Nonlinear Fluorescence Research Articles

A single-particle mechanofluorescent sensor

Monitoring mechanical stresses in microchannels is challenging. Herein, we report the development of a mechanofluorescence sensor system featuring a fluorogenic single polydiacetylene (PDA) particle, fabricated using a co-flow microfluidic method. We construct a stenotic vessel-mimicking capillary channel, in which the hydrodynamically captured PDA particle is subjected to controlled fluid flows. Fluorescence responses of the PDA particle are directly monitored in real time using fluorescent microscopy. The PDA particle displays significant nonlinear fluorescence emissions influenced by fluid viscosity and the presence of nanoparticles and biomolecules in the fluid. This nonlinear response is likely attributed to the torsion energy along the PDA’s main chain backbone. Computational fluid dynamic simulations indicate that the complete blue-to-red transition necessitates ~307 μJ, aligning with prior research. We believe this study offers a unique advantage for simulating specific problematic regions of the human body in an in vitro environment, potentially paving the way for future exploration of difficult-to-access areas within the body.

Postfilament-Induced Two-Photon Fluorescence of Dyed Liquid Aerosol Enhanced by Structured Femtosecond Laser Pulse

Laser-induced fluorescence spectroscopy (LIFS) is actively used for remote sensing of atmospheric aerosols and is currently one of the most sensitive and selective techniques for determining small concentrations of substances inside particles. The use of high-power femtosecond laser sources for LIFS-based remote sensing of aerosols contributes to the development of new-generation fluorescence atmospheric lidars since it makes it possible to overcome the energy threshold for the nonlinear-optical effects of multiphoton absorption in particles and receive the emission signal at long distances in the atmosphere. Our study is aimed at the development and experimental demonstration of the technique of nonlinear laser-induced fluorescence spectroscopy (NLIFS) based on the remote excitation of aerosol fluorescent emission stimulated by a spatially structured high-power femtosecond laser pulse. Importantly, for the first time to our knowledge, we demonstrate the advances in using stochastically structured plasma-free intense light channels (postfilaments) specially formed by the propagation of femtosecond laser radiation through a turbulent air layer to improve NLIFS efficiency. A multiple increase in the received signal of two-photon-excited fluorescence of polydisperse-dyed aqueous aerosols by the structured postfilaments is reported.

Influence of NiCo2O4/PbS nanocomposite on the structural, optical and electrical properties of Polymethyl Methacrylate polymer

Poly(methyl methacrylate) (PMMA)/(1-x)NiCo2O4/xPbS polymers were prepared using the casting hydrothermal and solid state reaction methods. The different phases formed in (1-x)NiCo2O4/xPbS nanocomposites were determined using the X-ray diffraction (XRD) technique. XRD and scanning electron microscopy (SEM) techniques were used to explore the structure and morphology of the formed polymers. The influence of (1-x)NiCo2O4/xPbS nanocomposite doping on the absorption, transmission, extinction coefficient, absorption coefficient, refractive index, nonlinear optical parameters and fluorescence spectra of PMMA polymer was explored using diffused reflectance and fluorescence spectrophotometer techniques. The direct and indirect optical band gap (Eg) values decreased from (5.31 and 5.06) eV (for undoped PMMA) to (4.66 and 4.17) eV (for doped PMMA with x = 0.1 filler), respectively. Several models based on the Eg value were used to find out the value of the refractive index of different polymers. The impact of doping on the dielectric constant, relaxation time, energy density, electrical conductivity and electric modulus of the PMMA polymer was also studied using an LCR meter.

Improved image contrast in nonlinear light-sheet fluorescence microscopy using i2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^2$$\\end{document}PIE Pulse compression

Nonlinear microscopy has become an invaluable tool for biological imaging, offering high-resolution visualization of biological specimens. In this manuscript, we present the application of a spectral phase measurement technique, i2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^2$$\\end{document}PIE, to compress broad-bandwidth supercontinuum pulses for two-photon excitation fluorescence light-sheet fluorescence microscopy. The results demonstrated a significant improvement in the two-photon excitation response achieved. We also showed that the implementation of i2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^2$$\\end{document}PIE allowed for enhanced image contrasts when compared to conventional compression techniques, with i2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^2$$\\end{document}PIE producing an image contrast improvement over conventional methods by over 50%.

