Probe Size Research Articles

An Application for the Quantitative Analysis of Pharmaceutical Tablets Using a Rapid Switching System Between a Near-Infrared Spectrometer and a Portable Near-Infrared Imaging System Equipped with Fiber Optics.

We present a rapid switching system between a newly developed near-infrared (NIR) spectrometer and its imaging system to select the spot size of a diffuse reflectance (DR) probe. In a previous study, we developed a portable NIR imaging system, known as D-NIRs, which has significant advantages over other systems. Its high speed, high spectral resolution, and portability are particularly useful in the process of monitoring pharmaceutical tablets. However, the spectral accuracies relating to the changes in the formulation of the pharmaceutical tablets have not been fully discussed. Therefore, we improved the rapid optical switching system and present a new model of D-NIRs (ND-NIRs) here. This system can automatically switch the optical paths of the DR and NIR imaging probes, greatly contributing to the simultaneous measurement of both the imaging and spot. The NIR spectra of the model tablets, including 0-10% ascorbic acid, were measured and simultaneous NIR images of the tablets were obtained. The predicted results using spot sizes for the DR probe of 1 and 5 mm diameter, resulted in concentrations of R2 = 0.79 and 0.94, with root mean square errors (RMSE) of 1.78 and 0.89, respectively. For tablets with a high concentration of ascorbic acid, the NIR imaging results showed inhomogeneity in concentration. However, the predicted values for the low concentration samples appeared higher than the known concentration of the tablets, although the homogeneity of the concentration was confirmed. In addition, the optimal spot size using NIR imaging data was estimated to be 5-7 mm. The results obtained in this study show that the spot size of the fiber probe, attached to a spectrometer, is important in developing a highly reliable model to determine the component concentration of a tablet.

The influence of grain boundaries and grain orientations on the stochastic responses to low load nanoindentation in Cu

Mechanical properties that are considered to be deterministic in the macro-scale have been shown to be stochastic in the sub-micron length scale. The origin of such stochastic responses is not well understood. This work examines the potential influence of grain boundaries and grain orientations on the stochastic nature of pop-in and hardness measurement in annealed high purity polycrystalline Cu samples during low load nanoindentation. Statistical analysis on pop-in load and hardness showed that variations of these measurements depend on crystal orientations and is influenced by the indenter probe size. Analysis on the pop-in load statistics showed that pop-ins are likely initiate from an atomic sized precursor that leads to dislocation generation or expansion. Variation in hardness measurements near an arbitrary chosen grain boundary and the apparent grain boundary hardening effect observed may be related to the higher density of dislocations at and near the grain boundary.

Multiple particle tracking microrheology measured using bi-disperse probe diameters.

Multiple particle tracking microrheology (MPT) is a powerful tool for quantitatively characterizing rheological properties of soft matter. Traditionally, MPT uses a single particle size to characterize rheological properties. But in complex systems, MPT measurements with a single size particle can characterize distinct properties that are linked to the materials' length scale dependent structure. By varying the size of probes, MPT can measure the properties associated with different length scales within a material. We develop a technique to simultaneously track a bi-disperse population of probe particles. 0.5 and 2 μm particles are embedded in the same sample and these particle populations are tracked separately using a brightness-based squared radius of gyration, Rg2. Bi-disperse MPT is validated by measuring the viscosity of glycerol samples at varying concentrations. Bi-disperse MPT measurements agree well with literature values. This technique then characterizes a homogeneous poly(ethylene glycol)-acrylate:poly(ethylene glycol)-dithiol gelation. The critical relaxation exponent and critical gelation time are consistent and agree with previous measurements using a single particle. Finally, degradation of a heterogeneous hydrogenated castor oil colloidal gel is characterized. The two particle sizes measure a different value of the critical relaxation exponent, indicating that they are probing different structures. Analysis of material heterogeneity shows measured heterogeneity is dependent on probe size indicating that each particle is measuring rheological evolution of a length scale dependent structure. Overall, bi-disperse MPT increases the amount of information gained in a single measurement, enabling more complete characterization of complex systems that range from consumer care products to biological materials.

