Spherical Probe Research Articles

Determining effective refractive index and elasticity of nanoscale metal - thin, soft polymer bilayers using interference signatures of a glass probe

HypothesisThin metal films like silver (Ag) and gold (Au) on PDMS are perfect candidates for surface-enhanced Raman spectroscopy (SERS) active substrates whose optical and mechanical properties are often subjected to precise tuning. Measurement of such properties often requires multiple sophisticated experimental techniques and numerical analysis. When depositing a nanoscale thin metal film like Ag or Au on the polymer surface, the refractive index and elastic modulus of this bilayer structure could vary with the metal deposition time and properties of soft substrates. ExperimentsIn this work, we demonstrate a single experimental methodology to measure the refractive index and elasticity of thin metal films coated on PDMS. Using Dual-Wavelength Reflection Interference Contrast Microscopy (DW-RICM) measurements of a spherical glass probe of known shape, the refractive indices of Ag/PDMS and Au/PDMS substrates of varying metal deposition time, PDMS elasticity, and PDMS coating thickness are extracted corresponding to two different wavelengths. FindingsThe extracted refractive indices of metal/PDMS substrates decrease with increasing metal deposition time, decreasing PDMS elasticity, and increasing PDMS coating thickness. The extracted refractive indices are found to be in good agreement with corresponding UV/VIS spectroscopy measurements. Lastly, their elastic moduli are also obtained using Hertz's theory on the observed contact radius of the glass sphere on the aforementioned substrates.

Polymer optical fiber detector adapted for low-dose-rate gamma-ray detection.

In this Letter, a polymer optical fiber (POF) detector with a convex spherical aperture microstructure probe is designed for low-energy and low-dose rate gamma-ray detection. Simulation and experimental results demonstrate that this structure has a higher optical coupling efficiency and that the angular coherence of the detector depends strongly on the depth of the probe micro-aperture. By modeling the relationship between angular coherence and micro-aperture depth, the optimal depth of the micro-aperture is determined. The sensitivity of the fabricated POF detector is 701 cps at 59.5-keV gamma-ray of 2.78 µSv/h and the maximum percentage error of the average count rate at different angles is 5.16%.

Influence of cantilever tip geometry and contact model on AFM elasticity measurement of cells.

We have measured the elastic properties of live cells by Atomic Force Microscope (AFM) using different tip geometries commonly used in AFM studies. Soft 4-sided pyramidal probes (spring constant = 12 mN/m and 30 mN/m, radius 20 nm), 3-sided pyramidal probes (spring constant = 100 mN/m, radius of curvature 65-75 nm), flat (circular) probes (spring constant = 63 mN/m, radius 290 nm) and spherical probes (spring constant = 43 mN/m, radius 5 μm) have been used. Cells (3T3 fibroblasts) having elastic moduli around 0.5 kPa were investigated. We found that cell measured stiffness shows a systematic dependence on tip geometry: the sharper the tip, the higher the average modulus values. We hypothesize that the blunter the tip, the larger the contact area over which the mechanical response is measured or averaged. If there are small-scale stiffer areas (like actin bundles) they will be easier to pick up by a sharp probe. This effect can be seen in the wider distribution of the histograms of the measured elastic moduli on cells. Furthermore, non-linear responses of cells may be present due to the high average pressures applied by sharp probes, which would lead to an overestimation of the Young's modulus. Pressure versus contact radius simulations for the different tip geometries for a 0.5 kPa sample suggested similar average pressure for Bio-MLCTs, PFQNM and cut tips, except spherical tips that showed much lower average pressure at the same 400 nm indentation. However, real data of the cells suggested different results. Using the same indentation depth (400 nm) PFQNM and Bio-MLCTs showed similar average pressure and it decreased for cut and spherical tips. The calculated contact area at 400 nm cell indentation, using the obtained apparent Young's modulus for each tip geometry, showed the following distribution: Bio-MLCTs < PFQNM < cut << spherical. In summary, tip geometry as well as average pressure and tip-sample contact area are important parameters to take into account when measuring mechanical properties of soft samples. The larger the tip radius, the larger the contact area that will lead to a more evenly distribution of the applied pressure.

