Study On GO/MXene Functionalized Long Period Fiber Grating Sensor For Biochemical Sensing

Optic fiber sensors have the advantages of small size,light weight,anti-electromagnetic interference and low production cost,and can be used to measure many parameters without labels,with high sensitivity and in complex environments.Therefore,the optical fiber sensors shows great potential and application values in the development of modern measurement technology.Long period fiber gratings（LPFG）,due to the special mode coupling,the evanescent wave of cladding mode is affected by variation of surrounding refractive index（SRI）,concentrations,composition,and molecular interactions of the LPFG surface medium,so it owned unique advantages in sensing measurement and surface functionalization.In this paper,by using CO₂ laser heating method by taper the standard single mode fiber（SMF）to fabricated the Micro-tapered Long period fiber grating（MTLPFG）,the MTLPFG enables coupling between fundamental core mode and higher-order cladding mode to produce a series of attenuation bands,which provides ideal inherent sensitivity to the SRI.The 2D materials Graphene oxide（GO）and Ti₃C₂T_x were functionlized onto the prepared MTLPFG’s surface,to achieved in detect the heavy metal cobalt ion and lead ion solution and the concentration of pepsin biomolecules.The main research achievements of this paper include:1.We proposed a highly sensitive label-free chemical sensor for the detection of heavy metal ions.The sensor was derived from MTLPFG functionalized by graphene oxide and poly-dopamine（PDA）modified graphene oxide,respectively.Because of the combination of chemical bonding and optical tweezer effect,the materials were deposited on the MTLPFG fiber grating surface.The morphology and elemental composition of the nanocomposites were characterized by scanning electron microscope（SEM）,Fourier-transform infrared spectroscopy（FT-IR）,and X-ray photoelectron spectroscopy（XPS）.We demonstrate a high sensitivity MTLPFG detection of cobalt ions in a large concentration range from 1 ppb to 10⁷ ppb.The highest sensitivity of 2.4×10^-3 d B/ppb at the PDA concentrations of 0.05 g/L was obtained by MTLPFG functionalized with PDA-GO（PDA-GO-MTLPFG）.The result was significantly higher than GO-deposited MTLPFG（GO-MTLPFG）and bare MTLPFG.Further,the Ti₃C₂T_x-MXene powder was using liquid-phase exfoliation method to produce few layer Ti₃C₂T_xnanosheets,and uniformly deposited onto MTLPFG surface.The Ti₃C₂T_x-MTLPFG device was prepared to detect the concentration of lead ions solution of 1 ppt-10⁹ ppt.The surface of the device was characterized by SEM and Raman spectroscopy,and the fabrication of the device was verified.Compared the sensing performance of bare-MTLPFG and Ti₃C₂T_x-MTLPFG,indicated that Ti₃C₂T_x coated MTLPFG with the higher sensitivity to MTLPFG.Specifically,the wavelength shifts of Ti₃C₂T_x-MTLPFG is 4 times higher than MTLPFG and the transmission depth shows 5 times,respectively.Due to the adsorption of lead ions on Ti₃C₂T_x material,the mode coupling of MTLPFG changes.2.We construct a label-free and sensitive micro-tapered long-period fiber grating（MTLPFG）sensor that functionalized by graphene oxide（GO）was proposed for pepsin detection.The GO that activated oxygen groups by EDC/NHS was deposited onto MTLPFG surface.On account of large specific surface area and oxygen containing groups of GO,the amide bonding between biomolecules and GO can be formed throughπ-πinteraction.The spectrum variation trend during sensing process obeys Langmuir absorption mode,which illustrates biomolecule adsorption on GO layer.The bare MTLPFG and GO-MTLPFG separately demonstrate the limit of detection（LOD）of 56.1 ng/ml,10.8 ng/ml,which corresponding to the effectively detection range of 50-1000 ng/ml,10-1000 ng/ml,respectively.