Intensive Illumination Research Articles

Synchronous Photoactivation-Imaging Fluorophores Break Limitations of Photobleaching and Phototoxicity in Live-cell Microscopy.

Fluorescence microscopy is one of the most important tools in the studies of cell biology and many other fields, but two fundamental issues, photobleaching and phototoxicity, associated with the fluorophores have still limited its use for long-term and strong-illumination imaging of live cells. Here, we report a new concept of fluorophore engineering chemistry, synchronous photoactivation-imaging (SPI) fluorophores, activating and exciting fluorophores by a single light source to thus avoid the repeated switches between activation and excitation lights. The chemically reconstructed, nonemissive fluorophores can be photolyzed to allow continuous replenishing of "bright-state" probes detectable by standard fluorescent microscopes in the imaging process so as to bypass the photobleaching barrier to greatly extend the imaging period. Equally importantly, SPI fluorophores substantially reduce photocytotoxicity due to the scavenging of reactive oxygen species (ROS) by a photoactivable group and the slow release of "bright-state" probes to minimize ROS generation. Using SPI fluorophores, the time-lapsed confocal (>16 h) and super-resolution (>3 h) imaging of subcellular organelles under intensive illumination (50 MW/cm2) were achieved in live cells.

Photo-Oxidative Protection of Chlorophyll a in C-Phycocyanin Aqueous Medium.

In this study, potential protection of chlorophyll a from illumination and oxidation-induced decomposition has been examined using C-phycocyanin (C-PC) aqueous medium. Photo-oxidation resistance of chlorophyll a was monitored in various aqueous media using ultraviolet-visible spectroscopy and direct-infusion atmospheric pressure chemical ionization mass spectrometry analysis. The spectroscopy results showed that chlorophyll a in C-PC medium experienced the lowest rate of conversion to its derivatives; thus, it was demonstrated that chlorophyll a was mostly intact in the C-PC medium. Furthermore, the C-PC treated with chlorophyll a showed the lowest concentrations of malondialdehyde, and chlorophyll a in C-PC medium did not cause serious damage to human liver cells in vitro after intensive illumination. Therefore, we propose a new method of protecting chlorophyll a from photodegradation and oxidation using C-PC aqueous medium.

Optical clearing of living brains with MAGICAL to extend i nvivo imaging.

SummaryTo understand brain functions, it is important to observe directly how multiple neural circuits are performing in living brains. However, due to tissue opaqueness, observable depth and spatiotemporal resolution are severely degraded in vivo. Here, we propose an optical brain clearing method for in vivo fluorescence microscopy, termed MAGICAL (magical additive glycerol improves clear alive luminance). MAGICAL enabled two-photon microscopy to capture vivid images with fast speed, at cortical layer V and hippocampal CA1 in vivo. Moreover, MAGICAL promoted conventional confocal microscopy to visualize finer neuronal structures including synaptic boutons and spines in unprecedented deep regions, without intensive illumination leading to phototoxic effects. Fluorescence emission spectrum transmissive analysis showed that MAGICAL improved in vivo transmittance of shorter wavelength light, which is vulnerable to optical scattering, thus unsuited for in vivo microscopy. These results suggest that MAGICAL would transparentize living brains via scattering reduction.

Photodegradation of surface passivated GaAs nanowires

Efficiency of in situ AlGaAs and GaP and ex situ nitride surface passivation of p+ GaAs nanowires was studied. The efficiency was estimated by comparing of the photoluminescence intensity of the passivated nanowires with the unpassivated nanowire. The AlGaAs and nitride passivation lead to the increasing of the PL intensity by three orders of magnitude while the GaP passivation increases PL intensity only by one order. Photodegradation of the passivated NWs under intensive laser illumination was observed. AlGaAs, GaP and nitride passivated NWs photodegrade after one-minute exposure under laser power densities of 500, 300 and 30 kW/cm2, respectively.

