1,289 research outputs found
Endogenous and exogenous polyamines in the organogenesis in Curcuma longa L.
No full textThe present work evaluated the development of different Curcuma longa L. explants (leaves basis, root tips and ancillary buds from rhizome) stimulated by exogenous polyamines, combined with naphtalen-acetic acid (NAA) or with 6-benzyl-aminopurine (BAP), to produce callus and its subsequent
differentiation. The explants, isolated from field plants, were previously subjected to a basic cleaning method and were inoculated onto Murashige and Skoog culture medium (MS) [Murashige, T.S., Skoog, F., 1962. A revised medium for rapid growth and bioassays with tobacco tissue culture. Physiologia Plantarum 15, 473–497] supplemented with NAA (2.0 mg L-1 ). Buds were subjected to different treatments, with or without 5.0 and 10.0 mmol L-1 exogenous polyamines (mixture of putrescine:spermine:spermidine, 1:1:1) combined with NAA. The calluses obtained were transferred into the same
medium, supplemented with the mixture of polyamines combined with BAP, in order to induce plant differentiation. For C. longa, buds were the most efficient explants for callus induction (p < 0.05). The application of exogenous polyamines (5.0 and 10.0 mmol L-1 ) produced the most developed callus, with numerous roots. The medium supplemented with 10 mmol L-1 polyamine mixture, combined with BAP, induced good regeneration, producing vigorous plants and excellent shoot formation.Polyamines addition promoted the formation of callus, roots and leaves, representing an important factor in the determination of indirect organogenesis in C. longa L., and putrescine content may be considered a valuable marker of the differentiation process in this specie, as well as the enzyme peroxidase
Growth of liquid bridge in AFM
No full textCapillary forces are dominant in adhesive forces measured with an atomic force microscope (AFM) in ambient air, which are thought to be dependent on water film thickness, relative humidity and the free energy of the water film. In this paper, besides these factors, we study the nature of the 'pull-off' force on a variety of atmospheres as a function of the contact time. It is found that capillary forces strongly depend on the contact time. In lower relative humidity atmosphere, the adhesion force is almost independent of the contact time. However, in higher relative humidity, the adhesion force increases with the contact time. Based on the experiment and a model that we present in this paper, the growth of the liquid bridge can be seen as undergoing two processes: one is water vapour condensation; the other is the motion of the thin liquid film that is absorbed on the substrate. The experiment and the growth model presented in this paper have direct relevance to the working mechanism of AFM in ambient air
In situ stiffness adjustment for AFM probes
No full textThe choice on which cantilever to use for Atomic Force Microscopy (AFM) depends on the type of the experiment being done. Usually, the cantilevers have to be exchanged when a different stiffness is required and the entire alignment has to be repeated. In the present work, we have developed a method to adjust the stiffness of the AFM cantilever in situ, without having to exchange the cantilever. The adjustment is achieved by changing the effective length of the cantilever by electrostatic pull-in. By applying a voltage between the cantilever and an electrode (with an insulating layer at the point of contact), the cantilever snaps to the electrode, reducing the cantilever’s effective length. The working principle of this concept is demonstrated with a proof-of-concept experiment. The electrode was positioned close to a commercially available cantilever with a robotic nano-manipulator. To confirm the change in stiffness, the resonance frequency of the cantilever was measured for varying electrode positions. The results match the theoretical expectation. For the cantilever that was tested, we obtained stiffness tuning from 0.2 N/m to 27 N/m, covering two orders of magnitude in one cantilever. This proof-of-concept is the first step towards a micro fabricated prototype, that integrates the electrode positioning system and cantilever that can be used for actual AFM experiments.Micro and Nano EngineeringPrecision and Microsystems EngineeringMechanical, Maritime and Materials Engineerin
Dosing of femto liter volumes using hollow cantilever AFM
No full textThe subject discussed in this thesis is the dosing of droplets in the femto (10-15) liter range. In this study, droplets were dispensed using a hollow cantilever atomic force microscope (AFM). Dispensing small volumes finds its applications in for example in single cell manipulation, where a drug is delivered inside a single cell to study the reaction of the cell to the drug. The working principle of an AFM can be compared with a vinyl player: a small needle is scanning a surface, which can be used for imaging with atomic resolution. For controlled dispensing of small droplets the needle and the cantilever were made hollow and a commercially available AFM system was adapted for fluidic applications. The hollow cantilever AFM chip is connected by tubing to a syringe which acts as fluidic reservoir. Small droplets of water will evaporate almost immediately; to increase the “lifetime” of the droplet a climate controller was added to increase the humidity. Therefore the influence of the climate controller on the AFM system was studied. With the described system droplets in the femto liter range were dispensed on a surface, however controlled dispensing remained a challenge. Therefore this research investigates the parameters influencing the droplet size and how these parameters can be controlled to dispense a desired volume. Two different ways of dispensing are experimentally investigated: just by touching the substrate and using the surface forces to pull liquid from the cantilever onto the substrate and by applying pressure to the liquid reservoir. For dispensing by surface forces, parameters such as surface energy and contact time are investigated to deliver a desired volume. A trend was observed that with increasing contact time an increase in volume is dispensed. For dispensing with additional pressure, a correlation was found between the time of applied pressure and dispensed volume. Dispensing of droplets of around 0.4 ? with a variation of 0.05 ? has been shown.Micro and Nano EngineeringPrecision and Microsystems EngineeringMechanical, Maritime and Materials Engineerin