Effects of H2 enrichment on combustion characteristics in inverse swirl diffusion flames of H2-doped jet fuel using OH, CH2O, fuel and temperature imaging

Hydrogen (H2) and jet fuel co-firing is regarded as a promising transition strategy of decarbonization in aviation industry. Considering the simplicity and safety during highly hydrogen enrichment conditions, the inverse swirl diffusion (ISD) combustion holds research value. Given the current lack of understanding for the flame properties of H2-enriched pre-evaporative jet fuel ISD co-combustion, in this work, the simultaneous planar laser-induced fluorescence (PLIF) of hydroxyl (OH), formaldehyde (CH2O), and fuel, as well as the non-linear excitation regime two-line atomic fluorescence (NTLAF) thermography imaging, are used to study the effects of hydrogen enrichment on ISD flame intricate structure and temperature field. The results show the positive effects of H2 enrichment. The ISD flames display a blue hue and the increase in doping hydrogen helps the flames stabilize under global-lean conditions with almost no CO emission and low CO2 emission at the chamber exit. And the H2 enrichment contributes to inhibiting the CH2O formation upstream, reducing the generation of isolated reaction islands and promoting the strength of the flame wings, favoring the suppression of flame instability. In contrast, when at low H2 enrichment rate, the shift of the heat release zone and high-temperature zone, and the enlargement of the cold zone, are found in flame upstream. The analysis of the probability distribution functions (PDF) of temperatures confirms the effective effects of hydrogen on inhibiting the local flame fluctuations. Although the increase in the overall temperature level due to the hydrogen addition would lead to a promotion in NOx generation, the discussion on the structural analysis and flame propagation stability of ISD flames demonstrates the significance of H2 enrichment for the achievement of leaner low-NOx combustion of ultra-H2-enriched jet fuel in the future.

Integration of nonlinear two-photon excited fluorescence and photocatalysis boosts overall water splitting performance.

A nonlinear two-photon excited fluorescence photocatalytic system was constructed for the first time by integrating (ZnO)1-x(GaN)x photocatalyst and a fluorescence solution of phenanthridine derivatives. This work offers a strategy for increasing the photocatalytic solar spectral utilization rate and boosting the expectation for photocatalytic solar-to-hydrogen efficiencies.

Characterization of degradation effects on wood ultrastructure by non-linear imaging

The characterization of deterioration processes in wooden artifacts is crucial for assessing their state of conservation and ensuring their preservation. Advanced imaging techniques are currently being explored to study the effect of chemical changes on the structural and mechanical properties of wood. Combined second harmonic generation and two-photon excited fluorescence (SHG/TPEF) imaging is a recently introduced non-destructive method for the analysis of cellulose-based samples. The study of age-related wood degradation based on nonlinear signal variation is a promising avenue. This work involves nonlinear multimodal analysis of naturally aged and dendrochronologically dated spruce samples. SHG/TPEF imaging and fluorescence lifetime imaging microscopy (FLIM) were used to demonstrate the influence of molecular deterioration and rearrangement of biopolymers on the fluorescence emitted by lignin and the second harmonic signal generated by cellulose. Imaging based on spectral filter detection and time-resolved analysis of the nonlinear fluorescence signal was used to delineate and potentially quantify ageing-induced morpho-chemical changes in the ultrastructure of wood cells. The analysis of cell structures by optical sectioning revealed variations between wood samples of different ages and different cell structures.

Fast wavefront shaping for two-photon brain imaging with multipatch correction.

