Preparation And Application Of An Optic-Fiber Graphene Field Effect Transistor Biosensor

Biosensors are analytical devices that convert biological reaction or biological components into useful signals.Biosensors have been booming and rapidly being applied in recent years due to their low cost,fast analysis and processing,high device selectivity,and ease of miniaturization and integration.Most biosensors focus on detecting static targets.However,many ions or biomolecules are dynamic processes that are constantly generated,consumed or transferred over time and space during the reaction or in the biological system,and are not static.In this paper,an optic-fiber graphene field effect transistor biosensor based on optical fiber sensing technology and graphene field effect transistor(FET)is designed,and a home-made dual-channel detection system is built according to the characteristics of optic-fiber graphene FET biosensor.At the same time,the sensor is used to realize the real-time detection of the pH value in different solutions and the kinetic process for real-time detection of DNA molecule hybridization.This biosensor construction process is based on the optic-fiber end face.Au electrode is fabricated on the top of the fiber as a source and a drain of the FET by magnetron sputtering and femtosecond pulsed laser ablation.The graphene is transferred to the optic-fiber end face by a wet method to form an electrical detection channel between the source and the drain of FET.This biosensor utilizes the characteristics of optical fiber sensing technology,and uses an optical fiber to convert different fluorescence intensity into a voltage through an photomultiplier tube(PMT)as an optical detection channel.Different molecules are detected by photoelectric dual-channel detection.The dual-channel detection system mainly includes a upper processor,an optical path and a circuit path.The optical path part mainly includes optical fiber,laser,high-pass filter,fiber collimator,dichroic mirror,objective lens,and PMT.The circuit path part mainly includes five modules: PMT power supply and gain control circuits,PMT signal processing circuits,AD signal acquisition module,FET gate voltage control and output circuits,and FET equivalent resistance measurement circuits.The upper processor is written by Labview in G language,which can realize the switch and gain of controlling double path detection at the upper processor,and it shows the final result by “The combination of number and shape”.Graphene has some characteristics such as zero band gap structure,high electron mobility and unique bilateral properties.Fluorescein and the derivative 6'-Carboxyfluorescein(6'-FAM)have different degrees of ionization of fluorescence intensity in different pH solutions.In termsof pH detection,On the one hand,The optic-fiber graphene FET biosensor monitors the pH change based on the fluorescence intensity of the solution in different pH values;on the other hand,the optic-fiber graphene FET biosensor monitors the pH change of the solution based on the change of the Dirac point of the graphene in the solution with different pH values.In detecting DNA hybridization,the 6'-FAM modified probe aptamer was immobilized to the graphene surface using 1-Pyrenebutanoic acid succinimidyl ester as an anchor,and the fluorescent group on the probe aptamer was quenched by graphene oxide.When a target DNA is added,the probe aptamer is detached from the graphene oxide to bind to the target DNA,thereby allowing the fluorescent group modified on the probe aptamer to resume florescence.Therefore,the optical detection channel is established according to the change of the fluorescent group,and the electrical detection channel is established according to the change of the conductivity and the movement of the Dirac point of the graphene.The fiber-optic graphene FET biosensor is used in conjunction with a home-made dual-channel detection system to reflect the change in pH and the hybridization of DNA in real time by recording changes in fluorescence intensity and graphene conductivity and Dirac points.Compared with the traditional biosensor with single detection method,the fiber graphene FET biosensor can detect more sensitively and reliably.Compared with the real-time detection biosensor developed at present,the fiber-optic graphene FET biosensor has the same detection sensitivity but reduces the size of the sensor to micron.At the same time,the successful detection of pH value and DNA proves the feasibility of the design and manufacture of the fiber-optic graphene FET biosensor,and also provides a new idea for the integration of multi-sensor and its wide application.