摘要:

A protocol for sample preparation that may offer a good tool for the study of proteins with the scanning tunneling microscope is described. Gold surfaces have been mechanically polished and then incubated overnight with 4,4’‐dipyridyl disulfide (DPDS) dissolved in ethanol. This mixed disulfide is able to produce an ordered hydrophilic monolayer above the gold surface, with the pyridine group exposed to the outer surface. Furthermore, the treatment with DPDS significantly improves the wettability of the gold substrates, as seen by taking measurements of the solid/liquid contact angles. Human liver ferritin (HLF) molecules have successively been deposited. Samples have also been characterized under ultrahigh vacuum conditions by means of Auger and photoemission spectroscopy. With regard to the untreated gold surfaces, we found the usual structures of the valence band of gold, as well as almost contaminant free outer layers. Samples treated with DPDS and later with the HLF showed their fingerprints in the ‘‘new’’ valence band together with a good stability under the Auger beam.

ISSN:1071-1023    

DOI:10.1116/1.587270

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

C‐phycocyanin (C‐PC) was isolated from blue‐green algaspirulinaplatensis. A scanning tunneling microscope (STM) has been used to investigate its three‐dimensional structure. The samples were dialyzed before the STM experiment, and then deposited on highly oriented pyrolytic graphite (HOPG). The measurement was carried out in ambient condition at room temperature. STM images showed thatC‐phycocyanin was uniformly distributed on solid‐state substrate HOPG. The shape ofC‐phycocyanin is disklike with a channel in the center. It is concluded that STM has great potential to observe the structure of biliproteins and phycobilisomes.

ISSN:1071-1023    

DOI:10.1116/1.587271

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Biological materials such as hexagonal packed intermediate (HPI) layers, DNA, tobacco mosaic virus and collagen deposited on various substrates with noncontact dynamic force microscopy under ambient conditions were investigated. This method is highly suited for the investigation of soft organic matter where a minimized interaction between tip and sample is needed for nondestructive and reliable operation. Hence, additional anchoring of the biological specimens was no longer found to be crucial. The vertical and lateral resolution limits of this gentle method were determined to be<0.1 nm and 1–2 nm, respectively, allowing very stable and high resolution results on all investigated systems. By taking approach curves and monitoring the dynamic properties of the cantilever (resonance frequency andQvalue) during the experiment, the interaction mechanism between tip and sample was found to be dominated by attractive van der Waals interaction and capillary forces. Furthermore, initial results from a HPI layer imaged with noncontact dynamic force microscopy in a water environment are presented.

ISSN:1071-1023    

DOI:10.1116/1.587272

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

The extracellular and periplasmic surface topography of theE.coliouter membrane protein OmpF reconstituted into 2D crystals in the presence of phospholipids were investigated with a scanning force microscope in buffer solution. Topographs exhibiting 2 nm lateral resolution are in good agreement with data from electron microscopy and x‐ray crystallography, and indicate the exciting possibility to monitor structural changes of ‘‘live systems’’ at molecular resolution by scanning force microscopy.  

ISSN:1071-1023    

DOI:10.1116/1.587273

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Uncoated tobacco mosaic virus (TMV) can reliably be imaged in humid air (relative humidity above 30%) at relatively high voltages (typically 7 to 10 V) and at very low currents (typically 0.1 to 0.5 pA). Imaging works best with tips that show a small dependence of working distance on tunneling voltage. With such tips, a thickness of the virus of 10 nm and more is measured. When using tips of unsuitable characteristics, heights much smaller than 10 nm and even negative values are found. From these observations, a voltage drop over the TMV on the order of volts can be deduced, which depends on tunneling current and humidity.

ISSN:1071-1023    

DOI:10.1116/1.587274

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

The molecular structure of melanins has been a focus of study for many years and only recently has a molecular model (MM) been proposed based upon x‐ray scattering results. In order to test the validity of the model, scanning tunneling microscopy (STM) and spectroscopy have been performed on the same tyrosine‐derived melanin, which has been characterized in the x‐ray scattering studies and has been shown to exhibit characteristics of natural melanins. The STM measurements of the lateral and vertical dimensions provide a characteristic fundamental size which agree well with the x‐ray scattering‐derived MM. We find that the compact three‐dimensional structure is best described as a planar morphology of finite lateral extent (≊2 nm) with a vertical extent (<1 nm) which is believed to consist of stacks of a basic two‐dimensional amorphous polymer of 5,6 indolequinone units. Molecular mechanics and orbital calculations of representative amorphous models support the x‐ray scattering and STM results.

ISSN:1071-1023    

DOI:10.1116/1.587275

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Images have been obtained of two types of chimeric B72.3 anti‐TAG‐72 mutant hinge IgG4 antibodies using scanning tunneling microscopy. The antibodies were specifically engineered to show differences in their conformation due to site specific modifications in their hinge regions. To overcome initial difficulties due to tip sweeping effects, the method of immobilization employed was spray deposition on mica followed by rotary shadowing with platinum/carbon (Pt/C). Topographic data were obtained, and differences between the two mutant forms of the antibody were clearly visible.

ISSN:1071-1023    

DOI:10.1116/1.587276

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Scanning tunneling microscopy (STM) observations made on pBR322 DNA are compared with methods known to give information on DNA intrinsic curvature: polyacrylamide gel retardation, electron microscopy and computer modeling. It is concluded that STM is a powerful method for studying DNA structural features. Moreover, it is the only method to reveal simultaneously nanometric scale detail and long‐range information. Use of STM for analyzing fine DNA structural features in regions involved in gene regulation should make an important contribution to genetics.  

ISSN:1071-1023    

DOI:10.1116/1.587277

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Magnetotactic bacteria and live human platelets were investigated by atomic force microscopy (AFM). Contributions to the measured height profiles due to different local mechanical properties were determined by force modulation microscopy. We found that in the case of the thick‐walled bacteria the intracellular structures did not significantly influence the overall topology measured by AFM. The magnetosomes were only visible in the force modulation mode, in the case of the platelets the images were dominated by the cytoskeleton and the organelles. The local composition of the cytoskeleton was analyzed by subsequent steps of degradation of certain fibers with specific drugs during AFM imaging.  

ISSN:1071-1023    

DOI:10.1116/1.587278

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

This paper reports direct imaging of cells with a new scanning mode for atomic force microscopy (AFM), a tapping mode for AFM (TMAFM). Two kinds of cells,Escherichiacoli(E.coli) and cultured hamster ovary (CHO) cells, prepared on indium tin oxide (ITO) glasses were observed in air. The TMAFM yielded very reproducible images without appreciable modifications of the sample surfaces. The images were examined in two modes of the data representation; normal height‐mode and deflection‐mode (similar to a first derivative of height‐mode data) representations. The deflection‐mode image of theE.colisample showed much finer surface details than the conventional height‐mode one, while the height‐mode image of the CHO sample provided more detailed structure than the deflection‐mode one.

ISSN:1071-1023    

DOI:10.1116/1.587279

出版商:American Vacuum Society    

年代:1994

数据来源: AIP