Nonlinear fluorescence microscopy promotes in-vivo optical imaging of cellular structure at diffraction-limited resolution deep inside scattering biological tissues. Active compensation of tissue-induced aberrations and light scattering through adaptive wavefront correction further extends the accessible depth by restoring high resolution at large depth. However, those corrections are only valid over a very limited field of view within the angular memory effect. To overcome this limitation, we introduce an acousto-optic light modulation technique for fluorescence imaging with simultaneous wavefront correction at pixel scan speed. Biaxial wavefront corrections are first learned by adaptive optimization at multiple locations in the image field. During image acquisition, the learned corrections are then switched on the fly according to the position of the excitation focus during the raster scan. The proposed microscope is applied to in vivo transcranial neuron imaging and demonstrates multi-patch correction of thinned skull-induced aberrations and scattering at 40-kHz data acquisition speed.

Reducing the Inner Filter Effect in Microplates by Increasing Absorbance? Linear Fluorescence in Highly Concentrated Fluorophore Solutions in the Presence of an Added Absorber.

The fluorescence attenuation caused by the absorption of the excitation and/or emission light is called the Inner Filter Effect (IFE) and can lead to a nonlinear fluorescence concentration response. In this article, we propose the AddAbs (Added Absorber) method, which counterintuitively corrects IFE by increasing the absorbance of the sample. In this method, an equal amount of a highly absorbing chromophore is added to each sample to compensate for the nonuniform quenching caused by different fluorophore concentrations. The AddAbs method was able to provide a linear fluorescence response (R2 > 0.999) for very concentrated fluorophore solutions with extreme IFE over more than 97% of the concentration range with less than 1% deviation in calibration slope. The true limit for the AddAbs method with respect to fluorophore concentration was apparently not reached and could be higher than measured (Aex,1cm > 33.94). The IFE-corrected data are obtained by a single fluorescence measurement per sample without additional mathematical procedures. The method also does not require absorbance measurements, so it can be performed in non-transparent microplates with similar results. In addition, preliminary measurements indicate that the method is also suitable for measurements in standard cuvettes using a fluorimeter with a 90° angle setup.

BGO quenching effect on spectral measurements of cosmic-ray nuclei in DAMPE experiment

The Dark Matter Particle Explorer (DAMPE) is a satellite-borne detector designed to measure high energy cosmic-rays and γ-rays. As a key sub-detector of DAMPE, the Bismuth Germanium Oxide (BGO) imaging calorimeter is utilized to measure the particle energy with a high resolution. The nonlinear fluorescence response of BGO for large ionization energy deposition, known as the quenching effect, results in an under-estimate of the energy measurement for cosmic-ray nuclei. In this paper, various models are employed to characterize the BGO quenching factors obtained from the experimental data of DAMPE. Applying the proper quenching model in the detector simulation process, we investigate the tuned energy responses for various nuclei and compare the results based on two different simulation softwares, i.e. GEANT4 and FLUKA. The BGO quenching effect results in a decrease of the measured energy by approximately 2.5% (5.7%) for carbon (iron) at ∼10 GeV/n and <1% above 1 TeV/n, respectively. Accordingly, the correction of the BGO quenching effect leads to an increase of the low-energy flux measurement of cosmic-ray nuclei.

Temperature and flame structure imaging in kerosene swirl-stabilized spray flames at low air flow using TLAF and OH-PLIF

Air flowrate is an important parameter for airbrast nozzles and low air inlet flow rate in airbrast type combustors will lead to worse atomization, combustion instability, and increased pollutant emissions. Using non-linear excitation regime two-line atomic fluorescence (NTLAF) thermography imaging and planar laser-induced fluorescence of hydroxyl radical (OH-PLIF), temperature and flame structure in the near-nozzle area are investigated at different low air flow rate to study the combustion deterioration of kerosene swirl-stabilized spray flames. In this concerned area, combustion occurs mainly at the near-wall region but a few OH signals are present at the centerline region except for the kerosene LIF particles. With the air supply getting low, the near-wall OH signals get low, corresponding to the change of indium Stokes and anti-Stokes fluorescence. The temperature in the centerline region is presented to be reduced and the region for the temperature threshold filter expands, indicating the reduction of the downstream hot combustion products brought back by weak swirl, which is closely related to the extremely low air flowrate. Under extremely low air flow rate, the highly fluctuating temperature and weak gas-liquid mixed combustion at the centerline area may tend to cause combustion instability or ignition failure.

