Photon Correlation Spectroscopy Data Research Articles

Beam Effects on Atomic Dynamics in Metallic Glasses Studied With Electron Correlation Microscopy.

Electron correlation microscopy (ECM) is used to investigate atomic dynamics in metallic glasses (MG) close to metastable equilibrium. It temporally correlates diffracted intensities of a time series of dark-field images to deduce a metric for structural decays. The measurement parameters, such as time and temperature, must be chosen according to the material of interest. In this work, ECM was extended to measurements at room temperature. To ensure, or select, a time window with quasi-thermodynamic equilibrium/steady-state measurement conditions, two-time correlation functions of diffracted intensities were calculated. The dynamics at room temperature are partly driven by the electron beam, thus affecting the material and the results. A systematic analysis of the influence of the electron beam is presented, revealing an inverse relation between electron dose rate and intensity correlation decay times at 300 kV acceleration voltage. However, the underlying dynamical mechanisms, described by a stretching exponent, are found to be independent of the applied electron dose rate for a Pd40Ni40P20 MG. An extrapolation of the results to infinite long measurement times and zero dose rate agrees with X-ray photon correlation spectroscopy data and justifies the application of beam-driven ECM at room temperature to study the dynamics of disordered systems.

Synthesis of CuO nanoparticles stabilized with gelatin for potential use in food packaging applications

In the present study, a method for the synthesis of gelatin-stabilized copper oxide nanoparticles was developed. Synthesis was carried out by direct chemical precipitation. Copper sulfate, chloride, and acetate were used as precursors for the copper oxide synthesis. Gelatin was used as a stabilizer. It was found that the formation of monophase copper oxide II only occurred when copper acetate was used as a precursor. Our results showed that particles of the smallest diameter are formed in an aqueous medium (18 ± 6 nm), and those of th largest diameter—in an isobutanol medium (370 ± 131 nm). According to the photon correlation spectroscopy data, copper oxide nanoparticles synthesized in an aqueous medium were highly stable and had a monomodal size distribution with an average hydrodynamic radius of 61 nm. The study of the pH effect on the colloidal stability of copper oxide nanoparticles showed that the sample was stable in the pH range of 6.8 to 11.98. A possible mechanism for the pH influence on the stability of copper oxide nanoparticles is described. The effect of the ionic strength of the solution on the stability of the CuO nanoparticles sol was also studied, and the results showed that Ca2+ ions had the greatest effect on the sample stability. IR spectroscopy showed that the interaction of CuO nanoparticles with gelatin occurred through the hydroxyl group. It was found that CuO nanoparticles stabilized with gelatin have a fungicidal activity at concentration equivalent 2.5 · 10−3 mol/L and as a material for food nanopackaging can provide an increase in the shelf life of products on the example of strawberries and tomatoes. We investigated the possibility of using methylcellulose films modified with CuO nanoparticles for packaging and storage of hard cheese “Holland”. The distribution of CuO nanoparticles in the methylcellulose film was uniform. We found that methylcellulose films modified with CuO nanoparticles inhibited the growth and development of QMAFAM, coliforms, yeast and mold in experimental cheese sa mples. Our research has shown that during the cheese storage in thermostat at 35 ± 1 °C for 7 days, CuO nanoparticles migrated to the product from the film. Nevertheless, it is worth noting that the maximum change in the concentration of copper in the experimental samples was only 0.12 µg/mg, which is not a toxic concentration. In general, the small value of migration of CuO nanoparticles confirms the high stability of the developed preparation. Our results indicated that the CuO nanoparticles stabilized with gelatin have a high potential for use in food packaging – both as an independent nanofilm and as part of other packaging materials.

Investigation of surface structure, electrokinetic and stability properties of highly dispersed Ho2O3–Yb2O3/SiO2 nanocomposites

