Low Intensity UV Light Research Articles

In2O3 nanocubes and ZnWO4 nanorod-based triboelectric nanogenerator for self-powered humidity sensors

In this study, a self-powered photo-induced humidity sensor was developed using ZnWO4/In2O3 heterostructure based Triboelectric Nanogenerator (TENG). The ZnWO4/In2O3 heterostructure-based TENG generates 44 V voltage and 1 µA current by finger tapping. The ZnWO4/In2O3 heterostructures were synthesized via hydrothermal method. SEM analysis confirmed the In2O3 nanocubes grown on ZnWO4 nanorods. XRD analysis confirmed the polycrystalline nature of ZnWO4/In2O3 heterostructures and the average crystallite size was found to be 32.66 nm. XPS analysis confirmed the presence of Zn2+, In3+, W4+, and O2- oxidation states. Optical properties were analyzed by UV–visible spectroscopy and maximum absorbance was found in the region (315–400 nm) since it is capable of absorbing UV light. In this work, the effect of very low-intensity UV light (2 mW/cm2) on a battery-less moisture detection was investigated at different moisture levels (10–90%RH). The sensor response was around 27.50 at 90%RH of photo-induced self-powered humidity sensor. Also, the fast response and recovery times were observed as 260 ms and 620 ms respectively in the illumination of UV light. The photo-induced self-powered humidity sensor showed highly sensitive and stable for a long time and it can be commercialized for indoor and outdoor humidity detection.

Beyond duodenoscope-transmitted infections: Analysis of surface bioburden and UV-C mitigation within a tertiary care endoscopy unit

An inpatient endoscopy unit is a care hub for patients from throughout the hospital and can be the site of healthcare-associated infections (HAIs). Shared surfaces and other nonmedical devices (keyboards) have been increasingly recognized as sites of pathogen transmission. Beyond standard cleaning of high-touch target areas, we queried whether the addition of automated devices delivering low-intensity doses of ultraviolet (UV)-C radiation could further reduce bioburden in an academic endoscopy unit. Bioburden on previously identified high-touch/communal surfaces was measured before and after the installation of automated, low-intensity UV-light emitting devices (UV Angel) that passively monitor and disinfect targeted surfaces with Ultraviolet-C light (UV-C) light. High-touch sites (keyboards) had a baseline bacterial contamination of >80%, whereas individual procedure rooms and common areas had a >57% contamination rate. Following the implementation of automated UV-C light decontamination, bioburden was reduced on average by >91% at high-touch surfaces and within procedure rooms. Nonsterile hubs of patient care could serve as sites of "silent" HAI transmission. We have identified high-touch surfaces within an endoscopy unit that have a high bioburden of bacterial contamination and demonstrated that the installation of passive, automated UV-C light disinfection devices can reduce bioburden significantly, possibly mitigating HAI transmission between patients.

Tetra-Dentate Cycloaddition Catalysts for Rapid Photopolymerization Reactions

[4 + 4] and [2 + 2] cycloadditions are unique reactions since they form and deform cycloadducts under irradiation due to their inherent reversible nature. Whereas promising for the field of recycling, these reactions usually suffer from two major shortcomings: long reaction durations (hours) and the requirement of high-intensity light (∼100 W/cm2), typically at a short wavelength (<330 nm). We demonstrate several tetra-dentate catalysts that can overcome these fundamental limitations. Among them is a tin complex that enables 76% conversion within only 2 min of irradiation at 395 nm, much faster than the known ruthenium-based catalyst, under irradiation with light intensity two orders of magnitude lower than that reported in the literature. Due to the short photopolymerization time, low intensity (27 mW/cm2), and long UV light (395 nm), this unique complex opens new avenues for recycling three-dimensional printing products based on photopolymerization of cycloaddition reactions.

