Silicon Nitride Cantilever Research Articles

Comparative Evaluation of Interaction Force Characteristics for the Lipopolysaccharide of Yersinia pseudotuberculosis and Antibodies by Optical Trapping and Atomic Force Microscopy

Optical tweezers and atomic force microscopy were used for comparative evaluation of the interaction force between the lipopolysaccharide of Yersinia pseudotuberculosis and monoclonal antibodies. This paper discusses the peculiarities of two methods which allow determining significant differences in the values of the measured force required to rupture the interaction of probe sensitized by lipopolysaccharide (polystyrene microsphere for optical tweezers and silicon nitride cantilever for atomic force microscopy) with substrate (glass and mica, respectively) covered with monoclonal antibodies. In atomic force microscopy, the cantilever slides along the substrate for some time after the piezo stage is brought to a stop, causing changes in the spatial structure of sensitins and, therefore, redistribution of multiple bonds between the lipopolysaccharide agglomerate and antibodies. No significant displacement of the microsphere along the substrate occurs when an optical tweezers setup is used, and, unlike atomic force microscopy, the breaking of a complex bond between lipopolysaccharide and complementary antibodies is recorded in the form of a single and short-term (1–2 ms) leap of the photodetector signal employing optical tweezers. The recorded values of the force required to rupture the interaction measured by both methods are relative and vary depending on the chosen experimental conditions. It is shown that the non-specific component of the force needed to break the interaction measured by atomic force microscopy is significantly higher than that determined with optical tweezers.

Mechanical and physicochemical characteristics of sub-millimeter and macrobubbles: Insights from AFM analysis, zeta potential measurements and rise velocity

This study presents the change in mechanical and physicochemical behaviour of macrobubbles and sub-millimeter bubbles with respect to pH. While macrobubbles conventionally range from 100 μm to 2 mm in diameter, this study focuses on the comparatively less-explored sub-millimeter bubble range, centered around a median diameter of 500 μm. The difference in sub-millimeter bubbles (500 μm) compared to their larger counterparts (1100 μm) within macrobubble size range were evidenced through atomic force microscopy (AFM) analysis, zeta potential measurements, and rise velocity experiments. The adhesion force and energy between bubbles and the silicon nitride cantilever tip showed a decreasing trend with increasing pH, notably diminishing by about 50% beyond pH 9. Although no significant differences were statistically revealed between the two bubble sizes at lower pH, the adhesion force and energy were consistently smaller for macrobubble compared to sub-millimeter bubble at higher pH beyond pH 9. This finding suggests that the electrical double layer (EDL) interactions are influenced by the specific surface area, particularly in the alkaline region. Zeta potential measurements exhibited a cubic trend, with an isoelectric point at pH 3.5 and a minimum zeta potential at pH 11. The study also depicted a similar trend in the rise velocity of bubbles, suggesting a direct relationship between bubble stiffness and its rise velocity. Therefore, changes in pH affected the bubbles' properties, while on the other hand, certain physicochemical properties are also influenced by bubble sizes.

Модель контакта и оценка молекулярной cоставляющей силы трения

According to the level of the measurement scale, the friction force changes its nature and is determined by different depend-encies. The paper views a procedure for determining a friction force molecular component based on the evaluation of specif-ic shearing resistance of molecular links un-der the elastic interaction of a silicon nitride cantilever needle having a steel sample, used for scanning a section of a sample surface in the nanometer range with an atomic force microscope (AFM) «FemtoScan» under low loads. A sensitive element (measuring device) of an atomic force microscope acts as a force sensor for measuring both: a normal load very roughly, and a change in the force, applied to the cantilever under known stiffness, including the value of the cantilever rod form alteration. It also changes the load on the sensitive element (to assess the mo-lecular component of the friction force, the route of the «smoothest» surface itself was chosen). The paper also provides an analytical assessment of the contact interaction parameters of a cantilever needle in a nano-scale, rep-resented as a spheri-cal indenter, with an elastic half-space as a surface under study, based on the Hertz theory. Analysis of the calculation and experiment data on measuring the resistance force of the indenter during scanning of the surface under study, showed good convergence of the results with a deviation of even values from the experimental data of no more than 7,5 %. Calculations using the established formulas showed that with an increase in the load on the contact at the nanoscale, the coefficient of friction decreases due to a faster growth of contact spots in the elastic state (provided that angularity of inequalities related to sub-roughness remains constant), which was also confirmed in the course of the experiment.

