Wavelength Of Exciting Light Research Articles

Reactive PLIF Method for Characterisation of Micromixing in Continuous High-Throughput Chemical Reactors

This work aimed to test and optimise reactive Planar Laser-Induced Fluorescence (PLIF) methods for the visualisation of the micromixing regions in chemical reactors using standard PLIF and Particle Image Velocimetry (PIV) equipment with the laser source 512 nm. Two methods were tested: (i) an acid–base reaction with fluorescein as the reaction-sensitive tracer and (ii) Fenton’s reaction, with Rhodamine B as the reaction tracer. Both test-reactions were studied in stopped-flow equipment to define suitable operational conditions, namely the chemical composition of the inflow streams, the concentration of reagents and fluorophore, and suitable excitation light wavelength. The visualisation of the micromixing regions was tested in a continuous flow reactor with a T-jet geometry. A laser light sheet emitted from an Nd:YAG laser illuminated the axial section of the demonstration reactor. The mixing dynamics and the reaction course were visualised with the acid–base reactive PLIF images. Fenton’s reactive PLIF method showed the overall distribution of mixing and reaction regions. The main contribution of this work is benchmarking two methods with costs that enable the visualisation of micromixing regions in continuous high-throughput reactors.

Excitation wavelength- and intensity-dependent stepwise two-photon-induced photochromic reaction.

The photochromic molecules showing wavelength-selective or light intensity-dependent photoresponse are receiving increased attention in recent years. Although a photoswitch with a single chromophore can control the ON and OFF states of a function, that consisting of multi-chromophores would be useful for the specific control in complex systems. Herein, we designed stepwise two-photon induced photochromic molecules (PABI-PIC and PABI-PIC2) consisting of two different photochromic units (PABI and PIC). One-photon absorption reaction in the UV light region of PABI-PIC generates the short-lived transient biradical (BR) that absorbs an additional photon in the visible and UV light region in a stepwise manner to produce the two-photon photochemical product, the quinoidal species (Quinoid). The photochromic properties of these transient species are completely different in color and fading speed. In addition, PABI-PIC also shows the excitation wavelength-dependent photochromism because the excited states of the PABI and PIC units are electronically orthogonal. Therefore, the stepwise photochromic properties of PABI-PIC are easily controlled depending on the excitation light intensity and wavelength. These molecular designs are important for the development of advanced photoresponsive materials.

Biocompatible Probes Based on Rare-Earth Doped Strontium Aluminates with Long-Lasting Phosphorescent Properties for In Vitro Optical IMAGING.

In recent decades, the demand for biomedical imaging tools has grown very rapidly as a key feature for biomedical research and diagnostic applications. Particularly, fluorescence imaging has gained increased attention as a non-invasive, inexpensive technique that allows real-time imaging. However, tissue auto-fluorescence under external illumination, together with a weak tissue penetration of low wavelength excitation light, largely restricts the application of the technique. Accordingly, new types of fluorescent labels are currently being investigated and, in this search, phosphorescent nanoparticles promise great potential, as they combine the interesting size-dependent properties of nanoscale materials with a long-lasting phosphorescence-type emission that allows optical imaging well after excitation (so avoiding autofluorescence). In this work, core-shell structures consisting of SrAlO:Eu,Dy luminescent cores encapsulated within a biocompatible silica shell were prepared, showing a green persistent phosphorescence with an afterglow time of more than 1000 s. A high-energy ball milling procedure was used to reduce the size of the starting phosphors to a size suitable for cellular uptake, while the silica coating was produced by a reverse micelle methodology that eventually allows the excitation and emission light to pass efficiently through the shell. Confocal fluorescence microscopy using HeLa cancer cells confirmed the potential of the all-ceramic composites produced as feasible labels for in vitro optical imaging.

Photo-activation of mitochondrial ATP synthesis.