Effects of β-Sitosteryl Sulfate on the Properties of DPPC Liposomes.

The effect of β-sitosteryl sulfate (PSO4) on the liposomal size, stability, fluidity, and dispersibility of DPPC liposomes prepared by vortex mixing, bath-sonication, and probe-sonication has been studied. PSO4 significantly decreases the particle size of the multilamellar liposomes (MLVs). The sizes of the vortexmixed and the bath-sonicated liposomes vary as a function of PSO4 concentration. On the other hand, PSO4 has only little effect on the particle sizes of probe sonicated liposomes. In some cases, the liposomal stability at higher PSO4 concentrations depends on the preparation method. PSO4 improves the dispersibility of the DPPC liposomes and enhances their hydration. It also increases the fluidity of the liposomes prepared by each method. Our results suggest that liposomes consisting of DPPC and PSO4 can be suitable as a cosmetic or pharmaceutical ingredient for the effective delivery of the active components into the body.

Microscale mapping of extracellular matrix elasticity of mouse joint cartilage: an approach to extracting bulk elasticity of soft matter with surface roughness.

Cartilage is composed of cells and an extracellular matrix, the latter being a composite of a collagen mesh interpenetrated by proteoglycans responsible for tissue osmotic swelling. The matrix composition and structure vary through the tissue depth. Mapping such variability requires tissue sectioning to gain access. The resulting surface roughness, and concomitant proteoglycan loss contribute to large uncertainties in elastic modulus estimates. To extract elasticity values for the bulk matrix which are not obfuscated by the indeterminate surface layer, we developed a novel experimental and data analysis methodology. We analyzed the surface roughness to optimize the probe size, and performed high-resolution (1 μm) elasticity mapping on thin (∼12 μm), epiphyseal newborn mouse cartilage sections cut parallel to the bone longitudinal axis or normal to the articular surface. Mild fixation prevented the major proteoglycan loss observed in unfixed specimens but not the stress release that resulted in thickness changes in the sectioned matrix. Our novel data analysis method introduces a virtual contact point as a fitting parameter for the Hertz model, to minimize the effects of surface roughness and corrects for the finite section thickness. Our estimates of cartilage elasticity converge with increasing indentation depth and, unlike previous data interpretations, are consistent with linearly elastic material. A high cell density that leaves narrow matrix septa between cells may cause the underestimation of elastic moduli, whereas fixation probably causes an overestimation. The proposed methodology has broader relevance to nano- and micro-indentation of soft materials with multiple length scales of organization and whenever surface effects (including roughness, electrostatics, van der Waals forces, etc.) become significant.

Theory and practice of electron diffraction from single atoms and extended objects using an EMPAD.

What does the diffraction pattern from a single atom look like? How does it differ from the scattering from long-range potential? With the development of new high-dynamic range pixel array detectors to measure the complete momentum distribution, these questions have immediate relevance for designing and understanding momentum-resolved imaging modes. We explore the asymptotic limits of long-range and short-range potentials. We use a simple quantum mechanical model to explain the general and asymptotic limits for the probability distribution in both real and reciprocal space. Features in the scattering potential much larger than the probe size cause the bright field (BF) disk to deflect uniformly, while features much smaller than the probe size, instead of a deflection, cause a redistribution of intensity within the BF disk. Because long-range and short-range features are encoded differently in the diffraction pattern, it is possible to separate their contributions in differential phase-contrast (DPC) or center-of-mass (CoM) imaging. The shape profiles for atomic resolution CoM imaging are dominated by the shape of the probe gradient and not the highly singular atomic potentials or their local fields. Instead, only the peak height shows an atomic number sensitivity, whose precise dependence is determined by the convergence angle. At lower convergence angles, the contrast oscillates with increasing atomic number, similar to BF imaging. The range of collection angles impacts DPC and CoM imaging differently, with CoM being more sensitive to the upper cutoff limit, while DPC is more sensitive to the lower cutoff.

