Scattered Light Signal Research Articles

Metal-insulator transition and nonlinear optical responseof sputter-deposited V3O5 thin films

The compound V3O5, a member of the vanadium oxide Magnéli series, exhibits a metal-insulator transition near 430 K, the highest known temperature value among all vanadium oxides. It has been studied before mainly in single-crystal form, and for the very few cases in which thin films have been fabricated before, the procedure has required extensive post-deposition annealing of other oxides or vanadium metal at high temperatures in tightly controlled atmospheres. For the present work, V3O5 films were deposited directly on SiO2 glass substrates, without subsequent annealing, by DC magnetron sputtering. X-ray diffraction study of the samples evidenced oxygen deficiency, accommodated by oxygen vacancies. Resistivity measurements from 300 to 500 K revealed the metal-insulator transition by Tc ∼ 430 K, with an associated resistivity change by a factor of 20, and no detectable hysteresis in heating-cooling cycles, in agreement with most single-crystal studies. Resistivity values obtained were, however, lower than published results for bulk crystal values, particularly at temperatures below Tc. This was attributed to conduction electrons generated by the oxygen vacancies. Gradual resistivity increase in a very thin sample, through heating in air at temperatures up to 500 K, lends support to this argument. Using a pump-probe scattering technique, the V3O5 films were also probed for ultrafast nonlinear optical response. A reduction in the transient relative scattered light signal was recorded, which reached –10% within ∼800 fs. This observed response, likely related to the photoinduced insulator-to-metal phase transition, should stimulate additional interest in this material.

Static and dynamic light scattering by red blood cells: A numerical study.

Light scattering is a well-established experimental technique, which gains more and more popularity in the biological field because it offers the means for non-invasive imaging and detection. However, the interpretation of light-scattering signals remains challenging due to the complexity of most biological systems. Here, we investigate static and dynamic scattering properties of red blood cells (RBCs) using two mesoscopic hydrodynamics simulation methods—multi-particle collision dynamics and dissipative particle dynamics. Light scattering is studied for various membrane shear elasticities, bending rigidities, and RBC shapes (e.g., biconcave and stomatocyte). Simulation results from the two simulation methods show good agreement, and demonstrate that the static light scattering of a diffusing RBC is not very sensitive to the changes in membrane properties and moderate alterations in cell shapes. We also compute dynamic light scattering of a diffusing RBC, from which dynamic properties of RBCs such as diffusion coefficients can be accessed. In contrast to static light scattering, the dynamic measurements can be employed to differentiate between the biconcave and stomatocytic RBC shapes and generally allow the differentiation based on the membrane properties. Our simulation results can be used for better understanding of light scattering by RBCs and the development of new non-invasive methods for blood-flow monitoring.

Platelet Detection in Unaltered Whole Blood

Abstract Platelets are non-nucleated cellular fragments circulating in the peripheral blood, derived from megakaryocytes. They are critical in the maintenance of hemostasis. Alterations in their function are associated with a range of clinical conditions. Using flow cytometry, light scatter signals from platelets typically overlap signals from red blood cells (RBC). Since RBC outnumber platelets by more than an order of magnitude in whole blood, platelets are typically studied by depleting samples of RBCs by centrifugation methods or selective RBC cell lysis. These sample preparation procedures require manipulations that may affect platelet health and function, and result in loss of cells. Additionally, lysed samples require labeling of the platelets with a fluorescent marker to adequately resolve the platelets from debris/noise. We present a novel technique for resolving leukocytes and platelets from RBC in whole blood using orthogonal light scatter from 2 lasers. This method exploits the differences in light-scattering properties between RBCs and platelets and white blood cells (WBC). Hemoglobin readily absorbs 405 nm laser light, reducing the scatter signal from RBC relative to WBCs and platelets, resulting in a reproducible scatter pattern when analyzing human whole blood with both blue (488 nm) and violet (405 nm) side scatter. Using this approach, a distinct platelet population can be discerned in unaltered whole blood, requiring only dilution of whole blood in buffer. Combining this approach with acoustic cytometry allows great flexibility in determining optimal dilution and sample collection rates for minimal coincidence and rapid analysis. For research use only. Not for use in diagnostic procedures.

Targeted Enlargement of Aptamer Functionalized Gold Nanoparticles for Quantitative Protein Analysis.

