Design And Mechanism Research Of Fluorescence Fiber-optic Probe Via External Vertical Excitation

This paper mainly concerns the design and mechanism research of afluorescence fiber-optic probe via external vertical excitation. First of all, from themode transmission process between different cladding sections, and the modecoupling effect based on defective end-face total internal reflection (TIR), separately,working mechanism of the novel fluorescence fiber-optic probe is analyzed, and someexperiments will be designed to verify the accuracy of the above analysis. Second,taking the novel probe as experiment platform, fluorescence excitation mechanism inthe free droplet and fluorescence collection performance of the receiving fiber (r-fiber)with a continuous tapered sensing end (s-end) are described. Finally, in order tocomplete quantitative and qualitative analysis of typical β-lactam antibiotics detection,according to fluorescence quenching effect of the target antibiotics to merbromin,fluorescence fiber-optic detection system with a sample cell and fluorescencefiber-optic probe via external vertical excitation are taken as measuring devices,respectively. The specific research and results of this paper include:1、A novel fluorescence fiber-optic probe structure with high signal-to-noiseratio is provided, whose incident fiber (i-fiber) and r-fiber are separated from eachother for achieving external vertical excitation of incident light. In other words, lightfrom i-fiber output end-face excites the free fluorescence droplet on the core surfaceof r-fiber s-end along the vertical direction. When s-end face of r-fiber is immerged inthe refractive index matching fluid, only a small part of ultimate energy is from theforward transmission of fluorescence signal, while the majority originates from thebackward transmission, which will be reversed after end-face TIR. The aboveabnormal phenomena indicate that, mode coupling effect based on defective end-faceTIR causes the energy transfer from undetectable modes to detectable modes, hence,parts of end-face TIR ray carrying much back-propagation energy are responded.Compared with smooth sensing end-face, the rough one makes much more contribution to the energy collection of fluorescence signal, which provides a furthervalidation for the enhancement on mode coupling effect of surface defects.2、Through regulating the distance between light exit of i-fiber and bare coresegment of r-fiber, a fluorescent sample fluid droplet is reshaped, and fluorescenceoutput signal with a highest signal-to-noise ratio is obtained when i-fiber is locatedabove the r-fiber. Incident light within the fluorescence droplet is classified accordingto its propagation trajectory near the r-fiber, and the energy contribution of differentray group to the evanescent wave excitation is analyzed, respectively. Fluorescencecollection performance of the r-fiber with a continuous tapered sensing end isinvestigated, and novel fluorescence fiber-optic probe via external vertical excitationhas more advantages than traditional tapered fiber-optic probe.3、In the quantitative analysis experiment of typical β-lactam antibiotics basedon fluorescence fiber-optic detection system with a sample cell, the concentration ofpenicillin G, ampicillin and amoxicillin over range of0.4~7.0mg/L,0.3~6.0mg/Land0.3~5.5mg/L is in good linear relationship with the intensity variation afterfluorescence quenching, and correlation coefficients for the above three antibioticsare R2=0.9946,0.9943,0.9954, respectively. Meanwhile, in the qualitative analysisexperiment based on fluorescence fiber-optic probe via external vertical excitation,comparing the trend of fluorescence peak intensity under different cone length ofs-end and different penicillin concentration, the application feasibility of novelfiber-optic probe is verified.