Research On Fiber Optical Evanescent Wave Sensor For Online Monitoring Of Biofilm Activity

Evanescent wave sensing technology is a high sensitive microanalysis technology, widely used in clinical medicine, water quality monitoring, food safe and biological warfare agent detection. Mechanism of the technology is made use of the absorption that material surrounding the fiber core interacted with the specific band evanescent wave. The material content can be detected through using variation of light density caused by the absorption. The structural parameters of sensing region will influence on the sensitivity of fiber optical evanescent wave sensor. Therefore, theoretical model for sensing region is a primary task for researching evanescent wave sensing technology. Mathematical models are established based on the geometrical optics, respectively for penetration depth and taper parameters in conical transition region, effective absorptive path and sensing fiber core and length in uniform sensing region. Penetration depth in different tapered parameters and effective absorptive path in different are discussed and simulated. The simulation result indicates that penetration depth can be increased about three times through selecting suitable taper parameters and reaches a maximum when the taper ratio is equaled to 0.4, and the effective absorptive path can be enhanced when decrease fiber core and increase fiber length in the sensing region. These results can be used to guide to make high sensitive fiber optical evanescent wave sensor. Silica optical fiber and HF corrosive reagent is selected, and tapered fiber optical evanescent wave sensor is manufactured based on the static-dynamic combination etching method. In this paper, biofilm active detection system based on the fiber spectrometer is used firstly to get absorption spectrogram for the process of biofilm development. The feature absorption wavelength of biofilm can be got from the absorption spectrogram and electron microscope figure of biofilm development on the sensing region. According to this absorption wavelength, suitable wavelength LED and PIN photoelectric detector are selected, then a biofilm active monitor system is developed based on the PWM. The experimental results from this two monitor systems show that the absorbance time-varying in feature wavelength is according with bacteria number time-varying, basically implementing the online monitoring of biofilm active.