, an orderly porous anodic alumina (PAA) optical waveguide sensor is presented with a simple and low‐cost fabrication method. Both the gold film and PAA film undergo interface hydrophilic treatment. The refractive index (RI) sensitivity and resolution for the first order of transverse magnetic (TM1) mode reached 64.67 deg RIU−1 and 1.73 × 10−6 RIU, respectively. Small and large molecules are used to verify its sensing feasibility. For the detection of small molecule, the glucose molecule is used and its limit of detection (LOD) of 39.03 mg L−1, that is 0.22 × 10−3 m, is achieved. In addition, bovine serum albumin (BSA) is used as a model of large molecule to adsorb onto the surface of PAA film due to the characteristic of BSA molecule. The results show that the adsorption of BSA onto the PAA surface belongs to 1:1 model of Langmuir adsorption and the LOD reached 2.67 × 10−12 m based on the threefold standard deviation theory and Langmuir fitting. Further, in the experiment of fluorescence enhancement, the LOD as low as 770.72 × 10−15 m for BSA/Cy5 is obtained, owing to the high adsorption capacity of PAA nanostructure and field enhancement of the PAA waveguide.