Metal Oxide Based Optical Fiber for Methane Gas Detection

Semiconductor metal oxide (SMO) as a sensing layer for gas detection has been widely used. Many researches have been performed to enhance the sensing performance including its sensitivity, reliability and selectivity. Electrical sensors that use resistivity as an indicator of its sensing are popular and well established. However, the optical based sensor is still much to explore in detecting gas. By integrating it with SMO, the sensor offers good alternative to overcome some drawbacks from electrical sensors

Optical fiber coated Zinc Oxide (ZnO) nanorods decorated with Palladium (Pd) for hydrogen sensing

A novel hydrogen (H-2) sensor was developed using acid-etched optical fiber coated with zinc oxide (ZnO) nanorods. The sensing performance was done by comparing the acid-etched fiber coated with ZnO nanorods with and without decorated Palladium (Pd). The conventional optical single-mode fiber (SMF) with a diameter of 125 mu m has been modified as a transducing platform by etching it to 11 mu m diameter using hydrofluoric acid (HF) to enhance the evanescent field of the light propagates in the fiber core. The etched fiber was coated with ZnO nanorods via hydrothermal process by using seeding and growth solution method. The sensing layer was characterized through Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray (EDX) and X-Ray Diffraction (XRD) to verify the properties of ZnO. Catalyst Palladium (Pd) was sputtered onto the ZnO nanorods to improve H-2 detection. The developed sensor operating temperature was found to be 150 degrees C that produces 6.36 dBm increase in response towards the 1% concentration of H-2 in synthetic air. It was then tested with different concentration of H-2. The sensor decorated with Pd has better performance in sensing compared to non-decorated Pd based on the output power versus time. The sensor best response and recovery times is 6 and 5 min respectively, for acid-etched optical fiber coated with ZnO nanorods decorated with Pd for 0.75% of H-2 concentrations at 150 degrees C. The results indicate the optical fiber sensor might improve the performance towards H-2 as oppose to the conventional electrical sensor

Gasochromic response of optical sensing platform integrated with polyaniline and poly(3,4-ethylenedioxythiophene) exposed to NH3 gas

The optical NH3 gas sensing performance of polyaniline (PANI) and poly(3,4-ethylenedioxythiophene (PEDOT) in the form of bilayers and copolymers was analysed in this study. The order of the bilayers and the presence of acid dopant on the fabrication of the sensing platform produced different absorbance responses upon exposure to NH3 gas. The limit of detection of the bilayer (PANI(aq.)/PEDOT(aq.)) was 7.86 ppm which is under the threshold limit value of NH3, with response and recovery times of 2.33 min and 46.8 s, respectively. The gasochromic behaviour of PANI and PEDOT during the adsorption of NH3 gas was closely related to the changes in the oxidation state which have simultaneously altered the colour intensity of the respective sensing layer

Optical ammonia gas sensor of poly(3,4-polyethylenedioxythiophene), polyaniline and polypyrrole: a comparative study

In this work, the optical sensing performance of three different types of conducting polymers, polyaniline (PANI), poly(3,4-ethylenedioxythiophene) (PEDOT) and polypyrrole (PPy) towards ammonia (NH3) gas has been evaluated. The sensing analyses of the respective conducting polymers were measured in the optimised wavelength ranges that manifest absorbance response upon exposure to NH3 gas. Based on the dynamic response where the respective conducting polymers were exposed to NH3 gas within the concentration range of 0.0625 % to 1 %, PEDOT exhibited the highest sensitivity (9.03/%) towards NH3 gas comparing to PANI and PPy with the detection limit of 2.73 ppm, which is in agreement with their respective conductivity trends

Optical fiber coated Zinc Oxide (ZnO) nanorods decorated with Palladium (Pd) for hydrogen sensing

