Absorbed Photon Energy Research Articles

Light-triggered dissociation of self-assembled β-amyloid aggregates into small, nontoxic fragments by ruthenium (II) complex

Alzheimer's disease is the most common progressive neurodegenerative disease, affecting more than 13% of the population over age 65. Over the last decades, researchers have focused on understanding the mechanism of amyloid formation, the hallmark of various amyloid diseases including Alzheimer's and Parkinson's. In this paper, we successfully demonstrate the dissociation of β-Amyloid (Aβ) aggregates into small, less-amyloidic fragments by photoexcited [Ru(bpy)3]2+ through destabilization of β-sheet secondary structure. We validated the light-triggered dissociation of amyloid structure using multiple analytical tools. Furthermore, we confirmed that photoexcited [Ru(bpy)3]2+ reduces cytotoxicity of Aβ aggregates. Our work should open a new horizon in the study of Alzheimer's amyloid aggregation by showing the potential of photoexcited dye molecules as an alternative therapeutic strategy for treating Alzheimer's disease in future.

Water equivalence of some 3D dosimeters: a theoretical study based on the effective atomic number and effective fast neutron removal cross section

Effective atomic numbers for photon energy absorption (\( Z_{{{\text{PEA}}_{\text{eff}} }} \)) and their corresponding electron numbers \( (N_{{{\text{PEA}}_{\text{eff}} }} ) \), and effective macroscopic removal cross sections of fast neutrons (ΣR) were calculated for 27 different types of three-dimensional dosimeters, four types of phantom materials, and water. The values of \( Z_{{{\text{PEA}}_{\text{eff}} }} \) and \( N_{{{\text{PEA}}_{\text{eff}} }} \) were obtained using the direct method for energies ranging from 10 keV to 20 MeV. Results are presented relative to water, for direct comparison over the range of examined energies. The effect of monomers that are used in polymer gel dosimeters on the water equivalence is discussed. The relation between ΣR and hydrogen content was studied. Micelle gel dosimeters are highly promising because our results demonstrate perfect matching between the effective atomic number, electron density number, and fast neutron attenuation coefficient of water.

Optical Effect of Varying Acceptors in Pyrene Donor–Acceptor–Donor Chromophores

Three donor–acceptor–donor (D–A–D) pyrene chromophores are described and compared by DFT computations. The two properties of low energy photon absorption and low energy electrochemical reduction are demonstrated through a pyrene framework. Altering the electron‐acceptor strength of the pyrene core by chemical oxidation or installation of a thiadiazole dioxide heterocycle results in the formation of D–A–D chromophores with absorption bands up to 900 nm and LUMO energy levels of approximately –4.1 eV vs. vacuum.

Effective Atomic Number and Kerma for Photon Energy Absorption of Organic Scintillators

An attempt has been made to calculate the effective atomic number and Kerma for photon energy absorption of organic scintillators in the energy region 1 keV to 20 MeV. We have chosen seven organic scintillators viz., anthracene, stilbene, naphthalene, p -terphenyl, PPO, butyl PBD and PBD. The Z PEA, eff and Kerma values are calculated by using mass-energy absorption coefficient from Hubbell and Seltzer. We also calculated Z PI, eff for total photon interaction with coherent scattering by using WinXCom and compared with the Z PEA, eff.

Photostimulation of mitochondria as a treatment for retinal neurodegeneration

Absorption of photon energy by neuronal mitochondria leads to numerous downstream neuroprotective effects. Red and near infrared (NIR) light are associated with significantly less safety concerns than light of shorter wavelengths and they are therefore, the optimal choice for irradiating the retina. Potent neuroprotective effects have been demonstrated in various models of retinal damage, by red/NIR light, with limited data from human studies showing its ability to improve visual function. Improved neuronal mitochondrial function, increased blood flow to neural tissue, upregulation of cell survival mediators and restoration of normal microglial function have all been proposed as potential underlying mechanisms of red/NIR light.

Synthesis and Photoluminesence Study of Reduced Graphene Oxide (rGO)/ZnO for Solar Energy Absorbing Materials

Materials combining reduced graphene oxide (rGO) from coconut shells and commercial ZnO have been synthesized by dry-mixing in weight ratio of 1:2, 2:2, and 3:2. For photoluminesence (PL) characterization, the solutions with concentration of rGO/ZnO in aquadest up to 0.003 mg/mL were prepared. The absorbing photon energy by the samples at wavelength 280-426 nm (ultraviolet-purple) has induced electron transition to conduction band. Further, the returning electron to valence band was followed by photon emission at wavelength of 530-880 nm (green-infrared). The PL intensity was observed to drastically enhance with increasing content of rGO in the solution by 252.5%, 285.0% and 291.3% for the corresponding samples compared to the solution containing pure ZnO. The rGO/ZnO materials exhibit higher absorbance with wider wavelength range, and therefore can potentially be used as solar energy absorbing materials to enhance the efficiency of solar cell.