A self-powered triboelectric UV photodetector based on coupling impedance matching and photoresistive effect by sensing-electrode model

Self-powered photodetectors can satisfy the development demands of Internet of things towards minimization, integration, intelligence and multifunctionality. In this work, we have reported a self-powered triboelectric UV photodetector (SPTUD) based on coupling impedance matching and the photoresistive effect. A sensing-electrode model is validated through replacing the traditional electrode by ZnO nanoparticle film in a single-electrode mode triboelectric nanogenerator (S-TENG). Working both as the photoresistive material and electrode, the resistance variation range of the ZnO film matches well with the resistance dependence of S-TENG. The output voltage is significantly affected by the variations in variable resistances of ZnO film altered by UV light intensity due to the impedance matching effect. As a self-powered UV photodetector, the voltage signal of SPTUD increases from 0.5 V to 1.1 V with increasing light intensity from 0 to 0.61 mW/cm2 under 375 nm UV light illumination. It can efficiently detect low-intensity UV light of 0.17 mW/cm2 with a voltage responsivity of 2.66 V (mW cm−2)−1. For demonstration, a wearable self-powered UV photodetection system based on the S-TENG and SPTUD is integrated in a bracelet. The reference-electrode and sensing-electrode are designed to connected with chip LEDs for visualized UV light photodetection to remind people to take effective measures for harmful UV light protection out of door. This work proposes the concept of sensing-electrode model, and we believe it will pave a new avenue for the next-generation of self-powered triboelectric sensors.

PH-Responsive swimming behavior of light-powered rod-shaped micromotors.

Micromotors have emerged as promising devices for a wide range of applications e.g., microfluidics, lab-on-a-chip devices, active matter, environmental monitoring, etc. The control over the activity of micromotors with the ability to exhibit multimode swimming is one of the most desirable features for many of the applications. Here, we demonstrate a rod-shaped light-driven micromotor whose activity and swimming behavior can easily be controlled. The rod-shaped micromotors are fabricated through the dynamic shadowing growth (DSG) technique, where a 2 μm long arm of titanium dioxide (TiO2) is grown over spherical silica (SiO2) particles (1 μm diameter). Under low-intensity UV light exposure, the micromotors exhibit self-propulsion in an aqueous peroxide medium. When activated, the swimming behavior of micromotors greatly depends on the pH of the medium. The swimming direction, i.e., forward or backward movement, as well as swimming modes like translational or rotational motion, can be controlled by changing the pH values. The observed dynamics has been rationalized using a theoretical model incorporating chemical activity, hydrodynamic flow, and the effect of gravity for a rod-shaped active particle near a planar wall. The pH-dependent translational and rotational dynamics of micromotors provide a versatile platform for achieving controlled and responsive behaviors. Continued research and development in this area hold great promise for advancing micromotors and enabling novel applications in microfluidics, micromachining, environmental sciences, and biomedicine.

In Vivo Modification of Microporous Structure in Bacterial Cellulose by Exposing Komagataeibacter xylinus Culture to Physical and Chemical Stimuli.

Bacterial cellulose (BC) samples were obtained in a static culture of K. xylinus under the effect of a low-intensity magnetic field, UV light, NaCl, and chloramphenicol. The effect of such stimuli on the amount of BC produced and its production rate, specific area, pore volume, and pore diameter were evaluated. The polysaccharide production was enhanced 2.28-fold by exposing K. xylinus culture to UV light (366 nm) and 1.7-fold by adding chloramphenicol (0.25 mM) to the medium in comparison to BC control. All the stimuli triggered a decrease in the rate of BC biosynthesis. BC membranes were found to be mesoporous materials with an average pore diameter from 21.37 to 25.73 nm. BC produced under a magnetic field showed the lowest values of specific area and pore volume (2.55 m2 g−1 and 0.024 cm3 g−1), while the BC synthesized in the presence of NaCl showed the highest (15.72 m2 g−1 and 0.11 cm3 g−1). FTIR spectra of the BC samples also demonstrated changes related to structural order. The rehydration property in these BC samples is not mainly mediated by the crystallinity level or porosity. In summary, these results support that BC production, surface, and structural properties could be modified by manipulating the physical and chemical stimuli investigated.

