Sensitivity enhancement of lossy mode resonance-based ethanol sensors by graphene oxide coatings

A layer by layer (LbL) coating made of polyethyleneimine (PEI) and graphene oxide (GO) is deposited onto an optical fiber ethanol sensor based on lossy mode resonances (LMR) in order to improve its response. The new sensor including the PEI/GO coating shows a better linearity and a sensitivity four times higher than the sensor without the coating. To our knowledge, this is the first time that a LbL coating made of PEI and GO is included in an optical fiber sensor based on LMR

Graphene Oxide in Lossy Mode Resonance-Based Optical Fiber Sensors for Ethanol Detection

The influence of graphene oxide (GO) over the features of an optical fiber ethanol sensor based on lossy mode resonances (LMR) has been studied in this work. Four different sensors were built with this aim, each comprising a multimode optical fiber core fragment coated with a SnO2 thin film. Layer by layer (LbL) coatings made of 1, 2 and 4 bilayers of polyethyleneimine (PEI) and graphene oxide were deposited onto three of these devices and their behavior as aqueous ethanol sensors was characterized and compared with the sensor without GO. The sensors with GO showed much better performance with a maximum sensitivity enhancement of 176% with respect to the sensor without GO. To our knowledge, this is the first time that GO has been used to make an optical fiber sensor based on LMR

Lossy Mode Resonance Generation by Graphene Oxide Coatings onto Cladding-Removed Multimode Optical Fiber

In this work, we have studied the suitability of graphene oxide-based thin films to be not only excellent sensitive coatings but also lossy mode resonance (LMR)-generating materials. Thin films of graphene oxide (GO) and polyethylenimine (PEI) fabricated by means of layer-by-layer assembly were selected in this study. Two optical fiber devices with 8 and 20 bilayers of the LMR-generating coating were fabricated and characterized as refractometers. Both devices show no hysteresis and high sensitivity, improving previously reported values. This research opens very promising and exciting possibilities in the field of optical fiber sensors based on LMR, strategically including specific recognition groups to the device surface to exploit this high sensitivity for monitoring a range of target analytes. The carboxylate functional groups at the edges of the GO sheets should provide excellent attachment sites for the required coupling chemistry to realize such devices

Systematic covalent crosslinking of graphene oxide membranes using 1,3,5 triazine 2,4,6 triamine for enhanced structural intactness and improved nanofiltration performance

From its physicochemical characteristics, graphene oxide (GO) is a promising versatile next generation membrane material. Its unique characteristics like ultrafast permeation and hydrophilicity makes it a favourable separation membrane nanomaterial in water purification. However, a fundamental problem in the use of GO in nanofiltration is decreased performance overtime due to the pore size widening phenomenon. This paper explored the use of an amine group containing compound, 1,3,5 triazine, 2,4,6 triamine (melamine) to covalently interlink the GO nanosheets to counteract this swelling phenomenon. Prior to membrane fabrication, covalent interactions between GO and the crosslinker, melamine were successfully confirmed through thermogravimetric analysis (TGA), x-ray photoelectron spectroscopy (XPS), X-ray Diffraction (XRD) and Fourier Transform Infra-Red (FTIR) spectroscopy characterisations. Following these characterisations, crosslinked membranes were successfully fabricated and enhanced nanofiltration performance was confirmed. Resultantly, the surface morphology of the membranes was recorded via Scanning Electron Microscopy (SEM) characterisations while a lab-scale nanofiltration device was constructed for flux and rejection analysis. Evidently, performance improvement with covalent crosslinking was imminent as an up to a 100% rejection of methylene blue was achieved for the crosslinked membranes. Structural integrity of GO membranes has indeed been improved through crosslinking

Highly efficient and stable PANI/TRGO nanocomposites as active materials for electrochemical detection of dopamine

Thermally reduced graphene oxides (TRGOs), produced at 400 and 700°C, and polyaniline (PANI) were used for one-pot facile hydrothermal synthesis of binary nanocomposites (PANI/TRGO). The morphology and chemical composition of these materials were thoroughly characterized by means of scanning electron microscopy, nitrogen sorption at 77 K, elemental analysis, X-ray photoelectron spectroscopy, X-ray diffraction, and sheet resistance measurements. Cyclic voltammetry, differential pulse voltammetry and electrochemical impedance spectroscopy were used for electrochemical characterization. The scanning electron microscopy (SEM) observation revealed that the morphology of TRGOs has a crucial impact on the distribution of PANI in the composites. A more homogenous distribution of PANI was achieved for PANI/TRGO-700 due to the higher degree of exfoliation of the starting material TRGO-700. The synthesized composites were investigated as modifiers of glassy carbon electrodes (GCEs) for the electrochemical sensing of dopamine. Both, the PANI distribution and an appropriate oxygen content are key for DA sensing. Thus, the better performance of PANI/TRGO-700 as an active material was revealed, achieving a LOD of 430 nM, an excellent sensitivity (6.7 µA µM−1) and stability after 30 days

High-performance optical fiber humidity sensor based on lossy mode resonance using a nanostructured polyethylenimine and graphene oxide coating

In this study, a rapid optical fiber sensor for humidity with high sensitivity and wide detection range has been constructed, based on lossy mode resonance (LMR). A thin film made of alternating polyethylenimine (PEI) and graphene oxide (GO) layers was selected as sensitive coating. It was deposited on a SnO2-sputtered fiber core in a dip-assisted layer-by-layer assembly. The structure and surface chemistry of the raw materials were investigated by means of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Key properties such as sensitivity, linearity, hysteresis, stability and response and recovery times were characterized. The sensor exhibited excellent sensitivity, especially at high relative humidity (RH) levels, and short reaction and retrieval periods. This research provides a viable and practical way to fabricate high performance humidity optical fiber sensors with GO-based nanostructured coatings

Optical fiber exhaled breath sensor based on lossy mode resonance using a graphene oxide sensitive coating

Optical fiber sensors (OFS) have attracted increasing attention due to their benefits over traditional sensors, such as small size, biocompatibility, remote sensing ability or safety in flammable environments. Among the different existing configurations of OFS, those based on electromagnetic resonances are very popular as they are reliable, robust and very sensitive. In particular, sensors based on lossy mode resonance (LMR) are very interesting as a wide range of materials, including metal oxides and polymers, can support them and they do not require specific equipment to tune the optical polarization. Graphene-based materials like graphene oxide (GO) or reduced graphene oxide (rGO) have become the most explored materials since Novoselov and Geim achieved its isolation in 2004. Their superior properties, such as high surface area or extreme sensitivity to the external environment, make them ideal candidates for the fabrication of the sensitive coatings required by LMR-based sensors. In this work, the fabrication and characterization of a small and portable exhaled breath LMR-based OFS using GO as sensitive coating is presented. Refractive index changes have been detected showing a fast repetitive behavior with a response time of 150 ms from inhalation to exhalation and a high average sensitivity of 410 nm/RIU