Abstract: Exposing a fused silica sample to a strong, waveform-controlled, few-cycle optical field increases the dielectric’s optical conductivity by more than 18 orders of magnitude in less than 1 femtosecond, allowing electric currents to be driven, directed and switched by the instantaneous light field. Two studies published in this issue highlight the potential for ultrafast signal manipulation in dielectrics using optical fields. When it comes to electrical signal processing, semiconductors have become the materials of choice. However, insulators such as dielectrics could be attractive alternatives: they have a fast response in principle, but usually have extremely low conductivity at low electric fields and break down in large fields. The electronic properties of dielectrics can be controlled with few-cycle laser pulses that permit damage-free exposure of dielectrics to high electric fields. Agustin Schiffrin et al. demonstrate that strong optical laser fields with controlled few-cycle waveforms can reversibly transform a dielectric insulator into a conductor within the optical period (within one femtosecond). Martin Schultze et al. address the crucial issue of ultrafast reversibility, demonstrating that the dielectric can be repeatedly switched 'on' and 'off' with light fields, without degradation. The time it takes to switch on and off electric current determines the rate at which signals can be processed and sampled in modern information technology1,2,3,4. Field-effect transistors1,2,3,5,6 are able to control currents at frequencies of the order of or higher than 100 gigahertz, but electric interconnects may hamper progress towards reaching the terahertz (1012 hertz) range. All-optical injection of currents through interfering photoexcitation pathways7,8,9,10 or photoconductive switching of terahertz transients11,12,13,14,15,16 has made it possible to control electric current on a subpicosecond timescale in semiconductors. Insulators have been deemed unsuitable for both methods, because of the need for either ultraviolet light or strong fields, which induce slow damage or ultrafast breakdown17,18,19,20, respectively. Here we report the feasibility of electric signal manipulation in a dielectric. A few-cycle optical waveform reversibly increases—free from breakdown—the a.c. conductivity of amorphous silicon dioxide (fused silica) by more than 18 orders of magnitude within 1 femtosecond, allowing electric currents to be driven, directed and switched by the instantaneous light field. Our work opens the way to extending electronic signal processing and high-speed metrology into the petahertz (1015 hertz) domain.

Abstract: Studies of the optical properties and catalytic capabilities of noble metal nanoparticles (NPs), such as gold (Au) and silver (Ag), have formed the basis for the very recent fast expansion of the field of green photocatalysis: photocatalysis utilizing visible and ultraviolet light, a major part of the solar spectrum. The reason for this growth is the recognition that the localised surface plasmon resonance (LSPR) effect of Au NPs and Ag NPs can couple the light flux to the conduction electrons of metal NPs, and the excited electrons and enhanced electric fields in close proximity to the NPs can contribute to converting the solar energy to chemical energy by photon-driven photocatalytic reactions. Previously the LSPR effect of noble metal NPs was utilized almost exclusively to improve the performance of semiconductor photocatalysts (for example, TiO2 and Ag halides), but recently, a conceptual breakthrough was made: studies on light driven reactions catalysed by NPs of Au or Ag on photocatalytically inactive supports (insulating solids with a very wide band gap) have demonstrated that these materials are a class of efficient photocatalysts working by mechanisms distinct from those of semiconducting photocatalysts. There are several reasons for the significant photocatalytic activity of Au and Ag NPs. (1) The conduction electrons of the particles gain the irradiation energy, resulting in high energy electrons at the NP surface which is desirable for activating molecules on the particles for chemical reactions. (2) In such a photocatalysis system, both light harvesting and the catalysing reaction take place on the nanoparticle, and so charge transfer between the NPs and support is not a prerequisite. (3) The density of the conduction electrons at the NP surface is much higher than that at the surface of any semiconductor, and these electrons can drive the reactions on the catalysts. (4) The metal NPs have much better affinity than semiconductors to many reactants, especially organic molecules. Recent progress in photocatalysis using Au and Ag NPs on insulator supports is reviewed. We focus on the mechanism differences between insulator and semiconductor-supported Au and Ag NPs when applied in photocatalytic processes, and the influence of important factors, light intensity and wavelength, in particular estimations of light irradiation contribution, by calculating the apparent activation energies of photo reactions and thermal reactions.

