Green Light Illumination Research Articles

Photoinduced Dynamics and Toxicity of a Cancer Drug in Proximity of Inorganic Nanoparticles under Visible Light.

Drug sensitization with various inorganic nanoparticles (NPs) has proved to be a promising and an emergent concept in the field of nanomedicine. Rose bengal (RB), a notable photosensitizer, triggers the formation of reactive oxygen species under green-light irradiation, and consequently, it induces cytotoxicity and cell death. In the present study, the effect of photoinduced dynamics of RB upon complexation with semiconductor zinc oxide NPs is explored. To accomplish this, we successfully synthesized nanohybrids of RB with ZnO NPs with a particle size of 24 nm and optically characterized them. The uniform size and integrity of the particles were confirmed by high-resolution transmission electron microscopy. UV/Vis absorption and steady-state fluorescence studies reveal the formation of the nanohybrids. ultrafast picosecond-resolved fluorescence studies of RB-ZnO nanohybrids demonstrate an efficient electron transfer from the photoexcited drug to the semiconductor NPs. Picosecond-resolved Förster resonance energy transfer from ZnO NPs to RB unravel the proximity of the drug to the semiconductor at the molecular level. The photoinduced ROS formation was monitored using a dichlorofluorescin oxidation assay, which is a conventional oxidative stress indicator. It is observed that the ROS generation under green light illumination is greater at low concentrations of RB-ZnO nanohybrids compared with free RB. Substantial photodynamic activity of the nanohybrids in bacterial and fungal cell lines validated the in vitro toxicity results. Furthermore, the cytotoxic effect of the nanohybrids in HeLa cells, which was monitored by MTT assay, is also noteworthy.

Transfer of an exfoliated monolayer graphene flake onto an optical fiber end face for erbium-doped fiber laser mode-locking

This paper presents, for the first time, the successful transfer of exfoliated monolayer graphene flake to the optical fiber end face and alignment to its core. By fabricating and optimizing a polymeric poly(methyl methacrylate) (PMMA) and polyvinyl alcohol (PVA) substrate, it is possible to obtain a contrast of up to 11% for green light illumination, allowing the identification of monolayer graphene flakes that were transferred to optical fiber samples and aligned to its core. With Raman spectroscopy, it is demonstrated that graphene flake completely covers the optical fiber core, and its quality remains unaltered after the transfer. The generation of mode-locked erbium-doped fiber laser pulses, with a duration of 672 fs, with a single-monolayer graphene flake as a saturable absorber, is demonstrated for the first time. This transfer technique is of general applicability and can be used for other two-dimensional (2D) exfoliated materials.

The development and characterization of an exogenous green-light-regulated gene expression system in marine cyanobacteria.

A green-light-regulated gene expression system derived from Synechocystis sp. PCC 6803 was constructed and introduced into the marine cyanobacterial strain Synechococcus sp. NKBG 15041c. The regulation system was evaluated using gfp uv as a reporter gene under red-light illumination and under simultaneous red- and green-light illumination. Expression of the reporter gene was effectively repressed under red-light illumination and increased over 10-fold by illuminating with green light. Control vectors missing either the ccaS sensor histidine kinase gene or the ccaR response regulator gene showed no detectable induction of GFPuv expression. Green-light induction of gfp uv expression was further confirmed by quantitative reverse transcription PCR. The constructed system was effective at regulating the recombinant expression of a target gene using green light in a marine cyanobacterial strain that does not naturally possess such a green-light regulation system. Thus, constructed green-light-regulated gene expression system may be used as a core platform technology for the development of marine cyanobacterial strains in which bioprocesses will be regulated by light.

Bioelectronic Light‐Gated Transistors with Biologically Tunable Performance

Light-activated bioelectronic silicon nanowire transistor devices are made by fusing proteoliposomes containing a bacteriorhodopsin (bR) proton pump onto the nanowire surface. Under green-light illumination, bR pumps protons toward the nanowire, and the pH gradient developed by the pump changes the transistor output. Furthermore, co-assembly of small biomolecules that alter the bilayer permeability to other ions can upregulate and downregulate the response of field-effect transistor devices.

Visible light activated room temperature gas sensors based on nanocrystalline ZnO sensitized with CdSe quantum dots

This work reports the study of photoconductivity and visible light activated room temperature gas sensors properties of nanocrystalline ZnO thick films sensitized with colloidal CdSe quantum dots (QDs). Nanocrystalline zinc oxide (ZnO) was synthesized by the precipitation method. Colloidal CdSe quantum dots were obtained by high temperature colloidal synthesis. Sensitization was effectuated by three different procedures including direct adsorption of CdSe QDs stabilized with oleic acid on ZnO surface, anchoring to the ZnO surface through a bifunctional molecule of mercaptopropionic acid (MPA), and coating of CdSe QDs with a monolayer of MPA with subsequent adsorption on ZnO surface. Sensor measurements demonstrated that obtained QD CdSe/ZnO nanocomposites can be used for NO2 detection under visible (green) light illumination at room temperature without any thermal heating.