Stabilizing CsPbBr3 quantum dots with conjugated aromatic ligands and their regulated optical behaviors

Surface modifications of lead halide perovskite quantum dots (QDs) are promising for perusing improved stability and regulated optical properties. We have successfully introduced 1-alkyl-3-methyl-imidazolium cations, a kind of ionic liquids with conjugated aromatic head groups, as proper surface ligands via ligands exchange (LE) method. After surface modification, it is found that there is approximately 10 cm−1 chemical shift of the infrared (IR) absorption peak for the ligand compared to its derived raw imidazolium salts, suggesting that there is interaction between the imidazolium cations and the QDs. The theoretical simulations on structure optimization and frontier molecular orbitals (FMOs) prove that the interaction is enabled by a preferred N-Pb bonding on the surface and a close matching in energy levels of the ligands and CsPbBr3. X-ray photoelectron spectroscopy (XPS) results show a significant decrease in ligand density as well as a better passivation of surface Pb2+ defects. The modified QDs show better stabilities for their solution can survive after 72 h duration of intensive light illumination whilst obvious aggregation and degradation is found after only 24 h for the parent QDs solution. Accordingly, the modified QDs present better performance as phosphor in the white light-emitting diodes (WLEDs) device. The research gives an insight into the surface engineering of QDs with conjugated head groups, and suggests the potential application of the modified QDs as inks in flexible devices and phosphors in WLEDs.

Artificial Light at Night Promotes Activity Throughout the Night in Nesting Common Swifts (Apus apus)

The use of artificial light at night (ALAN) is a rapidly expanding anthropogenic effect that transforms nightscapes throughout the world, causing light pollution that affects ecosystems in a myriad of ways. One of these is changing or shifting activity rhythms, largely synchronized by light cues. We used acoustic loggers to record and quantify activity patterns during the night of a diurnal bird – the common swift – in a nesting colony exposed to extremely intensive artificial illumination throughout the night at Jerusalem’s Western Wall. We compared that to activity patterns at three other colonies exposed to none, medium, or medium-high ALAN. We found that in the lower-intensity ALAN colonies swifts ceased activity around sunset, later the more intense the lighting. At the Western Wall, however, swifts remained active throughout the night. This may have important implications for the birds’ physiology, breeding cycle, and fitness, and may have cascading effects on their ecosystems.

Suppressed phase separation of mixed-halide perovskites confined in endotaxial matrices

The functionality and performance of a semiconductor is determined by its bandgap. Alloying, as for instance in InxGa1-xN, has been a mainstream strategy for tuning the bandgap. Keeping the semiconductor alloys in the miscibility gap (being homogeneous), however, is non-trivial. This challenge is now being extended to halide perovskites – an emerging class of photovoltaic materials. While the bandgap can be conveniently tuned by mixing different halogen ions, as in CsPb(BrxI1-x)3, the so-called mixed-halide perovskites suffer from severe phase separation under illumination. Here, we discover that such phase separation can be highly suppressed by embedding nanocrystals of mixed-halide perovskites in an endotaxial matrix. The tuned bandgap remains remarkably stable under extremely intensive illumination. The agreement between the experiments and a nucleation model suggests that the size of the nanocrystals and the host-guest interfaces are critical for the photo-stability. The stabilized bandgap will be essential for the development of perovskite-based optoelectronics, such as tandem solar cells and full-color LEDs.

Epicuticular Wax Composition of Leaves of Tilia L. Trees as a Marker of Adaptation to the Climatic Conditions of the Steppe Dnieper

The relationship between the adaptive ability of different linden genotypes to the changing climatic conditions of the Steppe Dnieper and the epicuticular wax component composition of tree leaves was investigated. Specificity of the epicuticular wax hydrocarbon composition of linden autochthonous species (T. cordata) and introduced species (T. platyphyllos and T. begoniifolia) was established. For all genotypes, significant differences in the composition of epicuticular waxes from the surface of shaded and sun-adapted leaves were identified. The greatest accumulation of the epicuticular waxes was on the leaves of T. platyphyllos both under the shading conditions and illumination (11.0 and 17.6 μg/cm2, respectively). The general pattern for the genus Tilia L. species consisted in a substantial increase in the content of very long-chain n-alkanes simultaneously with a sharp decrease in the free fatty acid content in the composition of epicuticular waxes under the intensive illumination of leaves.