The ability to selectively amplify the detection signals for targets over interferences is crucial when analyzing proteins in a complicated sample matrix. Here, we describe a targeted enlargement strategy that can amplify the light-scattering signal from aptamer-functionalized gold nanoparticles (Apt-AuNP) with high specificity for quantitative protein analysis. This strategy is achieved by labeling target proteins with competitively protected Apt-AuNP probes and enlarging the probes with gold enhancement. This competitive protection strategy could effectively eliminate nonspecific protein adsorptions from a sample matrix, leading to a highly specific labeling of the target protein. As a result, the subsequent amplification of the light-scattering signal by gold enhancement only occurs in the presence of the target protein. This strategy was successfully demonstrated by analyzing human α-thrombin in human serum samples in a Western blot format.

Discovery of a low-mass companion inside the debris ring surrounding the F5V star HD 206893

Uncovering the ingredients and the architecture of planetary systems is a very active field of research that has fuelled many new theories on giant planet formation, migration, composition, and interaction with the circumstellar environment. We aim at discovering and studying new such systems, to further expand our knowledge of how low-mass companions form and evolve. We obtained high-contrast H-band images of the circumstellar environment of the F5V star HD206893, known to host a debris disc never detected in scattered light. These observations are part of the SPHERE High Angular Resolution Debris Disc Survey (SHARDDS) using the InfraRed Dual-band Imager and Spectrograph (IRDIS) installed on VLT/SPHERE. We report the detection of a source with a contrast of 3.6x10^{-5} in the H-band, orbiting at a projected separation of 270 milliarcsecond or 10 au, corresponding to a mass in the range 24 to 73 Mjup for an age of the system in the range 0.2 to 2 Gyr. The detection was confirmed ten months later with VLT/NaCo, ruling out a background object with no proper motion. A faint extended emission compatible with the disc scattered light signal is also observed. The detection of a low-mass companion inside a massive debris disc makes this system an analog of other young planetary systems such as beta Pictoris, HR8799 or HD95086 and requires now further characterisation of both components to understand their interactions.

Simultaneous Characterization of Nanoparticle Size and Particle-Surface Interactions with Three-Dimensional Nanophotonic Force Microscopy.

The behavior of a nanoparticle in solution depends strongly on the particle's physical and chemical characteristics, most notably the particle size and the surface properties. Accurately characterizing these properties is critical for quality control in a wide variety of industries. To understand a complex and polydisperse nanoparticle suspension, however, ensemble averaging is not sufficient, and there is a great need for direct measurements of size and surface properties at the individual nanoparticle level. In this work, we present an analysis technique for simultaneous characterization of particle-surface interactions and size using near-field light scattering and verify it using Brownian-dynamics simulations. Using a nanophotonic waveguide, single particles can be stably held near the waveguide's surface by strongly localized optical forces. By tracking the dynamic 3D motion of the particle under the influence of these forces using an optical microscope, it is possible to extract the particle-surface interaction forces, as well as to estimate the size and refractive index of the nanoparticle. Because of the strong light-scattering signal, this method is viable for high-throughput characterization of particles as small as 100 nm in only a few seconds each.

The efficacy assessments of alkylating drugs induced by nano-Fe3O4/CA for curing breast and hepatic cancer

A new method to evaluate the anticancer activity at the molecular level has been developed. In our assay, the interaction between alkylating anticancer drugs-Fe3O4/CA with DNA has been investigated for the Resonance Light Scattering (RLS) signal enhancement. Water-based nano-Fe3O4, as a probe, has the ability of good solubility, biodegradability and low bulk resistivity etc. The experimental results show that, the activity order of three kinds of drugs is Nimustine (ACNU)>Semustine (Me-CCNU)>Chlormethine (HN2), which is satisfied with the results of the cell apoptosis experiment and the IC50 by MTT method. This assay is simple, sensitive and high efficient. And the theoretical basics for the development of new anticancer drugs as well as the assessments of their efficacy to cure breast and hepatic cancer have been provided.