Half-wet nanomechanical sensors for cellular dynamics investigations

Testing devices based on cell tracking are particularly interesting as diagnostic tools in medicine for antibiotics susceptibility testing and in vitro chemotherapeutic screening.In this framework, the application of nanomechanical sensors has attracted much attention, although some crucial aspects such as the effects of the viscous damping, when operating in physiological conditions environment, still need to be properly solved. To address this problem, we have designed and fabricated a nanomechanical force sensor that operates at the interface between liquid and air.Our sensor consists of a silicon chip including a 500 μm wide Si3N4 suspended membrane where three rectangular silicon nitride cantilevers are defined by a lithographically etched gap. The cantilevers can be operated in air, fully immersed in a liquid environment and in half wetting condition, with one side in contact with the solution and the opposite one in air. The formation of a water meniscus in the gap prevents the leakage of medium to the opposite side, which remained dry and is used to reflect a laser to measure the cantilever deflection. This configuration enables to keep the cells in physiological environment while operating the sensor in dry conditions.The performance of the sensor has been applied to monitor the motion and measures the forces developed by migrating breast cancer cell. The functionalization of one side of the cantilever and the use of a purposely designed chamber of measurements enable the confinement of the cell only on one side of the cantilever.Our data demonstrate that this approach can distinguish the adhesion and contraction forces developed by different cell lines and may represents valuable tool for a fast and quantitative in-vitro screening of new chemotherapeutic drugs targeting cancer cell adhesion and motility.

Atomic force microscopy comparative analysis of the surface roughness of two posterior chamber phakic intraocular lens models: ICL versus IPCL

BackgroundTo compare the anterior surface roughness of two commercially available posterior chamber phakic intraocular lenses (IOLs) using atomic force microscopy (AFM).MethodsFour phakic IOLs were used for this prospective, experimental study: two Visian ICL EVO+ V5 lenses and two iPCL 2.0 lenses. All of them were brand new, were not previously implanted in humans, were monofocal and had a dioptric power of − 12 diopters (D). The anterior surface roughness was assessed using a JPK NanoWizard II® atomic force microscope in contact mode immersed in liquid. Olympus OMCL-RC800PSA commercial silicon nitride cantilever tips were used. Anterior surface roughness measurements were made in 7 areas of 10 × 10 μm at 512 × 512 point resolution. The roughness was measured using the root-mean-square (RMS) value within the given regions.ResultsThe mean of all anterior surface roughness measurements was 6.09 ± 1.33 nm (nm) in the Visian ICL EVO+ V5 and 3.49 ± 0.41 nm in the iPCL 2.0 (p = 0.001).ConclusionIn the current study, we found a statistically significant smoother anterior surface in the iPCL 2.0 phakic intraocular lenses compared with the VISIAN ICL EVO+ V5 lenses when studied with atomic force microscopy.

Corneal stromal roughness after VisuMax and Intralase femtosecond laser photodisruption: An atomic force microscopy study.

PurposeTo compare the induced corneal stromal bed roughness measured with atomic force microscopy (AFM) after LASIK flap creation with the IntraLase 60 kHz and the VisuMax femtosecond laser platforms.MethodsThree freshly enucleated porcine eyes were operated with each femtosecond laser in this experimental study. Standard LASIK treatment parameters were used for the experiment. After LASIK flap creation, the corneal stromal roughness was assessed using a JPK NanoWizard II® AFM in contact mode immersed in liquid. Olympus OMCL-RC800PSA commercial silicon nitride cantilever tips were used. Surface measurements were made in 10 regions of the central cornea of each sample measuring 20 x 20 microns, at 512 x 512 point resolution. Roughness was measured using the root-mean-square (RMS) value within the given regions.ResultsMeasurements from 30 regions of the 3 eyes (10 measurements per eye) in the Intralase (FS1) group, and 30 regions of the 3 eyes (10 measurements per eye) in the VisuMax (FS2) group were analyzed. There was a statistically significant difference in mean ± standard deviation RMS values between the FS1 and the FS2 groups (360 ± 120 versus 230 ± 100 nm respectively; P< 0.00001).ConclusionThis AFM study indicates that the surface of the stromal bed after LASIK flap creation is smoother in the FS2 group than the FS1 group.