Preparation of a spherical biochar colloidal probe and its application in deciphering the mechanism of biochar mitigating membrane fouling

To better unravel biochar’s interface behavior and mitigation mechanism on membrane fouling, spherical biochar colloidal probes were prepared by adhering microspheres to the free end of the probe cantilever. The prepared colloidal probes were used to measure the interaction forces between the membrane and foulant/biochar and between the foulant and foulant/biochar by atomic force microscopy (AFM). The study investigated the differences in physicochemical properties of biochars and their mitigating effects on membrane fouling caused by bovine serum albumin (BSA). Results indicated that dosing biochar strengthened the electrostatic repulsion between BSA and membranes, thereby, mitigating the adhesion or deposition of BSA on the membrane surface. Additionally, spherical biochar (SBC) and hydrochar (HC) exhibited better membrane fouling mitigation than conventional biochar (CBC) due to better physicochemical properties, adsorption capacity, and a more porous fouling layer structure composed of microparticles. Importantly, the stronger adhesion force of SBC-PVDF (0.90 mN/m) than BSA-PVDF (0.50 mN/m) alleviated membrane fouling in the initial stage of the filtration, and the adhesion force of SBC-BSA (0.049 mN/m) alleviated membrane fouling in the later stage, resulting in higher water flux. The interaction force between mature SBC and BSA was comparable to that between BSA and BSA (0.14 mN/m) and stronger than that between original SBC and BSA (0.049 mN/m), implying further membrane fouling mitigation.

Orientation-dependent indentation reveals the crosslink-mediated deformation mechanisms of collagen fibrils.

The spatial arrangement and interactions of the extracellular matrix (ECM) components control the mechanical behavior of tissue at multiple length scales. Changes in microscale deformation mechanisms affect tissue function and are often hallmarks of remodeling and disease. Despite their importance, the deformation mechanisms that modulate the mechanical behavior of collagenous tissue, particularly in indentation and compression modes of deformation, remain poorly understood. Here, we develop an integrated computational and experimental approach to investigate the deformation mechanisms of collagenous tissue at the microscale. While the complex deformation arising from indentation with a spherical probe is often considered a pitfall rather than an opportunity, we leverage this orientation-dependent deformation to examine the shear-regulated interactions of collagen fibrils and the role of crosslinks in modulating these interactions. We specifically examine tendon and cervix, two tissues rich in collagen with quite different microstructures and mechanical functions. We find that interacting, crosslinked collagen fibrils resist microscale longitudinal compressive forces, while widely used constitutive models fail to capture this behavior. The reorientation of collagen fibrils tunes the compressive stiffness of complex tissues like cervix. This study offers new insights into the mechanical behavior of collagen fibrils during indentation, and more generally, under longitudinal compressive forces, and illustrates the mechanisms that contribute to the experimentally observed orientation-dependent mechanical behavior. STATEMENT OF SIGNIFICANCE: Remodeling and disease can affect the deformation and interaction of tissue constituents, and thus mechanical function of tissue. Yet, the microscale deformation mechanisms are not well characterized in many tissues. Here, we develop a combined experimental-computational approach to infer the microscale deformation mechanisms of collagenous tissues with very different functions: tendon and cervix. Results show that collagen fibrils resist microscale forces along their length, though widely-used constitutive models do not account for this mechanism. This deformation process partially modulates the compressive stiffness of complex tissues such as cervix. Computational modeling shows that crosslink-mediated shear deformations are central to this unexpected behavior. This study offers new insights into the deformation mechanisms of collagenous tissue and the function of collagen crosslinkers.

A novel DNA detection using spherical identification probe and strand displacement reaction-initiated silver nanocluster switch.

Herein, we developed a novel fluorescent assay using spherical identification probes and toehold-mediated strand displacement reaction-initiated silver nanoclusters (AgNCs) "on-off" signal switch. In this strategy, the target was captured by the spherical probes to induce the activity of exonuclease III (Exo III), catalyzing the cyclic cleavage of substrates to produce a mass of trigger strands. After magnetic bead separation, the intermediates in the supernatant activated downstream toehold-mediated strand displacement reaction to change the structure of silver nanocluster templates, leading to fluorescence intensity reduction. Furthermore, it is demonstrated that the application of spherical identification probes could reduce the signal leakage and the limit of detection. In addition, AgNCs with perfect optical property were ingeniously combined to realize signal output, which reduced the cost and time of synthesis. Under the optimal conditions, the sensing method displayed a good linear range from 250pM to 25nM with a detectable minimum concentration of 250pM. And the practical application potential in complex biological matrices was also evaluated. Considering these advantages, this constructed strategy opens a new path for nucleic acid detection with better performance. A simple, label- and hairpin-free fluorescent system based on spherical identification probe and toehold-mediated strand displacement reaction-initiated silver nanoclusters (AgNCs) "on-off" signal switch was successfully constructed to detect target DNA.

