Research On S Fiber Taper Sensor Based On Graphene Oxide

Compared with the electromagnetic sensor,the optical fiber sensor has the advantages of fast response speed,electromagnetic interference resistance,and wide detection range.Optical fiber sensing technology has developed vigorously in recent years,and with the improvement of living standards and the development of life sciences,people have paid more and more attention to aspects such as life health,food safety,and biochemistry.In this paper,we take the combination of S fiber taper structure and graphene oxide as the starting point,and propose two types of sensors based on biochemical aspects: one is a S fiber taper humidity sensor and the other is a S fiber taper protein concentration sensor.The S fiber taper structure is a Mach-Zehnder interferometer with the advantages of small size and simple preparation.Graphene oxide is a twodimensional nanomaterial,which has the advantages of large specific surface area,many functional groups,and adsorption of molecules.Firstly,We proposed a S fiber taper humidity sensor based on graphene oxide.The S fiber taper structure was off-axis with a fusion splicer,and then graphene oxide was coated on the surface of the S fiber taper by the self-assembly technology.Graphene oxide adsorbs water molecules,and finally affects the refractive index of the surface of the S fiber taper,thereby achieving humidity sensing.The substrate of this sensor was characterized by scanning electron microscopy,Raman spectroscopy,and atomic force microscopy.It not only proves that graphene oxide is coated relatively uniformly on the surface of the S fiber taper,but also measures the film thickness to be 1.75 um.Then experimentally obtained when the graphene oxide was coated 12 times and the tapered waist diameter of the S fiber taper was 27 um,the sensor maximum intensity sensitivity is –0.361 dB/%RH and the maximum wavelength sensitivity is 365 pm/%RH in the range of 84% to 95%RH,which is 90 times greater than the humidity sensitivity of the S fiber taper without graphene oxide coating.Finally,we studied the characteristics of refractive index,desorption time,stability,and temperature cross sensitivity.The experimental results show that the maximum refractive index sensitivity is 128dB/RIU,and the effect of temperature fluctuations at room temperature on the humidity test is less than 2% RH.Thanks to the compact structure of the sensor,the humidity sensor not only has good stability,but also has desorption time faster.Next,we proposed a S fiber taper concentration sensor based on graphene oxide and trypsin composite substrate.By activating the carboxyl group of graphene oxide on the surface of the S fiber taper,trypsin was fixed to the surface of graphene oxide,and the bovine serum albumin solution was hydrolyzed by trypsin,thereby affecting the refractive index of the surface of the S fiber taper and achieving label-free detection of protein concentration.Firstly,it was proved that the composite substrate was coated on the surface of the S fiber taper by scanning electron microscope,and the effect of composite substrate on protein concentration sensing was also studied.Then three different concentrations of bovine serum albumin solution were used to test the sensor.In the concentration range of 1mg/ml to 5mg/ml,the maximum sensitivity of the sensor is-2.09dB/(mg/ml),in the concentration range of 1mM to 8mM,the maximum sensitivity of the sensor is-0.459dB/mM,and in the concentration range of 2?M to 8?M,the maximum sensitivity of the sensor is-0.722dB/?M.The minimum detection limit of this sensor can reach ?M concentration.Finally,the refractive index and temperature response of the sensor were tested.The experimental results show that the sensor has a maximum refractive index sensitivity of 328dB/RIU,and the temperature fluctuation in the room temperature range has little effect on the results of protein concentration sensing.