Research Of Fiber Optic Biosensor Based On Evanescent Wave

The detection of chemical and biological agent is a key problem in environment protecting, food monitoring, defending against terrorist or biological weapons in modern battlefield or society. Traditional laboratory methods can accurately detect the chemical and biological agents, but need expensive device, special operators, and are also time consuming, which limit their widely applications. Thus, it is an urgent demand to develop rapid, economic, portable, accurate and simply operated biological agent detection device.This paper starts the research with the evanescent wave formed by laser propagation in fiber probe. Based on the exciting characteristic of evanescent wave on probe surface, and the spatial separation between the fluorescent complexes bound to the core and those free in solution, we construct a biosensor system structure totally with fibers for the first time in China by combining the high specificity of antigen-antibody immunoreactions. Some key problems such as probe structure and the coupling of probe and fiber bundle are also studied with corresponding experiments in this paper. Moreover, the structure of the system is further optimized, and a series of substituted experiments are performed by labeling the probe in direct binding assays, just like the method of fluorescent labeling immunoassay. The experiment results show that the detection limit for the labeling concentration of the fiber probe reaches to 0.001umol/L, which can satisfy the applying requirements of precision in actual analyte detection. The experiment results confirm the feasibility of the system and the validity of corresponding research method. The research of the system establishes a massive foundation for analyte detection combined with the immunoassay method. The main contributions of this paper are listed as follows:Firstly, the fiber probe used in the system is lucubrated. To improve the detecting ability of the system, we optimize the structure of the probe and design a special fiber probe-processing device. The probes produced by this device are used in our experiments, which ensure the accurate and reduplicative process of qualified probes with designed parameters.Secondly, by analyzing the propagation trajectory of excitation ray in fiber probe, we discover the limiting problem of coupling beam in fiber probe, and point out the existence of the case with less limiting and the case with over limiting. Moreover, we present a method for solving this problem in system designing. The new limiting method breaks through the scope of conventional analysis, which is limited in mode matching and evanescent wave exciting theory, strengthens the structural integrity in system designing and researching, and gives a reliable way for solving the problem of false detection caused by the transmission of propagation ray in probe to solution. Thirdly, correlation detection methods are introduced into the study of fiber biosensor based on evanescent wave. Considering that the fluorescence signal excited and coupled by evanescent wave is too faint to be detected directly, we introduce correlation detection analyzing method into the system research, which enhances the system's detection ability. In order to reduce the number of discrete components and instruments, the virtual instrument based on LabVIEW is applied. Thus, the research cost is reduced and the research period is shortened, while the integrity of the system structure is enhanced.Lastly, a biosensor system structure totally with fibers based on evanescent wave is constructed for the first time in China. The new system uses silica fiber and plastic fiber bundle to transmit excitation laser beam and fluorescence signal respectively. By using the new lens coupling method based on diode laser with tailed fiber to replace the discrete laser source and coupling lens, and adopting electronically modulation to replace the conventional mechanical chopper modulation in the modulating of laser signal outputted by diode laser, all components in system are linked organically, the collimation needs to light path is lowered, the weight and the cubage of the system are decreased, while the stability, integrity and portability of the system are enhanced. Subsequently, by labeling the probe in direct binding assays, we detect some groups of probes with this fiber biosensor. The experiment results show that the detection limit for the labeling concentration of the fiber probe reaches to 0.001umol/L, which can satisfy the applying requirements of precision in actual analyte detection.