Application of a dual functional blocking layer for improvement of the responsivity in a self-powered UV photodetector based on TiO2 nanotubes.

A layer of graphene quantum dots (GQDs) was applied on the photoanode of a self-powered photoelectrochemical (PEC) UV photodetector based on TiO2 nanotubes (NTs). The GQDs layer acted as a dual functional layer and improved the photodetector performance by both UV light absorption and blocking the charge carriers recombination at the photoanode/electrolyte interface. The short circuit current density (Jsc) and thereby the responsivity of the PEC UV photodetector was enhanced by 473%. The highest value of the responsivity in this work obtained for the PEC UV photodetector with the dual functional GQDs layer was as much as 42.5 mA W−1. This value is far better than previously reported responsivities of the PEC devices based on TiO2 NTs as a photoanode. This high responsivity was obtained under the illumination of a very low intensity UV light (365 nm, 2 mW cm−2) and 0 V bias. Moreover, the sensitivity of the PEC UV photodetector with the dual functional GQDs layer has been improved by 345%, which is almost 3.5 times higher compared to the sensitivity of its counterpart without the GQDs coating. The devices with the dual functional GQDs layer present a splendid repeatability and stability. The rise time and the decay time of this device were measured to be 0.73 s and 0.88 s under the on/off switching UV LEDs, respectively. The electrochemical impedance spectroscopy (EIS) results prove the role of the GQDs layer as an effective blocking layer on the photoanode, hindering the charge carrier recombination at the photoanode/electrolyte interface. This study shows that application of the dual functional GQDs layer in the PEC UV photodetector based on TiO2 NTs is an effective approach for improving the responsivity and sensitivity of a self-powered PEC UV PD, which brought us the possibility of detecting low UV index radiation and using the self-powered photodetectors in cutting-edge wearable electronic devices for the aim of health, safety and environmental monitoring.

Low Intensity UV Light Detection by Al2O3Separated MoS2/CuO Junction

This work reports a Pd/MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /CuO/ITO structure based dual band photodetector for UV and visible region. In the proposed photodetector, type II heterojunction is formed between n-type MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and n-type CuO. The MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and CuO layers are separated by a thin insulating layer of Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> that helps in effectively suppressing the dark current. At −1 V bias voltage, the proposed photodetector depicts the responsivity, detectivity, and external quantum efficiency (EQE) as 2.55 A/W, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times 10^{13}$ </tex-math></inline-formula> Jones, and 848% at 302 nm (with power <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$12.9 \mu \text{W}$ </tex-math></inline-formula> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) while the corresponding values at 608 nm (with power <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$135.5 \mu \text{W}$ </tex-math></inline-formula> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) are found to be 1.33 A/W, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5.13\times 10^{12}$ </tex-math></inline-formula> Jones and 237 % respectively.

Structural Design of TiO2/Si Hybrid Photoelectrode and Pt-Free Counter Photoelectrodes for Charge Carrier Separation in Water-Splitting Reactions

A TiO2/Si hybrid photoelectrode (HPE) (photoanode) consisting of TiO2 and a Si n++p++nn++ photoelectrode, and a Pt-free counter photoelectrode (photocathode) consisting of Au or Ag clusters and a Si n++pp++ junction were manufactured and investigated. TiO2 was deposited on the Si n++p++nn++ photoelectrode to widen the spectral selectivity from UV to visible light. The alternative Pt-free counter photoelectrodes were manufactured with a slightly different structure, where Au or Ag clusters were deposited on the n++ layer of the Si n++pp++ junction. The photocurrent of the Si n++p++nn++ photoelectrode and the TiO2/Si HPE was measured using the Pt electrode or the Pt-free counter photoelectrodes. The analysis was carried out in the dark and under low-intensity UV light irradiation. The TiO2/Si HPE with the Pt-free counter photoelectrode (Ag clusters/Si n++p++nn++ junction) showed an increase of up to 74.2% in photocurrent compared with the Pt counter electrode. A deep-insight analysis for the new and simple design of the promising TiO2/Si HPE and the Pt-free counter photoelectrodes for hydrogen evolution from water was carried out.

