Greater Light Absorption Research Articles

Green diatom mutants reveal an intricate biosynthetic pathway of fucoxanthin

Fucoxanthin is a major light-harvesting pigment in ecologically important algae such as diatoms, haptophytes, and brown algae (Phaeophyceae). Therefore, it is a major driver of global primary productivity. Species of these algal groups are brown colored because the high amounts of fucoxanthin bound to the proteins of their photosynthetic machineries enable efficient absorption of green light. While the structure of these fucoxanthin-chlorophyll proteins has recently been resolved, the biosynthetic pathway of fucoxanthin is still unknown. Here, we identified two enzymes central to this pathway by generating corresponding knockout mutants of the diatom Phaeodactylum tricornutum that are green due to the lack of fucoxanthin. Complementation of the mutants with the native genes or orthologs from haptophytes restored fucoxanthin biosynthesis. We propose a complete biosynthetic path to fucoxanthin in diatoms and haptophytes based on the carotenoid intermediates identified in the mutants and invitro biochemical assays. It is substantially more complex than anticipated and reveals diadinoxanthin metabolism as the central regulatory hub connecting the photoprotective xanthophyll cycle and the formation of fucoxanthin. Moreover, our data show that the pathway evolved by repeated duplication and neofunctionalization of genes for the xanthophyll cycle enzymes violaxanthin de-epoxidase and zeaxanthin epoxidase. Brown algae lack diadinoxanthin and the genes described here and instead use an alternative pathway predicted to involve fewer enzymes. Our work represents a major step forward in elucidating the biosynthesis of fucoxanthin and understanding the evolution, biogenesis, and regulation of the photosynthetic machinery in algae.

Temperature sensing and bioimaging realized in NaErF4:40%Tm@NaYF4 with extremely intense red upconversion and suitable R/G emission ratio

The practical application of light thermometer based on the FIR (520/540) has been greatly limited due to the strong absorption of green light by biological tissues. The sensitivity of the temperature sensor located in a biological window (FIR-BW) also needs to be improved. Based on this, we designed and synthesized an upconversion nanoparticles (UCNPs) with suitable R/G ratio and red visual output to prebreaking the limitation of strong absorption of biological tissue, while improving the sensitivity of temperature sensor and in vivo fluorescence imaging. In this paper, NaErF4:40%Tm@NaYF4, a high efficient red UCNPs with R/G ratio (6.86), is first utilized as an optical thermometer, accomplished through the fluorescence intensity ratio (FIR) of thermally coupled stark sublevels of 4S3/2/4F9/2 (FIR(540/654)). In the studied temperature range, the maximum absolute and relative sensitivity (Sa and Sr) is 0.47% K−1 and 2.61% K−1 at 298 K, respectively, which is much higher than most previous reports about FIR-based temperature sensors. Additionally, we investigated the in vivo bioimaging behavior of NaErF4:40%Tm@NaYF4 in detail. The superior biocompatibility, the distribution to the main organs with the blood circulation system, and the bright red fluorescence signals were observed under 980 nm laser radiation. All the results imply that NaErF4:40%Tm@NaYF4 is a promising candidate for optical thermometry and in vivo bioimaging with high sensitivity.

A hybrid type of chromatic acclimation regulated by the dual green/red photosensory systems in cyanobacteria.