ATP production by mitochondria isolated from Saccharomyces cerevisiae cells was accelerated upon both direct and indirect mitochondrial photo-activation (MPA). The extent of direct MPA was dependent on the wavelength of excitation light. Direct MPA was created by light in cytochrome c spectral absorption bands (440, 520 and 550nm), this light was absorbed producing electronically excited cytochrome c, and the excitation energy of the latter was used in the ATP production chain. The activity of cytochrome c was tested with 600nm light, where cytochrome c does not absorb, and thus ATP production rate remained the same as in darkness. Note that ATP production rates were significantly larger under light at 550, 520 and 440nm. Therefore, photo-activation of cytochrome c was the first step of MPA synthesis of ATP. Indirect MPA of ATP production also proceeded via electronically excited cytochrome c, by energy transfer from electronically excited Co/BN film to cytochrome c located in the inner mitochondrial membrane (IMM). Co/BN excitons were generated by photons absorbed by the Co/BN film, which was not in contact with the mitochondrial sample. Next, these excitons propagated along the Co/BN film to the part of the film that was in contact with the mitochondrial sample. There the exciton energy was transferred to cytochrome c located in the IMM, producing electronically excited cytochrome c. Thus, excited cytochrome c was generated in a way different from that of direct MPA. Next, the energy of excited cytochrome c was used in activated ATP synthesis, with virtually the same effect for 519 and 427nm excitation. Thus, the first step of ATP synthesis in indirect MPA was the exciton energy transfer from Co/BN film to cytochrome c located in the IMM, producing an electronically excited cytochrome c molecule. A phenomenological mechanism of direct and indirect MPA was proposed, and the model parameters were obtained by fitting the model to the experimental data. However, more information is needed before the detailed mechanism of ATP synthesis activation by electronically excited cytochrome c could be understood. The present results support the earlier proposed hypothesis of indirect MPA of ATP production in vertebrate retina in daylight.

Adjustable color response during plasmon resonance by monochromatic light irradiation.

A combination of plasmonic nanoparticles with a semiconductor is a feasible approach to realize multiple color exhibitions. The phenomenon is based on plasmon-driven charge separation between electrons and metal ions, but suitable only for light excitation with different wavelengths. Here, we introduce a color-adjustable method under monochromatic light irradiation. A smart strategy is proposed to construct sandwich structures of a hydrogel coating layer, thermally deposited Ag nanoparticles, and mesoporous TiO2 matrices. The contacting mode of TiO2 and nano-Ag at the Schottky interface is strongly dependent on the pore morphology of the oxide. Surface and interface plasmon resonances result in sample color switching from cyan to green and from brown to purple, respectively. The color response ability is further controlled by hydrogel coating, besides the exciting light wavelength. This Letter paves a bright way for colorful displays and information encryption.

Fluorescence enhanced microfluidic sensor with CsPbI3 probe for lubricant copper ions on-site rapid detection based on SiO2 inverse opal photonic crystals

Cu2+ content in diesel engine lubricating oil refers to a vital parameter suggesting the quality of oil and judging mechanical wear. Accordingly, the on-site rapid copper ions content determination in lubricant is of great significance to safe operation of diesel engines. However, most of the current researches on detection are carried out in laboratory, requiring the use of large-scale equipment such as spectrometer, which are not suitable for rapid on-site detection. Quantum dot-based optical microfluidic chip provides the possibility for heavy metal ions on-site detection, but it is subject to the defect of weak fluorescence intensity, thereby the increase in sensitivity is limited. In the present study, a microfluidic sensor using SiO2 inverse opal photonic crystals (IOPCs) to heighten CsPbI3 perovskite quantum dots (PQDs) photoluminescence (PL) intensity is proposed, which can realize rapid Cu2+ content detection in lubricant. Firstly, the selective detection characteristic of CsPbI3 on Cu2+ was studied. Experimental results showed that the photoluminescence of CsPbI3 was significantly quenched by Cu2+ because electrons were effectively transferred from CsPbI3 to Cu2+. Subsequently, to enhance the fluorescence intensity of CsPbI3 probe, the SiO2 IOPCs structure was formed in chip detection well. The effective PL intensity of CsPbI3 PQDs was enhanced by the photonic stopband effect formed by the periodically arranged micro-nano structure of photonic crystals. This enhancement effect was attributed to the coupling effect between stopband with excitation and emission light. As the stopband of SiO2 IOPCs was coupled with the excitation light wavelength and emission light wavelength of CsPbI3, the enhancement factors could reach 17-fold and 22-fold, respectively. The mentioned strategy could effectively improve the detection sensitivity of the microfluidic sensor and reduce the detection limit to 0.34 nM. Moreover, the formed microfluidic sensor system can be used for determination of Cu2+ content in lubricating oil on site. Meanwhile, the sturdy porous structure of SiO2 IOPCs also facilitated target metal ions to be captured and enriched.