Graphene/GaN diodes for ultraviolet and visible photodetectors

The Schottky diodes based on graphene/GaN interface are fabricated and demonstrated for the dual-wavelength photodetection of ultraviolet (UV) and green lights. The physical mechanisms of the photoelectric response of the diodes with different light wavelengths are different. For UV illumination, the photo-generated carriers lower the Schottky barrier and increase the photocurrent. For green light illumination, as the photon energy is smaller than the bandgap of GaN, the hot electrons excited in graphene via internal photoemission are responsible for the photoelectric response. Using graphene as a transparent electrode, the diodes show a ∼mS photoresponse, providing an alternative route toward multi-wavelength photodetectors.

On the Response Time of Thin-Film Silicon Lateral Metal-Semiconductor-Metal Photodetectors

In this letter, we study the response time characteristics of lateral hydrogenated amorphous silicon (a-Si:H) and nanocrystalline silicon metal-semiconductor- metal (MSM) photodetectors. Devices with response time of 71 μs under green light illumination with λ = 525 nm (the wavelength of choice for indirect X-ray imaging) have been fabricated. The results show 42-fold and 4.2-fold improvement over the state of art single layer a-Si:H and double layer a-Si:H/molybdenumdisulphide (MoS2) MSM detectors, respectively.

A green-light inducible lytic system for cyanobacterial cells

BackgroundCyanobacteria are an attractive candidate for the production of biofuel because of their ability to capture carbon dioxide by photosynthesis and grow on non-arable land. However, because huge quantities of water are required for cultivation, strict water management is one of the greatest issues in algae- and cyanobacteria-based biofuel production. In this study, we aim to construct a lytic cyanobacterium that can be regulated by a physical signal (green-light illumination) for future use in the recovery of biofuel related compounds.ResultsWe introduced T4 bacteriophage-derived lysis genes encoding holin and endolysin under the control of the green-light regulated cpcG2 promoter in Synechocystis sp. PCC 6803. When cells harboring the lysis genes were illuminated with both red and green light, we observed a considerable decrease in growth rate, a significant increase in cellular phycocyanin released in the medium, and a considerable fraction of dead cells. These effects were not observed when these cells were illuminated with only red light, or when cells not containing the lysis genes were grown under either red light or red and green light.These results indicate that our constructed green-light inducible lytic system was clearly induced by green-light illumination, resulting in lytic cells that released intracellular phycocyanin into the culture supernatant. This property suggests a future possibility to construct photosynthetic genetically modified organisms that are unable to survive under sunlight exposure. Expression of the self-lysis system with green-light illumination was also found to greatly increase the fragility of the cell membrane, as determined by subjecting the induced cells to detergent, osmotic-shock, and freeze-thaw treatments.ConclusionsA green-light inducible lytic system was constructed in Synechocystis sp. PCC 6803. The engineered lytic cyanobacterial cells should be beneficial for the recovery of biofuels and related compounds from cells with minimal effort and energy, due to the fragile nature of the induced cells. Furthermore, the use of light-sensing two-component systems to regulate the expression of exogenous genes in cyanobacteria promises to replace conventional chemical inducers in many bioprocess applications, impacting the limiting water management issues.

Rectifying behavior and photoinduced characteristic in La‐doped BaSnO3/p‐Si heterojunctions

Photoinduced properties of Ba0.99La0.01SnO3/p‐Si heterojunctions that exhibit rectifying characteristic have been investigated. It is found that the heterojunction shows particular photoinduced characteristics at reverse bias when illuminated by violet or green light. The photocurrent rises rapidly with reverse bias but saturates beyond a critical voltage under green light illumination, whereas the photocurrent shows a linear increase with reverse bias under violet light illumination. Given the experimental results, we attribute the observed photoinduced behavior to the balancing sequence of the width of the depleted layer and the penetration depth of the laser in the heterojunction.