Cyanobacteria are phototrophic bacteria that perform oxygenic photosynthesis. They use a supermolecular light-harvesting antenna complex, the phycobilisome (PBS), to capture and transfer light energy to photosynthetic reaction centers. Certain cyanobacteria alter the absorption maxima and/or overall structure of their PBSs in response to the ambient light wavelength-a process called chromatic acclimation (CA). One of the most well-known CA types is the response to green and red light, which is controlled by either the RcaEFC or CcaSR photosensory system. Here, we characterized a hybrid type of CA in the cyanobacterium Pleurocapsa sp. Pasteur Culture Collection (PCC) 7319 that uses both RcaEFC and CcaSR systems. In vivo spectroscopy suggested that strain PCC 7319 alters the relative composition of green-absorbing phycoerythrin and red-absorbing phycocyanin in the PBS. RNA sequencing and promoter motif analyses suggested that the RcaEFC system induces a gene operon for phycocyanin under red light, whereas the CcaSR system induces a rod-membrane linker gene under green light. Induction of the phycoerythrin genes under green light may be regulated through a yet unidentified photosensory system called the Cgi system. Spectroscopy analyses of the isolated PBSs suggested that hemidiscoidal and rod-shaped PBSs enriched with phycoerythrin were produced under green light, whereas only hemidiscoidal PBSs enriched with phycocyanin were produced under red light. PCC 7319 uses the RcaEFC and CcaSR systems to regulate absorption of green or red light (CA3) and the amount of rod-shaped PBSs (CA1), respectively. Cyanobacteria can thus flexibly combine diverse CA types to acclimate to different light environments.

Transparent absorber composed of two stacked ultrathin metal films perforated with small holes.

A transparent absorber refers to the device which can absorb light strongly within a narrow frequency range but transmit light efficiently outside that range. Because of the contradiction between absorption and transmission, however, the performances of the transparent absorbers are usually compromised. In this work, we propose a transparent absorber based on a sandwiched metal-insulator-metal (MIM) structure, i.e., two perforated ultrathin metal films separated by a central dielectric layer. This structure has the advantage that the narrow-band absorption can be greatly enhanced because of the cooperation of surface-plasmon polariton (SPP) mode and multiple reflections in the dielectric cavity. Moreover, the ultrathin thickness of the stacked metal films enables high transmission when the wavelength of incident light deviates from the SPP resonance. A semi-analytical Fabry-Perot model has been employed to describe the optical properties, which agrees well with the simulation. The dependence of optical properties on the structural parameters has also been studied systematically. In addition, by covering the transparent absorber with an antireflection layer, highly efficient absorption of red (∼87% @ 629 nm), green (∼89% @ 524 nm), or blue (∼68% @ 472 nm) light and high transmission (∼80%) in the transparent region have been suggested. With its excellent visible-wavelength selective absorption, polarization independence, high angle-tolerance, and structural simplicity, the proposed MIM transparent absorber may have potential applications in the display technology and other smart scenarios.

Earliest Photic Zone Niches Probed by Ancestral Microbial Rhodopsins.

For billions of years, life has continuously adapted to dynamic physical conditions near the Earth’s surface. Fossils and other preserved biosignatures in the paleontological record are the most direct evidence for reconstructing the broad historical contours of this adaptive interplay. However, biosignatures dating to Earth’s earliest history are exceedingly rare. Here, we combine phylogenetic inference of primordial rhodopsin proteins with modeled spectral features of the Precambrian Earth environment to reconstruct the paleobiological history of this essential family of photoactive transmembrane proteins. Our results suggest that ancestral microbial rhodopsins likely acted as light-driven proton pumps and were spectrally tuned toward the absorption of green light, which would have enabled their hosts to occupy depths in a water column or biofilm where UV wavelengths were attenuated. Subsequent diversification of rhodopsin functions and peak absorption frequencies was enabled by the expansion of surface ecological niches induced by the accumulation of atmospheric oxygen. Inferred ancestors retain distinct associations between extant functions and peak absorption frequencies. Our findings suggest that novel information encoded by biomolecules can be used as “paleosensors” for conditions of ancient, inhabited niches of host organisms not represented elsewhere in the paleontological record. The coupling of functional diversification and spectral tuning of this taxonomically diverse protein family underscores the utility of rhodopsins as universal testbeds for inferring remotely detectable biosignatures on inhabited planetary bodies.