Micro Fabricated MEMS Colorimetric Devices to Measure Zika-Induced Residual Stress and Mass Loading

Microfabricated silicon nitride cantilever beams, with gold disks and triangles were used to study and quantify residual stresses generated by binding with the thiol end groups of Zika aptamers and then with Zika. Binding with aptamers and Zika generated large tensile residual stresses ~ 53 MPa that deflected the beams and changed their reflective color. It also caused the triangular gold patches to detach from their nitride substrates affecting the substrates' “golden” color. Dynamic measurements of the nitride beams' vibrations were used to measure mass loading by Zika with the sensitivity of 2 kHz/ng. The residual stress built-up due to binding with Zika in excess of 9 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> Zika/beam caused nitride beams to buckle. Zika-induced residual stress measured using the triangular patches was 96 MPa. Large-scale cellulose acetate beams were then used to observe the residual stresses caused by 20 nm gold layer (0.24 MPa), aptamers (0.3 MPa), and then with Zika (0.5 MPa). Acetate beam displacement was used to “sense” Zika with 2 x 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> μm/Zika sensitivity.

Adsorption Behavior of Perfluorosulfonic Acid Ionomers on a Pt(111) Surface Observed By Atomic Force Microscopy

Understanding of the adsorbed structure of ionomers on the Pt electrocatalyst and carbon support surfaces are very important to improve the cell performance of polymer electrolyte membrane fuel cells (PEMFCs). The effect of the solvent composition and temperature on the adsorbed structure of ionomers have been studied by using various techniques, such as 19F nuclear magnetic resonance (19F NMR) spectroscopy, cryogenic scanning electron microscopy (cryo-SEM), dynamic light scattering (DLS), small angle X-ray scattering (SAXS), small angle neutron scattering (SANS), and electron spin resonance (ESR) techniques. However, it has not been fully clarified yet, due to the complexity of the system composed of a variety of ingredients including the Pt electrocatalyst, carbon support, ionomers, solvent and other contaminants. Thus, we have investigated the adsorbed structure of ionomers on the Pt(111) surface as a model of an electrocatalyst by using atomic force microscopy (AFM) at various solvent compositions. A droplet of aqueous solutions of Nafion was placed on Pt (111) surfaces mounted on the AFM sample holder. AFM measurements were performed with Acoustic AC mode AFM using Agilent 5500 AFM microscope (Agilent Technologies, USA) with a silicon nitride cantilever. The images were recorded over a period of ~30 minutes with a scanning area of 1 µm × 1 µm. In a 2 wt% aqueous solution of Nafion, relatively small aggregates of Nafion ionomers with a height of ~2-3 nm were observed at the Pt(111) surface. Amount of adsorption increased with time and, eventually, the surface was entirely covered by randomly oriented aggregates with a thickness of ~4 nm. In a 0.2 wt% aqueous solution, aggregates larger than those observed in the 2 wt% aqueous solution were imaged, suggesting that larger aggregates were formed in the lower concentration solution. Such a concentration-dependent adsorption behavior is further discussed on the basis of solvent composition and conformation of Nafion ionomers in liquid phase. References Masuda, H. Naohara, S. Takakusagi, P. R. Singh, K. Uosaki: Chemistry Letters, 38, 884 (2009).Masuda, S. Faridah, P. Singh, H. Naohara, K. Uosaki, Journal of Physical Chemistry C, 117, 15704 (2013).Masuda, K. Ikeda, K. Uosaki, Langmuir, 29, 2420 (2013).

