Coupled mode surface plasmon resonance sensor: in situ detection of humidity with starch biofilm

An environment friendly coupled mode surface plasmon resonance sensor structure with starch biofilm as sensing element for humidity detection of environment is fabricated and demonstrated. The surface plasmon resonances were created using PVC layer fabricated between silver and starch biofilm on a rectangular prism. The analyses of fabricated sensor have been done by both wavelength and angular interrogation methods. The proposed sensor has maximum sensitivity 0.45 nm/%RH in wavelength interrogation method and 0.09°/%RH in angular interrogation method. Here the variations in humidity of environment, changes the refractive index of starch biofilm and hence in the surface plasmon resonances. Also, the proposed sensor shows a linear variation in resonance wavelength and resonance angle with respect to the variation in humidity of environment.