Effect of the Wavelength and Intensity of Excitation Light on the Efficiency of Photogeneration of Singlet Oxygen by Photodithazine in the Presence of Pluronic F127 in Model Processes of Photo-Oxidation

Effect of the Wavelength and Intensity of Excitation Light on the Efficiency of Photogeneration of Singlet Oxygen by Photodithazine in the Presence of Pluronic F127 in Model Processes of Photo-Oxidation

Dielectrophoresis assisted high-throughput detection system for multiplexed immunoassays

Digital ELISA is introduced as a novel platform with unique advantages for detecting multiple kinds of single-molecule in the sample. How to improve the sensitivity of detection is the direction of current related research. Here, we report an immunoassay method that applied electrokinetic effects to isolate the individual encoded beads and confine in micro-wells to improve the efficiency of cytokines detection simultaneously. The microfluidic design provided a non-uniform electric field to induce dielectrophoresis (DEP) force and to manipulate the beads. Two wavelengths of excitation light excited the encoded beads for simultaneous detection of reporters. The light was confined to the bottom slide via the principle of total internal reflection. Finally, the concentration of captured cytokines was obtained by picking up each bead from the image and then integrating the intensity of fluorescent light emitted from the reporters. The results demonstrated that the fill percentage of encoded beads was raised from 10-20% to 60–80% via DEP effect. By comparing the fluorescence color of the particle, itself and its surface, the concentration of four target cytokines, IL-2, IL-6, IL-10 and TNF-α, were calculated to the pg/ml level. The spike and recovery experiments verified the efficiency, more than 70% of the target molecules were captured. The reliability of our method was verified by flow cytometry as well. In conclusion, we expect the application of DEP can increase the sensitivity of digital ELISA for multiple rapid detection.

Microstructure and photoluminescence properties of anodized aluminum oxide films treated by argon ion

Nano-porous anodized aluminum oxide (AAO) films were prepared by secondary anodization, and these AAO films were subjected to argon ion treatment with different sputtering durations by radio frequency (RF) sputtering. FE-SEM, XRD, and ATR-FTIR were used to study the morphology and structural characteristics of the AAO films. The photoluminescence (PL) spectra of the AAO films were studied with variable wavelengths of excitation light, the results show that the argon ion treatment has a significant effect on the microstructure and the PL properties of the AAO films. The influence of argon ion treatment on the microstructure and the relationship between the PL properties is discussed.

Two-Photon Fluorescence Imaging.

Two-photon fluorescence imaging is a powerful tool for observing the dynamics of cells in vivo in intact tissue and is well suitable for imaging neuronal activity for neuroscience research. Due to the nonlinear two-photon absorption, the optical sectioning ability is inherent, resulting in two-photon images with high signal contrast and signal-to-noise ratio with efficient illumination. In addition, the longer wavelength excitation light in two-photon imaging compared to one-photon imaging suffers less scattering and absorption by tissue, which allows deeper penetration. Today, two-photon microscopy is being rapidly developed to adapt to various biological applications for high-speed, high-resolution, large-volume, long-term imaging in freely behaving animals.

Quantum-assisted photoelectric gain effects in perovskite solar cells

Further boosting the power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) without excessively increasing production expenses is critical for practical applications. Here, we introduce silicon quantum dots (SiQDs) to enable perovskites to harvest additional sunlight without changing PSC processes. These SiQDs can convert shorter wavelength excitation light (300–530 nm) into visible region light and reflect longer wavelength perovskite-unabsorbed visible light (550–800 nm), leading to broadband light absorption enhancement in PSCs. As a result, the SiQD-based photocurrent gain can improve the external quantum efficiencies of PSCs over a wide wavelength range of 360–760 nm, yielding relatively enhanced short-circuit current density (+1.66 mA/cm2) and PCE (+1.4%). Surprisingly, even the PSC with a low-purity perovskite layer shows an ultrahigh PCE improvement of 5.6%. Our findings demonstrate QD-assisted effects based on earth-abundant and environmentally friendly silicon, leading to effective optical management that remarkably promotes the performance of PSCs and enables the balance of costs to be substantially addressed.

Evaluation of photoluminescence from milk with various vitamin B2 concentrations

Concentrations of vitamin B2 in milk were evaluated based on photoluminescence (PL) peak intensities at around λ = 545 nm. PL was measured in a back-scattering configuration using a 3.2 mm diameter optical fibre bundle irradiated by ultra-violet LEDs, violet LEDs or a blue LED as the excitation light. The tip of the optical fibre bundle was dipped into commercially available whole milk, low-fat milk and non-fat milk. PL peaking at 545 nm was observed under LED irradiation. Vitamin B2 concentrations were measured using a standard addition method and a calibration curve method. Deviation between the vitamin B2 concentration measured by PL using a standard addition method and those by HPLC technique varied with wavelength of excitation light and was smallest with violet LED (405 nm) excitation. The standard deviation of results measured by PL using a calibration curve method was better than those using a standard addition method.