A series of highly dispersed Ho2O3–Yb2O3/SiO2 nanocomposites was synthesized using a liquid-phase method and examined using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), nitrogen adsorption–desorption, transmission electron microscopy (TEM), Scanning Electron Microscopy (SEM), and photon correlation spectroscopy (PCS). X-ray fluorescence spectrometry (XRF) confirmed a similar amount of weight percentage of Ho, Yb and Si oxides in the prepared samples. Samples HoYbSi1 (Ho2O3:Yb2O3:SiO2 = 0.5:10:89.5, wt. %), HoYbSi2 (Ho2O3:Yb2O3:SiO2 = 1:10:89, wt. %) and HoYbSi3 (Ho2O3:Yb2O3:SiO2 = 2:10:88, wt. %) calcined at 550 °C are amorphous. TEM and SEM analysis confirm a sphere-like morphology with a quite homogeneous size and shape. As compared with the initial silica, the agglomerated particles of nanocomposites in the aqueous medium are in the range from 200 to 850 nm according to PCS data. The effect of anionic polyacrylic acid (PAA) adsorption on fumed silica (SiO2) and Ho2O3–Yb2O3/SiO2 nanocomposite surfaces on suspension stability was studied. The turbidymetry method was used to monitor the initial silica and triple nanooxides suspensions stability as a function of time.

Distributed X-ray photon correlation spectroscopy data reduction using Hadoop MapReduce.

Multi-speckle X-ray photon correlation spectroscopy (XPCS) is a powerful technique for characterizing the dynamic nature of complex materials over a range of time scales. XPCS has been successfully applied to study a wide range of systems. Recent developments in higher-frame-rate detectors, while aiding in the study of faster dynamical processes, creates large amounts of data that require parallel computational techniques to process in near real-time. Here, an implementation of the multi-tau and two-time autocorrelation algorithms using the Hadoop MapReduce framework for distributed computing is presented. The system scales well with regard to the increase in the data size, and has been serving the users of beamline 8-ID-I at the Advanced Photon Source for near real-time autocorrelations for the past five years.

On the use of two-time correlation functions for X-ray photon correlation spectroscopy data analysis.

Multi-time correlation functions are especially well suited to study non-equilibrium processes. In particular, two-time correlation functions are widely used in X-ray photon correlation experiments on systems out of equilibrium. One-time correlations are often extracted from two-time correlation functions at different sample ages. However, this way of analysing two-time correlation functions is not unique. Here, two methods to analyse two-time correlation functions are scrutinized, and three illustrative examples are used to discuss the implications for the evaluation of the correlation times and functional shape of the correlations.

Physicochemical properties of lipopeptide-based liposomes and their complexes with siRNA

siRNA/cationic liposome complexes are efficient systems for transmembrane delivery. The aim of this study was to prepare a novel complex consisted of lipotripeptide OrnOrnGlu(C16H33)2 and siRNA molecule and examined their physicochemical properties. Electron microscopy study has shown that the siRNA/liposome complex (m/m 1/10) tends to form sandwich-like structures that may protect nucleic acid from nuclease degradation. Photon correlation spectroscopy data indicate that the particle size increased after siRNA adding, but did not exceed 300 nm in diameter, while z-potential of lipoplexes decreased from 22 mV to 14 mV, compared to the empty liposomes thus indicating positive charge neutralization by negatively charged siRNA. These data allow to hypothesize that such size and total positive charge could provide efficient cellular uptake by endocytosis. That may have good prospects for gene silencing therapy.

Coherent X-ray scattering reveals nature of dynamical transitions in nanoparticle–polymer suspensions

We report the microrheological behavior and dynamics of the suspensions of polystyrene-grafted gold nanoparticles (PGNPs) mixed with linear polystyrene (PS) as a function of the PS concentration and size asymmetry parameter, xi (=M-g/M-m, with M-g and M-m being the grafted and free chain molecular weights, respectively) = 2.76 and 0.14. Diffusive wave spectroscopy (DWS) is used for measuring the frequency dependent micro-rheology parameter, the loss modulus G `'(omega)(similar to omega(alpha)). For suspensions with xi = 0.14 a transition of a, from similar to 1 to similar to 1.6, is observed at a critical fraction of added polymers. On the other hand, a is always similar to 1 for the suspensions with xi = 2.76. Corresponding x-ray photon correlation spectroscopy (XPCS) data on the same samples reveals a sharp transition in the nature of dynamics of PGNPs, from exponential to logarithmic, in suspensions with x = 0.14, while for suspensions with xi = 2.76 this dynamical transition is not observed. Interestingly, the dynamical transition in xi = 0.14 based samples occurs at the same fraction of added polymers, where the transition of a from similar to 1 to similar to 1.6 was observed, thus providing a clear correlation between microscopic dynamics and micro-rheology. The conformational transitions of the grafted polymers is found to be the reason behind the observed differences in the dynamic behavior of the two systems. The important role of advanced x-ray scattering techniques in unravelling subtle aspects of nanoscale complex polymer and soft colloidal dynamics is thus revealed. (C) 2016 Elsevier Ltd. All rights reserved.

