Study On Principle And Biosensing Of Dual-channels Probe Based On 81° Tilted Optical Fiber Grating

Fiber grating biosensors have the advantages of micro-size,label-free and high sensitivity to the external environment refractive index(RI),and can be combined with various precious metal nanoparticle materials to form extremely sensitive fiber grating localized surface plasmon resonance(LSPR)sensors,can also be integrated with twodimensional materials such as graphene oxide(GO)to form sensors with good biological affinity.Therefore,various fiber grating LSPR biosensors integrated with GO have attracted increasing attention.Among them,the 81° tilted fiber grating(81°TFG)is a "special fiber grating" with a grating period(?28?m)between the long period fiber grating(LPFG)and the fiber Bragg grating(FBG),due to its higher RI sensitivity and extremely low temperature cross-sensitivity have been widely used in physical,biological,chemical and other sensing fields.However,all types of sensors made for 81°TFG are single-channel transmissive sensors.With the diversification of the types and characteristics of the target parameters to be measured,conventional single-channel transmissive sensors have gradually failed to meet the needs of actual detection.Based on this,combined with the advantages of GO and LSPR technology,this paper proposed a dual-channels probe type 81°TFG-LSPR biosensor integrated with GO,analyzed its principle and spectral characteristics,and used hepatocellular carcinoma marker alpha-fetoprotein(AFP)molecule to identify the performance of the dual channel biosensor for immunodetection.The main research contents of this topic are as follows:(1)Firstly,the research status of optical fiber(including fiber grating)in the field of biosensing at home and abroad was reviewed.Then based on FBG coupled mode theory and tilted fiber Bragg grating(TFBG)coupled mode theory,the 81°TFG coupled mode theory was elaborated.Finally,the spectral characteristics,RI and temperature sensing principle of 81°TFG were analyzed.(2)Manufactured a dual-channels sensor based on the probe type 81°TFG and analyzed its spectral characteristics.Firstly,the end face of transmissive 81°TFG was plated with silver film to form probe type 81°TFG,and a dual-channels sensor was constructed by a 2×2 coupler and two 81°TFG probes,and conducted experimental research on its spectral response and RI sensing characteristics.The experimental results showed that when one of the channels of the dual-channels sensor was fixed and the other channel was placed in a solution with a different RI,the spectrum of the fixed channel was almost not affected by the change of the external environment RI of the other channel,but was placed in a solution with a different RI.The spectra corresponding to the channel of the channel will change with the change of the external environment RI.The two channels were independent of each other and hardly affect each other,indicated that the idea of constructing a dual-channels probe type 81°TFG biosensor is completely feasible.When different biomolecule recognition units are modified on its surface,it will have the ability to detect two different target biomolecules at the same time.(3)Manufactured a dual-channels probe type 81°TFG-LSPR AFP immunosensor integrated with GO.The dual-channels immunosensor was used to simultaneously complete the detection and control of AFP antigen molecules,and the specificity and clinical characteristics of the sensor were measured and analyzed in a complex human serum environment.Firstly,used the same method to modify the large-size gold nanoshells(Au Ns)particles and GO on the surface of the grating area of the two81°TFG probes that constitute the dual-channels sensor,and then AFP monoclonal antibodies(AFP MAbs)were used as the specific recognition unit to modify the grating surface to achieve a dual-channels probe type 81°TFG-LSPR AFP immunosensor.Then used the sensor to perform specific control experiments on the AFP antigens solution at the same time,The results showed that,the detection limit for AFP antigens was between 1?10 pg/ml,the detection saturation was ?200 ng/ml,and the detection sensitivity was ?0.155 nm/log(mg/ml).Finally,used a 20% Hydrofluoric acid(HF)solution to slightly etch the grating surface of the two 81°TFG probes to remove all coatings on the surface of the optical fiber,and again used the same method described above to perform surface modification and biological functionalization of the two81°TFG probes.The two channels are respectively completed the clinical testing for the six groups of healthy sera from different groups of people and the six groups of liver cancer patient sera from different groups of people.The results showed that the healthy human serum in this test contained a small amount of AFP,and the AFP concentration was slightly higher than 100pg/ml after 10 times dilution,while the AFP molecular concentration in the serum of liver cancer patients after 10 times dilution should be about 100ng/ml,which is about 1000 times that of the APF concentration in the healthy serum.Compared with the single-channel transmission type 81°TFG sensor,the dualchannels probe type 81°TFG sensor could realize the simultaneous control detection of positive and negative samples of target molecules,thus enhanced the reliability of the clinical detection application process,and probe type structure operation is more convenient,so it has great application potential.