Study of the Properties of Two-Dimensional MoS2 and WS2 Films Synthesized by Chemical-Vapor Deposition

Molybdenum- and tungsten-disulfide films are synthesized by chemical-vapor deposition. The set of optimal synthesis parameters (temperature, time, and amount and ratio of precursors) is established at which MoS2 domains with maximum lateral sizes of up to 250 μm on sapphire and MoS2 and WS2 domains up to 80 μm in size on SiO2 can be grown. Domain intergrowth leads to the formation of homogeneous single-layer MoS2 films. The Raman spectra of the synthesized films contain two characteristic peaks corresponding to the atomic vibrations in MoS2 and WS2. Photoluminescence of the single-layer and bilayer MoS2 films with a maximum intensity of 670 ± 2 nm and of the single-layer WS2 films with a maximum intensity of 630 ± 2 nm is detected. The photoluminescence spectral maps (the dependences of the photoluminescence intensity on the luminescence and excitation-light wavelengths) are measured. According to the measured data, the photoluminescence excitation spectrum of MoS2 has a maximum at 350 ± 5 nm and the photoluminescence excitation spectrum of WS2 has a maximum at 330 ± 5 nm. The I–V characteristics of the synthesized films are photosensitive in the visible spectral range.

Rapid and ultrasensitive surface-enhanced Raman spectroscopy detection of mercury ions with gold film supported organometallic nanobelts

Rapid, ultrasensitive and reliable detection of mercury ions (Hg2+) by surface enhanced Raman spectroscopy (SERS) is of importance, but is restricted by the extremely low Raman cross section of the Hg2+. Here, we report a facile methodology that can realize such detection based on the organometallic Cu(CH4N2S)Cl · 0.5H2O nanobelts and SERS. In the assay, Hg2+ react with the nanobelts coated on a SERS active gold nanoparticle (NP) film to form ultrafine HgS NPs in situ. Subsequently, solid HgS is SERS determined to mirror the presence of Hg2+. Importantly, such detection is rapid and ultrasensitive. Within 10 min, limit of detection (LoD) of ppt level can be realized. The high detection efficiency is attributed to the superhydrophilicity, rich micropores and ultrathin nature of the organometallic nanobelts besides the strong SERS effect of Au NP film. In addition, this detection is highly resistant to various metal ions (Cu2+, Fe3+, Bi3+, Cr3+, Na+, Ni2+, Cd2+, etc) and is highly reliable in actual water (lake and tap water). Finally, influences of some substrate parameters and detection conditions on the test results are revealed. The optimal thickness of the gold NP film is about 80 nm, and the optimal wavelength of excitation light is about 633 nm. A small amount of Cu(CH4N2S)Cl · 0.5H2O nanobelts or a large volume of Hg2+ contaminated solution contributes to low LoDs. We believe that this work provides a rapid and sensitive detection for Hg2+.

Effect of pH and excitation light wavelength on the activation energy of thermal quenching of tryptophan fluorescence

The activation energy of temperature quenching (E) of tryptophan fluorescence at pH 1–13 exhibited a maximum corresponding to the isoelectric point (pHi ≈ 6) of tryptophan at all exciting light wavelengths. The values of E nonmonotonically changed with the excitation wavelength. This behavior was explained by photoinduced electron transfer from the higher singlet-excited Sn (n > 1) states of tryptophan.

Исследование свойств двумерных пленок МоS-=SUB=-2-=/SUB=- и WS-=SUB=-2-=/SUB=-, синтезированных химическим газофазным методом

Abstract Molybdenum- and tungsten-disulfide films are synthesized by chemical-vapor deposition. The set of optimal synthesis parameters (temperature, time, and amount and ratio of precursors) is established at which MoS_2 domains with maximum lateral sizes of up to 250 μm on sapphire and MoS_2 and WS_2 domains up to 80 μm in size on SiO_2 can be grown. Domain intergrowth leads to the formation of homogeneous single-layer MoS_2 films. The Raman spectra of the synthesized films contain two characteristic peaks corresponding to the atomic vibrations in MoS_2 and WS_2. Photoluminescence of the single-layer and bilayer MoS_2 films with a maximum intensity of 670 ± 2 nm and of the single-layer WS_2 films with a maximum intensity of 630 ± 2 nm is detected. The photoluminescence spectral maps (the dependences of the photoluminescence intensity on the luminescence and excitation-light wavelengths) are measured. According to the measured data, the photoluminescence excitation spectrum of MoS_2 has a maximum at 350 ± 5 nm and the photoluminescence excitation spectrum of WS_2 has a maximum at 330 ± 5 nm. The I – V characteristics of the synthesized films are photosensitive in the visible spectral range.