Abstract: Decades ago, Veselago predicted that a material with simultaneously negative electric and magnetic polarization responses would yield a 'left-handed' medium in which light propagates with opposite phase and energy velocities--a condition described by a negative refractive index. He proposed that a flat slab of left-handed material possessing an isotropic refractive index of -1 could act like an imaging lens in free space. Left-handed materials do not occur naturally, and it has only recently become possible to achieve a left-handed response using metamaterials, that is, electromagnetic structures engineered on subwavelength scales to elicit tailored polarization responses. So far, left-handed responses have typically been implemented using resonant metamaterials composed of periodic arrays of unit cells containing inductive-capacitive resonators and conductive wires. Negative refractive indices that are isotropic in two or three dimensions at microwave frequencies have been achieved in resonant metamaterials with centimetre-scale features. Scaling the left-handed response to higher frequencies, such as infrared or visible, has been done by shrinking critical dimensions to submicrometre scales by means of top-down nanofabrication. This miniaturization has, however, so far been achieved at the cost of reduced unit-cell symmetry, yielding a refractive index that is negative along only one axis. Moreover, lithographic scaling limits have so far precluded the fabrication of resonant metamaterials with left-handed responses at frequencies beyond the visible. Here we report the experimental implementation of a bulk metamaterial with a left-handed response to ultraviolet light. The structure, based on stacked plasmonic waveguides, yields an omnidirectional left-handed response for transverse magnetic polarization characterized by a negative refractive index. By engineering the structure to have a refractive index close to -1 over a broad angular range, we achieve Veselago flat lensing, in free space, of arbitrarily shaped, two-dimensional objects beyond the near field. We further demonstrate active, all-optical modulation of the image transferred by the flat lens.

Abstract: Photochemistry has the potential to significantly impact multiple aspects of chemical synthesis, in part because photoinduced reactions can be used to construct molecular architectures that would otherwise be difficult to produce. Nevertheless, organic chemists have been slow to embrace photochemical synthesis because of technical complications associated with the use of ultraviolet light. Our laboratory has been part of an effort to design synthetically useful reactions that utilize visible light. This strategy enables the synthesis of a diverse range of organic structures by generation of a variety of reactive intermediates under exceptionally mild conditions. This Perspective article describes the reasoning that led to the conception of our first experiments in this area, the features of our reaction design that have been most powerful in the discovery of new processes, and a few of the possible future areas in which visible light photocatalysis might have a large impact.

Abstract: In 1942, Walls described the concept of a 'nocturnal bottleneck' in placental mammals, where these species could survive only by avoiding daytime activity during times in which dinosaurs were the dominant taxon. Walls based this concept of a longer episode of nocturnality in early eutherian mammals by comparing the visual systems of reptiles, birds and all three extant taxa of the mammalian lineage, namely the monotremes, marsupials (now included in the metatherians) and placentals (included in the eutherians). This review describes the status of what has become known as the nocturnal bottleneck hypothesis, giving an overview of the chronobiological patterns of activity. We review the ecological plausibility that the activity patterns of (early) eutherian mammals were restricted to the night, based on arguments relating to endothermia, energy balance, foraging and predation, taking into account recent palaeontological information. We also assess genes, relating to light detection (visual and non-visual systems) and the photolyase DNA protection system that were lost in the eutherian mammalian lineage. Our conclusion presently is that arguments in favour of the nocturnal bottleneck hypothesis in eutherians prevail.

Abstract: Organic corrosion inhibitors (OCIs), including ultraviolet light filters, are widely used in plastics, rubbers, colorants, and coatings to increase the performance of products. Derivatives of benzotriazole (BTR), benzothiazole (BTH), and benzophenone (BP) are high-production volume OCIs that have been detected in the environment and human tissues. However, knowledge of their occurrence in indoor environments, as well as human exposure to them, is still lacking. In this study, BTR, BTH, BP and their 12 derivatives were determined in indoor dust for the first time. All three groups of OCIs were found in all 158 indoor dust samples from the U.S. and three East Asian countries (China, Japan, and Korea). The geometric mean (GM) concentration of the sum of six BTRs (GM CΣBTRs) ranged from 20 to 90 ng/g among the four countries studied, with a maximum CΣBTRs of ∼2000 ng/g found in a dust sample from China. Tolyltriazole was the major derivative of BTR measured in dust. GM CΣBTHs in indoor dust from the four countries ranged from 600 to 2000 ng/g. 2-OH-BTH was the predominant BTH in dust from the U.S., Japan, and Korea. GM CΣBPs in dust ranged from 80 to 600 ng/g, with 2-OH-4-MeO-BP and 2,4-2OH-BP, contributing to the majority of ∑BP concentrations. Based on the concentrations of three types of OCIs in indoor dust, human exposure through dust ingestion was calculated. Daily intake of OCIs through dust ingestion was higher for people in the U.S., Japan, and Korea than in China; the residents in urban China are exposed to higher levels of OCIs via dust ingestion than are those in rural China.

