摘要:

The excitation frequency of the cantilever is a key parameter in tapping mode atomic force microscopy (AFM) that determines the tip‐sample forces. If the driving frequency is adjusted to values slightly above the resonance frequency stable imaging with net attractive forces can be achieved without manipulation of the quality factor of the cantilever resonance. A reduction of the driving frequency below the resonance leads to a repulsive imaging regime with minimized repulsive forces. These phenomena are studied by numerical simulations that show the variations of the interaction forces between tip and sample due to variations of the driving frequency. The interaction forces can be tuned over the entire range from net attractive to net repulsive by adjustment of the excitation frequency. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1639721

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Regarding the performance of an atomic force microscope adapted to a complex task, not only its sensitivity matters e.g. to finally build a cryogenic electrostatic force microscope. While allowing a stable measurement, the instrument has to be compact to enter the cryostat, it must be easy to adjust under these conditions, and it should allow a certain flexibility in its operational modes. Furthermore, linearity of the measurement is desired at for a range that is adapted to the measurement. Under this focus, we compare an interferometric detection scheme to standard optical beam deflection. A fiber‐optical interferometric detection gains in compactness and mechanical stability relative to the optical beam deflection, but at the price of intrinsic non‐linearities. The need to adjust the interferometric cavity turns into another advantage. Three conceptually different arrangements compatible with electrostatic force microscopy are discussed that additionally allow for a sample‐independent control of the cantilever’s position. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1639722

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We report the use of piezoelectric quartz tuning forks as force sensors for variable temperature magnetic force microscopy. As the Q‐factor of the sensor alters with temperature we have investigated the effect of electronically varying the Q‐factor at constant temperature to elucidate how the sensitivity of the sensor depends on the Q‐factor. We find that the sensitivity improves in proportion to the Q‐factor. The signal‐to‐noise ratio also improves as the Q‐factor is increased. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1639723

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Analysis of biomolecules at single molecular level has been revealing the mechanism of their function. Mechanical property of protein molecules, in the other hand, has been studied using atomic force microscope (AFM) and other techniques, which is going to give a basal for understanding these complicated and sophisticated macromolecules as nano‐machinery. For further evolution of these studies, simultaneous monitoring of function and mechanical perturbation will help to find the relation between mechanical structure and function of these molecules. Using a system combining AFM and total internal reflection fluorescence microscope (TIRFM), we showed that fluorescent protein, GFP molecule, was picked up with AFM probe and possible to investigate its fluorescence. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1639724

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Enzyme activities of V8 protease on AFM tip were investigated by measuring its force curves. The enzyme was immobilized onto the surface of the chemically modified AFM tip; two kinds of peptides were immobilized to the mica surface by a hetero‐reactive reagent. One peptide was designed to be recognized and digested by the enzyme. Another was designed so as not to be recognized by the enzyme. Force curves were obtained by plotting the applied force on the cantilever as a function of the sample displacement. Force applied on the cantilever, over 1.5 nN, was often observed when the tip contacted to a peptide that was digestible by the enzyme. In contrast a force of less than 0.4 nN was observed for contact with other peptides. Large force over 1.5 nN seemed to be caused by rupturing of the intermediate form of the enzyme and the peptide. It was suggested that enzyme molecules on the AFM tip can recognize the target sequence of the peptide. This method can be a tool to analyze biomolecules on a surface. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1639725

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Atomic force microscope (AFM) can be successfully used for simple and fast solution of many applied biological problems. In this paper the survey of the results of the application of atomic force microscope SolverP47BIO (NT‐MDT, Russia) in State Research Center of Virology and Biotechnology “Vector” is presented. The AFM has been used: ‐ in applied virology for the counting of viral particles and examination of virus‐cell interaction; ‐ in microbiology for measurements and indication of bacterial spores and cells; ‐ in biotechnology for control of biotechnological processes and evaluation of the distribution of particle dimension for viral and bacterial diagnostic assays. The main advantages of AFM in applied researches are simplicity of the processing of sample preparation and short time of the examination. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1639726

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

&lgr;‐DNA molecules have been deposited on mica partially covered by a Pt film and visualized by AFM operating both in standard contact and spreading resistance (SRM) modes. Depend on procedure of deposition, DNA molecules have different apparent heights and contrast in spreading resistance mode. We demonstrate that the absence of conductivity is caused by a very large compression deformation of DNAs under deposition technique. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1639727

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Regularly striped patterns are observed when imaging supported, mixed bilayers of the phospholipid DPPC and a synthetic &agr;‐helical transmembrane peptide (WALP) with contact mode AFM at ambient temperature. Temperature dependent AFM is used here as a tool to observe the temperature behavior of this system. Melting in a 2 mol&percent; peptide/DPPC system starts at 36°C. The domains lie higher than the surrounding lipid bilayer at low temperatures (< 36°C), but change to lower lying areas above that temperature. In contrast, pure lipid bilayers do not start melting until 40.5°C. Melting seems to start at defects present in the lipid bilayer. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1639728

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The interaction of 100 &mgr;M cytotoxic metals with pancreatic cells was studied at membrane level by Atomic/Lateral Force Microscopy (AFM/LFM), an approach that gave both topographic (with typical 10–15 nm resolution) and chemical information (LFM) on the membrane. Different modifications at membrane level took place as consequence of distinct metal‐dependent pattern of cell degradation. In particular the morphology of pancreatic cells change upon cadmium, lead and zinc uptake with several areas of lateral friction contrasts (due to different chemical composition) detected after Cd and Zn but not after Pb loading. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1639729

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Biology of the toxins violently depends on their carbohydrate‐binding centres’ organization. Toxin tetramerization can lead to both increasing of lectin‐binding centres’ number and changes in their structural organization. A number and three‐dimensional localization of such centres per one molecule strongly influence on toxins’ biological properties. Ricin was used to obtain the AFM images of natural dimeric RIPsII structures as far as ricinus agglutinin was used for achievement of AFM images of natural tetrameric RIPsII forms. It is well‐known that viscumin (60 kDa) has a property to form tetrameric structures dependently on ambient conditions and its concentration. Usage of the model dimer‐tetramer based on ricin‐agglutinin allowed to identify viscumin tetramers in AFM scans and to differ them from dimeric viscumin structures. Quantification analysis produced with the NT‐MDT software allowed to estimate the geometrical parameters of ricin, ricinus agglutinin and viscumin molecules. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1639730

出版商:AIP    

年代:1903

数据来源: AIP