A novel nanosensor composed of aptamer bio-dots and gold nanoparticles for determination of thrombin with multiple signals

Thrombin is a crucial multifunctional enzyme involved in many physiological and pathological processes. Its detection is of great importance. In this work, a novel bio-dots nanosensor for detection of thrombin with colorimetric, fluorometric and light-scattering signals is developed. This nanosensor is composed of thrombin-binding aptamer bio-dots (TBA-dots) and gold nanoparticles (AuNPs), where TBA-dots serve as fluorometric reporter and AuNPs function as multiple roles as colorimetric reporter, light scattering reporter and fluorescence quencher. TBA-dots retain inherent structures of aptamer to specifically interact with thrombin and simultaneously induce the aggregation of AuNPs. The mechanism of the sensing system is based on distance-dependent aggregation of AuNPs and fluorescence resonance energy transfer (FRET). The nanosensor needs no further surface functionalization required for the as-prepared bio-dots and AuNPs, which provides a sensitive method for the selective detection of thrombin with a detection limit as low as 0.59nM. In addition, it provides a brand new perspective for bio-dots and its potential use in bioanalysis.

Radial profiles of the Phoebe ring: A vast debris disk around Saturn

We present observations at optical wavelengths with the Cassini Spacecraft’s Imaging Science System of the Phoebe ring, a vast debris disk around Saturn that seems to be collisionally generated by its irregular satellites. The analysis reveals a radial profile from 80–260 Saturn radii (RS) that changes behavior interior to ≈110RS. We attribute this to either the moon Iapetus...sweeping up small particles, or to orbital instabilities that cause the ring to flare up vertically. Our study yields an integrated I/F at 0.635 µm along Saturn’s shadow in the Phoebe ring’s midplane from 80–250 RS of 2.7−0.3+0.9×10−9. We develop an analytical model for the size-dependent secular dynamics of retrograde Phoebe ring grains, and compare this model to the observations. This analysis implies that 1) the “Phoebe” ring is partially sourced by debris from irregular satellites beyond Phoebe’s orbit and 2) the scattered light signal is dominated by small grains (≲20 µm in size). If we assume that the Phoebe ring is generated through steady-state micrometeoroid bombardment, this implies a power-law size distribution with index >4, which is unusually steep among Solar System rings. This suggests either a steep size distribution of ejecta when material is initially released, or a subsequent process that preferentially breaks up large grains.

Online analysis of protein inclusion bodies produced in E. coli by monitoring alterations in scattered and reflected light.

The online monitoring of recombinant protein aggregate inclusion bodies during microbial cultivation is an immense challenge. Measurement of scattered and reflected light offers a versatile and non-invasive measurement technique. Therefore, we investigated two methods to detect the formation of inclusion bodies and monitor their production: (1) online 180° scattered light measurement (λ=625nm) using a sensor platform during cultivation in shake flask and (2) online measurement of the light reflective interference using a porous Si-based optical biosensor (SiPA). It could be shown that 180° scattered light measurement allows monitoring of alterations in the optical properties of Escherichia coli BL21 cells, associated with the formation of inclusion bodies during cultivation. A reproducible linear correlation between the inclusion body concentration of the non-fluorescent protein human leukemia inhibitory factor (hLIF) carrying a thioredoxin tag and the shift ("Δamp") in scattered light signal intensity was observed. This was also observed for the glutathione-S-transferase-tagged green fluorescent protein (GFP-GST). Continuous online monitoring of reflective interference spectra reveals a significant increase in the bacterium refractive index during hLIF production in comparison to a non-induced reference that coincide with the formation of inclusion bodies. These online monitoring techniques could be applied for fast and cost-effective screening of different protein expression systems.

DNA-Directed Assembly of Nanogold Dimers: A Unique Dynamic Light Scattering Sensing Probe for Transcription Factor Detection.

We have developed a unique DNA-assembled gold nanoparticles (AuNPs) dimer for dynamic light scattering (DLS) sensing of transcription factors, exemplified by estrogen receptor (ER) that binds specifically to a double-stranded (ds) DNA sequence containing estrogen response element (ERE). Here, ERE sequence is incorporated into the DNA linkers to bridge the AuNPs dimer for ER binding. Coupled with DLS, this AuNP dimer-based DLS detection system gave distinct readout of a single ‘complex peak’ in the presence of the target molecule (i.e., ER). This unique signature marked the first time that such nanostructures can be used to study transcription factor-DNA interactions, which DLS alone cannot do. This was also unlike previously reported AuNP-DLS assays that gave random and broad distribution of particles size upon target binding. In addition, the ERE-containing AuNP dimers could also suppress the light-scattering signal from the unbound proteins and other interfering factors (e.g., buffer background), and has potential for sensitive detection of target proteins in complex biological samples such as cell lysates. In short, the as-developed AuNP dimer probe coupled with DLS is a simple (mix and test), rapid (readout in ~5 min) and sensitive (low nM levels of ER) platform to detect sequence-specific protein-DNA binding event.