Engineering of a green‐light inducible gene expression system in Synechocystis sp. PCC6803

In order to construct a green-light-regulated gene expression system for cyanobacteria, we characterized a green-light sensing system derived from Synechocystis sp. PCC6803, consisting of the green-light sensing histidine kinase CcaS, the cognate response regulator CcaR, and the promoter of cpcG2 (PcpcG2). CcaS and CcaR act as a genetic controller and activate gene expression from PcpcG2 with green-light illumination. The green-light induction level of the native PcpcG2 was investigated using GFPuv as a reporter gene inserted in a broad-host-range vector. A clear induction of protein expression from native PcpcG2 under green-light illumination was observed; however, the expression level was very low compared with Ptrc, which was reported to act as a constitutive promoter in cyanobacteria. Therefore, a Shine-Dalgarno-like sequence derived from the cpcB gene was inserted in the 5′ untranslated region of the cpcG2 gene, and the expression level of CcaR was increased. Thus, constructed engineered green-light sensing system resulted in about 40-fold higher protein expression than with the wild-type promoter with a high ON/OFF ratio under green-light illumination. The engineered green-light gene expression system would be a useful genetic tool for controlling gene expression in the emergent cyanobacterial bioprocesses.

Voltage dependence of proton pumping by bacteriorhodopsin mutants with altered lifetime of the M intermediate.

The light-driven proton pump bacteriorhodopsin (BR) from Halobacterium salinarum is tightly regulated by the [H+] gradient and transmembrane potential. BR exhibits optoelectric properties, since spectral changes during the photocycle are kinetically controlled by voltage, which predestines BR for optical storage or processing devices. BR mutants with prolonged lifetime of the blue-shifted M intermediate would be advantageous, but the optoelectric properties of such mutants are still elusive. Using expression in Xenopus oocytes and two-electrode voltage-clamping, we analyzed photocurrents of BR mutants with kinetically destabilized (F171C, F219L) or stabilized (D96N, D96G) M intermediate in response to green light (to probe H+ pumping) and blue laser flashes (to probe accumulation/decay of M). These mutants have divergent M lifetimes. As for BR-WT, this strictly correlates with the voltage dependence of H+ pumping. BR-F171C and BR-F219L showed photocurrents similar to BR-WT. Yet, BR-F171C showed a weaker voltage dependence of proton pumping. For both mutants, blue laser flashes applied during and after green-light illumination showed reduced M accumulation and shorter M lifetime. In contrast, BR-D96G and BR-D96N exhibited small photocurrents, with nonlinear current-voltage curves, which increased strongly in the presence of azide. Blue laser flashes showed heavy M accumulation and prolonged M lifetime, which accounts for the strongly reduced H+ pumping rate. Hyperpolarizing potentials augmented these effects. The combination of M-stabilizing and -destabilizing mutations in BR-D96G/F171C/F219L (BR-tri) shows that disruption of the primary proton donor Asp-96 is fatal for BR as a proton pump. Mechanistically, M destabilizing mutations cannot compensate for the disruption of Asp-96. Accordingly, BR-tri and BR-D96G photocurrents were similar. However, BR-tri showed negative blue laser flash-induced currents even without actinic green light, indicating that Schiff base deprotonation in BR-tri exists in the dark, in line with previous spectroscopic investigations. Thus, M-stabilizing mutations, including the triple mutation, drastically interfere with electrochemical H+ gradient generation.

Effect of light wavelength on motility and magnetic sensibility of the magnetotactic multicellular prokaryote ‘Candidatus Magnetoglobus multicellularis’

'Candidatus Magnetoglobus multicellularis' is a magnetotactic microorganism composed of several bacterial cells. Presently, it is the best known multicellular magnetotactic prokaryote (MMP). Recently, it has been observed that MMPs present a negative photoresponse to high intensity ultraviolet and violet-blue light. In this work, we studied the movement of 'Candidatus Magnetoglobus multicellularis' under low intensity light of different wavelengths, measuring the average velocity and the time to reorient its trajectory when the external magnetic field changes its direction (U-turn time). Our results show that the mean average velocity is higher for red light (628nm) and lower for green light (517nm) as compared to yellow (596nm) and blue (469nm) light, and the U-turn time decreased for green light illumination. The light wavelength velocity dependence can be understood as variation in flagella rotation speed, being increased by the red light and decreased by the green light relative to yellow and blue light. It is suggested that the dependence of the U-turn time on light wavelength can be considered a form of light-dependent magnetotaxis, because this time represents the magnetic sensibility of the magnetotactic microorganisms. The cellular and molecular mechanisms for this light-dependent velocity and magnetotaxis are unknown and deserve further studies to understand the biochemical interactions and the ecological roles of the different mechanisms of taxis in MMPs.