Tight Focus Vector Light Field of Hybrid Double Circularly Polarized Beams

Based on the Richard-Wolf diffraction theory, we demonstrate the tightly focused optical field distribution with two beams circularly polarized light. We deduced the expression of the double-beam superimposed vortex light intensity of left-handed circularly polarized light and right-handed circularly polarized light under the focusing condition of a high numerical aperture objective lens. Based on the different vortex topological charge values, amplitudes and initial phases of the dual beams, we numerically simulated the light intensity distribution of the superimposed hybrid focused light field. It is found that a variety of peculiar vortex spots can be obtained through the tight focus stacking of the double beams. These complex hybrid focused light fields with different polarizations can be used in fields such as optical field micro-manipulation or nonlinear fluorescence microscopy imaging.

Studies of Local DNA Backbone Conformation and Conformational Disorder Using Site-Specific Exciton-Coupled Dimer Probe Spectroscopy.

The processes of genome expression, regulation, and repair require direct interactions between proteins and DNA at specific sites located at and near single-stranded-double-stranded DNA (ssDNA-dsDNA) junctions. Here, we review the application of recently developed spectroscopic methods and analyses that combine linear absorbance and circular dichroism spectroscopy with nonlinear 2D fluorescence spectroscopy to study the local conformations and conformational disorder of the sugar-phosphate backbones of ssDNA-dsDNA fork constructs that have been internally labeled with exciton-coupled cyanine (iCy3)2 dimer probes. With the application of these methods, the (iCy3)2 dimer can serve as a reliable probe of the mean local conformations and conformational distributions of the sugar-phosphate backbones of dsDNA at various critical positions. The results of our studies suggest a possible structural framework for understanding the roles of DNA breathing in driving the processes of protein-DNA complex assembly and function.

Halogen engineering of organic-inorganic hybrid perovskites displaying nonlinear optical, fluorescence properties and phase transition.

In order to meet the needs of social development, increasing research attention has been paid to multifunctional molecular-based phase-transition materials. The traditional phase-transition materials with a single functional property can be transformed into magnificent ones by adding additional functional properties-for instance photoluminescence and magnetic order- because having two or more functional properties simultaneously greatly broadens the fields of their applications. At present, there are very few multifunctional phase-transition materials showing excellent performance, and the crystal structure design and performance optimization of materials still need to be studied in depth. Herein, we report the development of two organic-inorganic hybrid materials: (MBA)2ZnI4 (1, MBA = 4-methoxybenzylammonium) with switchable dielectricity and a high phase-transition temperature (Tc = 359.55 K), and (MBA)2ZnBr4 (2) with green luminescence (λexc = 314 nm) and nonlinear optical properties (0.75× KDP). A two-dimensional (2D) fingerprint analysis of the Hirshfeld surface plots revealed a significant difference between the hydrogen-bonding interaction before the phase transition and that afterwards. The two compounds were further verified, from energy band structure calculations, to be direct-band-gap semiconductors. In conclusion, this work has provided a viable strategy, involving the application of chemical modifications, for designing various functional materials.

Synthesis of novel 2-(benzhydryloxy) phenoxy-substituted zinc phthalocyanine, third-order nonlinear optical and fluorescence properties

Synthesis of novel 2-(benzhydryloxy) phenoxy-substituted zinc phthalocyanine, third-order nonlinear optical and fluorescence properties

Exploiting Dynamic Nonlinearity in Upconversion Nanoparticles for Super-Resolution Imaging.