Evanescent Light-Scattering Microscopy for Label-Free Interfacial Imaging: From Single Sub-100 nm Vesicles to Live Cells.

Advancement in the understanding of biomolecular interactions has benefited greatly from the development of surface-sensitive bioanalytical sensors. To further increase their broad impact, significant efforts are presently being made to enable label-free and specific biomolecule detection with high sensitivity, allowing for quantitative interpretation and general applicability at low cost. In this work, we have addressed this challenge by developing a waveguide chip consisting of a flat silica core embedded in a symmetric organic cladding with a refractive index matching that of water. This is shown to reduce stray light (background) scattering and thereby allow for label-free detection of faint objects, such as individual sub-20 nm gold nanoparticles as well as sub-100 nm lipid vesicles. Measurements and theoretical analysis revealed that light-scattering signals originating from single surface-bound lipid vesicles enable characterization of their sizes without employing fluorescent lipids as labels. The concept is also demonstrated for label-free measurements of protein binding to and enzymatic (phospholipase A2) digestion of individual lipid vesicles, enabling an analysis of the influence on the measured kinetics of the dye-labeling of lipids required in previous assays. Further, diffraction-limited imaging of cells (platelets) binding to a silica surface showed that distinct subcellular features could be visualized and temporally resolved during attachment, activation, and spreading. Taken together, these results underscore the versatility and general applicability of the method, which due to its simplicity and compatibility with conventional microscopy setups may reach a widespread in life science and beyond.

Dust particle diffusion in ion beam transport region.

Dust particles of μm size produced by a monoplasmatron ion source are observed by a laser light scattering. The scattered light signal from an incident laser at 532 nm wavelength indicates when and where a particle passes through the ion beam transport region. As the result, dusts with the size more than 10 μm are found to be distributed in the center of the ion beam, while dusts with the size less than 10 μm size are distributed along the edge of the ion beam. Floating potential and electron temperature at beam transport region are measured by an electrostatic probe. This observation can be explained by a charge up model of the dust in the plasma boundary region.

Standardized quantification of human bone marrow mesenchymal stromal cells based on a flow cytometric assay

Conclusion The mesenchymal stromal cell (MSC) content is a major quality determinant of human bone marrow aspirates (BMA). It depends on the aspiration site, contamination with peripheral blood, as well as the aspiration procedure, and it negatively correlates with donor age. The common way of quantifying MSCs is based on the cultivation of cells using the colony forming unit– fibroblast (CFU-F) assay, which is time consuming and highly variable. Cuthbert et al. described a close linear relationship between the number of CFU-F colonies counted manually after 14 days of culture and the number of CD271bright cells per mL of BMA1. The aim of this work was the optimization of a fast and reproducible flow cytometry–based MSC quantification method enabling prospective quality assessment of BMA. In previous experiments we have shown that only CD271bright cells, which also express MSCA-1, give rise to CFU-F. MSCs were isolated from 2×107 bone marrow mononuclear cells (BM MNC) using CD271 (LNGFR)-APC and Anti-APC MicroBeads. Samples of all fractions were labeled with CD45-FITC. PI fluorescence and light scatter signals were used for gating live cells. The positive fraction contained CD271+ cells with a purity of about 86% (Mean: 83±4.1%; n = 4). This population contained about 73% CD271CD45 cells (A, orange fraction) and about 13% CD271CD45 cells (A, red fraction). Further separation of CD271 and CD271 cells was achieved by flow sorting. The different fractions were cultivated and CFU-F numbers were counted after 14 days. The numbers of CFU-F were about 40-fold higher when MSCs were cultivated from the CD271/ CD45 fraction compared to MSCs obtained by plastic adherence (PA). No CFU-Fs were detected in the CD271– and CD271CD45 cell fractions (A). Counterstaining of isolated CD271+ cells revealed a 100% co-expression of MSCA-1 in CD271CD45 cells (B). CD271CD45 MSCs met ISCT criteria2 after culture expansion (3 passages) with respect to MSCspecific marker expression (C) and their differentiation potential towards osteocytes, adipocytes, and chondrocytes (D, left to right)

Linear light-scattering of gold nanostars for versatile biosensing of nucleic acids and proteins using exonuclease III as biocatalyst to signal amplification.