First experimental feasibility study of VIPIC: a custom-made detector for X-ray speckle measurements.

The Vertically Integrated Photon Imaging Chip (VIPIC) was custom-designed for X-ray photon correlation spectroscopy, an application in which occupancy per pixel is low but high time resolution is needed. VIPIC operates in a sparsified streaming mode in which each detected photon is immediately read out as a time- and position-stamped event. This event stream can be fed directly to an autocorrelation engine or accumulated to form a conventional image. The detector only delivers non-zero data (sparsified readout), greatly reducing the communications overhead typical of conventional frame-oriented detectors such as charge-coupled devices or conventional hybrid pixel detectors. This feature allows continuous acquisition of data with timescales from microseconds to hours. In this work VIPIC has been used to measure X-ray photon correlation spectroscopy data on polystyrene latex nano-colliodal suspensions in glycerol and on colloidal suspensions of silica spheres in water. Relaxation times of the nano-colloids have been measured for different temperatures. These results demonstrate that VIPIC can operate continuously in the microsecond time frame, while at the same time probing longer timescales.

Polymer Film Surface Fluctuation Dynamics in the Limit of Very Dense Branching

The surface fluctuation dynamics of melt films of densely branched comb polystyrene of thickness greater than 55 nm and at temperatures 23–58 °C above the bulk Tg can be rationalized using the hydrodynamic continuum theory (HCT) known to describe melts of unentangled linear and cyclic chains. Film viscosities (ηXPCS) inferred from fits of the HCT to X-ray photon correlation spectroscopy (XPCS) data are the same as those measured in bulk rheometry (ηbulk) for three combs. For the comb most like a star polymer and the comb closest to showing bulk entanglement behavior, ηXPCS > ηbulk. These discrepancies are much smaller than those seen for less densely branched polystyrenes. We conjecture that the smaller magnitude of ηXPCS – ηbulk for the densely grafted combs is due to a lack of interpenetration of the side chains when branching is most dense. Both Tg,bulk and the specific chain architecture play key roles in determining the surface fluctuations.

Enhancement of Multiphoton Emission from Single CdSe Quantum Dots Coupled to Gold Films

Single molecule time-resolved fluorescence spectroscopy of CdSe/ZnS core-shell quantum dots (QDs) localized near a rough gold thin film demonstrates significant enhancement of multiphoton emission while at the same time showing a decrease in single photon emission. A rigorous analysis of time-resolved photon correlation spectroscopy and fluorescence lifetime data on single quantum dots at room temperature reveals an increase in radiative recombination rate of multiexcitons that is much higher than expected and, perhaps more significantly, is not correlated with concomitant increases in single exciton recombination rates. We believe that these results confirm a stronger coupling of multiexcitons to plasmon modes via a coupling to plasmon multipole modes.

Spin Label and SAXS Study of Cetylpalmitate Solid Lipid Nanoparticles Loaded with Dibucaine

Dibucaine (DBC) belongs to the amino amide family of local anesthetics. Unlike other anesthetic compounds it possesses a rigid, butyl substituted, quinolinic ring that imposes restrictions to its interaction with membranes. Solid Lipid Nanoparticles (SLN) has been attracting attention as a promising drug delivery system because it combines advantages such as versatility, use of safe excipients, a wide potential for the controlled drug release of drugs and good shelf stability. The aim of this study was to develop SLN prepared with cetylpalmitate (CP) as the lipid matrix and poloxamer 188 as a colloidal stabilizer to encapsulate DBC. Nanoparticles were prepared with the high pressure hot homogenization method and characterized by transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS) and electron paramagnetic resonance (EPR). The association constant or partition coefficient was measured (177.02 ± 6.31). TEM images disclosure structures with delineated spherical surfaces and homogenous size distribution (ca. 250-300 nm), in good agreement with photon correlation spectroscopy data; incorporation of DBC did not change the morphology and size of the nanoparticles. SAXS data showed that the lipids in the SLN are organized in a liquid crystal-like structure, with small amounts of water inside it (the same results were observed in the SLN loaded with DBC). EPR spectra of 5-nitroxyl stearic acid incorporated into SLN were compatible with SAXL data and revealed that dibucaine insertion into the nanoparticles changed the lipid packing sensed by the spin label, decreasing its isotropic signal. In conclusion we have shown that DBC can be successfully incorporated into SLN, changing its lipid packing without destabilizing the overall nanoparticle structure, indicating that this is a promising drug delivery system. Supported by FAPESP (# 06/00121-9), CAPES, CNPq.