Scale effect in mechanical characterization of WC-Co composites

The study of mechanical response of materials at small length scales has gained importance due to the recent advances in micro- and nano-fabrication as well as testing systems. However, most of the reported work has been dedicated to investigate single-crystals or boundary-containing metallic systems, while much less attention has been paid to composite materials, and in particular those combining soft and hard phases. In this work, a systematic procedure is followed for machining micropillars of diameters ranging from 1 to 4μm in a WC-Co composite with a WC mean grain size around 1μm, by means of focused ion beam milling. In-situ uniaxial compression of the micropillars and subsequent field emission scanning electron microscopy inspection were conducted. Clear size effects are evidenced. Smaller test specimens (probe size approaching the mean WC size) exhibit deformation/failure mechanisms observed for WC crystals; while for bigger sample sizes, the mechanical response involves several mechanisms directly linked with the microstructural characteristics of the bulk-like cemented carbide material. On the other hand, independent of micropillar size, carbide-carbide or carbide-binder interfaces are found to be preferential sites for nucleation of critical damage events.

A comparison of quality control methods for scratch detection on polished metal surfaces

Scratch detection and the location of the scratch on the surface is important in the quality control of multilayered, functional and polished surfaces. Visual examination in good lighting conditions has been previously used to detect scratches, but interest to see finer scratches and their location should consider use of the optical microscope, and compare it with other imaging methods at the same magnification. Stainless steel was polished, scratched and then one specific location analyzed at the same magnification with all methods to determine the level of scratch detection. Atomic force microscopy, as the technique with a higher resolution, was used to determine the mean depth of every scratch as a reference. An image was then recorded with the different techniques and the number of visible scratches counted. Profilometry did not clearly identify scratches due to limitation of the 2 μm probe size. Light microscopy provided the fastest and most appropriate technique for quality control, detecting 70% of the scratches. Scanning electron microscopy only showed 35% of the scratches at the same magnification, but provided a good 2-D image of the scratch and the resulting metal pile-up.

Investigating dye performance and crosstalk in fluorescence enabled bioimaging using a model system.

Detailed imaging of biological structures, often smaller than the diffraction limit, is possible in fluorescence microscopy due to the molecular size and photophysical properties of fluorescent probes. Advances in hardware and multiple providers of high-end bioimaging makes comparing images between studies and between research groups very difficult. Therefore, we suggest a model system to benchmark instrumentation, methods and staining procedures. The system we introduce is based on doped zeolites in stained polyvinyl alcohol (PVA) films: a highly accessible model system which has the properties needed to act as a benchmark in bioimaging experiments. Rather than comparing molecular probes and imaging methods in complicated biological systems, we demonstrate that the model system can emulate this complexity and can be used to probe the effect of concentration, brightness, and cross-talk of fluorophores on the detected fluorescence signal. The described model system comprises of lanthanide (III) ion doped Linde Type A zeolites dispersed in a PVA film stained with fluorophores. We tested: F18, MitoTracker Red and ATTO647N. This model system allowed comparing performance of the fluorophores in experimental conditions. Importantly, we here report considerable cross-talk of the dyes when exchanging excitation and emission settings. Additionally, bleaching was quantified. The proposed model makes it possible to test and benchmark staining procedures before these dyes are applied to more complex biological systems.

Fully integrated silicon probes for high-density recording of neural activity.