Gold nanomaterials promise a wide range of potential applications in chemical and biological sensing, imaging, and catalysis. In this paper, we demonstrate a facile method for room-temperature synthesis of gold nanostars (AuNSs) with a size of ~50 nm via seeded growth. Significantly, the AuNSs are found to have high light-scattering properties, which are successfully used as labels for sensitive and selective detection of nucleic acids and proteins by using exonuclease III (Exo III) as a biocatalyst. For DNA detection, the binding of targets to the functionalized AuNS probes leads to the Exo III-stimulated cascade recycling amplification. As a result, a large amount of AuNSs are released from magnetic nanoparticles (MNPs) into solution, providing a greatly enhanced light-scattering signal for amplified sensing process. Moreover, a binding-induced DNA three-way junction (DNA TWJ) is introduced to thrombin detection, in which the binding of two aptamers to thrombin triggers assembly of the DNA motifs and initiates the subsequent DNA strand displacement reaction (SDR) and Exo III-assisted cascade recycling amplification. The detection limits of 89 fM and 5.6 pM are achieved for DNA and thrombin, respectively, which are comparable to or even exceed that of the reported isothermal amplification methods. It is noteworthy that based on the DNA TWJ strategy the sequences are independent on target proteins. Additionally, the employment of MNPs in the assays can not only simplify the operations but also improve the detection sensitivity. Therefore, the proposed amplified light-scattering assay with high sensitivity and selectivity, acceptable accuracy, and satisfactory versatility of analytes provides various applications in bioanalysis.

Optical Signatures of Antiferromagnetic Ordering of Fermionic Atoms in an Optical Lattice

We show how off-resonant light scattering can provide quantitative information on antiferromagnetic ordering of a two-species fermionic atomic gas in a tightly-confined two-dimensional optical lattice. We analyze the emerging magnetic ordering of atoms in the mean-field and in random phase approximations and show how the many-body static and dynamic correlations, evaluated in the standard Feynman-Dyson perturbation series, can be detected in the scattered light signal. The staggered magnetization reveals itself in the magnetic Bragg peaks of the individual spin components. These magnetic peaks, however, can be considerably suppressed in the absence of a true long-range antiferromagnetic order. The light scattered outside the diffraction orders can be collected by a lens a with highly improved signal-to-shot-noise ratio when the diffraction maxima are blocked. The collective and single-particle excitations are identified in the spectrum of the scattered light. We find that the spin-conserving and spin-exchanging atomic transitions convey information on density, longitudinal spin, and transverse spin correlations. The different correlations and scattering processes exhibit characteristic angular distribution profiles for the scattered light and, e.g., the diagnostic signal of transverse spin correlations could be separated from the signal by the scattering direction, frequency, or polarization. We also analyze the detection accuracy by estimating the number of required measurements, constrained by the heating rate that is determined by inelastic light scattering events. The imaging technique could be extended to the two-species fermionic states in other regions of the phase diagram where the ground state properties are still not fully understood.

Simultaneous Determination of Thermal and Mutual Diffusivity of Binary Mixtures of n-Octacosane with Carbon Monoxide, Hydrogen, and Water by Dynamic Light Scattering

It is demonstrated that thermal and mutual diffusivities of binary mixtures of n-octacosane (n-C28H58) with carbon monoxide (CO), hydrogen (H2), and water (H2O) are simultaneously accessible by dynamic light scattering (DLS). As the light-scattering signals originating from thermal and concentration fluctuations appear in similar time scales, different data evaluation strategies were tested to achieve minimum uncertainties in the resulting transport properties. To test the agreement of the respective theoretical model with the DLS signals in the regression, an improved multifit procedure is introduced. With the selected data evaluation strategy, uncertainties of 4 to 15% and 4 to 30% in the thermal and mutual diffusivities, respectively, could be obtained for the binary mixtures. The mutual diffusivities for the mixtures measured at temperatures ranging from 398 to 523 K and pressures of 5 to 30 bar at saturation conditions are in good agreement with molecular dynamics simulations and data from the literature.

