Tapered Thin-Film Enhanced Optical Waveguide Surface Scattering-based Sensing Method For Rapid Aerosol Detection

Bioaerosol monitoring is essential for disease prevention and control, anti-chemical and counter- terrorism, and environmental and resource conservation. In this research, a tapered thin-film enhanced optical waveguide surface scattering-based sensing method was proposed for rapid bioaerosol detection. The method was implemented by measuring the scattered light intensity with time, enabling analysis of particle sedimentation process of biological aerosols on the waveguide surface and then the information on the bioaerosol sample was obtained. The formula for the relationship between the scattered light intensity and the number of particles adhered onto the waveguide surface from the bioaerosol was deduced, and a series of aqueous solutions with different concentrations of bovine serum protein (BSA) were prepared for generating the bioaerosol samples, and the single -mode glass slab waveguides made by ion-exchange were used to detect the deposition of BSA aggregates from the bioaerosol sample. A tapered thin film of Ta2O5 was locally sputtered on the glass waveguide for improving the detection sensitivity. Experimental results showed that the scattered light intensity increased with increasing the deposition time of BSA aggregates and had a good linear relationship with the BAS concentration of aqueous solution. When the glass waveguide was covered with the tapered film of Ta2O5 , the BSA detection sensitivity increased by 50 times in the case of excitation of the fundamental transvers electric mode (TE0). Moreover, the sensitivity measured with the TE0 mode was 4 times higher than that with the TM0 mode in the same waveguide. The single-mode slab glass waveguides locally covered with the tapered thin films of Ta2O5 had a simple structure and a good stability and were easy to fabricate. They were convenient to use serving as the surface-scattering-based sensors, had high sensitivity and low detection cost, showing a bright application prospect in real-time detection of bioaerosols.