Syndesmosis Instability

The syndesmosis is one of important stabilizer of the ankle joint and consists of a complex ligamentous structure: the anterior inferior tibiofibular ligament; the interosseous ligament; the posterior inferior tibiofibular and the transverse ligaments. The posterior syndesmosis plays the most important role providing 40–45% of the resistance to diastasis, while the AITFL provides around 35%. Major injuries of two of the syndesmosis components represent a loss of more than 50% of resistance to diastasis and may result in instability. Syndesmosis injury or a high ankle sprain, is a frequent athletic trauma accounting for 1% to 18% of all ankle sprains, 17 to 84% of all sport injuries, and 10% of all ankle fractures. Most of the mechanism injury is external rotation injury. A radiographic study suggested that about 20.3% of ankle sprains were combined with a syndesmosis injury. Without proper treatment, the chronic syndesmosis injury remains symptomatic for more than 6 months after the initial trauma, with persistent pain, functional disability, and early-stage ankle arthritis. Normally, syndesmosis widens 1 mm during normal gait. Widening of syndesmosis more than 1 mm can reduce tibiotalar contact surface about 42%. The degenerative changes can occur if the lateral talar shift more than 2 mm. Clinical tests for syndesmosis injuries are external rotation stress test, Cotton test, dorsiflexion-compression test, squeeze test, crossed-leg test, fibular translation and AITFL palpation. Standard radiographs are part of ankle trauma evaluation, especially for fracture exclusion, applying the Ottawa criteria. Computerized tomography (CT) scan is a useful tool to assess tibiofibular diastasis, fibular rotation and joint asymmetry, but shows low sensitivity. MRI is showing very high sensitivity and specificity in identification of syndesmotic injuries. For stable lesion can be treated with conservative means, including non weight bearing or protected weight bearing with a cast or walking boot and a rehabilitation protocol. An unstable lesion requires a surgical procedure to avoid long-term disability and chronic instability. Ankle arthroscopy remains essential for diagnosis and treatment. With accessory tools that measure the syndesmosis gap (e.g. 3.5 mm shaver canula or a metallic tools). Passage of a 3 mm spherical probe during external rotation indicates very high likelihood of rupture of both the AITFL and the IOL. Also, concomitant intra-articular pathologies (osteochondral lesions, other ligamentous rupture or loose bodies) can be presented, with 19% needs to be addressed, reinforcing the role of arthroscopy not only for diagnosis but also for treatment. It is also an excellent tool to evaluate anatomic reduction and residual diastasis.

Spherical Nucleic Acid Probe Based on 2′-Fluorinated DNA Functionalization for High-Fidelity Intracellular Sensing

Traditional spherical nucleic acids (SNAs) based on gold nanoparticles (AuNPs) assembled through Au-S covalent bonds are widely used in DNA-programmable assembly, biosensing, imaging, and therapeutics. However, biological thiols and other chemical substances can break the Au-S bonds and cause response distortion during the application process, specifically in cell environments. Herein, we report a new type of SNAs based on 2'-fluorinated DNA-functionalized AuNPs with excellent colloidal stability under high salt conditions (up to 1 M NaCl) and over a broad pH range (1-14), as well as resistance to biothiols. The fluorinated spherical nucleic acid probe (Au/FDNA probe) could detect targeted cancer cells with high fidelity. Compared to the traditional thiolated DNA-functionalized AuNP probe (Au-SDNA probe), the Au/FDNA probe exhibited a higher sensitivity to the target and a lower signal-to-background ratio. Furthermore, the Au/FDNA probe could discriminate target cancer cells in a mixed culture system. Using the proposed FDNA functionalization method, previously developed SNAs based on AuNPs could be directly adapted, which might open a new avenue for the design and application of SNAs.