Abstract: Mucosal melanoma displays distinct clinical and epidemiological features compared to cutaneous melanoma. Here we used whole genome and whole exome sequencing to characterize the somatic alterations and mutation spectra in the genomes of ten mucosal melanomas. We observed somatic mutation rates that are considerably lower than occur in sun-exposed cutaneous melanoma, but comparable to the rates seen in cancers not associated with exposure to known mutagens. In particular, the mutation signatures are not indicative of ultraviolet light- or tobacco smoke-induced DNA damage. Genes previously reported as mutated in other cancers were also mutated in mucosal melanoma. Notably, there were substantially more copy number and structural variations in mucosal melanoma than have been reported in cutaneous melanoma. Thus, mucosal and cutaneous melanomas are distinct diseases with discrete genetic features. Our data suggest that different mechanisms underlie the genesis of these diseases and that structural variations play a more important role in mucosal than in cutaneous melanomagenesis.

Abstract: ZnO nanowire inorganic/organic hybrid ultraviolet (UV) light-emitting diodes (LEDs) have attracted considerable attention as they not only combine the high flexibility of polymers with the structural and chemical stability of inorganic nanostructures but also have a higher light extraction efficiency than thin film structures. However, up to date, the external quantum efficiency of UV LED based on ZnO nanostructures has been limited by a lack of efficient methods to achieve a balance between electron contributed current and hole contributed current that reduces the nonradiative recombination at interface. Here we demonstrate that the piezo-phototronic effect can largely enhance the efficiency of a hybridized inorganic/organic LED made of a ZnO nanowire/p-polymer structure, by trimming the electron current to match the hole current and increasing the localized hole density near the interface through a carrier channel created by piezoelectric polarization charges on the ZnO side. The external efficiency of the hybrid LED was enhanced by at least a factor of 2 after applying a proper strain, reaching 5.92%. This study offers a new concept for increasing organic LED efficiency and has a great potential for a wide variety of high-performance flexible optoelectronic devices.

Abstract: In addition to the naturally occurring, physical, and systemic photoprotective agents reviewed in part I, topical ultraviolet radiation filters are an important cornerstone of photoprotection. Sunscreen development, efficacy, testing, and controversies are reviewed in part II of this continuing medical education article.

Abstract: Titanium dioxide (TiO2) and zinc oxide (ZnO) nanoparticles are important photocatalysts and as such have been extensively studied for the removal of organic compounds from contaminated air and water and for microbial disinfection. Despite much research on the effect of TiO2 and ZnO nanoparticles on different bacterial species, uncertainties remain about which bacteria are more sensitive to these compounds. Very few studies have directly compared the toxicity of ZnO to TiO2 under both light and dark conditions. In addition, authors investigating the photocatalytic inactivation of TiO2 and ZnO nanoparticles on bacteria have failed to investigate the reactive oxygen species (ROS) generation of the nanoparticles, making it difficult to correlate killing action with the generation of ROS. In this study, three types of metal nanoparticle (ZnO < 50 nm, ZnO < 100 nm and TiO2) have been characterised and ROS production assessed through the degradation of methylene blue (MB). The photocatalytic killing potential of three nanoparticle concentrations (0.01, 0.1 and 1 g/L) was then assessed on four representative bacteria: two gram-positive (S. aureus and B. subtilis) and two gram-negative (E. coli and P. aeruginosa). Results showed that out of the three nanoparticles tested, the TiO2 nanoparticles generated more ROS than the ZnO nanoparticles, corresponding to a greater photocatalytic inactivation of three of the four species of bacteria examined. The MB decomposition results correlated well with the bacterial inactivation results with higher TiO2 nanoparticle concentrations leading to greater ROS production and increased loss of cell viability. Although producing less ROS than the TiO2 nanoparticles under ultraviolet light, the ZnO nanoparticles were toxic to two of the bacterial species even under dark conditions. In this study, no correlation between cell wall type and bacterial inactivation was observed for any of the nanoparticles tested although both gram-positive bacteria were sensitive to ROS production. P. aeruginosa cells were resistant to all types of treatment and highlight a potential limitation to the application of these nanoparticles for water treatment.

