The Fabrication Of Two Graphene SPR Sensors And Their Application In Biomolecular Detection

Optical fiber sensors can be made into sensors of any shape because of their high sensitivity,strong adaptability to geometry,good insulation,remote control and monitoring,anti-electromagnetic and atomic radiation interference,excellent chemical properties of water,high temperature and corrosion resistance,which make them play an important role in the field of sensors.When the total reflection of light occurs at the connecting interface between the medium and the metal film,the evanescent wave will cause the free electrons on the metal surface to form the surface plasmon resonance when evanescent waves match the surface plasma,and light is absorbed by the plasmon on the metal surface,which is called surface plasmon resonance(SPR).Localized surface plasmon resonance(LSPR)is extremely similar to the SPR,but the localized surface plasmon exhibits a larger spectral width compared to the surface plasmon.When the subwavelength metal particle/dielectric layer is periodically stacked,the electromagnetic field coupling confined to the interface of each plasmonic generates a collective response.The dielectric deposited on noble metal nanoparticles can effectively transfer the charge and increase the electric field intensity at the nanointerface.In addition,the dielectric plays the role of spacer layer in the 3D structure,which is beneficial to the vertical charge density oscillation,and converts the plasma oscillation mode from plane to 3D structure.DNA hybridization is a biomolecular method to obtain genetic differences between organisms by evaluating genetic relationships between DNA sequence libraries.DNA hybridization has important theoretical value and practical significance in gene screening and detection,disease biomarkers,transcriptional profiles,and detection of single nucleotide variations.Based on the principle of SPR and LSPR,optical fiber SPR sensor and metamaterial structure sensor are prepared.Then we tested the fiber-optic sensor and the reaction kinetics according to the principle of biomolecular detection.First,we fabricated optical fiber SPR sensors based on the principle of SPR.We used nanoimprinting to process optical fibers into D type sensors.We used the method of growing graphene directly on copper.Then magnetron sputtered a layer of gold film and etched copper foil to obtain our ideal composite structure.This structure is then transferred to D fiber to obtain the D fiber SPR sensor we developed.This method makes the contact between the gold layer and the graphene layer closer to improve the SPR performance.Through comparative analysis,we verified that the presence of graphene can make the sensor have higher sensitivity.In the detection of ethanol solution,a red shift of 40 nm was found between the refractive index of1.3330 and 1.3657.After calculation,we know that the sensitivity of our designed sensor is 1223nm/RIU.We also know that the sensor has good stability and repeatability through data analysis.Then,based on the principle of LSPR,we proposed a structure of three-dimensional multilayer silver nanoparticles and graphene,and applied it to U type fiber to prepare a metamaterial structure U type fiber sensor.In this study,the silver film was formed based on the silver mirror reaction method,which has the advantages of low production cost,high sensitivity,short operation time,simple steps,and increased contact area between silver film and analyte molecules,which makes the fiber sensor have higher detection sensitivity.A layer of 3 nm thick graphene was grown by reducing graphene oxide to form an spacer layer in the silver film.By discussing and studying the plasmon resonance behavior of this sensor,the results of the five periodic layers are evaluated and judged.We find that the third periodic layer is the optimal number of periodic layers.A single layer silver and graphene fiber sensor with the same thickness as the third periodic layer was also prepared.At the same time,we also give the simulation proof obtained by FDTD.Finally,according to the principle and steps of biomolecular detection,we made our fiber sensor into a bio-fiber sensor,and tested its specificity and reaction kinetics.Using the proposed biofiber sensor,the plasmon resonance behavior in different concentrations of target DNA is discussed and studied.The analysis results show that all our prepared biofiber sensors can sensethe nucleotide bonds that occur between double-stranded DNA helices,and thus distinguish DNA base mismatches.In addition,we evaluated the reaction kinetics of biofiber sensors.Based on these experimental results,our proposed biofiber sensor is expected to open up new avenues for detection in the fields of medicine and biotechnology.