A novel hydrogen (H2) sensor was developed using acid-etched optical fiber coated with zinc oxide (ZnO) nanorods. The sensing performance was done by comparing the acid-etched fiber coated with ZnO nanorods with and without decorated Palladium (Pd). The conventional optical single-mode fiber (SMF) with a diameter of 125 μm has been modified as a transducing platform by etching it to 11 μm diameter using hydrofluoric acid (HF) to enhance the evanescent field of the light propagates in the fiber core. The etched fiber was coated with ZnO nanorods via hydrothermal process by using seeding and growth solution method. The sensing layer was characterized through Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray (EDX) and X-Ray Diffraction (XRD) to verify the properties of ZnO. Catalyst Palladium (Pd) was sputtered onto the ZnO nanorods to improve H2 detection. The developed sensor operating temperature was found to be 150 °C that produces 6.36 dBm increase in response towards the 1% concentration of H2 in synthetic air. It was then tested with different concentration of H2. The sensor decorated with Pd has better performance in sensing compared to non-decorated Pd based on the output power versus time. The sensor best response and recovery times is 6 and 5 min respectively, for acid-etched optical fiber coated with ZnO nanorods decorated with Pd for 0.75% of H2 concentrations at 150 °C. The results indicate the optical fiber sensor might improve the performance towards H2 as oppose to the conventional electrical sensor

H2 sensor based on tapered optical fiber coated with MnO2 nanostructures

A novel hydrogen (H2) sensor was developed using optical fiber coated with manganese dioxide (MnO2) nanostructures. Optical multimode fiber (MMF) of 125 μm in diameter as the transducing platform was tapered to 20 μm to enhance the evanescent field of the light propagates in the fiber core. The tapered fiber was coated with MnO2 nanograins synthesised via chemical bath deposition (CBD) process. Catalytic Palladium (Pd) was sputtered onto the MnO2 layer to improve the H2detection. The sensing layer was characterized through Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray (EDX), X-ray Diffraction (XRD) and Raman Spectroscopy to verify the properties of MnO2. Two sets of sensors consist of as-prepared MnO2 and 200 °C annealed MnO2 were tested towards H2 gas. The tapered optical fiber coated with Pd/MnO2 nanograins was found to be sensitive towards H2with different concentrations in synthetic air at 240 °C operating temperature. The annealed sensor showed higher response and sensitivity as compared to the as-prepared sensors when measured in the visible to near infra-red optical wavelength range. The absorbance response of the annealed Pd/MnO2 on fiber has increased to 65% as compared to 20% for the as-prepared Pd/MnO2 upon exposure to 1% H2in synthetic air

Impact of opioid-free analgesia on pain severity and patient satisfaction after discharge from surgery: multispecialty, prospective cohort study in 25 countries

Background: Balancing opioid stewardship and the need for adequate analgesia following discharge after surgery is challenging. This study aimed to compare the outcomes for patients discharged with opioid versus opioid-free analgesia after common surgical procedures.Methods: This international, multicentre, prospective cohort study collected data from patients undergoing common acute and elective general surgical, urological, gynaecological, and orthopaedic procedures. The primary outcomes were patient-reported time in severe pain measured on a numerical analogue scale from 0 to 100% and patient-reported satisfaction with pain relief during the first week following discharge. Data were collected by in-hospital chart review and patient telephone interview 1 week after discharge.Results: The study recruited 4273 patients from 144 centres in 25 countries; 1311 patients (30.7%) were prescribed opioid analgesia at discharge. Patients reported being in severe pain for 10 (i.q.r. 1-30)% of the first week after discharge and rated satisfaction with analgesia as 90 (i.q.r. 80-100) of 100. After adjustment for confounders, opioid analgesia on discharge was independently associated with increased pain severity (risk ratio 1.52, 95% c.i. 1.31 to 1.76; P < 0.001) and re-presentation to healthcare providers owing to side-effects of medication (OR 2.38, 95% c.i. 1.36 to 4.17; P = 0.004), but not with satisfaction with analgesia (beta coefficient 0.92, 95% c.i. -1.52 to 3.36; P = 0.468) compared with opioid-free analgesia. Although opioid prescribing varied greatly between high-income and low- and middle-income countries, patient-reported outcomes did not.Conclusion: Opioid analgesia prescription on surgical discharge is associated with a higher risk of re-presentation owing to side-effects of medication and increased patient-reported pain, but not with changes in patient-reported satisfaction. Opioid-free discharge analgesia should be adopted routinely

Hydrogen sensors using tapered optical fiber coated with metal oxide nanostructures synthesized via chemical bath deposition technique