Long-lasting silencing of orexin/hypocretin neurons using archaerhodopsin induces slow-wave sleep in mice

Orexin/hypocretin neurons have a crucial role in the regulation of sleep and wakefulness. Recent optogenetic studies revealed that the activation or inhibition of orexin neuronal activity affects the probability of sleep/wakefulness transition in the acute phase. To expand our understanding of how orexin neurons maintain wakefulness, we generated new transgenic mice in which orexin neurons expressed archaerhodopsin from Halorubrum strain TP009 (ArchT), a green light-driven neuronal silencer, using the tet-off system (orexin-tTA; TetO ArchT mice). Slice patch clamp recordings of ArchT-expressing orexin neurons demonstrated that long-lasting photic illumination was able to silence the activity of orexin neurons. We further confirmed that green light illumination for 1h in the dark period suppressed orexin neuronal activity in vivo using c-Fos expression. Continuous 1h silencing of orexin neurons in freely moving orexin-tTA; TetO ArchT mice during the night (the active period, 20:00–21:00) significantly increased total time spent in slow-wave sleep (SWS) and decreased total wake time. Additionally, photic inhibition increased sleep/wakefulness state transitions, which is also evident in animals lacking the prepro-orexin gene, orexin neurons, or functional orexin-2 receptors. However, continuous 1h photic illumination produced little effect on sleep/wakefulness states during the day (the inactive period, 12:00–13:00). These results suggest that orexin neuronal activity plays a crucial role in the maintenance of wakefulness especially in the active phase in mice.

Expression of myogenic genes in chickens stimulated in ovo with light and temperature

Since chicken myogenesis is tightly controlled by myogenic regulatory factors (MRFs), the external stimuli (e.g. light or temperature) affecting the proliferation and differentiation of the muscle cells have a primary effect on the gene expression of MRFs. The aim of this study was to analyze the expression of some of MRF genes (MyoD1, myogenin and Myf5) in response to the stimulation of chicken embryos with green light (AL group) or increased temperature (38.5°C; AT group) on day 18 of embryo development (18ED) as well as on days 4 (4PHD) and 8 (8PHD) post hatch. To achieve this goal a quantitative reverse transcription polymerase chain reaction was used. The most prominent differences in gene expression were observed before hatching. Relative expression of MyoD1 on 18ED was higher (p<0.05) in AL and control (AC) groups in comparison to the AT group. Myogenin expression on 18ED was lower (p<0.05) in control chickens than in both treated groups. Light stimulation in ovo decreased (p<0.05) the Myf5 expression on 18ED in comparison to the control group. Green-light illumination applied during in ovo development had more pronounced effects on mRNA level of MRFs genes measured during both the pre- and post hatch development. The elevated temperature applied during embryonic development affected only the 18ED time point. This suggests that the effect of green-light illumination on chicken myogenesis was more prolonged than that of elevated temperature.

Red-green-blue light sensitivity of oxide nanowire transistors for transparent display applications

In this study, the sensitivity of oxide nanowire transistors under red (R, 470 nm), green (G, 530 nm), and blue (B, 625 nm) light illumination was investigated. As the wavelength of light illuminating the nanowire channel region became shorter, a negative shift of threshold voltage, degradation of subthreshold slope, and increase of on-current were observed. This phenomenon can be explained in terms of photo-induced holes, creating interfacial traps between the gate dielectric and nanowire channel or reacting with oxygen ions on the surface of the nanowires. Thus, the attempt to minimize characteristic changes due to all RGB light sources was performed by employing ultraviolet–ozone treatment and passivation process. As a result, we could successfully fabricate oxide nanowire transistors providing high optical reliability which has broadened the possibilities for applying it to transparent and/or flexible pixel operation circuitry for displays with high optical reliability.

Photodynamic therapy with systemic meta‐tetrahydroxyphenylchlorin in the treatment of anal intraepithelial neoplasia, grade 3

Anal cancer and preneoplastic anal lesions (anal intraepithelial neoplasia, AIN) rising especially in men having sex with men (MSM). There are no widely accepted treatment standards for AIN. Photodynamic therapy (PDT) using the systemic sensitizer meta-tetrahydroxyphenylchlorin (mTHPC) has the potential to treat the anal area even when the exact borders of the preneoplastic anal lesion cannot easily be visualized. In this prospective intervention study, 15 HIV-positive MSM with AIN 3 were treated in 25 PDT-sessions using mTHPC intravenously administered at drug doses of 0.075-0.15 mg ml(-1) and illumination at 48 hours. The illumination was performed using a custom made applicator using either red light (652 nm) to a measured intended fluence of 10 and 20 J cm(-2) and green light (532 nm) to a measured intended fluence of 105, 210, and 340 J cm(-2) . Red and green illuminations were performed at a (green) equivalent fluence rate of 105 mW cm(-2) . Initial complete response was seen in 7/25 (28%) of treatments and another 4/25 (16%) initial partial responses. After an average 8 months, recurrences were detected in 7/11 (64%) of sessions that initially showed response. A total 4/25 (16%) showed persistent complete response 6-15 months after green light illumination. Red light illuminations caused more significant side effects combined with no persistent complete response. Reported side effects were intense pain, bloody and purulent rectal discharge, and anal stricture formation, in one patient. The results show that the use of systemic mTHPC is partially effective for the treatment of AIN 3.