Improved inversion procedure for particle size distribution determination by photon correlation spectroscopy

We propose a minimum variation of solution method to determine the optimal regularization parameter for singular value decomposition for obtaining the initial distribution for a Chahine iterative algorithm used to determine the particle size distribution from photon correlation spectroscopy data. We impose a nonnegativity constraint to make the initial distribution more realistic. The minimum variation of solution is a single constraint method and we show that a better regularization parameter may be obtained by increasing the discrimination between adjacent values. We developed the S-R curve method as a means of determining the modest iterative solution from the Chahine algorithm. The S-R curve method requires a smoothing operator. We have used simulated data to verify our new method and applied it to real data. Both simulated and experimental data show that the method works well and that the first derivative smoothing operator in the S-R curve gives the best results.

Properties of water in triton N-42 reverse micelles during the solubilization of HCl solutions according to FT-IR and photon correlation spectroscopy

FT-IR and photon correlation spectroscopy methods are used to study the distribution of free (bulk) and bound (hydration) water in Triton N-42 reverse micelles under the conditions of injection solubilization of hydrochloric acid solutions. The amount of each type of water is calculated depending on the solubilization capacity (Vs/Vo) and HCl concentration in the aqueous pseudophase. According to the IR spectroscopy data, the distribution of water is largely determined by the solubilization capacity of the micellar solution, while the fraction of bulk water exceeds significantly the value calculated by the geometric approach based on the photon correlation spectroscopy data. The difference shows that there is bulk water in the surface layer formed by oxyethyl groups of Triton N-42 molecules in spherocylindrical micelles.

Firmware lower-level discrimination and compression applied to streaming x-ray photon correlation spectroscopy area-detector data

We present a data acquisition system to perform on-the-fly background subtraction and lower-level discrimination compression of streaming x-ray photon correlation spectroscopy data from a fast charge-coupled device (CCD) area detector. The system is built using a commercial frame grabber with an on-board field-programmable gate array. The system is capable of continuously processing at least 60 CCD frames per second each consisting of 1024 × 1024 16-bit pixels with ≲ 15,000 photon hits per frame at a maximum compression factor of ≈95%.

Real-time compression of streaming X-ray photon correlation spectroscopy area-detector data

Abstract We present a data acquisition system to perform on-the-fly background subtraction and lower-level discrimination compression of streaming X-ray photon correlation spectroscopy (XPCS) data from a fast charge-coupled device area detector. The system is built using a commercial frame grabber with an on-board field-programmable gate array (FPGA). The system is capable of continuously processing 60 CCD frames per second each consisting of 1024×1024 pixels with up to 64 512 photon hits per frame.

MPICorrelator: A parallel code for performing time correlations

Abstract The MPICorrelator application is a parallel application for processing multi-speckle X-ray photon correlation spectroscopy data via a data-parallelized implementation of the multi-tau algorithm. MPICorrelator spreads the analysis across a number of computing nodes in a cluster. Leveraging a number of computing nodes in this manner has led to a 30 times decrease in the amount of time required to analyze a multi-speckle time series. The system has recently gone operational at the 8 ID I beamline and has demonstrated the ability to keep up with acquisition rates of megapixel frames acquired at 60 Hz. Future improvements will increase the analysis rate to allow for real-time operation and feedback on live acquired data.

Poly(amidoamine) Dendrimer Based MRI Contrast Agents Exhibiting Enhanced Relaxivities Derived via Metal Preligation Techniques

This report presents the preparation and characterization of three [Gd-C-DOTA](-1)-dendrimer assemblies by way of analysis, NMRD spectroscopy, and photon correlation spectroscopy (PCS). The metal-ligand chelates were preformed in alcohol media prior to conjugation to generation 4, 5, and 6 PAMAM dendrimers. The dendrimer-based agents were purified by Sephadex G-25 column chromatography. The combustion analysis, SE-HPLC, and UV-vis data indicated chelate to dendrimer ratios of 28:1, 61:1 and 115:1, respectively. Molar relaxivity measured at pH 7.4, 22 degrees C, and 3 T (29.6, 49.8, and 89.1 mM(-1) s(-1)) indicated the viability of conjugates as MRI contrast agents. 1/T(1) NMRD profiles were measured at 23 degrees C and indicated that at 22 MHz the 1/T(1) reached a plateau at 60, 85, and 140 mM(-1) s(-1) for the generation 4, 5, and 6 dendrimer conjugates, respectively. The PCS data showed the respective sizes of 5.2, 6.5, and 7.8 nm for G-4, 5, and 6 conjugates.

