Direct force measurements of biomolecular interactions by nanomechanical force gauge (original) (raw)
Related papers
Measurement Science and Technology, 2004
Calibration of atomic force microscope (AFM) cantilevers is necessary for the measurement of nanonewton and piconewton forces, which are critical to analytical applications of AFM in the analysis of polymer surfaces, biological structures and organic molecules. We have developed a compact and easy-to-use reference artefact for this calibration by bulk micromachining of silicon, which we call a cantilever microfabricated array of reference springs (C-MARS). Two separate reference cantilever structures, each nominally 3 µm thick, are fabricated from a single crystal silicon membrane. A binary code of surface oxide squares (easily visible in light, electron and atomic force microscopy) makes it easy to locate the position of the AFM tip along the length of the cantilevers. Uncertainty in location is the main source of error when calibrating an AFM using reference cantilevers, especially for those having spring constants greater than around 10 N m −1 . This error is effectively eliminated in our new design. The C-MARS device spans the range of spring constants from 25 N m −1 down to 0.03 N m −1 important in AFM, allowing almost any contact-mode AFM cantilever to be calibrated easily and rapidly.
An Atomic Force Microscope with Dual Actuation Capability for Biomolecular Experiments
We report a modular atomic force microscope (AFM) design for biomolecular experiments. The AFM head uses readily available components and incorporates deflection-based optics and a piezotube-based cantilever actuator. Jetted-polymers have been used in the mechanical assembly, which allows rapid manufacturing. In addition, a FeCo-tipped electromagnet provides high-force cantilever actuation with vertical magnetic fields up to 0.55 T. Magnetic field calibration has been performed with a micro-hall sensor, which corresponds well with results from finite element magnetostatics simulations. An integrated force resolution of 1.82 and 2.98 pN, in air and in DI water, respectively was achieved in 1 kHz bandwidth with commercially available cantilevers made of Silicon Nitride. The controller and user interface are implemented on modular hardware to ensure scalability. The AFM can be operated in different modes, such as molecular pulling or force-clamp, by actuating the cantilever with the available actuators. The electromagnetic and piezoelectric actuation capabilities have been demonstrated in unbinding experiments of the biotin-streptavidin complex. Atomic force microscopy (AFM) is best known for high-resolution imaging, but it is also a powerful tool for sensitive force measurements. The technology has been demonstrated successfully for various exciting biomolecular measurements, such as receptor/ligand interactions and protein folding/unfolding at single-molecule level 1–4. Structure, function, and energy landscape of biomolecules can be investigated via force spectroscopy experiments. The method is based on actuation of a functionalized microcantilever with attached biomolecules over a functionalized sample surface while monitoring the deflection of the cantilever, which is a measure of the force on the biomolecules. The cantilever is actuated over a wide range of speeds to obtain the energy landscape in detail. At low actuation speeds, drift in the system induces spurious deflection on the cantilever and adversely affects the measurements 5,6. On the other hand, the dynamics of the actuator and the cantilever determine the attainable actuation speed. A fundamental limit for immersed cantilevers at high speeds is the hydrodynamic drag 7,8. Cantilever geometry determines the effect of hydrodynamic drag. Smaller cantilevers tend to have less hydrody-namic drag as compared to larger ones 9. In addition to hydrodynamic drag, indirect actuation of the cantilever using a large-scale piezo actuator has detrimental effects. In a conventional AFM setup, a large piezo actuates the cantilever through its holder and this excites many other modes in the complete mechanical system 10,11. The resonant frequencies of the large mechanical assembly of the actuator and the holder are usually smaller than the resonant frequency of the cantilever. This sets a practical limitation for actuation at high speeds. Direct actuation of cantilevers in liquid using magnetic 12,13 , photothermal 14 , acoustic radiation pressure 15 and capacitive methods 16,17 have been proposed to overcome this problem. A magnetic actuator can be integrated into a conventional AFM setup by coupling an AFM head with an electromagnet or a permanent magnet. Magnetic cantilevers 18,19 , standard cantilevers attached with magnetic particles 13,20,21 or current-carrying cantilevers 22,23 can be used in these setups. Mechanical modification of a conventional AFM head makes it possible to add magnetic actua-tion capability. Rapid prototyping techniques are appealing for constructing customized AFM setups because they simplify the development of such setups according to user needs. Among different techniques, selective laser sintering (SLS) was previously used to develop a new AFM head for force spectroscopy applications 24. The
Atomic Force Microscopy as a Tool Applied to Nano/Biosensors
Sensors, 2012
This review article discusses and documents the basic concepts and principles of nano/biosensors. More specifically, we comment on the use of Chemical Force Microscopy (CFM) to study various aspects of architectural and chemical design details of specific molecules and polymers and its influence on the control of chemical interactions between the Atomic Force Microscopy (AFM) tip and the sample. This technique is based on the fabrication of nanomechanical cantilever sensors (NCS) and microcantilever-based biosensors (MC-B), which can provide, depending on the application, rapid, sensitive, simple and low-cost in situ detection. Besides, it can provide high repeatability and reproducibility. Here, we review the applications of CFM through some application examples which should function as methodological questions to understand and transform this tool into a reliable source of data. This section is followed by a description of the theoretical principle and usage of the functionalized NCS and MC-B technique in several fields, such as agriculture, biotechnology and immunoassay. Finally, we hope this review will help the reader to appreciate how important the tools CFM, NCS and MC-B are for characterization and understanding of systems on the atomic scale.