Prolonged Direct Harvesting of Photosynthetic Electrons from Living Algal Cells

Plant cells produce photosynthetic electrons (PEs) by splitting water during photosynthesis. In the beginning of photosynthesis, antenna complex embedded in thylakoid membrane absorbs photon energy and converts them into excited electrons with high quantum efficiency. These excited electrons, known as PEs, are transferred through electron acceptors in order to grow cell or store surplus energy as a form of carbonhydrates. However, since the energy state of the PEs is lowered once they are stored as organic matter, many researchers have tried to extract PEs from photosynthetic electron transfer chain before their conversion into organic matter. Such previous works include collection of PEs by electrochemical oxidizing through mediator as an electron interceptor and use of electrical linker materials such as CNTs, electrically-conducting polymer matrix, or conducting linker to working electrodes between photosynthetic components and the surface of electrodes. Although these works demonstrated the feasibility of harvesting PEs in large scale, there are still issues including efficiency decrease from mediator use and limited stability or requirement of additional electron donors of isolated photosynthetic extracts. In our previous study, we demonstrated direct extraction of PEs from living algal cell, chlamydomonas reinhardtii, by inserting nanoelectrode (NE) into cell membrane. However, in spite of highly efficient extraction of PEs, the maximum harvesting period of PEs was shorter than 1 hour. In this study, we developed a cantilever type of NE system in order to find the optimal shape and size of NE for extraction of PEs for a longer period of time. Fabrication of cantilever NE system started by milling the end of commercial AFM cantilever tip by focused ion beam (FIB). Then, Au was deposited on the cantilever by sputtering as a working electrode. Si3N4 was coated on top of the Au-coated NE to minimize noise signals. Then, additional FIB milling was performed to expose the Au layer at the tip of the NE for localized PE signal measurement. With this cantilever NE, we firstly investigated a relationship between NE size and the viability of inserted cells. It was confirmed that algal cells remained stable for up to 7 days when NE diameters smaller than 500 nm were used. Through continuous observation of inserted algal cells, their viability was ascertained by cell proliferation. After high stability of NE inserted cells was confirmed, direct extraction of PEs was attempted without any mediator. Light-triggered currents from the cells inserted by NEs were observed and the photosynthetic origin of the currents was confirmed by application of DCMU and the subsequent disappearance of the light-responsive currents. Since exposure to highly intense and continuous illumination can damage the pigments of the photosystems, the effect of illumination condition on the PE extraction was investigated. Up to the light intensity of 132 μmol photons m-2s-1, no photobleaching was observed from the NE-inserted cells and the stronger light intensity produced the higher photosynthetic currents. When NE-inserted cells were incubated in a dark except during illumination for photosynthetic current harvesting, about 150 fA of photosynthetic currents were measured over 7 days with 9 μmol photons m-2s-1 of light intensity at 400 mV against Ag/AgCl electrode. As another comparison, when NE-inserted cells were exposed to continuous illumination with 16.5 μmol photons m-2s-1 for 60 hours, more than twice amount of PEs was measured compared to dark incubated cells. Finally, NE-inserted cells were exposed to continuous illumination and th e photosynthetic currents were monitored simultaneously. It was shown that PEs were extracted steadily during several hours of illumination. These results indicated that PEs could be extracted for an extended period of time under various illumination conditions. In this work, the maximum photosynthetic currents measured were 2.5 pA after continuous illumination on a single NE-inserted cell.

Evaluation of photosynthetic performance and carbon isotope discrimination in perennial ryegrass (Lolium perenne L.) under allelochemicals stress