Revealing the synergistic effects of cells, pigments, and light spectra on light transfer during microalgae growth: A comprehensive light attenuation model

As the sole energy for photosynthesis, light decrease rapidly with path due to absorption by pigments and scattering by cells in microalgal suspensions. By comprehensively considering cell concentrations, pigment components, and light spectra, a modified Cornet model for light transmission in microalgal suspensions is established. The developed model better fits experimental data with a higher adjusted R2, which is 5% higher than the model that is based only on cell concentration. The attenuation of blue light is the most severe, followed by red and green light. Among the three main pigments, total carotenoids contribute the most to the absorption of blue and green light (with contribution coefficients of 89.26 ± 4.53% and 46.04 ± 3.77%, respectively), and chlorophyll a contributes the most to the absorption of red light (with a contribution coefficient of 75.33 ± 5.08%). This study provides a better understanding and prediction of light transmission during microalgal cultivation.

Two-Dimensional Janus Antimony Selenium Telluride with Large Rashba Spin Splitting and High Electron Mobility.

Janus two-dimensional materials with large Rashba spin splitting and high electron mobility are rarely reported but highly desired for nanoscale spintronics. Herein, using density functional theory calculations, we predicated Janus Sb2SexTe3–x (x = 1 or 2) monolayers simultaneously harboring these fascinating properties. The predicated monolayers are indirect semiconductors with great dynamical, thermal, and mechanical stability. The spin–orbital coupling (SOC) and the out-of-plane asymmetry lead to Rashba spin splitting at the conduction band minimum (CBM), which can be effectively tuned by the small uniaxial strain. The strong band dispersion at the CBM leads to small electron effective mass, consequently enabling a high electron mobility that reaches up to 6816.63 cm2 V–1 s–1. Moreover, Janus Sb2SexTe3–x monolayers possess great light absorption capability within the visible and infrared regions of solar light. Our findings highlight promising candidates for high-speed spintronic devices and may motivate more research efforts on carrier transport and SOC effects in Janus group V and VI monolayers.

Rapid efficient degradation pathway of tetracycline and Pb (II) reduction mechanism by a novel nanocomposite heterojunction photocatalysts

In this study, MoS2/TiO2 nanohybrids, formed through hydrothermal synthesis technique, was considered as a superior heterojunction for the removal of tetracycline (TC) and Pb (II) reduction under visible light irradiation. The Z-scheme MoS2/TiO2 nanohybrids was easily synthesized with much narrower nanoparticles, ~10 times the outstanding charge separation, and greater specific surface area than bulk MoS2 or TiO2. The MoS2/TiO2 nanohybrids achieved a stronger photocatalytic activity, which could degrade 94% TC within 60 min. The optimized nanohybrids catalysts demonstrated outstanding efficiency with the apparent reaction rate constants of 0.05 min−1 for TC removal, about 3–4 times as bigger as the removal rate of bulk components. Superoxide radical (˙O2−) was presumed as the conduct active species in the potential improvement mechanism of organized MoS2/TiO2 nanohybrids for photocatalytic activities was introduced. These can admit to prefer photodegradation pathways and mechanism of tetracycline by nanohybrids with visible light activity. The novel nanohybrids photocatalysts have great structural stability, greater light absorption, and superior cycle performance, which could be utilized as an efficient process of antibiotics degradation and Pb (II) removal.

Two-dimensional PtSe2/hBN vdW heterojunction as photoelectrocatalyst for the solar-driven oxygen evolution reaction: A first principles study

Designing and researching suitable photoelectrocatalyst for water splitting is crucial for the utilization of renewable and inexhaustible solar energy but remains a huge conundrum. Here, using first principles calculations, the two-dimensional PtSe2/hBN heterojunction was first conceived. However, the rapid recombination of electrons and holes will inhibit the visible light catalytic efficiency of the heterojunction. In order to realize effective spatial separation of electrons and holes of the heterojunction, we tuned the band gap by doping two carbon atoms on the hBN monolayer to obtain the type-Ⅱ PtSe2/hBNC heterojunction. Then through the comprehensive researches on structural, electronic and optical properties, it was found that the structure possesses excellent carrier mobility and exhibits a great oxygen evolution reaction performance with a low overpotential of 0.76 eV, which is an ideal photoelectrocatalyst and exhibits great light absorption performance. In this study, the possible mechanism of doped PtSe2/hBNC vdW heterojunction to promote photocatalysis and oxygen evolution ability was explained, which may pave the way for the practical design of more solar-driven high-quality water splitting photoelectrocatalysts.