Low-Intensity UV light sensor based on p-NiO/n-Si heterojunction

We studied the performance of a photodiode UV sensor based on a p-NiO/n-Si heterojunction. NiO thin film was prepared via a two-step process. In the first step, a thin film of Ni metal was evaporated on an n-Si substrate. Subsequently, the sample was thermally oxidized at 500 °C for 3 h in an ambient atmosphere. The phases and surface morphology of the prepared sample was determined by using x-ray diffraction analysis and scanning electron microscopy, respectively. The rectifying ratio of the prepared device was approximately 7 at a bias voltage of ±10 V, with a barrier height and ideality factor of 0.77 ± 0.03 eV and 16, respectively. The prepared device was tested for potential applications as a UV sensor. The prepared device exhibits high repeatability and fast response times of 1.5 s and 0.7 s for the rise and full time, respectively. The prepared photodiode responds to low-intensity UV light in the range from 30 μW·cm−2 to 430 μW·cm−2.

Highly Responsive Ultraviolet Sensor Based on ZnS Quantum Dot Solid with Enhanced Photocurrent

Detection of visible blind UV radiation is not only interesting but also of technologically important. Herein, we demonstrate the efficient detection of UV radiation by using cluster like ZnS quantum dot solid nanostructures prepared by simple reflux condensation technique. The short-chain ligand 3-mercaptopropionic acid (MPA) involved in the synthesis lead to the cluster like formation of ZnS quantum dots into solids upon prolonged synthesis conditions. The ZnS QD solid formation resulted in the strong delocalization of electronic wave function between the neighboring quantum dots. It increases the photocurrent value, which can be further confirmed by the decrease in the average lifetime values from 64 to 4.6 ns upon ZnS cluster like QD solid formation from ZnS QDs. The ZnS quantum dot solid based UV sensor shows good photocurrent response and a maximum responsivity of 0.31 (A/W) at a wavelength of 390 nm, is not only competitive when compared with previous reports but also better than ZnS and metal oxide-based photodetectors. The device exhibits a high current value under low-intensity UV light source and an on/off ratio of IUV/Idark = 413 at zero biasing voltage with a fast response. Further, photocurrent device has been constructed using ZnS quantum dot solid nanostructures with graphene hybrids as an active layer to improve the enhancement of photoresponsivity.

Preparation of PAN@TiO₂ Nanofibers for Fruit Packaging Materials with Efficient Photocatalytic Degradation of Ethylene.

Ethylene causes faster deterioration of perishable crops during postharvest transportation and storage. The present study aimed to develop TiO2-coated nanofibers with efficient photocatalytic activities to enhance the degradation of fruit-emitted ethylene. The consecutive electrospinning of polyacrylonitrile (PAN) and TiO2 deposition was successfully performed to produce PAN@TiO2 nanofibers. The scanning electron microscopy results indicate the uniform distribution of TiO2 nanoparticles on the surface of the PAN nanofiber. The PAN@TiO2 composite nanofibers exhibited enhanced photocatalytic activity for ethylene degradation under low-intensity UV light irradiation. Furthermore, a tomato fruit-ripening test confirmed the effectiveness of the PAN@TiO2 nanofibers. The PAN@TiO2 nanofibers exhibited effective ethylene degradation and slowed the color shift and softening of the tomatoes during storage. The results suggest great potential for use of the PAN@TiO2 composite nanofibers as ethylene scavenging packaging material for fresh fruits and vegetables.

