| Micro&nano fiber(MNF)attracts interests due to its small size,low loss,strong evanescent field and easy manufacture.Optical absorption spectroscopy is a widely used analytical method in the field of biological and chemical sensing.In this paper,the combination of MNF and optical absorption spectroscopy is carried out to detect the low concentration of substances in the solution.Here we discussed in two aspects,the absorption sensing mechanism of MNF and the stability of the sensing system.The MNF absorption spectroscopy sensor has been reported before,but the traditional Bill-Lambert's law couldn't explain two experimental results: 1.the nonlinear relationship between the absorbance of the MNF absorption sensor and the concentration of the detected substance;2.The MNF detection system has a higher absorbance value than the free space system at the same concentration of detected objects.Based on these two phenomena,we propose the adsorption enhancement mechanism,that is,the detected object is adsorbed on the surface of the micro-na fiber,resulting in the local concentration of the detected area being higher than the actual concentration of the solution.The main research contents of this paper are as follows:1,By comparing the methods of MNF production,the hydrogen flame fiber drawing platform is built and its stability is maintained under the joint efforts of the laboratory,In the case of reliable quality to achieve the implementation of the diameter of the detection and control.Then,PDMS substrate is used to protect the stability of MNF because of its larger surface energy,and the optical effect of the large refractive index substrate on the MNF is discussed by COMSOL simulation.2,The correctness of the proposed surface adsorption enhancement mechanism is proved by experiment and finite element simulation,and the experiment and simulation include that when the solution is stable,in MNF absorption sensing the absorbance in time comply with the kinetic adsorption process,but the absorbance does not change with time according to the Bill-Lambert's law.Using COMSOL simulation software to analyze the energy and surface and evanescent energy of MNF,it is found that the change trend of surface energy with optical fiber diameter is more consistent with the change of absorbance with diameter under experimental conditions,so the energy of surface fiber surface is closely related to the absorbance value.3,When the waist length is pulled to three times(21 mm)of the original,the absorbance is three times the original,indicating that the absorbance is still proportional to the length of the detection area.In this paper,the minimum 10 pM detection limit is achieved by using the 21 mm waist length and 760 nm diameter MNF to detect R6 G concentrations,which is lower than the concentration limit of the substance detected by the absorption spectroscopy has been reported.4,The sensing structure of MMF-MNHACF-MMF is proposed,which uses the hollow structure of hollow annular core fiber to break the Gaussian distribution of cylindrical fiber energy,push more energy away from the center,and then pull the hollow annular core fiber into MNF,so that it has stronger evanescent energy and surface energy.When it is used to absorption sensing,the diameter of the most suitable absorption sensor is near 2 ?m,which is larger than that of the cylindrical MNF 700 nm.The larger the diameter,the higher the repeatability when the MNF is manufactured,and the better the stability of the detection system,so it is of great significance for absorbing sensing and fading field sensors.In this paper,the performance of the absorbance of the MNF absorption sensor under the concentration gradient and diameter gradient is studied systematically.the adsorption enhancement mechanism of the MNF absorption sensing is proposed,and the MMF-MNHACF-MMF sensing structure is proposed to enhance the energy and surface energy of the fading field.It is of great value for optical fiber absorption sensing and evanescent sensing. |
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