Ambient ms profiling of meningiomas: intraoperative oncometabolite-based monitoring

The primary method of initial treatment of meningiomas is radical neurosurgical intervention. Various methods of intraoperative diagnostics currently in development aim to improve resection efficiency; we focus on methods based on molecular profiling using ambient ionization mass spectrometry. Such methods have been proven effective on various tumors, but the specifics of the molecular structure and the mechanical properties of meningiomas raise the question of applicability of protocols developed for other conditions for this particular task. The study aimed to compare the potential clinical use of three methods of ambient ionization in meningioma sample analysis: spray from tissue, inline cartridge extraction, and touch spherical sampler probe spray. To this end, lipid and metabolic profiles of meningioma tissues removed in the course of planned neurosurgical intervention have been analyzed. It is shown that in clinical practice, the lipid components of the molecular profile are best analyzed using the inline cartridge extraction method, distinguished by its ease of implementation and highest informational value. Analysis of oncometabolites with low molecular mass is optimally performed with the touch spherical sampler probe spray method, which scores high in both sensitivity and mass-spectrometric complex productivity.

Spherical probe for the thermophysical characterization of regoliths for planetary exploration using frequency methods

The objective of this paper is to analyse the capability of a spherical thermoprobe, recently proposed as a 3D heat flux sensor for regoliths, and additionally to characterize the thermophysical properties of regoliths. The sensor is based on the spherical structure of a Mars wind sensor. The characterization is carried out using frequency methods. Extensive experimental results have been obtained with eight regolith simulants made of glass microbeads. Errors in thermal conductivity and diffusivity are smaller than ±7%, for these simulants. • A thermoprobe is used to characterize the thermophysical properties of regoliths. • The spherical thermoprobe uses frequency methods. • The probe measures the thermal impedance in the frequency domain. • The thermoprobe measures the thermal conductivity and diffusivity of the regoliths.

Rate effects in detachment of a spherical probe from fibrillar adhesive surfaces

Rate effects in fibrillar adhesive surfaces have received increasing attention recently. However, the requirement for taking into account the viscoelastic behavior of the material, combined with the backing layer coupling, complicates the theoretical treatment. As a result, the role of rate effects, particularly on the array level, remains unclear. This work focuses on a general problem: a rigid spherical probe is detached from a viscoelastic fibrillar adhesive surface at a certain velocity. A theoretical framework is proposed based on the Lee & Radok corresponding principle and the Schapery approximation for crack initiation in viscoelastic solids. The fibril force across the array is explicitly determined during the dynamic detaching process. Simulation results reveal the influence of rate effects on the adhesion response, the preload dependence, and the effective work of adhesion of the fibrillar surface. As expected, the adhesion force monotonically increases with the retraction velocity. An interesting phenomenon is observed at intermediate velocities that modest preload is favorable to the pull-off force while an overlarge one would have an adverse effect. The pull-off force would finally approach a lower steady-state constant at a sufficiently high preload value. Most significantly, it is found that the dependence of the effective work of adhesion on the crack velocity is almost independent of the basic properties of the fibrillar surface when traversing typical parameter space. This indicates that the contribution of the viscoelastic-induced adhesion enhancement can be approximately decoupled as a multiplicative term in the overall effective work of adhesion. For a sufficiently large probe radius, this rate-dependent characteristic can be well captured by the continuum theory of viscoelastic crack propagation.

A New Technique to Infer Plasma Density, Flow Velocity, and Satellite Potential From Ion Currents Collected by a Segmented Langmuir Probe

Compared with other types of Langmuir probes, segmented probes are arguably the least often used, to diagnose the state of plasma. With linear dimensions of the order of centimeters, these probes would induce perturbations, which would make them impractical in many laboratory plasma experiments. Their size, and the fact that they consist of several equipotential faces or “segments,” from which individual currents are collected, introduces additional complexities in the construction of inference techniques for their characteristics. In this work, we focus on the use of spherical segmented probes mounted on a satellite and present new techniques to infer plasma (ion) densities, flow velocities, and satellite potentials, from currents collected by two segmented probes biased to two different fixed potentials relative to a spacecraft. This is done by carrying out 3-D kinetic self-consistent particle-in-cell (PIC) simulations to compute the response of a probe to space plasma under different environment conditions of relevance to satellites in low-Earth orbit (LEO) at low and mid-latitudes. Computed currents and the corresponding known plasma and satellite parameters used as input in the simulations are then used to create a solution library with which regression-based inference models are constructed, following standard machine learning techniques. The models trained with a subset of our synthetic dataset are found to yield excellent agreement with data in distinct validation sets. The models constructed with synthetic data are then applied to in situ measurements made with segmented Langmuir probes mounted on the Proba-2 satellite, and the inferences are compared with densities reported on the Proba-2 data portal. The advantage of our approach is that it readily produces uncertainty margins that are specifically related to the inference technique used.