Microgels containing methacrylic acid: effects of composition on pH-triggered swelling and gelation behaviours

pH-responsive microgels are cross-linked polymer colloids that swell when the pH approaches the pKa of the particles. In this work, we present a comprehensive investigation of pH-triggered particle swelling and gel formation for a range of microgels containing methacrylic acid (MAA). The microgels investigated have the general composition poly(A/MAA/X), where A and X are the primary co-monomer and cross-linking monomer, respectively. The primary co-monomers were methyl methacrylate (MMA), ethyl acrylate (EA) or butyl methacrylate. The cross-linking monomers were either butanediol diacrylate (BDDA) or ethyleneglycol dimethacrylate (EGDMA). The microgels were studied using scanning electron microscopy, photon correlation spectroscopy (PCS) and dynamic rheology measurements. Gel phase diagrams were also constructed. The particles swelled significantly at pH values greater than approximately 6.0. It was shown that poly(EA/MAA/X) microgels swelled more strongly than poly(MMA/MAA/X) microgels. Furthermore, greater swelling occurred for particles prepared using EGDMA than BDDA. Concentrated dispersions of all the microgels studied exhibited pH-triggered gel formation. It was found that the fluid-to-gel transitions for the majority of the six microgel dispersions investigated could be explained using PCS data. In those cases, gelation was attributed to a colloidal glass transition. Interestingly, the microgels that were considered to have the highest hydrophobic content gelation occurred under conditions where little particle swelling was evident from PCS. The data presented show that gelled poly(EA/MAA/BDDA) and poly(MMA/MAA/EGDMA) microgel dispersions have the strongest elasticities at pH = 7.

Diffusion and Viscosity in a Crowded Environment: from Nano- to Macroscale

Although water is the chief component of living cells, food, and personal care products, the supramolecular components make their viscosity larger than that of water by several orders of magnitude. Using fluorescence correlation spectroscopy (FCS), photon correlation spectroscopy (PCS), NMR, and rheology data, we show how the viscosity changes from the value for water at the molecular scale to the large macroviscosity. We determined the viscosity experienced by nanoprobes (of sizes from 0.28 to 190 nm) in aqueous micellar solution of hexaethylene-glycol-monododecyl-ether (in a range of concentration from 0.1% w/w to 35% w/w) and identified a clear crossover at the length scale of 17 +/- 2 nm (slightly larger than persistence length of micelles) at which viscosity acquires its macroscopic value. The sharp dependence of the viscosity coefficients on the size of the probe in the nanoregime has important consequences for diffusion-limited reactions in crowded environments (e.g., living cells).

Structural investigations on nanoemulsions, solid lipid nanoparticles and nanostructured lipid carriers by cryo-field emission scanning electron microscopy and Raman spectroscopy

Recently, colloidal dispersions based on solid lipids (solid lipid nanoparticles, SLN) and mixtures of solid and liquid lipids (nanostructured lipid carriers, NLC) were described as innovative carrier systems. A spherical particle shape is the basis of features such as a high loading capacity and controlled drug release characteristics due to smaller lipid–water interfaces and longer diffusion pathways when compared to thin platelets. The structures of SLN and the influence of oil load (NLC) on particle properties were investigated by photon correlation spectroscopy (PCS), laser diffractometry (LD), cryo-field emission scanning electron microscopy (cryo-FESEM), Raman spectroscopy and infrared spectroscopy (IR), and compared to a conventional nanoemulsion. PCS and LD data show similar size and size distribution for SLN and NLC (approximately 210 nm, polydispersity index approximately 0.15) and suggested a long term physical stability for the dispersions which had been stored for up to 12 months at different temperatures. Using cryo-FESEM droplets (for the nanoemulsion) and almost spherical particles for SLN and NLC were observed. Raman spectroscopy resulted in spectra for NLC that are weighted to the SLN spectra, suggesting an undisturbed crystal structure. Infrared spectra of the NLC are predominantly SLN in nature. Importantly the SLN bands are unshifted in the NLC spectrum indicating that the crystalline structure is unaffected by the presence of the oil.