Modified plastic optical fiber with CNT and graphene oxide nanostructured coatings for ethanol liquid sensing

Abstract

A high sensitivity and simple ethanol sensor based on an un-cladded multimode plastic optical fiber (UCPOF) coated with carbon nanotubes (CNTs) for the detection of different concentrations of ethanol in de-ionized water is developed and demonstrated. The UCPOF probe is fabricated by chemically removing the fiber cladding and integrated with CNT as a sensing layer. The effect of surface morphology on the sensor performance is investigated by characterizing another UCPOF coated with GO nanomaterial. The developed fibers are coated with CNTs and GO using drop casting technique. Energy dispersive X-ray spectroscopy (EDX), atomic-force microscopy (AFM) and scanning electron microscope (SEM) are used to investigate the element and morphology of the synthesized nanomaterials. The experimental results indicated that the absorbance spectrum of the CNT-based UCPOF sensor increases linearly with a higher sensitivity of 0.68/vol% and magnitude change of 95.4% as compared to 0.19/vol% and 56.3%, respectively, for the GO-based sensor. The UCPOF coated with CNT exhibits faster response and recovery than that of GO. The sensor shows high selectivity to ethanol amongst a range of diluted organic VOCs. The superior sensing performance of the developed fiber sensor indicates its high efficiency for ethanol detection in various industrial applications.

A Review of Optical Fibre Ethanol Sensors: Current State and Future Prospects

“…This change in absorption can manifest as a pure intensity change (no spectral modulation) or as a change in the transmitted light spectrum, e.g., through the appearance of dips or absorption edges in the received spectrum. Many geometrical deformations of optical fibres have been reported in the literature to enhance the sensitivity of absorbance-based ethanol sensors such as U-shaped, coil-shaped, meander-shaped and tapering sensors as well as a combination of bending and tapering sensors [ 35 , 41 , 54 , 55 , 56 ].…”

“…The sensor exhibited a resolution of 10 −7 Refractive Index Unit (RIU) with 99.76% linearity in the response. The sensitivity and limit of detection (LOD) were found to be 817.76 Optical Density/Refractive Index Unit (O.D./RIU) and 9.2 × 10 −7 RIU, respectively, as shown in Figure 4 b. Khalaf et al showed carbon nanotubes (CNT) to be sensitive to aqueous ethanol solutions in the range of 20% to 100% when they were coated on an unclad multimode POF (UCPOF) using a drop-casting technique [ 56 ]. The GO nanomaterial was also synthesised and used as a sensing layer to obtain a comprehensive view of the CNT-based sensor’s performance.…”

“…Some researchers have formulated techniques to mitigate temperature cross-sensitivity, including an inline C-shaped open-cavity FPI [ 68 ], a combination of FP cavity and Michelson interferometry [ 69 ], micro grooved FBG [ 42 ], a combination of FBG and LPG for simultaneous temperature and RI measurement [ 37 ] and etched FBGs [ 84 ]. Cross-sensitivity due to other chemicals can be minimised or avoided by improving the selectivity of sensors and some work has also been reported for improving selectivity by modifying POF with CNTs [ 56 ], by combining interferometric and LSPR techniques [ 72 ] and by using ethanol-selective enzymes [ 94 ]. However, these sensor systems exhibit other drawbacks such as the use of specialised essential non-commercial parts, complex interrogation methods, low mechanical strength, narrow measurement range and limited sample-by-sample measurement.…”

Immunosensing Based on Optical Fiber Technology: Recent Advances

“…As follows, FBGs consist of a set of narrowband reflectors, having equally spaced grating patterns, inscribed on the optical fiber. The grating period defines the wavelength of the light that is reflected, and the periodic perturbations in the sensors based on FBGs For the production of unclad optical fibers, the fiber cladding can be mechanically removed by the aid of a sharp blade [32], especially in the case of POFs [8], or through chemical etching [57,58], mainly applied in SOFs. Another approach consists in bending the fiber to obtain a U-shaped structure, which allows coupling from the core mode to the cladding modes, enhancing the penetration depth of the evanescent field and consequently the fiber sensitivity [59,60].…”

“…For the production of unclad optical fibers, the fiber cladding can be mechanically removed by the aid of a sharp blade [ 32 ], especially in the case of POFs [ 8 ], or through chemical etching [ 57 , 58 ], mainly applied in SOFs. Another approach consists in bending the fiber to obtain a U-shaped structure, which allows coupling from the core mode to the cladding modes, enhancing the penetration depth of the evanescent field and consequently the fiber sensitivity [ 59 , 60 ].…”