Atomic Force Microscopy Technology Research Articles

Atomic Force Microscopy, Passport to Nanobiology

Atomic Force Microscopy (AFM) plays important roles in nanobiology. We here review the recent development and application of AFM technology from the technical point of view. In the visualization mode, AFM produces not only static images at lower time-resolution in the seconds to minutes, but also motion images at higher time-resolution in the milliseconds. Furthermore, AFM combined with fluorescent techniques can now address varieties of biological questions from genes to proteins and from proteins to cells. In the force mode, the tip directly interacts with the molecules of interests to measure the inter- and/or intra-molecular physical properties.

New technologies in scanning probe microscopy for studying molecular interactions in cells.

Atomic force microscopy (AFM) is a specialised form of scanning probe microscopy, which was invented by Binnig and colleagues in 1986. Since then, AFM has been increasingly used to study biomedical problems. Because of its high resolution, AFM has been used to examine the topography or shape of surfaces, such as during the molecular imaging of proteins. This, combined with the ability to operate under known force regimes, makes AFM technology particularly useful for measuring intermolecular bond forces and assessing the mechanical properties of biological materials. Many of the constraints (e.g. complex instrumentation, slow acquisition speeds and poor vertical range) that previously limited the use of AFM in cell biology are now beginning to be resolved. Technological advances will enable AFM to challenge both confocal laser scanning microscopy and scanning electron microscopy as a method for carrying out three-dimensional imaging. Its use as both a precise micro-manipulator and a measurement tool will probably result in many novel and exciting applications in the future. In this article, we have reviewed some of the current biological applications of AFM, and illustrated these applications using studies of the cell biology of bone and integrin-mediated adhesion.

Atomic force microscopy with carbon nanotube probe resolves the subunit organization of protein complexes.

Among many scanning probe microscopies, atomic force microscopy (AFM) is a useful technique to analyse the structure of biological materials because of its applicability to non-conductors in physiological conditions with high resolution. However, the resolution has been limited to an inherent property of the technique; tip effect associated with a large radius of the scanning probe. To overcome this problem, we developed a carbon nanotube probe by attaching a carbon nanotube to a conventional scanning probe under a well-controlled process. Because of the constant and small radius of the tip (2.5-10 nm) and the high aspect ratio (1:100) of the carbon nanotube, the lateral resolution has been much improved judging from the apparent widths of DNA and nucleosomes. The carbon nanotube probes also possessed a higher durability than the conventional probes. We further evaluated the quality of carbon nanotube probes by three parameters to find out the best condition for AFM imaging: the angle to the tip axis; the length; and the tight fixation to the conventional tip. These carbon nanotube probes, with high vertical resolution, enabled us to clearly visualize the subunit organization of multi-subunit proteins and to propose structural models for proliferating cell nuclear antigen and replication factor C. This success in the application of carbon nanotube probes provides the current AFM technology with an additional power for the analyses of the detailed structure of biological materials and the relationship between the structure and function of proteins.

Atomic force microscopy imaging of living cells: progress, problems and prospects.

Recent development of atomic force microscopy (AFM) applications in imaging living cells is reviewed, focusing on technical progress and application advancements made in the following major areas: (i) high-resolution imaging of cellular structures, (ii) real-time monitoring of cellular dynamic processes, and (iii) detecting micromechanical properties of the cell. Technical and experimental difficulties frequently encountered in AFM applications in above areas are presented and possible strategies for overcoming these obstacles are discussed. Significant advances in the AFM study of living cells can be achieved from further development of AFM technology, sample preparation, and innovative applications.

Analysis of infected human mononuclear cells by atomic force microscopy

The surfaces of the human lymphoid cells of the line H9 chronically infected with the Human Immunodeficiency Virus HIV-1, and of human monocytes acutely infectedin vitro withMycobacterium Tuberculosis (MTB) were dried, fixed and imaged with atomic force microscopy (AFM). These images were compared with those of non-infected samples. Dried and fixed samples of infected cells can be distinguished from non-infected ones by AFM technology due to their different surface structures and by the presence of pathogenic (viral or mycobacterial) agents on the cell surface.

Prospects for scanned-probe microscopy

In the last 50+ years the electron microscope and allied instruments have led the way as means to acquire spatially resolved information about very small objects. For the material scientist and the biologist both, imaging using the information derived from the interaction of electrons with the objects of their concern, has had limitations. Material scientists have been handicapped by the fact that their samples are often too thick for penetration without using million volt instruments. Biologists have been handicapped both by the problem of contrast since most biological objects are composed of elements of low Z, and also by the requirement that sample be placed in high vacuum. Cells consist of 90% water, so elaborate precautions have to be taken to remove the water without losing the structure altogether. We are now poised to make another leap forwards because of the development of scanned probe microscopies, particularly the Atomic Force Microscope (AFM). The scanning probe instruments permit resolutions that electron microscopists still work very hard to achieve, if they have reached it yet. Probably the most interesting feature of the AFM technology, for the biologist in any case, is that it has opened the dream of high resolution in an aqueous environment. There are few restrictions on where the instrument can be used. AFMs can be made to work in high vacuum, allowing the material scientist to avoid contamination. The biologist can be made happy as well. The tips used for detection are made of silicon nitride,(Si3N4), and are essentially unaffected by exposure to physiological saline (about which more below). So here is an instrument which can look at living whole cells and at atoms as well.

Application of the atomic force microscope to integrated circuit failure analysis

In IC research centers over the past two years, the Atomic Force Microscope (AFM) has become a fairly common tool. Nondestructive imaging with nanometer resolution on uncoated samples in ambient conditions is proving to have a wide range of applications in IC research. Also, during this same period important advances have been made in scanning probe microscopy, particularly relating to atomic force probes. AFM technology has now found acceptance in IC manufacturing as well as research. These new advances include: large sample (full wafer) capability, sharper probe tips capable of measuring sidewalls as steep as 15 degrees from the vertical, noncontact topography measurements, frictional-force measurements, and cross-section analysis. True three-dimensional nanometer-scale metrology can now be applied to process control and failure analysis. Some uses and applications to semiconductors are (1) surface roughness measurment of polished silicon wafers for gate oxide performance improvements, (2) surface roughness of deposited layers, (3) grain-size measurement, (4) depth measurement for etcher control, (5) step-height measurement, (6) gate-oxide integrity, (7) deposited layer integrity over lines, (8) monitoring the effectiveness of cleaning steps, (9) cross-section imaging, (10) high-resolution imaging for process inspection, (11) planarization quality, (12) phase-shift mask development, (13) chrome photomasks — defect imaging and sizing, line-edge quality, (14) defect imaging and sizing, and (15) spin-on glass cure and pore-size process studies