Modelling viscoelasticity using Multifrequency AFM
No full textViscoelasticity is a material property that is relevant in a variety of nanoscale materials and interfaces in medicine and industry. Therefore, a method of mechanical quantification has become exceedingly desired. In this thesis the Atomic force microscope (AFM) is applied to accurately characterize the mechanical behavior of viscoelastic samples. The goal is to enhance viscoelastic characterization using the so-called Intermodulation AFM (ImAFM) technique by applying, adapting and improving multiple modelling and optimization methods. In ImAFM force reconstruction is performed by extracting intermodulations around resonance in the cantilever response. These intermodulations present new observables that can be used for characterization. This thesis investigates the potential of this technique in combination with an up-and-coming model describing viscoelastic interaction. A toolbox has been developed for numerical simulations of the model to resemble the experiments. The model has been evaluated in a variety of situations using sensitivity analysis in a large feasibility range, encompassing many complex dynamics. Because of the diversity in model dynamics a global optimization has been performed for experimental reconstruction.Mechanical Engineering | Dynamics of Micro and Nano System
Effect of Chain Length of Self-Assembled Monolayers on Adhesion Force Measurement by AFM
No full textIt has been confirmed experimentally that the adhesion force measured between an atomic
force microscope (AFM) tip and the self-assembled monolayers (SAMs) has a direct correlation with
the chain length of SAMs, and that the adhesion force decreases with the increase of the chain length.
In this paper, a theoretical model is put forward to calculate the adhesion force between the AFM
tip and the SAMs by integrating the Lennard–Jones potential. The theoretical results are in good
agreement with the existing experimental results
An approach to nano-chemical analysis through NC-AFM technique
No full textWe have measured the NC-AFM frequency shift dependence on the X-ray energy around the Au L3 absorption edge energy. We found a peak in the frequency shift just above the Au region at the Au L3 absorption edge energy while we could not detect any peak in the frequency shift when the NC-AFM tip was placed above the Si regions. This novel phenomenon indicated that the combination of energy-variable X-rays and NC-AFM provides us a new way to nano level chemical mapping at surface. We briefly discussed some possible mechanisms
Multiscale 3D-printing of microfluidic AFM cantilevers
No full textMicrofluidic atomic force microscopy (AFM) cantilever probes have all the functionalities of a standard AFM cantilever along with fluid pipetting. They have a channel inside the cantilever and an aperture at the tip. Such probes are useful for precise fluid manipulation at a desired location, for example near or inside cells. They are typically made by complex microfabrication process steps, resulting in expensive probes. Here, we used two different 3D additive manufacturing techniques, stereolithography and two-photon polymerization, to directly print ready-to-use microfluidic AFM cantilever probes. This approach has considerably reduced the fabrication time and increased the design freedom. One of the probes, 564 μm long, 30 μm wide, 30 μm high, with a 25 μm diameter channel and 2.5 μm wall thickness had a spring constant of 3.7 N m-1 and the polymer fabrication material had an elastic modulus of 4.2 GPa. Using these 3D printed probes, AFM imaging of a surface, puncturing of the cell membrane, and aspiration at the single cell level have been demonstrated.Micro and Nano EngineeringBiomaterials & Tissue Biomechanic
Dynamics of microfluidic cantilevers in a photothermal AFM
No full textAny resonance based sensing method such as AFM or mass sensing using microfluidic cantilevers require high frequency stability. For mass measurement, a stable frequency allows for a lower mass resolution. One of the most commonly used methods to actuate these resonators is using piezoacoustics. A major downside of this method is the presence of spurious resonances, which corrugate the frequency response and can potentially degrade mass sensitivity. One way get rid of these spurious peaks is byactuating photothermally (using laser light). This thesis is focused around designing and building a photothermal AFM to explore this. Additionally, some experiments are performed comparing piezoacoustic actuation to photothermal actuation in terms of the aforementioned frequency stability andspurious peaks.Mechanical Engineerin
Helium ion beam induced growth of hammerhead AFM probes
No full textThe authors report the direct-write growth of hammerhead atomic force microscope(AFM) probes by He+beam induced deposition of platinum-carbon. In order to grow a thin nanoneedle on top of a conventional AFM probe, the authors move a focused He+beam during exposure to a PtC precursor gas. In the final growth stage, a perpendicular movement of the beam results in the required three-dimensional (hammerhead) shape. The diameter of the needle depends on the ion beam dose, beam dwell time, and speed of the beam movement. A nanoneedle radius below 10?nm and a hammerhead smaller than 35?nm have been achieved. This fabrication process is robust and enables precise control over the three-dimensions of the hammerhead AFM probe. Finally, the authors test the capabilities of the fabricated AFM probes for two-dimensional metrology of sidewall angles and line-edge roughness of trenches and shark-fins in silicon.QN/Quantum NanoscienceApplied Science
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