Abstract: The use of azobenzene photoswitches has become a dependable method for rapid and exact modulation of biological processes and material science systems. The requirement of ultraviolet light for azobenzene isomerization is not ideal for biological systems due to poor tissue penetration and potentially damaging effects. While modified azobenzene cores with a red-shifted cis-to-trans isomerization have been previously described, they have not yet been incorporated into a powerful method to control protein function: the photoswitchable tethered ligand (PTL) approach. We report the synthesis and characterization of a red-shifted PTL, L-MAG0460, for the light-gated ionotropic glutamate receptor LiGluR. In cultured mammalian cells, the LiGluR+L-MAG0460 system is activated rapidly by illumination with 400-520 nm light to generate a large ionic current. The current rapidly turns off in the dark as the PTL relaxes thermally back to the trans configuration. The visible light excitation and single-wavelength behavior considerably simplify use and should improve utilization in tissue.

Abstract: Graphitic carbon nitride ($g$-C${}_{3}$N${}_{4}$) has recently triggered extensive investigations due to its potential applications, such as in direct photochemical water splitting, CO${}_{2}$ activation, and transition-metal-free spintronics. However, electronic, and particularly the optical properties of $g$-C${}_{3}$N${}_{4}$ still have not been well established. Based on one of the state-of-the-art approaches---many-body Green's function theory (i.e., $GW$ $+$ BSE)---absorption of ultraviolet light by $g$-C${}_{3}$N${}_{4}$ is found to be determined by strong excitonic effects with a significantly large binding energy assigned to the bound excitons. Dark states have also been found in $g$-C${}_{3}$N${}_{4}$, which can affect the photoluminescence yield of $g$-C${}_{3}$N${}_{4}$. We find that the band gap of $g$-C${}_{3}$N${}_{4}$ probably can be tuned by adjusting the condensation (dimensionality) to initiate excitonic absorption in the visible light region, which might help improve the solar energy conversion efficiency.

Abstract: Normal somatic cells do not divide indefinitely and have their finite replicative lifespan This property leads to an eventual arrest of cell division termed cell senescence Human diploid fibroblasts offer a typical model for studying cell senescence in vitro Various approaches to evoke oxidative stresses, such as the exposures of cells to ultraviolet light, ethanol, tert-butyl hydroperoxide (t-BHP), and peroxide hydrogen (H2O2), have been used to study the onset of cellular senescence The early onset of cellular senescence induced by these stresses is termed stress-induced premature senescence (SIPS) In this manuscript, we will mainly summarize the basic knowledge and experimental approaches important for the induction of SIPS by H2O2, since H2O2 is the most commonly used inducer of SIPS in vitro and an endogenous source of cellular oxidative stress Several assays methods generally used for testifying cell senescence are introduced

Abstract: Total joint arthroplasty is one of the most common and most successful orthopaedic procedures. Infection after total joint arthroplasty is a devastating problem that expends patient, surgeon, and hospital resources, and it substantially decreases the chances of a successful patient outcome. Postoperative infection affects approximately 1% to 7% of all total joint arthroplasties, at a cost of approximately $50,000 per infection. Decreasing postoperative periprosthetic joint infection is of the utmost importance for the total joint arthroplasty surgeon. Preoperative, perioperative, intraoperative, and postoperative measures to minimize infection and optimize patient outcomes in total joint arthroplasty are discussed. Preoperative measures include management of patients colonized by Staphylococcus aureus, nutritional optimization, and management of medical comorbidities. Perioperative measures include skin preparation and prophylactic antibiotics. Intraoperative measures include body exhaust suits, laminar flow, ultraviolet light, operating-room traffic control, surgical suite enclosures, anesthesia-related considerations, and antibiotic-loaded bone cement. Postoperative measures include continued antibiotic prophylaxis, blood transfusions, hematoma formation and wound drainage, duration of hospital stay, and antibiotic prophylaxis for future invasive procedures.

Abstract: High-performance membranes are attractive for molecular-level separations in industrial-scale chemical, energy and environmental processes. The next-generation membranes for these processes are based on molecular sieving materials to simultaneously achieve high throughput and selectivity. Membranes made from polymeric molecular sieves such as polymers of intrinsic microporosity (pore size<2 nm) are especially interesting in being solution processable and highly permeable but currently have modest selectivity. Here we report photo-oxidative surface modification of membranes made of a polymer of intrinsic microporosity. The ultraviolet light field, localized to a near-surface domain, induces reactive ozone that collapses the microporous polymer framework. The rapid, near-surface densification results in asymmetric membranes with a superior selectivity in gas separation while maintaining an apparent permeability that is two orders of magnitude greater than commercially available polymeric membranes. The oxidative chain scission induced by ultraviolet irradiation also indicates the potential application of the polymer in photolithography technology.