Ferulic (FA) and p-hydroxybenzoic acid (pHBA) are commonly found as phenolic compounds (PHC) in many forage and cereal crops. Although the effects of these PHC on seedling growth are relatively explored, not many information is available regarding the phytotoxicity on ecophysiological processes of perennial ryegrass adult plants. The experiment was conducted with the aim to evaluate the phytotoxic potential of PHC on the seedling growth, leaf water relation, chlorophyll fluorescence attributes and carbon isotope discrimination adult plants of perennial ryegrass (Lolium perenne L.). The results clearly indicated that PHC behaved as potent inhibitors of chlorophyll fluorescence yield (Fv/Fm) in leaves of L. perenne and plants showed poor tolerance against allelochemicals stress. Quantum yield (ΦPSII), chlorophyll fluorescence quenching (qP) and non-photochemical quenching (NPQ) were decreased following exposure to FA and pHBA. The portion of absorbed photon energy that was thermally dissipated (D) in L. perenne was decreased. Exposure of the L. perenne seedlings to FA and pHBA stress led to a decrease in fresh/dry weight, relative water content and leaf osmotic potential. Carbon isotope composition ratio (δ13C) was significantly less negative than the control following treatment with FA or pHBA. The results suggested that PHC uptake was a key step for the effectiveness of these secondary metabolites and their phytotoxicity on L. perenne adult plants was mainly due to the alteration of leaf water status accompanied by photosystem II damage. Acquisition of such knowledge may ultimately provide a better understanding about the mode of action of the tested compounds.

Calculation of photon shielding properties for some neutron shielding materials

The objective of the present study is to calculate photon shielding parameters for seven polyethylene-based neutron shielding materials. The parameters include the effective atomic number (Zeff), the effective electron density (Neff) for photon interaction and photon energy absorption, and gamma-ray kerma coefficient (kγ). The calculations of Zeff are presented as a single-valued and are energy dependent. While Zeff values were calculated via simplistic power-law method, the energy-dependent Zeff for photon interaction (ZPI-eff) and photon energy absorption (ZPEA-eff ) are obtained via the direct method for energy ranges of 1 keV–100 GeV and 1 keV–20 MeV, respectively. The kγ coefficients are calculated by summing the contributions of the major partial photon interactions for energy range of 1 keV–100 MeV. In most cases, data are presented relative to pure polyethylene to allow direct comparison over a range of energy. The results show that combination of polyethylene with other elements such as lithium and aluminum leads to neutron shielding material with more ability to absorb neutron and γ-rays. Also, the kerma coefficient first increases with Z of the additive element at low photon energies and then converges with pure polyethylene at energies greater than 100 keV.

Selective photoantisepsis.

Selective killing of pathogens by laser is possible due to the difference in absorption of photon energy by pathogens and host tissues. The optical properties of pathogenic microorganisms are used along with the known optical properties of soft tissues in calculations of the laser-induced thermal response of pathogen colonies embedded in a tissue model. The objective is to define the laser parameters that optimize pathogen destruction and depth of the bactericidal effect. The virtual periodontium is a computational model of the optical and time-dependent thermal properties of infected periodontal tissues. The model simulates the periodontal procedure: Laser Sulcular Debridement.1 Virtual pathogen colonies are placed at different depths in the virtual periodontium to determine the depth for effective bactericidal effects given various laser parameters (wavelength, peak power, pulse duration, scan rate, fluence rate) and differences in pathogen sensitivities. Accumulated background heat from multiple passes increases the depth of the bactericidal effect. In visible and near-IR wavelengths the large difference in absorption between normal soft tissue and Porphyromonas gingivalis (Pg) and Prevotella intermedia (Pi) results in selective destruction. Diode laser (810 nm) efficacy and depth of the bactericidal effect are variable and dependent on hemin availability. Both pulsed-Nd:YAG and the 810 nm diode lasers achieve a 2-3 mm deep damage zone for pigmented Pg and Pi in soft tissue without surface damage (selective photoantisepsis). The model predicts no selectivity for the Er:YAG laser (2,940 nm). Depth of the bactericidal effect is highly dependent on pathogen absorption coefficient. Highly sensitive pathogens may be destroyed as deep as 5-6 mm in soft tissue. Short pulse durations enable confinement of the thermal event to the target. Temporal selectivity is achieved by adjusting pulse duration based on target size. The scatter-limited phototherapy model of the infected periodontium is applied to develop a proper dosimetry for selective photoantisepsis. Dosimetry planning is essential to the development of a new treatment modality. Lasers Surg. Med. 48:763-773, 2016. © 2016 Wiley Periodicals, Inc.

A New Approach to the Absorption of Photon Energy among Retinal Cells Provides the Key to Some Old Problems in Color Vision

A New Approach to the Absorption of Photon Energy among Retinal Cells Provides the Key to Some Old Problems in Color Vision

Photon Energy Deposition in Strong-Field Single Ionization of Multielectron Molecules

Molecules exposed to strong laser fields may coherently absorb multiple photons and deposit the energy into electrons and nuclei, triggering the succeeding dynamics as the primary stage of the light-molecule interaction. We experimentally explore the electron-nuclear sharing of the absorbed photon energy in above-threshold multiphoton single ionization of multielectron molecules. Using CO as a prototype, vibrational and orbital resolved electron-nuclear sharing of the photon energy is observed. Different from the simplest one- or two-electron systems, the participation of the multiple orbitals and the coupling of various electronic states in the strong-field ionization and dissociation processes alter the photon energy deposition dynamics of the multielectron molecule. The population of numerous vibrational states of the molecular cation as the energy reservoir in the ionization process plays an important role in photon energy sharing between the emitted electron and the nuclear fragments.