Universal description of exciton diffusion length in organic photovoltaic cell

A physical model of exciton diffusion length in organic photovoltaic cell based on percolation theory and Forster resonant transfer rate is presented here. The calculated results show a good agreement with Monte Carlo simulation and experimental data, indicating that the proposed model can well describe the temperature and material disorder dependences of exciton diffusion length. More importantly, the effect of carrier density on the exciton diffusion length can also be discussed based on our model, specifically, more intensive light illumination will lead to larger exciton diffusion length. Furthermore, according to our analysis, the Gaussian distribution density of states (DOS) can be well replaced by an exponential DOS at certain exciton concentration, which would help us get an analytical model for the exciton diffusion length.

Raman study of laser-induced heating effects in free-standing silicon nanocrystals.

This paper demonstrates that free-standing silicon nanocrystals (Si NCs) have significantly different thermal conductivity properties compared to Si NCs embedded in a host matrix. The temperatures of Si NCs under laser illumination have been determined by measuring the ratio of the Anti-Stokes to Stokes intensities of the first order Si-Si transverse optical (TO) phonon mode. It is found that large free-standing Si NCs are easily heated up to ∼953 K by the laser light. The laser heating effects are reversible to a large extent, however the nature of the free-standing Si NCs is slightly modified after intensive illumination. The free-standing Si NCs can even be easily melted when exposed to a well-focused laser beam. Under these conditions, the blackbody radiation of the heated Si NCs starts to compete with the detected Raman signals. A simplified model of the heating effects is proposed to study the size dependence of the heated free-standing Si NCs with increasing laser power. It is concluded that the huge red-shift of the Si-Si TO mode observed under intensive laser illumination originates from laser-induced heating effects. In contrast, under similar illumination conditions Si NCs embedded in matrixes are hardly heated due to better thermal conductivity.

Multi-scale retinex improvement for nighttime image enhancement

We propose a retinex improvement for nighttime image enhancement. Retinex is often used on images under non-uniform illumination in terms of either color or lightness and has satisfactory results to achieve color constancy and dynamic range compression. Few studies focus retinex on nighttime images, especially those under extreme conditions (i.e., images with over-lighted or extremely under-lighted areas or with noise speckles), on which retinex operation can perform badly. Original multi-scale retinex (MSR) is extremely sensitive to noise speckles that cameras produce in low light areas, and it has unsatisfactory effect on areas with normal or intensive illumination. Moreover, original MSR uses a gain-offset method for prior-to-display treatment and can lead to apparent data loss on nighttime images. This paper replaces the logarithm function in MSR with a customized sigmoid function to minimize data loss, and adapts MSR to nighttime images by merging results from sigmoid-MSR with original images. Experiments show our framework, when applied to nighttime images, can preserve areas with normal or intensive lighting and suppress noise speckles in extreme low light areas.

Photosynthetic Properties of Some Free-Living and Lichenized Green Terrestrial Algae

The photosynthetic properties of four strains of free-living green terrestrial algae (Diplosphaera chodatii Bial., Parietochloris ovoideus Mikhailyuk et Demchenko, Myrmecia bisecta Reisigl, and Trentepohlia sp.) and two strains of green photobionts of lichens (Radiococcus signiensis (Broady) Kostikov et al. and Trebouxia australis Beck) were studied. As a result of our work the optimum light intensity for cultivating algae strains at a relative humidity of 45% was found: for Trentepohlia was ≤ 100 FEM / (m2·s), Radiococcus and Trebouxia ≤ 200 FEM / (m2·s), Parietochloris ≤ 400 FEM / (m2·s), and Diplosphaera and Myrmecia ≤ 800 FEM / (m2·s). Moreover, it was revealed that Trentepohlia sp., R. signiensis and T. australis are vulnerable to light, while M. bisecta, P. ovoideus, and D. chodatii are well adapted to intensive illumination. However, the strains T. australis and D. chodatii in their groups withstand high-speed photochemical damage even under optimal light intensity.

