Fibrin Strand

Nucleic acids, DNA, RNA and various proteins are the most common biomacromolecules examined with AFM. Visualization of conformations of individual DNA strands, DNA-protein complexes and other single macromolecules brings unique information that is hardly accessible by other methods.

(a) AFM image (400 x 400 nm) of double stranded DNA on mica obtained with NSC14/Hi-Res-C probe (now upgraded to Hi'Res-C14/Cr-Au).

(b) AFM image (400 x 400 nm) of hexagonal DNA self-assembly obtained with NSC14 AFM probe (now upgraded to HQ:NSC14).

Fig. 1. AFM images of double stranded DNA on mica (a) and hexagonal DNA self-assembly obtained with series 14 AFM probes. Scans courtesy of S.Magonov (Agilent). Sample courtesy of A. Koyfman (UCSB).

An example of an AFM image of DNA is given in Fig 1a. Supercoiling is one of the most interesting DNA-related phenomenon, which is the focus of many studies with emphasis on high-resolution imaging with ultra sharp AFM probes. High-resolution visualization of DNA is also the subject of studies addressing the formation of DNA-protein complexes and the results of enzyme cleavage. Other properties that have been successfully investigated with AFM are DNA stiffness and elasticity and the segmental dynamics of DNA. In the past five years, there has been intense research into the construction of 2D and 3D architectures using self-assembly of single stranded DNA macromolecules. AFM has become the most useful technique for the characterization of these arrays. One such example is the hexagonal DNA array is seen in Fig. 1b.

An example of AFM images of another biomacromolecule is given below.

(a) Fibrinogen molecules. Scan size 300 nm.

(b) Single fibrin strand. Scan size 400 nm.

Fig. 2. AFM images of fibrinogen molecules (a) and single fibrin strands (b). The image in (a) was obtained with a regular AFM probe of the 14 series and image in (b) with a Hi'Res-C AFM probe. The color contrast (red-to-white) covers a 0 - 3.5 nm height scale. Images courtesy of L. Chtcheglova.

Two AFM images of plasma protein fibrinogen and its assemblies known as fibrin are presented in Fig. 2a-b. These images demonstrate that Hi'Res-C AFM probes provide higher resolution in images of the fibrin, making fine features of the aggregate visible.

Topography image of individual fibrin molecules obtained using a General Purpose AFM probe is shown in Fig. 3.

Fig. 3. Tapping mode topography image of single molecules of fibrinogen on mica (Agilent 5500 AFM, General Purpose AFM probe). Scan size 350 x 350 nm. Scan height 1.5 nm. Image courtesy of S. Magonov, Agilent Technologies.

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