Spatially resolved random-access pump-probe microscopy based on binary holography.

In this Letter, we present a spatially resolved pump-probe microscope based on a digital micromirror device (DMD). The microscope system enables the measurements of ultrafast transient processes at arbitrarily selected regions in a 3-D specimen. To achieve random-access scanning, the wavefront of the probe beam is modulated by the DMD via binary holography. By switching the holograms stored in the DMD memory, the laser focus can be rapidly moved in space in a discrete fashion. The microscope system has a field of view of 65×130×155 μm3 in the x, y, and z axes, respectively; and a scanning speed of 8kHz which is limited by the response time of the lock-in amplifier. To demonstrate the pump-probe system, we measured the ultrafast transient reflectivity of 2-D gold patterns on a silicon substrate and on silicon nitride cantilever beams. The results show an excellent signal-to-noise ratio and spatial-temporal resolution, as well as the 3-D random scanning capability. The new pump-probe microscope is a versatile instrument to characterize ultrafast 3-D phenomena with high spatial and temporal resolution, e.g.,the propagation of localized surface plasmon resonance on curved surfaces.

Multifunctional Boron-Doped Diamond Colloidal AFM Probes.

Scanning probe microscopy techniques providing information on conductivity, chemical fluxes, and interfacial reactivity synchronized with topographical information have gained importance within the last decades. Herein, a novel colloidal atomic force microscopy (AFM) probe is presented using a spherical boron-doped diamond (BDD) electrode attached and electrically connected to a modified silicon nitride cantilever. These conductive spherical BDD-AFM probes allow for electrochemical force spectroscopy. The physical robustness of these bifunctional probes, and the excellent electrochemical properties of BDD renders this concept a unique multifunctional tool for a wide variety of scanning probe studies including conductive AFM, hybrid atomic force-scanning electrochemical microscopy, and tip-integrated chem/bio sensing.

Biomechanical Characterization of Human Pluripotent Stem Cell-Derived Cardiomyocytes by Use of Atomic Force Microscopy.

Atomic force microscopy (AFM) is not only a high-resolution imaging technique but also a sensitive tool able to study biomechanical properties of bio-samples (biomolecules, cells) in native conditions-i.e., in buffered solutions (culturing media) and stable temperature (mostly 37°C). Micromechanical transducers (cantilevers) are often used to map surface stiffness distribution, adhesion forces, and viscoelastic parameters of living cells; however, they can also be used to monitor time course ofcardiomyocytes contraction dynamics (e.g. beating rate, relaxation time), together with other biomechanical properties. Here we describe the construction of an AFM-based biosensor setup designed to study the biomechanical properties of cardiomyocyte clusters, through the use of standard uncoated silicon nitride cantilevers. Force-time curves (mechanocardiograms, MCG) are recorded continuously in real time and in the presence of cardiomyocyte-contraction affecting drugs (e.g., isoproterenol, metoprolol) in the medium, under physiological conditions. The average value of contraction force and the beat rate, as basic biomechanical parameters, represent pharmacological indicators of different phenotype features. Robustness, low computational requirements, and optimal spatial sensitivity (detection limit 200pN, respectively 20nm displacement) are the main advantages of the presented method.

Position and mode dependent optical detection back-action in cantilever beam resonators

Optical detection back-action in cantilever resonant or static detection presents a challenge when striving for state-of-the-art performance. The origin and possible routes for minimizing optical back-action have received little attention in literature. Here, we investigate the position and mode dependent optical back-action on cantilever beam resonators. A high power heating laser (100 µW) is scanned across a silicon nitride cantilever while its effect on the first three resonance modes is detected via a low-power readout laser (1 µW) positioned at the cantilever tip. We find that the measured effect of back-action is not only dependent on position but also the shape of the resonance mode. Relevant silicon nitride material parameters are extracted by fitting finite element (FE) simulations to the temperature-dependent frequency response of the first three modes. In a second round of simulations, using the extracted parameters, we successfully fit the FEM results with the measured mode and position dependent back-action. From the simulations, we can conclude that the observed frequency tuning is due to temperature induced changes in stress. Effects of changes in material properties and dimensions are negligible. Finally, different routes for minimizing the effect of this optical detection back-action are described, allowing further improvements of cantilever-based sensing in general.

