Electromechanical Imaging of Biological Systems with Sub-10 nm Resolution

Electromechanical imaging of tooth dentin and enamel has been performed with sub-10 nm resolution using piezoresponse force microscopy. Characteristic piezoelectric domain size and local protein fiber ordering in dentin have been determined. The shape of a single collagen fibril in enamel is visualized in real space and local hysteresis loops are measured. Because of the ubiquitous presence of piezoelectricity in biological systems, this approach is expected to find broad application in high-resolution studies of a wide range of biomaterials.Comment: 12 pages, 4 figures, submitted for publication in Appl. Phys. Let

Critical Point Mounting of Kinetoplast DNA for Atomic Force Microscopy

Atomic force microscope (AFM) images of intact kinetoplast DNA were obtained from samples prepared utilizing critical point drying. These images are compared with AFM images obtained using conventional methods for DNA deposition. Although the images obtained on chemically pretreated mica show more details than on unmodified mica, images obtained with critical point drying were superior. Kinetoplast networks with expected sizes and structures were routinely observed with critical point drying. The resolution of individual strands of DNA was greatly improved, and image artifacts associated with air dried samples were eliminated. Samples prepared using mildly sonicated kinetoplast DNA show isolated minicircles

Optical studies of Ge islanding on Si(111)

We report an experimental study of the optical properties of island layers resulting from molecular beam epitaxial deposition of Ge on Si(111) substrates. The combination of electroreflectance spectroscopy of the E1 transition and Raman scattering allows us to separately determine the strain and composition of the islands. For deposition at 500 °C a deposited layer of 1.36 nm of Ge assembles into 80 nm diameter islands 11 nm thick. The average Si impurity content in the islands is 2.5% while the average in-plane strain is 0.5%. Both strain and Si impurity content in islands decrease with increasing Ge depositio

Atomic Force Microscopy of DNA on Mica and Chemically Modified Mica

Atomic force microscopy (AFM) was used to image circular DNA adsorbed on freshly cleaved mica and mica chemically modified with Mg(II), Co(II), La(III), and Zr(IV). Images obtained on unmodified mica show coiling of DNA due to forces involved during the drying process. The coiling or super twisting appeared to be right handed and the extent of super twisting could be controlled by the drying conditions. Images of DNA observed on chemically modified surfaces show isolated open circular DNA that is free from super twisting, presumably due to strong binding of DNA on chemically modified surfaces

Calibration of Atomic Force Microscope Tips Using Biomolecules

Atomic force microscope (AFM) images of surfaces and samples mounted on substrates are subject to artifacts such as broadening of structures and ghost images of tips due to the finite size and shape of the contacting probe. Therefore, knowledge of the radius of the AFM probe tip is essential for the interpretation of images. We have deduced the shape of the AFM tip by imaging cylindrical biological molecules of various diameters such as deoxyribonucleic acid (DNA), tobacco mosaic virus (TMV), tobacco etch virus (TEV) and bacteriophage M-13 (M-13). Using a paraboloidal tip model and numerically solving equations of contact, the curvatures of the tip and lithographically sharpened tip were ascertained

Electromechanical imaging of biomaterials by scanning probe microscopy

The majority of calcified and connective tissues possess complex hierarchical structure spanning the length scales from nanometers to millimeters. Understanding the biological functionality of these materials requires reliable methods for structural imaging on the nanoscale. Here, we demonstrate an approach for electromechanical imaging of the structure of biological samples on the length scales from tens of microns to nanometers using piezoresponse force microscopy (PFM), which utilizes the intrinsic piezoelectricity of biopolymers such as proteins and polysaccharides as the basis for high-resolution imaging. Nanostructural imaging of a variety of protein-based materials, including tooth, antler, and cartilage, is demonstrated. Visualization of protein fibrils with sub-10 nm spatial resolution in a human tooth is achieved. Given the near-ubiquitous presence of piezoelectricity in biological systems, PFM is suggested as a versatile tool for micro- and nanostructural imaging in both connective and calcified tissues

Simultaneous elastic and electromechanical imaging by scanning probe microscopy: Theory and applications to ferroelectric and biological materials

An approach for combined imaging of elastic and electromechanical properties of materials, referred to as piezoacoustic scanning probe microscopy (PA-SPM), is presented. Applicability of this technique for elastic and electromechanical imaging with nanoscale resolution in such dissimilar materials as ferroelectrics and biological tissues is demonstrated. The PA-SPM signal formation is analyzed based on the theory of nanoelectromechanics of piezoelectric indentation and signal sensitivity to materials properties and imaging conditions. It is shown that simultaneous measurements of local indentation stiffness and indentation piezocoefficient provide the most complete description of the local electroelastic properties for transversally isotropic materials, thus making piezoacoustic SPM a comprehensive imaging and analysis tool. The contrast formation mechanism in the low frequency regime is described in terms of tip-surface contact mechanics. Signal generation volumes for electromechanical and elastic signals are determined and relative sensitivity of piezoresponse force microscopy (PFM) and atomic force acoustic microscopy (AFAM) for topographic cross-talk is established

Ferromagnetic Nanocomposite Films from Thermally Labile Nitride Precursors

A series of nanocomposite films containing Ni or Co nitride dispersed in a ceramic matrix of Al nitride, B nitride, or Sio nitride, were prepared by reactive sputtering of selected alloys or compounds such as Ni aluminide or Co silicide. Thermal treatment of the nitride composites in vacuum at {le}500 C leads to selective loss of N from CoN or Ni{sub 3}N to generate dispersions of the metal in the ceramic matrix. This treatment may be performed in a localized manner by means of a focused laser beam to generate microscopic features that are imaged by magnetic force microscopy. The films are potentially useful for data storage with superior chemical and mechanical stability provided by the ceramic matrix and high encoding density made possible because of the size of the magnetic particles of less than 10 nm generated in the thermal treatment. The films were characterized by chemical and physical means including FTIR, TEM, MFM, and magnetic measurements. Preliminary results on similar iron composites are also described