Sustainable and fast saliva-based COVID-19 virus diagnosis kit using a novel GO-decorated Au/FBG sensor

Monitoring the COVID-19 virus through patients’ saliva is a favorable non-invasive specimen for diagnosis and infection control. In this study, salivary samples of COVID-19 patients collected from 6 patients with the median age of 58.5 years, ranging from 34 to 72 years (2 females and 4 males) were analyzed using an Au/fiber Bragg grating (FBG) probe decorated with GO. The probe measures the prevalence of positivity in saliva and the association between the virus density and changes to sensing elements. When the probe is immersed in patients’ saliva, deviation of the detected light wavelength and intensity from healthy saliva indicate the presence of the virus and confirms infection. For a patient in the hyperinflammatory phase of desease, who has virus density of 1.2 × 108 copies/mL in saliva, the maximum wavelength shift and intensity changes after 1600 s were shown to be 1.12 nm and 2.01 dB, respectively. While for a patient in the early infection phase with 1.6 × 103 copies/mL, these values were 0.98 nm and 1.32 dB. The precise and highly sensitive FBG probe proposed in this study was found a reliable tool for quick detection of the COVID-19 virus within 10 s after exposure to patients’ saliva in any stage of the disease

Modification of intrinsic refractive index optical fiber sensor via precise cladding removal and heterogeneous ZnO/Ag bi-layer coating

Miniaturized refractive index sensor by combination of nanostructure thin films as a transformer sensitive layer and optical fiber as a signal carrier offers great potential for identifying the environmental features and understanding the novel sensor concepts. The partially unclad and bi-layer zinc oxide (ZnO) or silver (Ag) coated multimode glass and polymer optical fiber as a simple and reliable intrinsic fiber sensor was proposed in this work to detect the ambient refractive index changes (saline and crude oil having various concentrations) using two broadband sources of infrared radiation and ultraviolet-visible. The removing process to partially unclad the polymer and glass fiber was carried out precisely using our proposed dynamic monitoring process to prevent any interruption on propagating light by occurrence of damage on the core surface. The ZnO as an outer sensitive layer had three configuration which was spherical nanoparticle, horizontally and vertically oriented nanorods deposited on discontinuous Ag layer using mixture of electroless, dip coating and low temperature hydrothermal techniques because solo deposition technique was not possible. Ag nano-island shape deposition made the transition of evanescent wave to external media possibly through this semi-reflectance structure. ZnO coating avoided the formation of oxygen deficit defects, inhibited aging problem and trapping measurand molecules through mechanical interlock phenomena which altered its optical characteristics and improved sensitivity of the sensor. The x-ray diffraction spectra demonstrate that the level of crystallinity was higher for vertically oriented ZnO compared to others. Using field emission scanning electron microscope images, the width or length of vertically and horizontally oriented ZnO nanorods was measured. This shift is independent with the contact media. However, deep level emission depends strongly on the concentration of the contacted media. The shift observed for nanoparticle. The performance of fabricated probe to detect saline concentration changes for glass fiber coated with vertically oriented ZnO nanorods/Ag when IR light source employed, was supreme compared to the other samples and was reported to be 255.4 nm/RIU and 314.2 dB/RIU for wavelength and intensity sensing respectively. The durable polymer fiber coated with vertically oriented ZnO/Ag nanorods showed the intensity and wavelength sensitivity of 146.2 dB/RIU and 78.5nm/RIU respectively in identifying the variation of crude oil from 0 to 100%. The optimum length of glass and polymer fiber probe for maximum sensitivity was obtained for 3 cm and 2 cm respectively. The precise production techniques together with comprehensive analysis of the sensing mechanism lead to a deeper understanding of the liquid refractive index behavior applicable in quality control in water resource and oil reservoir

Comprehensive investigation of evanescent wave optical fiber refractive index sensor coated with ZnO nanoparticles