Development and clinical application of Vertebral Metrics: using a stereo vision system to assess the spine.

The biomechanical changes in the spinal column are considered to be the main responsible for rachialgia. Although radiological techniques use ionizing radiation, they are the most applied tools to assess the biomechanics of the spine. To face this problem, non-invasive techniques must be developed. Vertebral Metrics is an ionizing radiation-free instrument designed to detect the 3D position of each vertebrae in a standing position. Using a stereo vision system combined with low intensity UV light, recognition is achieved with software capable of distinguishing fluorescent marks. The fluorescent marks are the skin projection of the vertex of the spinal processes. This paper presents a major development of Vertebral Metrics and its evaluation. It performs a scan in less than 45s with a resolution on the order of 1mm, in each spatial direction, therefore, allowing an accurate analysis of the spine. The instrument was applied to patients without associated pathology. Statistically significant differences between consecutive scans were not found. A positive correlation between the 3D positions of each vertebra and the homologous position of the other vertebrae was observed. Using Vertebral Metrics, innovative results can be obtained. It can be used in areas such as orthopedics, neurosurgery, and rehabilitation. Graphical abstract ᅟ.

Electrically Tunable Binary-Phase Fresnel Lens Based on Polymer Dispersed Liquid Crystal

This is a proposal for a Fresnel lens with an electrically tunable binary-phase made of polymer dispersed liquid crystal (PDLC), which has relatively fast response time and low applied voltage. Simple fabrication is the major advantage of the proposed method. In this study, NOA65 and E7 were utilized with weight ratios of 60 wt.%: 40 wt.%. There was also the utilization of a relatively low intensity UV-light, 0.53 mW/cm 2 . The duration time of exposure was about 30 hours. The performance improvement of the Fresnel lens resulted from the infiltration of large LC droplet into the PDLC film. The phenomenon of black cross strip patterns could be explained with the use of the electro-hydrodynamics theory. The diffraction efficiency of the proposed lens was from 31.1 % to 41 % with the changes of externally applied voltage. This work presents an effective approach to get relatively complete phase separation in PDLC. The proposed method also provides great potential in developing high performance Fresnel lens. DOI: http://dx.doi.org/10.5755/j01.ms.23.2.16317

Degradable UV-crosslinked hydrogel for the controlled release of triclosan with reduced cytotoxicity

In order to realize the controlled release and limited toxicity of triclosan (TC), a degradable UV-crosslinked hydrogel was prepared. For this purpose, the acryloyl chloride-modified polyactide-poly(ethylene glycol)-polylactide block copolymer was firstly synthesized and then mixed with photoinitiator to form the hydrogel rapidly under a low-intensity UV light. The properties of hydrogel, such as hydrogel strength, swelling and degradation, had been studied. The results showed that the properties of hydrogel could be modulated by the concentration of copolymer. After the encapsulation of TC, the sustained-release capability and antibacterial effect of the obtained hydrogel were studied. It was found that the sustained release of TC could potentially reduce the side effects of TC. With controlled antibacterial activity, the use of TC would be safer and more efficient. Moreover, the biocompatibility of hydrogel was also evaluated by in vitro and in vivo assays, suggesting the great potential application in the delivery of TC. The novel aspects of this study include the cytotoxicity study and the in vitro and in vivo assays, which might be useful for other researchers in this field.

Photodegradable Gelatin-Based Hydrogels Prepared by Bioorthogonal Click Chemistry for Cell Encapsulation and Release.

In this study, we present a method for the fabrication of in situ forming gelatin and poly(ethylene glycol)-based hydrogels utilizing bioorthogonal, strain-promoted alkyne-azide cycloaddition as the cross-linking reaction. By incorporating nitrobenzyl moieties within the network structure, these hydrogels can be designed to be degradable upon irradiation with low intensity UV light, allowing precise photopatterning. Fibroblast cells encapsulated within these hydrogels were viable at 14 days and could be readily harvested using a light trigger. Potential applications of this new class of injectable hydrogel include its use as a 3D culturing platform that allows the capture and release of cells, as well as light-triggered cell delivery in regenerative medicine.