The study of epigenetic mechanisms based on the analysis of histone modification patterns by flow cytoametry

Epigenetic regulation of genes involved in cell growth, survival, or differentiation through histone modifications is an important determinant of cancer development and outcome. The basic science of epigenetics uses analytical tools that, although powerful, are not well suited to the analysis of heterogeneous cell populations found in human cancers, or for monitoring the effects of drugs designed to modulate epigenetic mechanisms in patients. To address this, we selected three clinically relevant histone marks (H3K27me3, H3K9ac, and H3K9me2), modulated their expression levels by in vitro treatments to generate high and low expressing control cells, and tested the relative sensitivity of candidate antibodies to detect the differences in expression levels by flow cytoametry using a range of sample preparation techniques. We identified monoclonal antibodies to all three histone marks that were suitable for flow cytoametry. Staining intensities were reduced with increasing formaldehyde concentration, and were not affected by ionic strength or by alcohol treatment. A protocol suitable for clinical samples was then developed, to allow combined labeling of histone marks and surface antigens while preserving light scatter signals. This was applied to normal donor blood, and to samples obtained from 25 patients with leukemia (predominantly acute myeloid leukemia). Significant cellular heterogeneity in H3K9ac and H3K27me3 staining was seen in normal peripheral blood, but the patterns were very similar between individual donors. In contrast, H3K27me3 in particular showed considerable inter-patient heterogeneity in the leukemia cell populations. Although further refinements are likely needed to fully optimize sample staining protocols, "flow epigenetics" appears to be technically feasible, and to have potential both in basic research, and in clinical application.

THE DEEP BLUE COLOR OF HD 189733b: ALBEDO MEASUREMENTS WITH HUBBLE SPACE TELESCOPE /SPACE TELESCOPE IMAGING SPECTROGRAPH AT VISIBLE WAVELENGTHS

We present a secondary eclipse observation for the hot Jupiter HD189733b across the wavelength range 290-570nm made using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. We measure geometric albedos of Ag = 0.40 \pm 0.12 across 290-450nm and Ag < 0.12 across 450-570nm at 1-sigma confidence. The albedo decrease toward longer wavelengths is also apparent when using six wavelength bins over the same wavelength range. This can be interpreted as evidence for optically thick reflective clouds on the dayside hemisphere with sodium absorption suppressing the scattered light signal beyond ~450nm. Our best-fit albedo values imply that HD189733b would appear a deep blue color at visible wavelengths.

GABA UPTAKE BY GAT1 MODULATES LONG-TERM OPTICAL CHANGES FOLLOWING ELECTRICAL STIMULATION OF THE PITUITARY GLAND NEUROINTERMEDIATE LOBE

Intrinsic optical changes that follow infundibular stalk stimulation of the neurointermediate lobe of the mouse pituitary gland exhibit three different phases that reflect three distinct physiological events. The first (E-wave) is the rapid light-scattering increase that is associated with a nerve terminal volume increase (mechanical spike), and that accompanies excitation of the neurohypophysial terminals by the invading action potential; the second (S-wave) is the slower light-scattering decrease that is tightly correlated with the secretion of the peptide hormones oxytocin and arginine vasopressin, and the third is the long-duration response (R-wave) that reflects cell volume changes in the pars intermedia. We have studied the E-wave and the S-wave in earlier publications. The R-wave, considered here, is sensitive to chloride replacement as well as to blockade of chloride channels. By blocking GABAAreceptors (which are ligand-gated chloride channels) with pharmacological agents, and by applying GABA directly into the bathing solution, or evoking its release from GABAergic inputs, we have demonstrated that this long-duration optical response is sensitive to chloride movements and reflects GABA-induced changes in the intrinsic optical properties of the pars intermedia. The full time-course of this optical response takes minutes and, therefore, has to embody some other process (or processes) related to the restoration of resting physiological chloride concentrations, following the opening and closing of GABAA-receptor channels. Here we demonstrate that the shape of the R-wave, the long-lasting light-scattering signal, is indeed affected by the activity of GAT1, one of the sodium- and chloride-dependent GABA transporters.