Laser threshold magnetometry using green-light absorption by diamond nitrogen vacancies in an external cavity laser

Nitrogen vacancy (NV) centers in diamond have attracted considerable recent interest for use in quantum sensing, promising increased sensitivity for applications ranging from geophysics to biomedicine. Conventional sensing schemes involve monitoring the change in red fluorescence from the NV center under green laser and microwave illumination. Due to the strong fluorescence background from emission in the NV triplet state and low relative contrast of any change in output, sensitivity is severely restricted by a high optical shot noise level. Here, we propose a means to avoid this issue, by using the change in green pump absorption through the diamond as part of a semiconductor external cavity laser run close to lasing threshold. We show theoretical sensitivity to magnetic field on the pT/sqrt(Hz) level is possible using a diamond with an optimal density of NV centers. We discuss the physical requirements and limitations of the method, particularly the role of amplified spontaneous emission near threshold and explore realistic implementations using current technology.

Upconversion Luminescent Nanostructure with Ultrasmall Ceramic Nanoparticles Coupled with Rose Bengal for NIR-Induced Photodynamic Therapy.

We designed a biodegradable hybrid nanostructure for near-infrared (NIR)-induced photodynamic therapy (PDT) using an ultrasmall upconversion (UC) phosphor (β-NaYF4:Yb3+, Er3+ nanoparticle: NPs) and a hydrocarbonized rose bengal (C18RB) dye, a hydrophobized rose bengal (RB) derivative. The UC-NPs were encapsulated along with C18RB in the hydrophobic core of the micelle composed of poly(ethylene glycol) (PEG)-block-poly(ε-caprolactone) (PCL). The UC-NPs were well shielded from the aqueous environment, owing to the encapsulation in the hydrophobic PCL core, to efficiently emit green UC luminescence by avoiding the quenching by the hydroxyl groups. The hydrophobic part of C18 of C18RB worked well to be involved in the PCL core and located RB on the surface of the PCL core, making the efficient absorption of green light and the emission of singlet oxygen to surrounding water possible. Moreover, as the location is covered by PEG, the direct contact of RB to cells is prohibited to avoid their irradiation-free toxic effect on the cells. The hybrid nanostructure proved to be degradable by the hydrolysis of PEG-b-PCL. This degradation potentially results in renal excretion by the decomposition of the nanostructure into sub-10 nm size particles and makes them viable for clinical uses. These nanostructures can potentially be used for PDT of cancer in deep tissues.

Plant biostimulating effects of the cyanobacterium Nostoc piscinale on maize (Zea mays L.) in field experiments

Biostimulants, when applied to plants in small amounts, increase crop yield and plant tolerance to abiotic and biotic stress. They play an important role in the development of new environmentally sustainable technologies. The aim of the current experiment was to investigate the potential of a cyanobacterium strain (Nostoc piscinale) to improve the growth, grain yield and stress tolerance of maize (Zea mays SY Zephir hybrid). Field trials were established at two sites. Freeze-dried biomass of N. piscinale resuspended in tap water (1g/L DW) was applied as a single foliar treatment (400 L/ha) at the V6-V7 phenological stage. Number of leaves, chlorophyll content, relative water content (RWC%) and free proline content were measured weekly. Grain yield, yield components and grain protein content were measured at harvest. N. piscinale treated maize had significantly earlier development in the vegetative growth stages with a higher number of leaves. Chlorophyll content (SPAD value) was significantly higher in the treated plants during the reproductive stages. There was little difference in the RWC and proline content compared to control plants. Faster vegetative growth and higher chlorophyll content in the cyanobacterium treated plants meant great photosynthetic light absorption over a longer period of time, resulting in significantly higher grain yield (6.5% and 11.5% at the two production sites) and increased grain protein content. Grain yield was significantly influenced by cob length and thousand grain weight. In conclusion, it was proved in field trials conducted in two different regions in Hungary that a single foliar application of a cyanobacterium-based biostimulant can contribute to crop production in a sustainable and environmentally friendly manner.