Effect of Surface Plasmon Resonance on the Photocatalytic Activity of Au/TiO&lt;SUB&gt;2&lt;/SUB&gt; Under UV/Visible Illumination

In this study, gold-loaded titanium dioxide was prepared by an impregnation method to investigate the effect of surface plasmon resonance (SPR) on photoactivity. The deposited gold nanoparticles (NPs) absorb visible light because of SPR. The effects of both the gold content and the TiO2 size of Au/TiO2 on SPR and the photocatalytic efficiency were investigated. The morphology, crystal structure, light absorption, emission from the recombination of a photoexcited electron and hole, and the degree of aggregation were investigated using transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-visible-diffuse reflectance spectra (UV-VIS-DRS), photoluminescence (PL) spectroscopy, and turbidimetry, respectively. Photocatalytic activity was evaluated by the decolorization of methyl orange solution over modified titania under UV and UV/GLED (green light emitting diode) illumination. Au/TiO2 NPs exhibited an absorption peak (530-570 nm) because of SPR. The results of our photocatalytic experiments indicated that the UV-inducedly photocatalytic reaction rate was improved by simultaneously using UV and green light illumination; this corresponds to the adsorption region of SPR. Au/TiO2 could use the enhanced electric field amplitude on the surface of the Au particle in the spectral vicinity of its plasmon resonance and thus improve the photoactivity. Experimental results show that the synergistic effect between UV and green light for the improvement of photoactivity increases with increasing the SPR absorption, which in turn is affected by the Au content and TiO2 size.

Concurrent synthetic control of dopant (nitrogen) and defect complexes to realize broadband (UV–650 nm) absorption in ZnO nanorods for superior photo-electrochemical performance

We report a facile solution based synthesis protocol to incorporate nitrogen within zinc oxide nanorods with substantially improved visible light harvesting via broadband absorption stretching from UV to deep visible wavelengths (650 nm). We also report a peculiar visible region maximum around 470 nm. Raman and X-ray photoelectron spectroscopy confirm incorporation of nitrogen along with other complex defects such as zinc interstitials and oxygen vacancies. Our N:ZnO appears pale orange as opposed to the pale yellow reported in other works. It exhibits significantly superior photo-electrochemical performance over undoped ZnO. Notably under monochromatic green light illumination (530 nm) N:ZnO shows a photocurrent density of 3.2 μA cm−2, whereas pristine ZnO fails to show any photo-response. The IPCE spectrum of N:ZnO follows the broadband absorption spectrum extending up to an unprecedented value of 650 nm, potentially expanding the scope for using our material in other solar energy harvesting applications.

Potential limitations in the use of KillerRed for fluorescence microscopy

KillerRed, a bright red fluorescent protein, is a genetically encoded photosensitizer, which generates radicals and hydrogen peroxide upon green light illumination. The protein is a potentially powerful tool for selective light-induced protein inactivation and cell killing, and can also be used to study downstream effects of locally increased levels of reactive oxygen species. The initial aim of this study was to investigate whether or not KillerRed-mediated reactive oxygen species production inside peroxisomes could trigger the sequestration of these organelles into autophagosomes. Green fluorescent protein-tagged microtubule-associated protein 1 light chain 3 was used as autophagosome marker. We observed that KillerRed also emits weak green fluorescence upon excitation at 480 nm, and this may lead to erroneous data interpretation in conditions where green fluorophores are used. We discuss this potential pitfall of KillerRed for biological imaging and formulate recommendations to avoid misinterpretation of the data.

Subwavelength focusing using a hyperbolic medium with a single slit

A hyperbolic dispersion medium with a planar surface that can be used for subwavelength focusing is proposed. By combining the hyperbolic medium in a single slit with diffraction limit width, a laser beam could be focused to a subwavelength spot in the near field. Compared to a conventional superlens, the subdiffraction focusing in this work has higher optical throughput. Using a planar hyperbolic medium, which is actually alternating silver/dielectric multilayers, we showed that the focusing resolution of the designed device is down to ~λ/5 using green light illumination (at a wavelength of 514.5 nm).