Sensory, motor and cognitive operations involve the coordinated action of large neuronal populations across multiple brain regions in both superficial and deep structures. Existing extracellular probes record neural activity with excellent spatial and temporal (sub-millisecond) resolution, but from only a few dozen neurons per shank. Optical Ca2+ imaging offers more coverage but lacks the temporal resolution needed to distinguish individual spikes reliably and does not measure local field potentials. Until now, no technology compatible with use in unrestrained animals has combined high spatiotemporal resolution with large volume coverage. Here we design, fabricate and test a new silicon probe known as Neuropixels to meet this need. Each probe has 384 recording channels that can programmably address 960 complementary metal-oxide-semiconductor (CMOS) processing-compatible low-impedance TiN sites that tile a single 10-mm long, 70 × 20-μm cross-section shank. The 6 × 9-mm probe base is fabricated with the shank on a single chip. Voltage signals are filtered, amplified, multiplexed and digitized on the base, allowing the direct transmission of noise-free digital data from the probe. The combination of dense recording sites and high channel count yielded well-isolated spiking activity from hundreds of neurons per probe implanted in mice and rats. Using two probes, more than 700 well-isolated single neurons were recorded simultaneously from five brain structures in an awake mouse. The fully integrated functionality and small size of Neuropixels probes allowed large populations of neurons from several brain structures to be recorded in freely moving animals. This combination of high-performance electrode technology and scalable chip fabrication methods opens a path towards recording of brain-wide neural activity during behaviour.

Flame exposure time on Langmuir probe degradation, ion density, and thermionic emission for flame temperature.

The paper examines the effect of exposure time of Langmuir probes in an atmospheric premixed methane-air flame. The effects of probe size and material composition on current measurements were investigated, with molybdenum and tungsten probe tips ranging in diameter from 0.0508 to 0.1651 mm. Repeated prolonged exposures to the flame, with five runs of 60 s, resulted in gradual probe degradations (-6% to -62% area loss) which affected the measurements. Due to long flame exposures, two ion saturation currents were observed, resulting in significantly different ion densities ranging from 1.16 × 1016 to 2.71 × 1019 m-3. The difference between the saturation currents is caused by thermionic emissions from the probe tip. As thermionic emission is temperature dependent, the flame temperature could thus be estimated from the change in current. The flame temperatures calculated from the difference in saturation currents (1734-1887 K) were compared to those from a conventional thermocouple (1580-1908 K). Temperature measurements obtained from tungsten probes placed in rich flames yielded the highest percent error (9.66%-18.70%) due to smaller emission current densities at lower temperatures. The molybdenum probe yielded an accurate temperature value with only 1.29% error. Molybdenum also demonstrated very low probe degradation in comparison to the tungsten probe tips (area reductions of 6% vs. 58%, respectively). The results also show that very little exposure time (<5 s) is needed to obtain a valid ion density measurement and that prolonged flame exposures can yield the flame temperature but also risks damage to the Langmuir probe tip.

Nanoparticle Regrowth Enhances Photoacoustic Signals of Semiconducting Macromolecular Probe for In Vivo Imaging.

Smart molecular probes that emit deep-tissue penetrating photoacoustic (PA) signals responsive to the target of interest are imperative to understand disease pathology and develop innovative therapeutics. This study reports a self-assembly approach to develop semiconducting macromolecular activatable probe for in vivo imaging of reactive oxygen species (ROS). This probe comprises a near-infrared absorbing phthalocyanine core and four poly(ethylene glycol) (PEG) arms linked by ROS-responsive self-immolative segments. Such an amphiphilic macromolecular structure allows it to undergo an ROS-specific cleavage process to release hydrophilic PEG and enhance the hydrophobicity of the nanosystem. Consequently, the residual phthalocyanine component self-assembles and regrows into large nanoparticles, leading to ROS-enhanced PA signals. The small size of the intact macromolecular probe is beneficial to penetrate into the tumor tissue of living mice, while the ROS-activated regrowth of nanoparticles prolongs the retention along with enhanced PA signals, permitting imaging of ROS during chemotherapy. This study thus capitalizes on stimuli-controlled self-assembly of macromolecules in conjunction with enhanced heat transfer in large nanoparticles for the development of smart molecular probes for PA imaging.