Abstract: UV light-induced surface-initiated atom-transfer radical polymerization (ATRP) was reported. This method uses TiO2 nanoparticles as photoactive materials to reduce Cu(II)/L to a Cu(I)/L complex under UV irradiation by a one-electron transfer process for ATRP with multiple usage of monomer solutions. The growth of polymer brushes can be manipulated by either varying the content of photoactive materials or regulating the irradiation intensity, thereby yielding polymer brushes with controllable thickness, composition, and architecture.

Abstract: Photoreactivity for photodegradation of 2-NAP on BiOCl nanosheets with dominant exposed (010) and (001) facets is studied under visible light via an exciton-free and nonsensitized mechanism. This phenomenon cannot be explained by semiconductor theory or self-sensitized (as those involve dyes) mechanisms. The photocatalytic activities are mainly owing to the formation of the surface state, which is confirmed to be the surface complex Bi–O–C10H7. This surface complex is characterized with ultraviolet–visible diffuse reflectance spectra, Fourier transformed infrared spectroscopy, Raman scattering, X-ray photoelectron spectroscopy, and photoelectrochemical measurement. The optical absorptivity of BiOCl is shifted from the ultraviolet light toward the visible light via a charge-transfer-complex pathway. Charge transfer after the excitation of visible light induces efficient visible photocatalytic activities. The results show that single-crystalline BiOCl nanosheets exposing (010) facets exhibit higher photoact...

Abstract: Growing concerns regarding the impact of the accumulation of plastic waste over several decades on the environmental have led to the development of biodegradable plastic. These plastics can be degraded by microorganisms and absorbed by the environment and are therefore gaining public support as a possible alternative to petroleum-derived plastics. Among the developed biodegradable plastics, oxo-biodegradable polymers have been used to produce plastic bags. Exposure of this waste plastic to ultraviolet light (UV) or heat can lead to breakage of the polymer chains in the plastic, and the resulting compounds are easily degraded by microorganisms. However, few studies have characterized the microbial degradation of oxo-biodegradable plastics. In this study, we tested the capability of Pleurotus ostreatus to degrade oxo-biodegradable (D2W) plastic without prior physical treatment, such as exposure to UV or thermal heating. After 45 d of incubation in substrate-containing plastic bags, the oxo-biodegradable plastic, which is commonly used in supermarkets, developed cracks and small holes in the plastic surface as a result of the formation of hydroxyl groups and carbon-oxygen bonds. These alterations may be due to laccase activity. Furthermore, we observed the degradation of the dye found in these bags as well as mushroom formation. Thus, P. ostreatus degrades oxo-biodegradable plastics and produces mushrooms using this plastic as substrate.

Abstract: [1] Signatures of sulfur mass-independent fractionation (S-MIF) are observed for sulfur minerals in Archean rocks, and for modern stratospheric sulfate aerosols (SSA) deposited in polar ice. Ultraviolet light photolysis of SO2 is thought to be the most likely source for these S-MIF signatures, although several hypotheses have been proposed for the underlying mechanism(s) of S-MIF production. Laboratory SO2 photolysis experiments are carried out with a flow-through photochemical reactor with a broadband (Xe arc lamp) light source at 0.1 to 5 mbar SO2 in 0.25 to 1 bar N2 bath gas, in order to test the effect of SO2 pressure on the production of S-MIF. Elemental sulfur products yield high δ34S values up to 140 ‰, with δ33S/δ34S of 0.59 ± 0.04 and Δ36S/Δ33S ratios of −4.6 ± 1.3 with respect to initial SO2. The magnitude of the isotope effect strongly depends on SO2 partial pressure, with larger fractionations at higher SO2 pressures, but saturates at an SO2 column density of 1018 molecules cm−2. The observed pressure dependence and δ33S/δ34S and Δ36S/Δ33S ratios are consistent with model calculations based on synthesized SO2 isotopologue cross sections, suggesting a significant contribution of isotopologue self-shielding to S-MIF for high SO2 pressure (>0.1 mbar) experiments. Results of dual-cell experiments further support this conclusion. The measured isotopic patterns, in particular the Δ36S/Δ33S relationships, closely match those measured for modern SSA from explosive volcanic eruptions. These isotope systematics could be used to trace the chemistry of SSA after large Plinian volcanic eruptions.