Molecular dynamics analysis of friction-triggering process with spherical probe

Molecular dynamics simulation with embedded atom method/Finnis–Sinclair potential function was utilised to study the friction properties of the friction-triggering process at the mesoscopic scale. The sliding friction process of a spherical probe with different diameters on the surface of a single-crystal aluminum matrix was simulated and the influences of sliding friction on the atomic behaviour of the surface under different contact conditions were analysed. The relationship between contact force and friction coefficient with spherical diameter was studied. The research shows that the plastic groove, normal force and friction force increase with the increase in probe diameter in the sliding friction process. The contribution of increasing spherical diameter to normal force is greater than that of friction force. The coefficient of friction varies with the ratio of the actual contact area to the normal force. After the running-in process is stable, the friction coefficient fluctuates around a certain value as theoretically verified by the two-term friction law. The increase in the diameter of the spherical probe leads to the increase in the number of dislocation atoms in the workpiece and the formation of dislocation rings, which result in the difference in the sliding friction process under indenters with different diameters. The results provide valuable reference for friction-triggering measurement based on 3D nanometre probes such as friction force microscopy.

Trojan Horse Delivery of Spherical Nucleic Acid Probes into the Cytoplasm for High-Fidelity Imaging of MicroRNAs.

We report a Trojan horse strategy to efficiently deliver the spherical nucleic acid probes (namely, nanoflares) into the cytoplasm for microRNA (miRNA) imaging with high fidelity, breaking through the cytoplasmic transport dilemma of RNA probes in living cells. The nanoflare is encapsulated into a "Trojan horse" consisting of zwitterionic choline phosphates (CPs) and acid-degradable crosslinkers; the former effectively promotes cell uptake and the latter triggers instantaneous liberation of the nanoflare probes from the lysosome to the cytoplasm. The exposed nanoflares in the cytoplasm can be lightened up by the target miRNAs specifically. Compared with the conventional nanoflares as well as the improved ones in previous reports, the "Trojan horse" nanoflares avoid nuclease degradation and thiol displacement during the delivery process, providing unprecedentedly high accuracy for intracellular miRNA imaging.

MoloVol: an easy-to-use program for analyzing cavities, volumes and surface areas of chemical structures.

Cavities are a ubiquitous feature of chemical structures encountered in various fields ranging from supramolecular chemistry to molecular biology. They are involved in the encapsulation, transport and transformation of guest molecules, thus necessitating a precise and accessible tool for estimating and visualizing their size and shape. MoloVol, a free user-parametrizable open-source software, developed for calculating a range of geometric features for both unit-cell and isolated structures, is presented here. MoloVol utilizes up to two spherical probes to define cavities, surfaces and volumes. The program was optimized by combining an octree data structure with voxel-partitioned space, allowing for even high-resolution protein structure calculations on reasonable timescales. MoloVol comes with a user-friendly graphic interface along with a command-line interface for high-throughput calculations. It was written in C++ and is available on Windows, macOS and Linux distributions.

Rotational and translational microrheology from shape-anisotropic particles

In this work, we report measurements of the mean squared angular and translational displacements of a colloidal dumbbell immersed in a viscoelastic fluid using digital microscopy. From the mean squared displacements, we obtain the mechanical properties of the media. Both angular and translational motions provide the same viscoelastic complex modulus and agree with that obtained from the translational motion of a spherical probe particle.

