研究目的
To demonstrate the suitability of graphene oxide-based thin films as both sensitive coatings and lossy mode resonance-generating materials in optical fiber sensors, simplifying device fabrication and enhancing sensitivity for refractometric applications.
研究成果
Graphene oxide-based thin films effectively serve as both sensitive and LMR-generating coatings in optical fiber sensors, enabling high-sensitivity refractometers with no hysteresis. The 8-bilayer device achieved sensitivities up to 12460 nm/RIU, surpassing previous materials. This approach simplifies fabrication and offers potential for functionalization with specific recognition groups, expanding applications to various analytes. Future work should focus on integrating selective chemistry for targeted sensing.
研究不足
The study is limited to refractometric applications using glycerol-water solutions; further validation with other analytes is needed. The sensitivity decreases with higher bilayer counts (e.g., 20 bilayers), and the fabrication process may require optimization for scalability. The spectrometer's range constrained measurements for certain RI values, and the coatings' long-term stability in varied environments was not assessed.
1：Experimental Design and Method Selection:
The study involved fabricating optical fiber sensors with graphene oxide (GO) and polyethylenimine (PEI) thin films using layer-by-layer assembly to generate lossy mode resonances (LMRs). The design rationale was to use GO as both the LMR-generating and sensitive coating, eliminating the need for additional metal oxide layers. Theoretical models for LMR generation were based on the permittivity conditions of the thin films.
2：Sample Selection and Data Sources:
A 200 μm-core multimode optical fiber (FT200EMT, Thorlabs, Inc.) was used, with cladding thermally removed. Samples included optical fiber devices with 8 and 20 bilayers of PEI-GO coatings, and silicon-based substrates for coating characterization. Data sources included transmission spectra from glycerol-water solutions with refractive indices (RI) of 1.333, 1.362, 1.392, and 1.
3：333, 362, 392, and List of Experimental Equipment and Materials:
420. 3. List of Experimental Equipment and Materials: Equipment included a halogen white light source (HL2000, Oceanoptics Inc.), spectrometer (USB2000, Oceanoptics), SEM (NanoSEM 450 FEG, FEI), profiling system (DektakXT, Bruker), cleaver (NorthLab ProCleave LD II), fusion splicer (Fitel S178A), and sonicator (Ultrawave limited). Materials included GO powder (Graphenea), PEI (Sigma Aldrich), KOH (Sigma Aldrich), glycerol, and ultrapure water.
4：Experimental Procedures and Operational Workflow:
The fiber core was hydroxylated, then coated with PEI and GO bilayers via dip-assisted layer-by-layer assembly (5-minute immersions each, with rinsing and drying). Coating deposition was monitored by capturing transmission spectra after each bilayer. Sensors were characterized statically by immersing in glycerol solutions and dynamically by alternating immersions in 40% and 60% glycerol solutions. Spectra were collected using OceanView software.
5：Data Analysis Methods:
Transmission spectra were analyzed using a MatLab routine to fit LMR absorption bands with a polynomial function (degree 2) for precise wavelength shift tracking. Sensitivities were calculated in nm/RIU, and response times were estimated based on signal change percentages.
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multimode optical fiber
FT200EMT
Thorlabs, Inc.
Used as the waveguide core for sensor fabrication after cladding removal.
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halogen white light source
HL2000
Oceanoptics Inc.
Served as the excitation source for transmitting light through the optical fiber sensor.
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spectrometer
USB2000
Oceanoptics
Collected and analyzed the transmitted light spectra to monitor LMR absorption bands.
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scanning electron microscope
NanoSEM 450 FEG
FEI
Used to examine the uniformity and texture of the deposited thin films on silicon substrates.
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profiling system
DektakXT
Bruker
Measured the thickness of the PEI-GO coatings deposited on silicon substrates.
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fusion splicer
Fitel S178A
Fitel
Spliced optical fiber fragments to pigtails for connection to the characterization setup.
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cleaver
NorthLab ProCleave LD II
NorthLab
Used to cleave optical fiber fragments for sensor assembly.
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sonicator
Ultrawave limited Cardiff CF2 1YY
Ultrawave
Used for pre-assembly sonication of GO suspension to enhance nanosheet separation.
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graphene oxide powder
Graphenea
Used as the primary material for fabricating the LMR-generating and sensitive coatings.
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polyethylenimine
product number 03880
Sigma Aldrich
Used in layer-by-layer assembly with GO to form the LMR-generating coating.
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potassium hydroxide
Sigma Aldrich
Used for hydroxylation of the optical fiber core to instigate a negative charge.
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