Photo-assisted electrodeposition of polypyrrole back contact to CdS/CdTe solar cell structures

Glass/indium tin oxide/CdS/CdTe photovoltaic structures were prepared using the high vacuum evaporation method, followed by a typical activation procedure, which involves annealing of the structures at 415–430°C in the presence of CdCl2 in air.The main purpose of this work was to prepare and evaluate the performance of complete CdS/CdTe solar cell structures with polypyrrole (PPy) back contact and compare it to the structures with standard, copper containing back contact.Back contact layers of PPy doped with ß-naphthalene sulfonate were deposited onto activated CdTe layers by photo-assisted electrodeposition technique in a three-electrode electrochemical cell. It was found that intensive white light illumination from a xenon lamp facilitates PPy deposition at a lower applied potential range and improves quality of obtained polymer films. Applied technique gives the possibility to deposit the PPy layer strictly onto illuminated photoactive CdTe surface eliminating possible short-circuiting through pinholes and cracks in CdTe photoabsorber layer. Furthermore, relatively low deposition potential values give the possibility to reduce electrochemical degradation of CdS/CdTe photovoltaic structure in an electrochemical cell.

Optical monitoring of the thermal spraying

An original approach has been made in monitoring the thermal spraying. Monitoring of the process is based on visualization of particle movement using both high speed videocamera and wide-band high intensive illumination and measurements of particle temperature and velocity. Synchronous with the registration of the particle parameters, surface temperature of the coating has been measured with 2-channel pyrometer with high spatial and temporal resolution. The results of investigations of the Cold Spray process and D-gun spraying are presented.

Self-Organization Processes of Nanostructure Formation by Laser Radiation in Metal

The current state of knowledge about mechanisms of metal nano-particles (NP) formation processes induced by the interaction of high-energy laser beam with surface of the metallic lattices (Au, Ag, Cu) is presented. The review includes an evaluation of the contribution of self-organized effects into the processes of the metal nano-structurization depending on the laser mode, external factors and internal parameters of an active zone. It was noticed that intensive pulsed laser illumination enabled to stimulate nano-fragmentation at the fluencies near and above the melting threshold of the metal in different mediums The laser induced processes of metallic particles formation by ablation of the metal target with consequent NP sizes stabilization by precise temperature tuning in the active zone, local plasmon resonance in liquids, and microablation mechanism in metal films in the conditions of surface plasmon resonance (SPR) due to self-organization effects are considered. Comparative analysis of the laser nano-technologies in air, vacuum, rarefied gas and liquid environments showed the advantages of self-organization in NP generation processes based on the SPR effects and their perspectives.

Novel machine vision methods for outdoor and built environments

Machine vision is potentially the most powerful sensing technique for intelligent automation. However, the existing techniques and algorithms only partially satisfy needs of complex environments (e.g. outdoor construction sites) mainly because of poor and/or unpredictably changing visibility conditions frequently encountered there (weather phenomena, mud and silt, partially buried objects, burst of intensive illumination, etc.). In this paper, we discuss principles of two methods that can significantly improve performances of vision system in such difficult conditions. The first method (based on gated imaging) is a specialized image acquisition technique while the second method addresses an important problem of object detection in complex environments. Both methods have been tested using images captured under visual conditions typically expected in such environments (e.g. many images are captured in high-turbidity water). The methods can be incorporated into more complex sensing systems, depending on needs and constraints of particular applications.