A study of GeV proton microprobe lens system designs with normal magnetic quadrupole

Abstract High energy proton irradiation has many applications to the study of radiation effects in semiconductor devices, biological tissues, proton tomography and space science. Many applications could be extended and enhanced by use of a high energy proton microprobe. However the design of a GeV proton microprobe must address significant challenges including beam collimation that minimizes ion scattering and the probe forming lens system for ions of high rigidity. Here we address the probe forming lens system design subject to several practical constraints including the use of non-superconducting normal magnetic quadrupole lenses, the ability to focus 1–5 GeV protons into 5 µm diameter microprobes and compatibility with the beam parameters of GeV proton accelerators. We show that 2, 3 and 4 lens systems of lenses with effective lengths up to 0.63 m can be employed for this purpose with a demagnification up to 58 and investigate the probe size limitations from beam brightness, lens aberrations and machining precision.

Apparent Anomalous Diffusion in the Cytoplasm of Human Cells: The Effect of Probes' Polydispersity.

This work, based on in vivo and in vitro measurements, as well as in silico simulations, provides a consistent analysis of diffusion of polydisperse nanoparticles in the cytoplasm of living cells. Using the example of fluorescence correlation spectroscopy (FCS), we show the effect of polydispersity of probes on the experimental results. Although individual probes undergo normal diffusion, in the ensemble of probes, an effective broadening of the distribution of diffusion times occurs-similar to anomalous diffusion. We introduced fluorescently labeled dextrans into the cytoplasm of HeLa cells and found that cytoplasmic hydrodynamic drag, exponentially dependent on probe size, extraordinarily broadens the distribution of diffusion times across the focal volume. As a result, the in vivo FCS data were effectively fitted with the anomalous subdiffusion model while for a monodisperse probe the normal diffusion model was most suitable. Diffusion time obtained from the anomalous diffusion model corresponds to a probe whose size is determined by the weight-average molecular weight of the polymer. The apparent anomaly exponent decreases with increasing polydispersity of the probes. Our results and methodology can be applied in intracellular studies of the mobility of nanoparticles, polymers, or oligomerizing proteins.

Linear shear rheology of aging β-casein films adsorbing at the air/water interface

In this work, the viscoelasticity of fragile β-casein films has been followed using different macro- and microrheological techniques. The modulus of the complex surface viscosity |η∗| varies with time, allowing for the monitoring of the protein adsorption and annealing. β-casein adsorption creates a soft glassy gel at the interface that experiences an aging process. Macrorheological experiments with multiple probe sizes in addition to microrheological experiments demonstrated the consistency of the surface rheological properties over a broad range of viscosities. Surface pressure measurements were performed to complement the characterization of the processes.

Characterization of the flow in a gas-solid bubbling fluidized bed by pressure fluctuation

Statistical, power spectral and chaos analysis methods were used to analyze pressure fluctuations in a bubbling fluidized bed. Effects of superficial gas velocity, static bed height, particle size and position of pressure probe on the flow behavior were investigated. It was shown that the flow behavior in terms of Kolmogorov entropy at the bottom of the bed was more complex than that at the upper part of the bed. Kolmogorov entropy decreased with increasing static bed height or particle size. In the range of 1.05<Ug/Umf<4.37, Kolmogorov entropy had a strong linear relationship with the average cycle frequency. The amplitude of pressure fluctuations increased with the superficial gas velocity and the static bed height. The average pressure increased linearly with the static bed height. The dominant frequency of pressure fluctuations in the bed decreased with the static bed height, but barely changed with the gas velocity when it reached a certain value. The changes of superficial gas velocity, static bed height, and particle size can be determined by the changes of the amplitude of pressure fluctuations, the average pressure and Kolmogorov entropy.

Microscale Mass Spectrometry Analysis of Extracellular Metabolites in Live Multicellular Tumor Spheroids.