Improvement in growth and yield of strawberry (Fragaria × ananassa Duch.) by mulch colour

Mulching is practiced in strawberry (Fragaria × ananassa Duch.) to conserve water, control weeds, and keep fruit clean, resultantly improving yield and quality. The most commonly used plastic mulch colour is black, but coloured mulch is reported to perform better than black polyethylene mulch. The present study was conducted over a period of three years to see the effect of different coloured polyethylene mulches on performance of strawberry under hot dry subtropical climatic conditions prevailing at Lucknow region of Uttar Pradesh, India. The experiment was laid out in randomized block design (RBD) with seven treatment combinations replicated four times. Strawberry performance for most of the physico-chemical parameters was recorded best under yellow polyethylene mulch followed by black polyethylene mulch over control. Vegetative growth, fruit yield and berry size was observed significantly better in yellow than black polyethylene mulch. However, fruit quality in respect of sugars, vitamin A and anthocyanin content was found superior in black polyethylene mulch. The inductive resonance effect of green and yellow light absorption by plant under yellow polyethylene mulch appears to have a role in enhancing photosynthesis resulting in better vegetative growth, fruit quality and higher yield of strawberry.

Nickel and sulfur codoped TiO2 nanoparticles for efficient visible light photocatalytic activity

In this work, Nickel (Ni) and sulfur (S) codoped TiO2 nanoparticles were prepared by a sol-gel technique. The as-prepared catalyst was characterized using X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), FT-Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), transmission electron microscopy (TEM), UV-Vis diffuse reflectance spectra (DRS) for investigating crystal structure, crystal phase, particle size and bandgap energy of these samples. The photocatalytic performances of all the prepared catalysts have been investigated for the degradation of methylene blue (MB) under visible light irradiation. It was noticed that Ni-S codoped TiO2(Ni-S/TiO2) nanoparticles exhibited much higher photocatalytic activity compared with pure, Ni and S doped TiO2 due to higher visible light absorption and probable decrease in the recombination of photo-generated charges. It was decided that the great visible light absorption was created for codoped TiO2 by the formation of impurity energy states near both the edges of the collection, which works as trapping sites for both the photogenerated charges to decrease the recombination process.

D–A–π–A organic dyes with tailored green light absorption for potential application in greenhouse-integrated dye-sensitized solar cells

In this paper, we present the design and synthesis of three organic dyes specially developed for the fabrication of dye-sensitized solar cells with potential application in greenhouses cladding.

Engineering of 2D/2D MoS2/CdxZn1−xS Photocatalyst for Solar H2 Evolution Coupled with Degradation of Plastic in Alkaline Solution

Sufficiently utilizing photogenerated electron/hole pairs for a coupled redox enables green, sustainable, and low‐cost photocatalysis. Herein, a series of MoS2/CdxZn1−xS photocatalysts with uniform 2D/2D structure are reported for solar water–reductive H2 products coupled with the degradation of polyethylene terephthalate (PET) plastic. The MoS2/Cd0.5Zn0.5S heterojunction with a loading mass of 4.3 wt% MoS2 exhibits the best H2 evolution rate of 15.90 mmol g−1 h−1 in an aqueous solution due to its appropriate redox ability, great light absorption, and carrier separation abilities. Then, the oxidation products of PET are analyzed by 1H‐NMR spectroscopy, which demonstrates the PET being efficiently degraded to molecule compounds, such as formate and acetate. The work provides a feasible solution to the problem of plastic pollution and meets the demand for sustainable clean energy simultaneously.