Combination of optical fiber and semiconductor metal oxide nanostructure provide a label-free refractive index (RI) sensor with an excellent limit of detection. ZnO NPs (nanoparticles) coated evanescent based multimode optical fiber sensor is established to detect different crude oil concentrations blended in diethyl ether. The efficacy of fabricated sensors with respect to wavelength shift and intensity changes is tested with different crude oil concentration from 0% (RI: 1.35) to 100% (RI: 1.47). By increasing the crude oil concentration, the maximum shift of ~10 nm towards lower wavelength is occurred. The signal in visible area originated from the electron–hole recombination at a deep level via singly ionized oxygen vacancies (VO +). Increasing the crude oil concentration leads to decreasing the transmission intensity up to 72% of its maximum value. Changes in refractive index of ZnO nanostructure from 2.671 to 2.726 with the change in oil concentration from 0% to 100% respectively, leads to different quantity of evanescent wave absorption taken placed. Different absorption rate and reflection angle in the cladding-ZnO interface are responsible for intensity modulation. The interaction of oxygen vacancies on ZnO surface, electron migration from donor media to the valance band and lowering the band-gap with decreasing the crude oil concentration are responsible for RI modification of ZnO. Therefore, an economic, high sensitive and multipurpose dual sensing scale has been proposed for crude oil detection

Intensity modulated silver coated glass optical fiber refractive index sensor

Miniature optical fiber sensors with thin films as sensitive elements could open new fields for optical fiber sensor applications. Thin films work as sensitive elements and a transducer to get response and feedback from environments, in which optical fibers act as a signal carrier. A novel Ag coated intensity modulated optical fiber sensor based on refractive index changes using IR and UV-Vis (UV-visible) light sources is proposed. The sensor with an IR light source has higher sensitivity compared to a UV-Vis source. When the refractive index is enhanced to 1.38, the normalized intensity of IR and UV-Vis light diminishes to 0.2 and 0.8, respectively

Detection of saline-based refractive index changes via bilayer ZnO/Ag-coated glass optical fiber sensor

The combination of sensitive nanostructure thin films and optical fiber offers the great prospective for understanding the novel sensor concepts. The partially unclad and bilayer zinc oxide (ZnO)/silver (Ag)-coated multimode glass fiber as a simple and reliable probe is proposed in this work to detect the ambient refractive index changes using two broadband sources of IR and UV–Vis. The wavelength and intensity of propagating light both are modulated when the saline concentration is varied. The appropriate etching time for partially removing the cladding suitable for both IR and UV–Vis sources is 53 min. The fabricated ZnO/Ag/fiber sensor exhibits excellent repeatability and high sensitivity to saline with different concentrations from 0 to 30% at room temperature. Among the sensors probe, higher sensitivity is observed for ZnO/Ag/fiber sample when IR is used as a light source. In this sensor by changing the refractive index of the media from ~ 1 to ~ 1.38, the normalized intensity drop to 0.6 of its maximum value and corresponding wavelength shifted from ~ 1559 to ~ 1585 nm. The high sensitivity of fabricated probe is attributed to two phenomena related to bilayer structure of sensing probe: first, the uncontinuous Ag coating which makes the optical tunneling to the outer layer be possible and, second, altering the optical properties of ZnO by oxygen absorbance through interaction of saline by ZnO nanostructure and changing the refractive index of the deposited layer. The wavelength and intensity are found to be less sensitive for both partially unclad and ZnO/Ag/fiber once UV–Vis is used as a light source, which is due to slighter penetration of evanescent wave in the cladding part compared to IR source

Comprehensive study on glycoprotein detection via polymer fiber sensor decorated with dome-like Ag nanoislands and ZnO nanorods

The surface plasmon resonance (SPR) based polymer fiber sensor is experimentally demonstrated via ZnO/Ag nano-heterostructure bi-layer coating with novel configuration. Glycoprotein detecting criteria is theoretically explained via changing the band gap and refractive index (RI) of ZnO, absorption of leaking light with analyte media, penetration depth of evanescence field, interaction of SPR with evanescence wave, hydrophilicity of ZnO surface and electrochemistry of the ZnO surface. The optical analysis of ZnO(nanorods)/Ag/polymer sample reveals that increasing the glycoprotein concentration, shifts (0.022 eV) the DL emission towards higher wavelength. Electron transferring from donor groups of glycoproteins when interact and bond with ZnO molecules are responsible for this shift. Plasmon resonance shift of ??: ~2.21º by increasing the glycoprotein dose from 0 to 0.209 ppm illustrates, interaction of SPR with evanescence wave. Sensitivity of developed polymer fiber sensor is calculated via analysis of output emission spectra and the maximum value achieved are 21 dB/ppm and 45.9 nm/ppm for intensity and wavelength respectively, having the minimum detection limit of 0.021 ppm. Our accurate designed fiber sensor can open up a new opportunity towards application in chemical and biological industries