Extracellular compounds in tumors play critical roles in intercellular communication, tumor proliferation, and cancer cell metastasis. However, the lack of appropriate techniques leads to limited studies of extracellular metabolite. Here, we introduced a microscale collection device, the Micro-funnel, fabricated from biocompatible fused silica capillary. With a small probe size (∼25 μm), the Micro-funnel can be implanted into live multicellular tumor spheroids to accumulate the extracellular metabolites produced by cancer cells. Metabolites collected in the Micro-funnel device were then extracted by a microscale sampling and ionization device, the Single-probe, for real-time mass spectrometry (MS) analysis. We successfully detected the abundance change of anticancer drug irinotecan and its metabolites inside spheroids treated under a series of conditions. Moreover, we found that irinotecan treatment dramatically altered the composition of extracellular compounds. Specifically, we observed the increased abundances of a large number of lipids, which are potentially related to the drug resistance of cancer cells. This study provides a novel way to detect the extracellular compounds inside live spheroids, and the successful development of our technique can benefit the research in multiple areas, including the microenvironment inside live tissues, cell-cell communication, biomarker discovery, and drug development.

Theory and Practice of Diffractometry on Single Tungsten Atoms using Electron Microscope Pixel Array Detectors

What does the diffraction pattern from a single atom look like? How does it differ from the scattering from long range potential? With the development of new high-dynamic range pixel array detectors to measure the complete momentum distribution, these questions have immediate relevance for designing and understanding momentum-resolved imaging modes. We explore the asymptotic limits of long range and short range potentials. We use a simple quantum mechanical model to explain the general and asymptotic limits for the probability distribution in both and real and reciprocal space. Features in the scattering potential much larger than the probe size cause the bright-field disk to deflect uniformly, while features much smaller than the probe size, instead of a deflection cause a redistribution of intensity within the bright-field disk. Because long range and short range features are encoded differently in the diffraction pattern, it is possible to separate their contributions in differential phase contrast (DPC) or Center-of-Mass (CoM) imaging. The shape profiles for atomic resolution CoM imaging are dominated by the shape of the probe gradient and not the highly-singular atomic potentials or their local fields. Instead, only the peak height shows an atomic-number sensitivity, whose precise dependence is determined by the convergence angle. At lower convergence angles, the contrast oscillates with increasing atomic number, similar to bright field imaging. The range of collection angles impacts DPC and CoM imaging differently, with CoM being more sensitive to the upper cutoff limit, while DPC is more sensitive to the lower cutoff.

Use of the Bohm’s formula and its analogues in probe diagnostics

Simple algorithms are developed to proceed the probe characteristics in a number of limiting regimes when the characteristic probe size, r p, is relatively large (r p > 103rD). It relates both to steady plasmas and to movement with the directed velocity, u. We consider the cases of collision-free (the Knudsen number, Kn≫1) and collisional (Kn≪1) plasmas. The majority of the proposed algorithms are tested in practice and confirm their reliability.

Multimodal Characterization of the Morphology and Functional Interfaces in Composite Electrodes for Li-S Batteries by Li Ion and Electron Beams.

We report the characterization of multiscale 3D structural architectures of novel poly[sulfur-random-(1,3-diisopropenylbenzene)] copolymer-based cathodes for high-energy-density Li-S batteries capable of realizing discharge capacities >1000 mAh/g and long cycling lifetimes >500 cycles. Hierarchical morphologies and interfacial structures have been investigated by a combination of focused Li ion beam (LiFIB) and analytical electron microscopy in relation to the electrochemical performance and physicomechanical stability of the cathodes. Charge-free surface topography and composition-sensitive imaging of the electrodes was performed using recently introduced low-energy scanning LiFIB with Li+ probe sizes of a few tens of nanometers at 5 keV energy and 1 pA probe current. Furthermore, we demonstrate that LiFIB has the ability to inject a certain number of Li cations into the material with nanoscale precision, potentially enabling control of the state of discharge in the selected area. We show that chemical modification of the cathodes by replacing the elemental sulfur with organosulfur copolymers significantly improves its structural integrity and compositional homogeneity down to the sub-5-nm length scale, resulting in the creation of (a) robust functional interfaces and percolated conductive pathways involving graphitic-like outer shells of aggregated nanocarbons and (b) extended micro- and mesoscale porosities required for effective ion transport.