An Off-Axis Measuring Method of Structural Parameters for Lenslet Array

Aiming at the problem that the vertex detection method is difficult to deal with the high-efficiency detection of the large-scale spherical lenslet array, a contact off-axis measuring method is proposed and the measurement accuracy and detection efficiency are verified by experiments. Firstly, by analyzing the 3D model of the relationship between a spherical lens and probe of profilometer, the mathematical model of probe trajectory arc is established based on the off-axis trajectory characteristics of the spherical lenslet array. Then, the error mechanism under the off-axis condition is analyzed, and a mathematical algorithm is proposed to restore the structural parameters at the main optical axis of the lens by using the process design value of the unit lens aperture. Finally, a comparative experiment is carried out between the off-axis detection method and vertex detection method. The experimental results demonstrate that: Compared with the coaxial detection method, the relative errors of the measured lens curvature radius R0 and the lens vector height f0 under the off-axis detection method are 1.71% and 1.95%, respectively. Under the sampling measurement scale, the detection efficiency of the off-axis detection method is 41 times higher than that of vertex detection method.

Friction between MXenes and other two-dimensional materials at the nanoscale

Two-dimensional (2D) materials have unique friction properties that are different from their 3D counterparts. MXenes, a large family of 2D transition metal carbides, carbonitrides, and nitrides, have recently attracted attention as solid lubricants on the macroscale. Here we experimentally investigate the friction of Ti3C2Tx and Ti2CTx MXenes against Ti3C2Tx and Ti2CTx MXenes, graphene, and MoSe2 at the nanoscale, using atomic force microscopy (AFM). Ti3C2Tx and Ti2CTx MXene coated SiO2 spherical AFM probes were used to slide against films of these materials with varying number of monolayers deposited on the substrate. We have found that over the 15 nm sliding distance the measured nanoscale coefficients of friction (COFs) for all the investigated 2D interfaces are below 0.01. At the same time, hydrogen bonding involving -O- and –OH surface terminating groups on MXenes induced higher friction forces for the MXene/MXene contacts compared to other contacts. Moreover, a less significant number-of-monolayers effect on the friction was observed for MXenes due to their thicker monolayers compared with other 2D materials in this study. These results further contribute to our understanding of the mechanisms of friction of MXenes and reveal the potential of MXenes as tunable lubricants at the nanoscale.

Modulus and adhesion of Sylgard 184, Solaris, and Ecoflex 00‐30 silicone elastomers with varied mixing ratios

AbstractTwo‐part, commercial silicone elastomers are used in a variety of fundamental soft materials research and industrial applications due to their wide availability, ease of use, low cost, and mechanical tunability. This work seeks to create a library of moduli for three common elastomer systems with varied mixing ratios: Sylgard 184, Solaris, and Ecoflex 00–30, as well as provide a comparison of their adhesive properties. Shear storage moduli are quantified using parallel plate oscillatory shear rheology. The work of debonding is measured with spherical probe adhesion testing, and the static, advancing, and receding contact angles are measured via goniometer. Sylgard 184 can have shear moduli ranging from ~0.5 kPa‐620 kPa, Solaris from ~0.6 kPa‐175 kPa, and EF from ~1.3 kPa‐35 kPa measured at a frequency of 0.01 rad/s. In general, increasing mixing ratios creates softer samples. Additionally, softer samples are universally more adhesive, regardless of the material system. When comparing the different material systems, Sylgard 184 is generally the most adhesive, followed closely by Solaris, and then by Ecoflex 00–30. Our study offers a baseline dataset of modulus values and comparative adhesion to help researchers determine an appropriate commercial silicone for their application.

The lightweight spherical samplers for simplified collection, storage, and ambient ionization of drugs from saliva and blood

The continuous monitoring of health conditions before, during, and after spaceflight is an important task in gravitational physiology. Thus a simple, non-invasive method for biological samples collection is required, but the specific limitations, such as weight and volume restrictions, limit the variety of suitable samplers. The physiological changes exist at microgravity (μG) conditions and could influence drug pharmacokinetics. Here we present the application of lightweight spherical sampler probes for the simplified sampling of human saliva with further detection of exogenous small molecules by the ambient mass spectrometry. The rigidity and spherical form of the sampler probes allow collecting saliva smears or biological fluids without additional instruments and improve the stability of the ionization process leading to the increased sensitivity of the analysis. The detection and quantitation of acetaminophen, which is used as a model substance, was proved to demonstrate the analytical capabilities of the proposed method to the saliva smears or whole blood samples even after long-term storage at room temperature. The further investigation of drug pharmacokinetic at μG conditions might be provided by means of proposed samplers.