The role of mixed vibronic Qy-Qx states in green light absorption of light-harvesting complex II

The importance of green light for driving natural photosynthesis has long been underappreciated, however, under the presence of strong illumination, green light actually drives photosynthesis more efficiently than red light. This green light is absorbed by mixed vibronic Qy-Qx states, arising from chlorophyll (Chl)-Chl interactions, although almost nothing is known about these states. Here, we employ polarization-dependent two-dimensional electronic-vibrational spectroscopy to study the origin and dynamics of the mixed vibronic Qy-Qx states of light-harvesting complex II. We show the states in this region dominantly arise from Chl b and demonstrate how it is possible to distinguish between the degree of vibronic Qy versus Qx character. We find that the dynamics for states of predominately Chl b Qy versus Chl b Qx character are markedly different, as excitation persists for significantly longer in the Qx states and there is an oscillatory component to the Qx dynamics, which is discussed. Our findings demonstrate the central role of electronic-nuclear mixing in efficient light-harvesting and the different functionalities of Chl a and Chl b.

Studies of Z-scheme WO3-TiO2/Cu2ZnSnS4 ternary nanocomposite with enhanced CO2 photoreduction under visible light irradiation

To date, the rapid increase of the CO2 concentration in the Earth's atmosphere is one of the primary causes of global warming, which leads to other environmental issues; however, the photocatalytic CO2 reduction is a process that offers environmental protection and valuable solar fuels generation simultaneously. Yet, the high CO2 activation barrier and inefficient proton supply are the main challenges, which substantially hamper the photo-conversion efficiency over heterogeneous catalysts. Herein, a Z-scheme mesoporous WO3-TiO2/CZTS ternary photocatalyst was synthesized through a two-stage strategy, and the photoreduction of CO2 with H2O vapor was carried out under the visible light irradiation. A synergistic effect among WO3, TiO2 and CZTS over CO2 reduction was observed by anchoring the CZTS over WO3-TiO2 nanocomposite. The ternary composite showed the enhanced CO/CH4 yield rates of 15.37/1.69 μmol h−1 g−1, which was significantly higher than that of pristine TiO2 (0.44/0 μmol h−1 g−1) and WO3-TiO2 composite (5.39/ 0.34 μmol h−1 g−1), attributing the high surface area with greater light absorption and suppressed the electron–hole recombination as a result of the intrinsic p–n heterojunction nature of the material. The apparent quantum efficiency was estimated to be 0.52 %. In addition, the possible reaction mechanism and pathways of photocatalytic CO2 reduction with H2O over heterogeneous catalysts were also presented.

Оптоволоконный датчик pH для микробиореакторов

A fiber-optic sensor for microbioreactors was designed and manufactured. It measures pH in the range from 6.5 to 9 with an accuracy of ± 0.2 for small volumes of liquid. The principle of detection is the measurement of blue and green LEDs light absorption in liquid with an indicator. Phenol red is used as a biocompatible indicator.

Electrostatic self-assembled Iridium(III) nano-photosensitizer for selectively disintegrated and mitochondria targeted photodynamic therapy

Photodynamic therapy (PDT) is one of effective cancer therapy methods. It is important to develop a PDT reagent with tumor-targeted ability, high phototoxicity and low dark toxicity. In this study, an iridium(III) complex (Irpy) can electrostatically self-assemble with hyaluronic acid (HA) to form nanostructured Irpy-HA, which exhibited stable spheroid structure and outstanding ability of singlet oxygen (1O2) generation. The photophysical property of Irpy has been well studied, which qualified green light absorption ability and could emit red phosphorescence. The nanostructure and stability of self-assembled Irpy-HA have been well investigated, which can keep its nanostructure at least 30 days. More importantly, Irpy-HA can target to a CD44 receptor in cancer cell membrane for enhancing internalization and selective disintegration. Then, Irpy can accumulate in mitochondria and generate 1O2 to realize PDT-induced cell apoptosis by green light irradiation. The Irpy-HA could be used as a nanophotosensitizer for effective photodynamic therapy.