Service Manuals, User Guides, Schematic Diagrams or docs for : Agilent MAC Mode Imaging of Biological Molecules with 7500 AFM - Application Note 5991-3672EN c20141020 [2]

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MAC Mode Imaging of Biological Molecules with 7500 AFM - Application Note 5991-3672EN c20141020 [2]


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Keysight Technologies
MAC Mode Imaging of Biological
Molecules with Keysight 7500 AFM
Application Brief




Introduction                                  examples of high-resolution MAC mode
                                              imaging of biological samples in liquid
One of the most appealing features of         using Keysight 7500 AFM will
atomic force microscopy (AFM) for the         be demonstrated.
field of biology is that it can operate
in aqueous environments, making this          Instrumentation
technique capable of monitoring or
measuring biological molecules under          The Keysight 7500 AFM/SPM
physiological conditions. In terms of         microscope is a high-performance
AFM imaging, the complexity of probe          instrument that delivers high resolution
oscillations and tip/sample force             imaging with integrated environmental
interactions in solutions is much higher      control functions. Keysight's patented
than that under ambient conditions. For       magnetic AC mode (MAC Mode) is              Figure 1. MAC mode imaging of lambda phage
instance, ordering of the liquid at a solid   offered as a system option. Switching       DNA in a buffer solution.
interface is a ubiquitous phenomenon          imaging modes with the Keysight
and such liquid structuring could have a
profound effect on the operation of an
                                              7500 AFM/SPM microscope is quick            Imaging of DNA in
                                              and convenient, a result from the
AFM, causing the tip to hop between           scanner's interchangeable, easy-            a Buffer Solution
different stable configurations in the        to-load nose cones. Every aspect of
ordered region of the fluid. A Keysight       the Keysight 7500 AFM's design and          Lambda phase DNA is used as the first
Technologies, Inc. patented magnetic          construction are optimized to reduce        example to demonstrate the effective
AC (MAC) mode is developed as a better        mechanical noise, and deliver industry      AFM imaging in liquid. When DNA in a
approach to AFM in liquid, in which only      leading performance. The compact            buffer solution containing Ni++ or Mg++
the cantilever part of an AFM probe is        and completely encapsulated scanner         is added to a mica substrate, these
coated with a thin magnetic coating           provides easy cantilever exchange, a        divalent cations can form a charge
and the introduction of an alternating        slot for (optional) preamps for STM         bridge between the negatively charged
magnetic field will induce a direct tip       and CSAFM operation, as well as an          phosphate groups on the DNA backbone
oscillation. This method eliminates           integrated, high-reliability connector to   and the negatively charged siloxy groups
the spurious resonances seen in fluid         interface with the control electronics.     on the mica. This will lead to stable
tapping mode. In addition, a substantial      All 7500 AFM's come with the lowest         immobilization of DNA molecules onto
signal-to-noise advantage is obtained         noise closed loop position detectors        the substrate. The amount of DNA that
for A/C mode AFM in fluids if the tip         to provide the ultimate convenience         can be adsorbed to bare mica strongly
is oscillated by direct application of a      and performance in imaging, without         depends on the DNA concentration in
magnetic force, as opposed to indirect        sacrificing resolution and                  the solution, soaking/reaction time,
mechanical excitation with an acoustic        image quality.                              as well as the buffer composition
transducer. In this application brief,                                                    and buffer pH. Figure 1 is an AFM
                                                                                                    Figure 2 (right). Careful examination also
                                                                                                    shows the donut like trimer structures
                                                                                                    that are likely connected by fibrous arms.
                                                                                                    This demonstrates that MAC mode
                                                                                                    AFM is a favorable method in studying
                                                                                                    the topography of soft and weakly
                                                                                                    attached biological samples, capable of
                                                                                                    revealing single- or even sub-molecular
                                                                                                    structures with high resolution under
                                                                                                    physiological conditions.


                                                                                                    Summary
                                                                                                    Using imaging of DNA and purple
Figure 2. MAC mode imaging of purple membrane proteins in a buffer solution.                        membrane proteins in well-controlled
                                                                                                    buffer solutions as two examples, it
                                                                                                    is demonstrated that high-resolution
topographic image showing a case of                 force microscopy (DFM) methods like             imaging of biological samples at single
high surface coverage of DNA molecule.              tapping mode and MAC mode are                   molecular level can be achieved readily
Individual DNA molecules with various               designed to reduce the lateral force            with Keysight 7500 AFM.
configurations are clearly observed.                exerted on the sample surface, thus
                                                    better suited for imaging soft and weakly
Molecular-level                                     attached biological samples. However,           AFM Instrumentation
                                                    tapping mode in solution is difficult to
Visualization of Purple                             operate. Also for delicate samples like
                                                                                                    from Keysight
                                                    PM, the force for imaging has to be very
Membrane Proteins via                               extremely low; otherwise the lattice
                                                                                                    Keysight Technologies offers high-precision
                                                                                                    modular AFM solutions for research
MAC Mode Imaging                                    structure of the PM would be easily             industry, and education. Exceptional
                                                    destroyed. Fortunately with MAC mode,           worldwide support is provided by
Bacteriorhodopsin is a light-driven                 the oscillation of the cantilever is directly   experienced application scientists and
proton pump in the cell membrane                    driven by an oscillating electromagnetic        technical service personnel. Keysight's
of Halobacterium salinarium. The                    field, thus the interaction force between       leading-edge R&D laboratories are
bacteriorhodopsin molecules adsorb                  the tip and the sample can be more              dedicated to the timely introduction and
on freshly cleaved mica substrate to                accurately controlled. Consequently,            optimization of innovative and easy-to-use
form a densely packed 2-dimensional                 high resolution images of the lattice           AFM technologies.
membrane. The membrane has a                        structure of PM can be achieved using           www.keysight.com/ind/afm
distinguished purple color, thus often              MAC mode in solution.
called purple membrane (PM) in the
literature. PM is stable on mica under              The densely-packed bacteriorhodopsin
a pH ranging from 4 to 9, and they can              molecules form highly ordered 2-D
form patches of several hundred nm to               trigonal lattices in the purple membrane.
several microns in size. The thickness of           A topography image of a patch of PM
the membrane is about 5.5nm in average              of about 200nm in size, obtained by
and changes slightly with pH. Contact               MAC mode, is presented in Figure 2
mode AFM has been used to image PM                  (left). The hexagonal arrangement of
in KCL solutions of different pH level.             the bacteriorhodopsin molecules with
Till today, most of the high resolution             a repeating unit of about 6nm and a
images of PM seen are achieved by                   corrugation of less than 0.8nm is clearly
contact mode AFM. However, contact-                 revealed by the MAC mode image. At
mode imaging is less suitable for weakly            high magnification, the arrangement of
attached bio-sample, because bio-                   bacteriorhodopsin trimers in each of the
molecules are often disrupted by the                repeating unit in the membrane revealed
AFM stylus during scanning. Dynamic                 a distinct donut-like shape, as seen in




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