Mechanism of subunit switching from NR2B to NR2C in mouse cerebellar granule cell cultures

To understand brain functions, it is important to observe directly how multiple neural circuits are performing in living brains. However, due to tissue opaqueness, observable depth and spatiotemporal resolution are severely degraded in vivo. Here, we propose an optical brain clearing method for in vivo fluorescence microscopy, termed MAGICAL (magical additive glycerol improves clear alive luminance). MAGICAL enabled two-photon microscopy to capture vivid images with fast speed, at cortical layer V and hippocampal CA1 in vivo. Moreover, MAGICAL promoted conventional confocal microscopy to visualize finer neuronal structures including synaptic boutons and spines in unprecedented deep regions, without intensive illumination leading to phototoxic effects. Fluorescence emission spectrum transmissive analysis showed that MAGICAL improved in vivo transmittance of shorter wavelength light, which is vulnerable to optical scattering, thus unsuited for in vivo microscopy. These results suggest that MAGICAL would transparentize living brains via scattering reduction.

Polarization of Surface Layers in PLZT Relaxor Ceramics

The possibility of inducing a polarization state in PLZT-10 relaxor ceramics under exposure to external electric fields and intensive light illumination at room temperature was shown in this paper. Such polarization state was studied by a dynamic method of investigating pyroelectric properties. It was established that a fairly stable polarization state can also be created in PLZT-10 ceramics when studying it by means of the piezoelectric force microscopy. In the latter case, hysteresis loops of a local piezoelectric response have been obtained.

Use of projection moiré for measuring the instantaneous out-of-plane deflections of composite plates subject to bird strike

For the new generation aircraft families, the use of fibre-reinforced plastics is considered for the leading edge of the wings. However, this leading edge is very prone to bird strike impact. This paper presents the use of the projection moiré technique to measure the instantaneous out-of-plane deflections of composite plates subject to bird strike. Very strict constraints with regard to (i) high-speed image acquisition, (ii) vibrations of the impact chamber, and (iii) projection and observation angles, complicated substantially the development of the set-up. Moreover, the high frame rates (12,000 fps) required a very intensive illumination. In the optimized configuration, a specially designed grating with gradually changing period is projected by means of special halide hydride lamps through one of the side windows of the impact chamber onto the composite plate riveted in a steel frame. The digital high-speed camera is mounted on the roof of the impact chamber and records through a mirror the object surface with the projected fringe pattern on it. Numerical routines based on local Fourier transform were developed to process the digital images to extract the phase and the out-of-plane displacements. The phase evaluation is possible due to the carrier frequency nature of the projected moiré pattern. This carrier frequency allows separation of the unwanted additive and multiplicative fringe pattern components in the frequency domain via the application of a proper mask. The numerical calculations were calibrated for the bird strike on an aluminum plate, where the plastic deformation could be checked after the test.

Turnover of ubiquinone-0 at the acceptor side of photosynthetic reaction center

The steady-state operation of photosynthetic reaction center from Rhodobacter sphaeroides was investigated by measuring the rate of cytochrome photo-oxidation under intensive continuous illumination (808 nm, 5 W cm(-2)). The native quinone UQ10 in Q(B) binding site of the reaction center was substituted by tailless UQ0 and the binding parameters and the turnover rate of the UQ0 was studied to test the recently discovered light-intensity dependent acceptor side effect (Gerencsér and Maróti 2006). The binding parameters of UQ0 (k(on) = 2.1 x 10(5) M(-1) s(-1) and k(off) = 100 s(-1)) were characteristic to the RC exposed to high light-intensity. The dissociation constant (K (D) = 480 microM) determined under high light intensity is 2-3 times larger than that determined from flash-experiments. The light-intensity dependent acceleration of cytochrome turnover measured on reaction center of inhibited proton binding was independent of the type of the quinone and was sensitive only to the size ("pressure") of the quinone pool. The dissociation constants of different types of semiquinones show similarly high (several orders of magnitude) increase in the modified conformation of the Q(B) binding pocket due to high intensity of illumination. This result indicates the exclusive role of the quinone headgroup in the binding of semiquinone to different conformations of the protein.