The Preparation Of Graphene And Its Applications In Optical Sensors

Graphene is a monolayer of sp₂ carbon atoms arranged in a hexagonal-honeycomb lattice.This unusual structure endows graphene extraordinary optics, electrical and thermotics properties, such as high carrier mobility(?200000 cm2 V^-1s^-1), high thermal conductivity?3000-5000W/m K?, high transparency?a monolayer of graphene absorbs only 2.3% of white light? and so on. Beyond that, high strength, flexibility and excellent biomolecular affinity make graphene a widely used material in sensors, especially optical sensors. In recent years,two-dimensional layered materials used in optical sensors have captured much attention. The discovery of graphene has the surface enhanced Raman scattering?SERS? effect, which promotes the applications of graphene in optical sensors. The optical biosensors for fast-nondestructive and label-free detection based on two-dimensional layered materials, such as graphene, have emerged at the right moment. In this paper, on the basis of these studies, we launched a series of studies of graphene combined with optical fiber sensors and SERS technique. High-quality, large-area, continuous and monolayer graphene was prepared by using chemical vapor deposition?CVD? method, and we designed graphene-optical fiber evanescent wave sensors and graphene-metal nanoparticles SERS substrates.?1? High-quality and monolayer graphene was grown on copper foil by using CVD method, and transferred from copper foil to skiness tapered fiber core by using the transfer carrier of PMMA. The material of plastic optical fiber is PMMA, so the striping process of PMMA carrier can be left out. The light source of the evanescent wave absorption?EWA?optical fiber sensor is LED and the receiver is the optical fiber spectrometer. We used glucose aqueous solution as the analyte and the concentrations was determined in the range of 0-40%,the output light intensity and concentrations formed a good linear relationship. This method is simple and feasible, and the EWA sensor is high sensitivity and stable performance.?2? Compared with the plastic optical fiber, quartz optical fiber has the smaller transmission loss. High-quality and monolayer graphene was grown on copper foil by using CVD method, and transferred from copper foil to skiness tapered fiber core by using dry transfer technology. The double-stranded DNA?DS-DNA? was selected as the analyte, and the concentration was determined in the range of 0-400?m. The absorbance?A? and the DS-DNA concentrations shown a reasonable linear variation, which can be attributed to the molecular enrichment of graphene by ?-? stacking. This is consistent with the theoretical analysis and this EWA sensor is high sensitivity. All the components of the sensor are coupled together by fusion splicer, which can eliminate the external disturbance.?3? The Cu nanoparticles?Cu NPs? with a uniform distribution were synthesized by liquor-phase reduction synthesis?LPRS? method on the flat quartsubstrate?3cm×3cm?. The monolayer graphene film was grown by CVD technology. Graphene was transferred onto the prepared Cu NPs layer, to fabricate graphene/Cu NPs/quartz substrate hybrids SERS substrate.On the one hand, graphene can protect Cu NPs from oxidation. On the other hand, the SERS effect based CM of graphene also makes the Raman signals be further enhanced.?4? Graphene shells with controllable number of layers were directly synthesized on Cu NPs by using CVD method to fabricate the graphene-encapsulated Cu NPs?G/Cu NPs?hybrid system for SERS. Graphene shells and Cu NPs are seamless connection. This is a big step forward for graphene-based SERS substrates. With adenosine and rhodamine 6G?R6G?as the analyte, the SERS effect of the G/Cu NPs substrate is far better than the transferred graphene-Cu NPs substrate or the pure Cu NPs substrate. The graphene shells can also effectively prevent surface oxidation of Cu NPs after exposure to ambient air and endow the hybrids system with a long lifetime. More importantly, this method can greatly shorten the distance between graphene shell and Cu NPs, makes for the electromagnetic field loss decreased to minimum. We modeled the enhancement of |E| of Cu NPs by using finite-difference timedomain analysis and the results are consistent with the experimental results. So we can provide a new way for the design of SERS substrate and the interpretation of SERS mechanism.?5? Porous Si possesses large specific area and governable nanoporous structure, which can increase the amount of the effective hot spots and further enhance the sensitivity of the SERS signals. We first time grown Mo S2 film on the pyramid-Si substrate, fabricated the Mo S2-pyramid-Si SERS substrate. With adenosine as the analyte, the SERS effect of the MoS2-pyramid-Si substrate is much better than that of MoS2-flat-Si substrate. This study hasproposed a new type of SERS substrate manufacturing method.