In this thesis, novel optical hydrogen (H2) sensors based on manganese dioxide (MnO2), zinc oxide (ZnO) and molybdenum trioxide (MoO3) nanostructures coated on tapered multimode fiber (MMF) via chemical bath deposition (CBD) were developed and investigated. The use of H2 as a clean fuel in various application requires practical and robust sensors as to minimize the risk of explosions associated with its volatile properties. Semiconducting metal oxides (SMO) has been widely used for decades in H2 sensing purpose due to its simplicity in fabrication, low cost and high sensitivity. Nanostructures SMO thin films as sensing layer has been reported to enhance the sensitivity of the sensors due to its high surface area to increase the gas molecules-sensing layer interaction. Typical SMO gas sensors are electrical based in which conductivity changes as it reacts to H2 gas. However, it has certain limitations such as easily affected by electromagnetic interference (EMI) thus compromise the signal response and small sparks could ignite massive explosion if the H2 concentration leaks is more than 4% in the environment. On the other hand, optical sensor which has yet well explored, offers advantages in term of size, light weight, resistant to EMI and resilient in high temperature environment. By integrating the optical transducer with SMO material, it can be employed as a hydrogen gas sensor. There are various methods of producing SMO material such as chemical and physical vapor deposition, RF sputtering, electrochemical deposition and thermal evaporation. These techniques require complicated setup with high operating temperature along with carrier gas during the process and need conductive substrate to perform the procedure. These techniques were also difficult to be implemented on optical fiber. Alternatively, chemical bath deposition method provides simple and easy setup, low operating temperature, low cost and environmental friendly. Therefore the author opted this method to fabricate H2 sensor using tapered optical fiber coated with selected SMO incorporated with palladium (Pd) as a catalyst to enhance the optical responses. In this study, the fabricated sensor is comprised of tapered multimode silica fiber (MMF) as the transducing platform. The tapering process is essential as to enhance the sensitivity to the environment through the interaction of evanescent field on the tapered surface area. The tapered region is then coated with sensing layer which is also important factors that influence the performance of the sensor. For this work, the author focused on a few kinds of SMO material well-known for their electrochromic properties which are manganese dioxide (MnO2), zinc oxide (ZnO) and molybdenum trioxide (MoO3), combined with Pd as the catalytic layer. The SMOs were grown via chemical bath technique and in-situ deposited onto the tapered optical fiber. The morphology of MnO2, ZnO and MoO3 synthesized and deposited on optical fiber were found to be nanograins, nanoflowers and nanogranules which were well distributed over the cylindrical shaped of the tapered optical fiber. The absorbance response of these sensors was characterized in terms of response and recovery times, sensitivity, repeatability and selectivity. It was discovered that the optimum thickness where the sensors of MnO2, ZnO and MoO3 exhibited maximum absorbance response are 300 nm, 280 nm and 250 nm respectively. It was revealed that the annealed sensor demonstrated higher sensitivity compared to as-prepared sensor. It was discovered that annealed Pd/MoO3 coated on tapered optical fiber sensor exhibited highest absorbance increase of 3.80 when exposed to 1% H2 at low operating temperature of 150oC as compared to other metal oxides nanostructures. The response and recovery times recorded were 1.2 min and 3.0 min. The developed MnO2, ZnO and MoO3 nanostructures coated on tapered optical fiber sensor for H2 using CBD technique are the first of its kind according to the author’s knowledge

H2 Gas Sensor Based on Pd/ZnO Nanostructures Deposited on Tapered Optical Fiber

A novel H2 sensor using tapered optical fiber coated with Pd/ZnO nanostructures have been developed. The ZnO nanostructures was synthesized and deposited onto tapered optical fiber via chemical bath deposition (CBD) method. The ZnO was characterized by FESEM, XRD and EDX to confirm the material properties. It was discovered that the sensor is sensitive towards different concentrations of H2 in synthetic air at 180° C of operating temperature. By varying the deposition time of ZnO coating, different thickness of ZnO layer can be obtained. It was observed that with 280 nm thickness, the maximum absorbance response can be achieved. Further investigation with sensor sample of as-prepared and annealed was carried out to study its sensing performance towards H2. The absorbance response of 280 nm thickness of annealed Pd/ZnO has increased 64% as compared to as-prepared Pd/ZnO upon 1% H2 exposure in the synthetic air when measured in the visible to near infra-red optical wavelength. It can be concluded that the Pd/ZnO optical fiber sensor with thickness around 280 nm provided better sensitivity in sensing H2 at 180°C as compared to other thicknesses investigated. © 2001-2012 IEEE