Modified polymer optical fiber sensors for crude oil refractive index monitoring

The oil concentration as a petroleum quality parameter is an eternal mystery that determines the oil value. We report detection of crude oil refractive index (RI) changes by modified polymer optical fiber (POF) sensor which is prepared via removing the majority of cladding part until ~ 100 nm thickness remains followed by the deposition of discontinuous silver (Ag) nanofilm as an inner layer (~ 20 nm thicknesses) and coating with different shapes of zinc oxide (ZnO) nanostructures including nanoparticles and horizontally and vertically oriented nanorods as an outer layer. Upon conversion from ZnO nanoparticles to vertically oriented ZnO nanorods, the rms roughness, optical band gap, and light transmittance are varied from ~ 23 to ~ 346 nm, ~ 3.45 to ~ 3.20 eV, and 31 to 27%, respectively. The higher sensing performance is obtained for the probe coated with vertically aligned ZnO nanorods at near-infrared wavelength and the value for intensity and wavelength sensitivity are 38 dB/RIU and 78 nm/RIU, respectively. This superior performance is originated from deep penetration of evanescent wave, high surface volume ratio, good crystallinity, adhesive interaction with crude oil molecules, large surface roughness, and high-order dispersion

Multi aspect investigation of crude oil concentration detecting via optical fiber sensor coated with ZnO/Ag nano-heterostructure

Determining the crude oil concentration changes as an essential factor in reservoir engineering, via proposed modified optical fiber sensor, offers a novel approach in oil production optimization. A highly sensitive optical fiber probe is fabricated via partially removing the cladding and coating the sensing part with zinc oxide/silver (ZnO/Ag) heterostructre layer. The ZnO outer layer has three configurations including nanoparticle, horizontally and vertically oriented nanorods. The fabricated optical fiber sensors are subjected to detect the crude oil concentration variations through detection of both wavelengths shift and intensity changes. The effect of ZnO outer layer shape, and the type of light source is used, on sensitivity of the probe is examined. Comprehensive investigation on shape dependent structural and optical properties of ZnO outer layer demonstrates that vertically oriented ZnO has larger surface area, higher average dispersion relation, better crystallinity, larger surface roughness and better adhesion (interaction) with crude oil molecules and these characteristics are responsible for its superior performance compare to other ZnO configurations. For the probe coated with vertically aligned ZnO nanorods when the infrared (IR) light source is used, the intensity and wavelength sensitivity of 0.044 dB/?%crude oil and 0.112 nm/? %crude oil are obtained respectively

Influence of ZnO nanostructure configuration on tailoring the optical bandgap: Theory and experiment

Exploiting the link between form and function of semiconductor nanostructure provides a new prospect for tailoring the features of nanoscale materials. However, achieving this remains a challenge in the fabrication of optoelectronic devices. Therefore, this research systematically presents theoretical and experimental investigations of shape dependent structural and optical properties of ZnO nanostructures (nanoparticles, vertically oriented nanorods and compact ZnO) synthesized using the electroless deposition technique to understand the principles of bandgap modification. FESEM, XRD, Photoluminescence (PL) and UV–Vis spectroscopic characterizations were employed. The characterizations show increase in lattice parameters, bandgap and density of dislocations from 0.3236 nm to 0.3258 nm, ~3.14 eV to ~3.51 eV and ~17 × 10-4 to ~39 × 10-4 , respectively as the ZnO nanostructures are transformed from compact ZnO to ZnO nanoparticles. The expansion in lattice parameter is attributed to lower compressive stress that exists in ZnO nanoparticles compared to compact ZnO. The blue shift (0.06 eV) in bandgap is ascribed to overlapping of the orbitals and energy level in ZnO nanoparticles which causes a substantial increase in energy gap between valence and conduction bands. The small size-induced hardening in ZnO nanoparticles accounts for their comparatively higher dislocation density. Theoretically, conversion from compact ZnO to ZnO nanoparticles extends the bandgap from 3.38 eV to 3.44 eV, which is consistent with the experimental results. This study confirms the shape dependency of the structure and bandgap of ZnO nanostructures, which may provide a new insight into future integrated optoelectronic device applications