Surface-Charge Anisotropy of Scheelite Crystals.

Atomic force microscopy was employed to measure the colloidal interactions between silicon nitride cantilever tips and scheelite crystal surfaces in 1 mM KCl solutions of varying pH. By fitting the Derjguin-Landau-Verwey-Overbeek (DLVO) theoretical model to the recorded force-distance curves, the surface-charge density and surface-potential values were calculated for three crystallographic surfaces including {112}, {101}, and {001}. The calculated surface-potential values were negative in both acidic and basic solutions and varied among crystallographic surfaces. The determined surface-potential values were within zeta-potential values reported in the literature for powdered scheelite minerals. The surface {101} was the most negatively charged surface, followed by {112} and {001}. The surface potential for {001} was only slightly affected by pH, whereas the surface potential for both {112} and {101} increased with increasing pH. Anisotropy in surface-charge density was analyzed in relation to the surface density of active oxygen atoms, that is, the density of oxygen atoms with one or two broken bond(s) within tungstate ions located in the topmost surface layer. On a surface with a higher surface density of active oxygen atoms, a larger number of OH(-) are expected to adsorb through hydrogen bonding, leading to a more negatively charged surface.

A Novel SU8 Polymer Anchored Low Temperature HWCVD Nitride Polysilicon Piezoresitive Cantilever

In this paper, we present a novel approach for fabricating piezoresistive silicon nitride cantilevers using polymer as an anchor. In our approach, the silicon nitride structural layers, as well as the polycrystalline silicon piezoresistive layer, are deposited by a low temperature hot-wire chemical vapor deposition process. The novelty of this process is that the silicon wafer is not consumed and is reusable, and the process also allows use of alternate materials for cantilever fabrication in place of silicon substrate. The fabricated silicon nitride cantilevers are characterized for their mechanical and electromechanical behavior.

Physics of nanomechanical spectrometry of viruses.

There is an emerging need of nanotools able to quantify the mechanical properties of single biological entities. A promising approach is the measurement of the shifts of the resonant frequencies of ultrathin cantilevers induced by the adsorption of the studied biological systems. Here, we present a detailed theoretical analysis to calculate the resonance frequency shift induced by the mechanical stiffness of viral nanotubes. The model accounts for the high surface-to-volume ratio featured by single biological entities, the shape anisotropy and the interfacial adhesion. The model is applied to the case in which tobacco mosaic virus is randomly delivered to a silicon nitride cantilever. The theoretical framework opens the door to a novel paradigm for biological spectrometry as well as for measuring the Young's modulus of biological systems with minimal strains.Electronic supplementary materialThe online version of this article (doi:10.1038/srep06051) contains supplementary material, which is available to authorized users.

A Reexamination of Phonon Transport Through a Nanoscale Point Contact in Vacuum

Using a silicon nitride cantilever with an integral silicon tip and a microfabricated platinum–carbon resistance thermometer located close to the tip, a method is developed to concurrently measure both the heat transfer through and adhesion energy of a nanoscale point contact formed between the sharp silicon tip and a silicon substrate in an ultrahigh vacuum atomic force microscope at near room temperature. Several models are used to evaluate the contact area critical for interpreting the interfacial resistance. Near field-thermal radiation conductance was found to be negligible compared to the measured interface thermal conductance determined based on the possible contact area range. If the largest possible contact area is assumed, the obtained thermal interface contact resistance can be explained by a nanoconstriction model that allows the transmission of phonons from the whole Brillouin zone of bulk Si with an average finite transmissivity larger than 0.125. In addition, an examination of the quantum thermal conductance expression suggests the inaccuracy of such a model for explaining measurement results obtained at above room temperature.