Polarization Transformation of Electromagnetic Radiation Upon Excitation of Surface Plasmon-Polaritons on a Metallic Grating

Plasmon-stimulated transformation (conversion) of radiation polarization by Au gratings with different ratios of excitation wavelength to lattice period (including high-frequency lattices with a wavelength to period ratio of close to 2 that are studied for the first time) and with different modulation depths are experimentally studied. Gratings for research are made by interference lithography using chalcogenide photoresists. Polarization conversion is studied by measuring angular dependences (on the incident and azimuthal angles) of the specular reflection of linearly polarized monochromatic He–Ne laser radiation. The maximum conversion efficiency for p-polarized into s-polarized radiation for low-frequency lattices with a period greater than the wavelength and lattices with an intermediate frequency (period slightly less than the wavelength) is found at azimuth ~45o and is determined by the modulation depth. However, the intensity of the resulting s-component is an order of magnitude less for high-frequency lattices on which surface plasmon-polaritons are excited at high incident angles and azimuthal angles significantly less than 45o than for lower-frequency lattices. Thus, the efficiency of polarization conversion stimulated by excitation of surface plasmons is determined not only by lattice modulation depth h/d but also by the ratio of the exciting light wavelength to the lattice period λ/d.

Directed UV and X-ray generation in nanomaterials at the optical excitation

Efficient electromagnetic emission of radiation in the spectral range with wavelengths shorter than exciting light wavelength was observed at the nanomaterials excitation by laser pulses. Emission was registered in a visible (blue-green) range, in vacuum UV and in soft X-ray. Luminescence was registered both in the air and in the vacuum chamber. Synthetic opal matrices and nanocomposites on their base (matrices infiltrated with different liquids) were used as samples. Luminescence was excited with the help of different lasers: ruby laser, second harmonic of Nd:YAG laser and copper vapor laser. In the visible range two regimes of luminescence were observed: fast (few μs) and slow (up to 12 s). Slow luminescence was registered at temperatures lower than 110 K. Spectra of X-ray emission were registered. The connection of this emission with the triboluminescence effect is considered.

OSL using a prototype fibre-mounted sensor and automated reader assembly

Application-viable yields of optically stimulated luminescence (OSL) are known to be provided by a number of materials, Al2O3:C nanoDot OSLDs being one of those currently favoured, dominating the world of commercial passive radiation dosimetry. Associated with the use of such materials is the need for versatile, high performance readout devices, opportunities remaining for novel developments in support of the OSL media, as emphasised herein. Present study focuses on the data acquisition capability of an in-house prototype OSL reader, luminescence stimulation being provided by a 30 mW green LED light (spectral mid-point ~ 515 nm). In providing for the additional versatility of making stand-off (at a distance) measurements, the dosimeter sensors (nanoDot OSLD chips) were attached to a polymethyl-methcrylate (PMMA) fibre cable, allowing characterization of the OSL (phosphorescence) at very low risk. Using this prototype instrument, key OSL features from an Al2O3:C sensor medium have been captured, excellent quantitative agreement being found between present results and those of others using other readers. One further feature of the current design is that it also allows investigation of the excitation light wavelength dependence of sensor media that could be competitive to Al2O3:C, there being the additional ability to swap out the OSL sensor, filters and other support components.

Selection of the optimal bands of first-derivative fluorescence characteristics for leaf nitrogen concentration estimation.

Laser-induced fluorescence technology provides a nondestructive and rapid method for monitoring leaf nitrogen concentration (LNC) based on its optical characteristics. Crop growth status can be efficiently diagnosed and quality evaluated by monitoring LNC. In this study, the first-derivative fluorescence spectrum (FDFS) was proposed and calculated based on the fluorescence spectra excited by 355, 460, and 556nm excitation lights for rice LNC estimation. Then, the performance of each band FDFS characteristics and the FDFS ratio for LNC estimation were comprehensively discussed using principal component analysis and backpropagation neural network (BPNN). We analyzed the number of FDFS characteristics' influence on the accuracy of LNC monitoring. Results showed that R2 does not clearly improve for the LNC monitoring based on the BPNN model when the number of extracted FDFS features exceeds 4 or 5. Therefore, the FDFS optimal band combination of different excitation light wavelengths mentioned was selected for LNC monitoring. The selected band combinations contained the majority of FDFS characteristics and could effectively be applied in monitoring LNC (for 355, 460, and 556nm excitation lights, with R2 of 0.764, 0.625, and 0.738, respectively) based on the BPNN model.