Optical Fiber Sensor Based On Biomolecular Photothermal Effect

With the increasing requirements for molecular detection technology in the biomedical field,the refractive index of optical fiber quartz material has become a key factor restricting the development of high-performance fiber integrated optofluidic devices.The main problem is that it is difficult for biomolecule solutions with low refractive index to interact with light,and the accuracy of biomolecule detection is not enough.In order to improve the efficiency of fiber-integrated optofluidic devices for the detection of biomolecules,how to enhance the efficient interaction between the optical field and the fluid in the microfluidic channel and effectively detect the physical effects generated is an urgent problem to be solved.Photothermal spectroscopy has good molecular selectivity,and the detected photothermal signal originates only from the optical absorption of molecule at a specific wavelength,avoiding the influence of scattering and reflection loss in the optical path to the measured signal.In this paper,the molecular photothermal effect is combined with the optical fiber sensor,and the two-dimensional material is coated to adsorb the molecules to be measured,which enhances the interaction between light and matter,and realizes high-sensitivity and specific detection of biomolecules such as sodium copper chlorophyllin.The sensor has broad application prospects in the fields of food safety detection,disease diagnosis and environmental monitoring.The main content of this paper includes:(1)An optical fiber biosensor based on the photothermal effect of porphyrin compounds is designed.The mode coupling theory and sensing principle of the long period fiber grating(LPFG)are analyzed.The excitation light was used to irradiate the sodium chlorophyll copper(SCC)solution to produce photothermal signal.The concentration of the SCC solution is measured by observing the change of the LPFG resonance intensity.The graphene oxide(GO)was coated on the surface of the LPFG to enhance the detection of photothermal signals,thereby increasing the sensitivity.The results show that the sensitivity of the device is nearly doubled compared with LPFG,which is 0.0587 d B(mg/L)^-1.Sensors based on molecular photothermal effects provide new ideas for biomolecule detection.(2)A tapered microfiber biosensor based on two-dimensional material coating is designed.Niobium carbide(Nb₂CT_x)is deposited on the surface of the tapered microfiber,combined with the photothermal effect of hemoglobin to achieve high-sensitivity and wide-range detection of molecules.In the concentration range of 0-10g/d L,the sensitivity is 7.581 nm(g/d L)^-1,and the limit of detection is 0.0026 g/d L,which is much lower than the normal human body level.The proposed biosensor provides a new means for clinical medical sensing functional devices.(3)An optofluidic system based on the photothermal effect of organophosphorus pesticides is designed.The Nb₂CT_x-tilted fiber Bragg grating was packaged in a microfluidic chip,and the solution is irradiated with excitation light to cause a shift in the resonance wavelength of the cladding mode,and temperature compensation was achieved by observing the resonance wavelength of the core mode.The limit of detection in the concentration range of 10-50 ppm chlorpyrifos can reach 0.35 ppm,and the obtained temperature compensation coefficient is 4.84 ppm/?.By comparing the spectral responses caused by several different molecules,the specificity of the photothermal detection technology was verified.This method has good application prospects in actual food safety monitoring.