α-Amino-3-hydroxy-5-methyl-4-isoxazole Propionic Acid (AMPA) and N-Methyl-d-aspartate (NMDA) Receptors Adopt Different Subunit Arrangements

Ionotropic glutamate receptors are widely distributed in the central nervous system and play a major role in excitatory synaptic transmission. All three ionotropic glutamate subfamilies (i.e. AMPA-type, kainate-type, and NMDA-type) assemble as tetramers of four homologous subunits. There is good evidence that both heteromeric AMPA and kainate receptors have a 2:2 subunit stoichiometry and an alternating subunit arrangement. Recent studies based on presumed structural homology have indicated that NMDA receptors adopt the same arrangement. Here, we use atomic force microscopy imaging of receptor-antibody complexes to show that whereas the GluA1/GluA2 AMPA receptor assembles with an alternating (i.e. 1/2/1/2) subunit arrangement, the GluN1/GluN2A NMDA receptor adopts an adjacent (i.e. 1/1/2/2) arrangement. We conclude that the two types of ionotropic glutamate receptor are built in different ways from their constituent subunits. This surprising finding necessitates a reassessment of the assembly of these important receptors.

An Analytical Model for Thermal Effect of Microcantilever-DNA Biosensors

The thermal effect of microcantilever-DNA biosensors is investigated by the energy method. Based on a liquid crystal theory for DNA solutions and a two-variable method for laminated cantilevers, an analytical model for nanomechanical cantilever motion under the combination of bio-interactions and thermal loadings is provided and then it is extended to T-shaped cantilevers. Then, the effects of chemo-physical properties of DNA biofilm (i.e., grafting density, nucleotide number, and ionic strength) and temperature change on deflections are discussed. In order to reduce noise signals, the controlling temperature and size optimization of cantilevers with different substrate materials and ionic strengths are also studied. Results show that SU-8 polymer cantilevers can preserve the sensitivity of molecule adsorption and thermal stability, which agrees well with the related experiments; the layer-to-layer thickness ratio of SU-8 polymer cantilevers should be as small as possible, while for silicon nitride cantilevers, there exists an optimal value. These results help to understand the sensitivity and reproducibility of biosensors.

Development of Electrochemical Cantilever Sensors for DNA Applications

In this work, we develop a generic DNA based sensing platform used for characterizing surface functionalization and detecting DNA hybridization. Silicon nitride cantilever sensors are fabricated with an integrated three-electrode system and integrated in a microfluidic chip. Cantilevers with gold electrodes are functionalized with thiol-modified single stranded DNA (ssDNA) probes to detect target DNA. During functionalization and hybridization, information related to nanomechanical changes on the surface are obtained by optical measurements of changes in cantilever deflection. Simultaneously, the process is monitored electrochemically. The results clearly indicate that the electrochemical cantilever sensor is very sensitive for detecting DNA hybridization at the cantilever surface.

Alignment of Integrin Surface Receptors with Z-Discs in Live Cardiomyocytes Revealed with High Resolution AFM Mapping

Mechanical sensing proteins connect with sarcomeric structures, such as the Z-disc, which impacts cardiomyocyte mechanotransduction. The extracellular matrix (ECM) plays a vital role acting as a passive scaffold and signaling network.We used atomic force microscopy (AFM) to map integrin receptor arrangement on adult rat ventricular myocytes (ARVM) to resolve ECM coupling surface receptor alignment with underlying sarcomere structures, particularly the Z-discs. Plated ARVM's were probed by an Asylum MFP-3D AFM with a silicon nitride cantilever (0.1 N/m) and pyramidal tip (radius ∼ 40 nm). Tip-surface adhesion forces were measured in scanning mode through a 10 μm X 2.5 μm (78 nm X 156 nm resolution) region. Bare gold and laminin (10 μg/ml) coated tips were used.Adhesion force maps from bare tip (Fig. 1 bottom) show clear banding patterns that register with features in the bright field image (Fig. 1 top) and have 1.72 μm sarcomere spacing. Peak adhesion forces are generally twice as large for the laminin coating relative to the bare tip, indicative of surface receptor binding. This AFM methodology offers a tool for characterizing a pathway for sarcomere-ECM coupling.View Large Image | View Hi-Res Image | Download PowerPoint Slide