A New Microdevice for SI-Traceable Forces in Atomic Force Microscopy
A new self-excited micro-oscillator is proposed as a velocity standard for dissemination of nanonewton-level forces that are traceable to the International System of Units (SI). The microfabricated oscillator is top-coated with magnetic thin films and closely surrounded with conductive microwires to enable both magnetic sensing and actuation. An analog control system will keep the actuation side of the device oscillating sinusoidally with a frequency up to 200 kHz and a nanometerlevel amplitude that is fairly insensitive to the quality factor. Consequently, the device can be calibrated as a velocity standard in air and used in ultra-high vacuum with a velocity shift of less than one percent. Because of the nanometer-level oscillation amplitude, the microdevice could be used to probe capacitance gradients near tips of cantilevers used for atomic force microscopy (AFM). Hence, the calibrated micro-oscillator could be used with electrostatic forces to calibrate AFM cantilevers as SI-traceable force transducers for fundamental metrology of electrical and mechanical nanoscale quantities.
Review of Scientific Instruments, 1999
Small cantilevers allow for faster imaging and faster force spectroscopy of single biopolymers than previously possible because they have higher resonant frequencies and lower coefficients of viscous damping. We have used a new prototype atomic force microscope with small cantilevers to produce stable tapping-mode images ͑1 mϫ1 m͒ in liquid of DNA adsorbed onto mica in as little as 1.7 s per image. We have also used these cantilevers to observe the forced unfolding of individual titin molecules on a time scale an order of magnitude faster than previously reported. These experiments demonstrate that a new generation of atomic force microscopes using small cantilevers will enable us to study biological processes with greater time resolution. Furthermore, these instruments allow us to narrow the gap in time between results from force spectroscopy experiments and molecular dynamics calculations.
An atomic force microscope tip designed to measure time-varying nanomechanical forces
Nature Nanotechnology, 2007
Tapping-mode atomic force microscopy (AFM), in which the vibrating tip periodically approaches, interacts and retracts from the sample surface, is the most common AFM imaging method. The tip experiences attractive and repulsive forces that depend on the chemical and mechanical properties of the sample, yet conventional AFM tips are limited in their ability to resolve these time-varying forces. We have created a specially designed cantilever tip that allows these interaction forces to be measured with good (sub-microsecond) temporal resolution and material properties to be determined and mapped in detail with nanoscale spatial resolution. Mechanical measurements based on these force waveforms are provided at a rate of 4 kHz. The forces and contact areas encountered in these measurements are orders of magnitude smaller than conventional indentation and AFM-based indentation techniques that typically provide data rates around 1 Hz. We use this tool to quantify and map nanomechanical changes in a binary polymer blend in the vicinity of its glass transition.
Wide cantilever stiffness range cavity optomechanical sensors for atomic force microscopy
Optics Express, 2012
We report on progress in developing compact sensors for atomic force microscopy (AFM), in which the mechanical transducer is integrated with near-field optical readout on a single chip. The motion of a nanoscale, doubly-clamped cantilever was transduced by an adjacent high quality factor silicon microdisk cavity. In particular, we show that displacement sensitivity on the order of 1 fm/(Hz) 1/2 can be achieved while the cantilever stiffness is varied over four orders of magnitude (≈ 0.01 N/m to ≈ 290 N/m). The ability to transduce both very soft and very stiff cantilevers extends the domain of applicability of this technique, potentially ranging from interrogation of microbiological samples (soft cantilevers) to imaging with high resolution (stiff cantilevers). Along with mechanical frequencies (>250 kHz) that are much higher than those used in conventional AFM probes of similar stiffness, these results suggest that our cavity optomechanical sensors may have application in a wide variety of high-bandwidth AFM measurements.
Laser Actuation of Cantilevers for Picometre Amplitude Dynamic Force Microscopy
Scientific Reports, 2014
As nanoscale and molecular devices become reality, the ability to probe materials on these scales is increasing in importance. To address this, we have developed a dynamic force microscopy technique where the flexure of the microcantilever is excited using an intensity modulated laser beam to achieve modulation on the picoscale. The flexure arises from thermally induced bending through differential expansion and the conservation of momentum when the photons are reflected and absorbed by the cantilever. In this study, we investigated the photothermal and photon pressure responses of monolithic and layered cantilevers using a modulated laser in air and immersed in water. The developed photon actuation technique is applied to the stretching of single polymer chains.