Ultrathin, Biomimetic, Superhydrophilic Layers of Cross-Linked Poly(phosphobetaine) on Polyethylene by Photografting

Ultrathin, biomimetic, superhydrophilic hydrogel layers, composed of cross-linked poly(2-methacryloyloxyethyl phosphorylcholine), are formed on low-density polyethylene films via ultraviolet-initiated surface graft polymerization. The layers are 19-58 nm thick as revealed by electron microscopy and have three-dimensional networks; the unique network structure, along with its zwitterionic nature, rather than surface roughness results in superhydrophilicity, that is, the water contact angle around 5°. This superhydrophilicity depends on a variety of factors, including the concentration of the monomer and cross-linker, the type of reaction solvents, the reaction and drying time, the intensity of UV light, and the way of measurement of water contact angles. Superhydrophilicity is obtained under a fixed ratio (e.g., 1/1) of the monomer to cross-linker, a reaction time over 120 s, a short drying time, (75%) ethanol as the reaction solvent, and low-intensity UV light, largely because these factors together generate optimal three-dimensional networks of cross-links.

Photopolymerizable nanogels as macromolecular precursors to covalently crosslinked water-based networks.

We present a strategy for directly and efficiently polymerizing aqueous dispersions of reactive nanogels into covalently crosslinked polymer networks with properties that are determined by the initial chemical and physical nanogel structure. This technique can extend the range of achievable properties and architectures for networks formed in solution, particularly in water where monomer selection for direct polymerization and the final network properties are quite limited. Nanogels were initially obtained from a solution polymerization of a hydrophilic monomethacrylate and either a hydrophilic PEG-based dimethacrylate or a more hydrophobic urethane dimethacrylate, which produced globular particles with diameters of 10-15 nm with remarkably low polydispersity in some cases. Networks derived from a single type of nanogel or a blend of nanogels with different chemistries when dispersed in water gelled within minutes when exposed to low intensity UV light. Modifying the nanogel structure changes both covalent and non-covalent secondary interactions in the crosslinked networks and reveals critical design criteria for the development of networks from highly internally branched, nanoscale prepolymer precursors.

Novel On‐Demand Bioadhesion to Soft Tissue in Wet Environments

Current methods of tissue fixation rely on mechanical-related technologies developed from the clothing and carpentry industries. Herein, a novel bioadhesive method that allows tuneable adhesion and is also applicable to biodegradable polyester substrates is described. Diazirine is the key functional group that allows strong soft tissue crosslinking and on-demand adhesion based on a free radical mechanism. Plasma post-irradiation grafting makes it possible to graft diazirine onto PLGA substrates. When the diazirine-PLGA films, placed on wetted ex vivo swine aortas, are activated with low intensity UV light, lap shear strength of up to 450 ± 50 mN cm(-2) is observed, which is one order of magnitude higher than hydrogel bioadhesives placed on similar soft tissues. The diazirine-modified PLGA thin films could be added on top of previously developed technologies for minimally invasive surgeries. The present work is focused on the chemistry, grafting, and lap shear strength of the alkyl diazirine-modified PLGA bioadhesive films.

Reducing scorpion fluorescence via prolonged exposure to ultraviolet light

Abstract A simple technique is presented for reducing the fluorescence of living scorpions by prolonged exposure to UV light. Scorpion's fluorescence peak can be eliminated by a 1-mo exposure to low intensity UV light. Although the fluorescence peak returns within 1 wk after removal from UV light exposure, the magnitude remains reduced. This technique potentially opens up new options for testing a variety of hypotheses about possible functions of scorpion fluorescence including potential effects on cuticle strength, visual responses, predation, cannibalism, and mating.