Photo-thermionic effect in vertical graphene heterostructures.

Finding alternative optoelectronic mechanisms that overcome the limitations of conventional semiconductor devices is paramount for detecting and harvesting low-energy photons. A highly promising approach is to drive a current from the thermal energy added to the free-electron bath as a result of light absorption. Successful implementation of this strategy requires a broadband absorber where carriers interact among themselves more strongly than with phonons, as well as energy-selective contacts to extract the excess electronic heat. Here we show that graphene-WSe2-graphene heterostructure devices offer this possibility through the photo-thermionic effect: the absorbed photon energy in graphene is efficiently transferred to the electron bath leading to a thermalized hot carrier distribution. Carriers with energy higher than the Schottky barrier between graphene and WSe2 can be emitted over the barrier, thus creating photocurrent. We experimentally demonstrate that the photo-thermionic effect enables detection of sub-bandgap photons, while being size-scalable, electrically tunable, broadband and ultrafast.

A comparative study of gamma-ray interaction and absorption in some building materials using Zeff-toolkit

ABSTRACTThe gamma-ray shielding behaviour of a material can be investigated by determining its various interaction and energy-absorption parameters (such as mass attenuation coefficients, mass energy absorption coefficients, and corresponding effective atomic numbers and electron densities). Literature review indicates that the effective atomic number (Zeff) has been used as extensive parameters for evaluating the effects and defect in the chosen materials caused by ionising radiations (X-rays and gamma-rays). A computer program (Zeff-toolkit) has been designed for obtaining the mean value of effective atomic number calculated by three different methods. A good agreement between the results obtained with Zeff-toolkit, Auto_Zeff software and experimentally measured values of Zeff has been observed. Although the Zeff-toolkit is capable of computing effective atomic numbers for both photon interaction (Zeff,PI) and energy absorption (Zeff,En) using three methods in each. No similar computer program is available in the literature which simultaneously computes these parameters simultaneously. The computed parameters have been compared and correlated in the wide energy range (0.001–20 MeV) for 10 commonly used building materials. The prominent variations in these parameters with gamma-ray photon energy have been observed due to the dominance of various absorption and scattering phenomena. The mean values of two effective atomic numbers (Zeff,PI and Zeff,En) are equivalent at energies below 0.002 MeV and above 0.3 MeV, indicating the dominance of gamma-ray absorption (photoelectric and pair production) over scattering (Compton) at these energies. Conversely in the energy range 0.002–0.3 MeV, the Compton scattering of gamma-rays dominates the absorption. From the 10 chosen samples of building materials, 2 soils showed better shielding behaviour than did other 8 materials.

Photophysical and photochemical properties of difluoroboronated 1,3-diketones having the ferrocene moiety studied by steady-state and laser flash photolyses

Abstract We synthesized 1,3-diketones having the ferrocene moiety (FcDKPhs) and the corresponding difluoroboronated complexes (Fc@Phs), and investigated the photophysical and photochemical properties in solution by steady-state and laser flash photolyses. FcDKPhs and Fc@Phs had absorption bands with large absorptivities in the UV-region and ones with small absorptivities in the Vis-region, but provided neither fluorescence nor phosphorescence. FcDKPhs decomposed upon exposure to UV–vis light while Fc@Phs were stable. No transient signals obtained upon laser flash photolysis of FcDKPhs and Fc@Phs demonstrated absence of intersystem crossing to the triplet states. Fc@Phs efficiently convert absorbed photon energy to heat.

Self-assembled molecular p/n junctions for applications in dye-sensitized solar energy conversion.

The achievement of long-lived photoinduced redox separation lifetimes has long been a central goal of molecular-based solar energy conversion strategies. The longer the redox-separation lifetime, the more time available for useful work to be extracted from the absorbed photon energy. Here we describe a novel strategy for dye-sensitized solar energy applications in which redox-separated lifetimes on the order of milliseconds to seconds can be achieved based on a simple toolkit of molecular components. Specifically, molecular chromophores (C), electron acceptors (A) and electron donors (D) were self-assembled on the surfaces of mesoporous, transparent conducting indium tin oxide nanoparticle (nanoITO) electrodes to prepare both photoanode (nanoITO|-A-C-D) and photocathode (nanoITO|-D-C-A) assemblies. Nanosecond transient-absorption and steady-state photolysis measurements show that the electrodes function microscopically as molecular analogues of semiconductor p/n junctions. These results point to a new chemical strategy for dye-sensitized solar energy conversion based on molecular excited states and electron acceptors/donors on the surfaces of transparent conducting oxide nanoparticle electrodes.