Single-beam super-resolution microscopy, also known as superlinear microscopy, exploits the nonlinear response of fluorescent probes in confocal microscopy. The technique requires no complex purpose-built system, light field modulation, or beam shaping. Here, we present a strategy to enhance this technique's spatial resolution by modulating excitation intensity during image acquisition. This modulation induces dynamic optical nonlinearity in upconversion nanoparticles (UCNPs), resulting in variations of nonlinear fluorescence response in the obtained images. The higher orders of fluorescence response can be extracted with a proposed weighted finite difference imaging algorithm from raw fluorescence images to generate an image with higher resolution than superlinear microscopy images. We apply this approach to resolve single nanoparticles in a large area, improving the resolution to 132 nm. This work suggests a new scope for the development of dynamic nonlinear fluorescent probes in super-resolution nanoscopy.

Filament-induced nonlinear hyperspectral fluorescence imaging

Hyperspectral fluorescence imaging is promising for many applications including gas sensing and imaging. However, achieving spectrally and spatially resolved images for quantitative multi-gas and multi-parameter analysis remains challenging, especially in a non-cooperative environment. Here, we report a simple technique, based on filament-induced nonlinear spectroscopy, for information-rich gas imaging. We obtained three-dimensional (3D) hyperspectral images for an alcohol/air flame with sub-millimeter spatial resolutions. For each hypercube, a broadband fluorescence fingerprint spectrum, containing 2500 spectral elements (350–600 nm at a spectral resolution of 0.1 nm), was acquired. This technique, with backward fluorescence detection, enabled high-spatial-resolution point-wise imaging in a non-cooperative situation, e.g., in a sealed tube. Without meticulously arranged cameras, the technique may open up new opportunities for remote gas imaging and tomography.

In vivo simultaneous nonlinear absorption Raman and fluorescence (SNARF) imaging of mouse brain cortical structures

Label-free multiphoton microscopy is a powerful platform for biomedical imaging. Recent advancements have demonstrated the capabilities of transient absorption microscopy (TAM) for label-free quantification of hemoglobin and stimulated Raman scattering (SRS) microscopy for pathological assessment of label-free virtual histochemical staining. We propose the combination of TAM and SRS with two-photon excited fluorescence (TPEF) to characterize, quantify, and compare hemodynamics, vessel structure, cell density, and cell identity in vivo between age groups. In this study, we construct a simultaneous nonlinear absorption, Raman, and fluorescence (SNARF) microscope with the highest reported in vivo imaging depth for SRS and TAM at 250–280 μm to enable these multimodal measurements. Using machine learning, we predict capillary-lining cell identities with 90% accuracy based on nuclear morphology and capillary relationship. The microscope and methodology outlined herein provides an exciting route to study several research topics, including neurovascular coupling, blood-brain barrier, and neurodegenerative diseases.

Oxygen-Varying Correlated Fluorescence for Determining the Stern-Volmer Constant of Porphyrin.

The achievement of the Stern-Volmer constant (KSV) of porphyrin, a parameter to describe the ability of energy transfer to oxygen, enables us to understand and engineer the functionalities of porphyrin. In this study, we propose a new method to obtain KSV by steady fluorescence based on the population correlation between the excited triplet state (T1) and the singlet excited state (S1). Nonlinear fluorescence intensity of porphyrin [hematoporphyrin monomethyl ether (HMME)] as a function of pump power is observed, and this nonlinearity is oxygen-concentration-dependent. These observations originated from the population correlation, where more intense pump power introduces a stronger population correlation. Most importantly, we have found that the oxygen content can influence this correlation via the quenching of T1 based on its sequent change of fluorescence intensity; KSV ∼ 28 kPa-1 can be obtained theoretically for HMME. Our investigation not only offers a promising method of achieving KSV conveniently by steady fluorescence but also enlightens the advances of regulable fluorescence correlation.

Construction of a Homogeneous Enzyme-Free Autocatalytic Nucleic Acid Machinery for High-Performance Intracellular Imaging of MicroRNA

Construction of a Homogeneous Enzyme-Free Autocatalytic Nucleic Acid Machinery for High-Performance Intracellular Imaging of MicroRNA