Contribution of PsbS Function and Stomatal Conductance to Foliar Temperature in Higher Plants.

Natural capacity has evolved in higher plants to absorb and harness excessive light energy. In basic models, the majority of absorbed photon energy is radiated back as fluorescence and heat. For years the proton sensor protein PsbS was considered to play a critical role in non-photochemical quenching (NPQ) of light absorbed by PSII antennae and in its dissipation as heat. However, the significance of PsbS in regulating heat emission from a whole leaf has never been verified before by direct measurement of foliar temperature under changing light intensity. To test its validity, we here investigated the foliar temperature changes on increasing and decreasing light intensity conditions (foliar temperature dynamics) using a high resolution thermal camera and a powerful adjustable light-emitting diode (LED) light source. First, we showed that light-dependent foliar temperature dynamics is correlated with Chl content in leaves of various plant species. Secondly, we compared the foliar temperature dynamics in Arabidopsis thaliana wild type, the PsbS null mutant npq4-1 and a PsbS-overexpressing transgenic line under different transpiration conditions with or without a photosynthesis inhibitor. We found no direct correlations between the NPQ level and the foliar temperature dynamics. Rather, differences in foliar temperature dynamics are primarily affected by stomatal aperture, and rapid foliar temperature increase during irradiation depends on the water status of the leaf. We conclude that PsbS is not directly involved in regulation of foliar temperature dynamics during excessive light energy episodes.

Ultraviolet to near-infrared downconversion in Yb3+–Na+ codoped Sr2CaWO6

This study investigated photoluminescent properties of Sr2CaWO6:Yb3+, Na+ phosphor. The samples were successfully synthesized via a solid-state reaction method with various doping concentrations. The phosphorcan efficiently absorb ultraviolet photons of 250–350nm and transfer its absorbed photon energy toYb3+ions. Then subsequent quantum cutting betweenWO6 groups and Yb3+ions takes place, down-converting an absorbed ultraviolet photon into two photons of 1007nm radiations. Analyses of decay curves of different samples reveal an efficient energy transfer from WO6 groupsto Yb3+ions. Cooperative energy transfer from host to Yb3+ ions is responsible for downconversion via lifetime analysis. Quantum efficiencies were calculated, and estimated maximum efficiency reached 190%. These phosphors combine wide wavelength absorption in the ultraviolet range with high quantum efficiency, enabling potential application of efficiency enhancement ofSisolar cell.

Demonstration of the operation principles of intermediate band solar cells at room temperature

In this work we report, for the first time at room temperature, experimental results that prove, simultaneously in the same device, the two main physical principles involved in the operation of intermediate band solar cells: (1) the production of sub-bandgap photocurrent by two optical transitions through the intermediate band; (2) the generation of an output voltage which is not limited by the photon energy absorption threshold. These principles, which had always required cryogenic temperatures to be evidenced all together, are now demonstrated at room temperature on an intermediate band solar cell based on InAs quantum dots with Al0.3Ga0.7As barriers.

Effective atomic numbers for photon energy absorption and energy dependence of some thermoluminescent dosimetric materials

Effective atomic number for photon energy absorption (Z peaeff ), the relative effective atomic number of the thermoluminescent dosimetric (TLD) materials with respect to air (Z reff ), and energy dependence (ED) of the TLD materials such as beryllium oxide (BeO), lithium tetraborate (Li 2 B 4 O 7 : Cu, Ag, P), aluminum oxide (Al 2 O 3 ), calcium fluoride (CaF 2 ), and titanium oxide (TiO 2 ) in the energy range of 1 keV to 20 MeV have been studied. The values of ZPEA eff and ZR eff show a broad peak and a maximum value around 20 keV for BeO, around 60 keV for CaF2 and TiO 2 , and around 40 keV for Al 2 O3 and Li 2 B 4 O 7 : Cu, Ag, P. Overall, the effective atomic number (Z eff ) varies linearly with ED for all the materials in the photon energy range of 1 keV to 20 MeV except TiO2 and thereby confirming the validity of a more commonly employed method of using the Z eff to calculate the measure of the ED in TLD. The ED values show a broad peak around 30 keV for CaF 2 and TiO 2 and around 20 keV for Al 2 O 3 and remain almost constant for the other two materials.