**Part 4**

**Viral Physiology** 

232 Atomic Force Microscopy Investigations into Biology – From Cell to Protein

Végh G.A., Nagy K., Bálin Z., Kerényi Á., Rákhely G., Váró G., and Szegletes Z. (2011).

Vie V., Van Mau N., Lesniewska E., Goudonnet J.P., Heitz F., and Le Grimellec C. (1998).

Werten P.J.L., Remigy H.W., de Groot B.L., Fotiadis D., Philippsen A., Stahlberg H.,

Wu H.W., Kuhn T., and Moy V.T. (1998). Mechanical properties of l929 cells measured by

Zasloff M. (1987). Magainins, a class of antimicrobial peptides from Xenopus skin: isolation,

Biomed. Biotechnol. doi:10.1155./2011/670589

phosphatidylcholine monolayers. Langmuir 14:4574-4583. Volkenstein,M. 1981. Physique des membanes. *In* Biophysique. Moscou. 345-75.

protein structure and function. Febs Letters 529:65-72.

crosslinking. Scanning 20:389-397.

Proc. Natl. Acad. Sci. U. S. A. 84:5449-5453.

Effect of antimicrobial peptide-amide,indolicidin on biological membranes. J.

Distribution of ganglioside G(M1) between two-component, two-phase

Grubmuller H., and Engel H.A. (2002). Progress in the analysis of membrane

atomic force microscopy: Effects of anticytoskeletal drugs and membrane

characterization of two active forms, and partial cDNA sequence of a precursor.

**11** 

*Mexico* 

**Atomic Force Microscopy in** 

Norma Hernández-Pedro, Edgar Rangel-López,

*Neuroimmunology Unit, National Institute of Neurology and Neurosurgery, Mexico City* 

Properties of biological samples, such as DNA, proteins, components of bacterial surfaces and viruses have been studied extensively and provided the driving force for the outstanding progress of detection methods used in cell biology and physiology. Methods like magnetic twisting cytometry, laser-tracking microrheology, magnetic tweezers, the optical stretcher, and various cell indenters; have been used in the study of cell properties, however, imaging resolution has been low. Atomic Force Microscope (AFM) was developed by Binning, Quate and Gerber in 1986, and since its commercialization, AFM has been a powerful research tool in the scientific community, demonstrating its capability to provide images of biomolecules with high resolution. One of the most important benefits of AFM is the requirement of a minimal amount of sample to perform an accurate diagnostic. Also, AFM does not require staining, labelling, or samples coating, and it is possible to acquire images with minimal pre-treatment in a short time (sometimes minutes). AFM can also be used for real-time and high-resolution imaging of hydrated biological specimens ranging

AFM is a member of the family of probe microscopes used to scan and characterize surfaces. It generates topographical images from a variety of materials with resolutions of a nanometer (nm) fraction. AFM consists of a microscale rectangular or "V"-shaped cantilever **(Table 1)**, typically made of silicon or silicon nitride, with a sharp tip (probe) at its end, with a tip radius of curvature on the order of 50–100 nm. The tip is mounted at the end of a flexible cantilever that serves as a force sensor. The topography of a sample is obtained by measuring and modulating the interaction forces between the tip and the sample, by maintaining a constant tip-sample separation and using Hooke's Law (F = -kx where F is force, k is the spring constant, and x is the cantilever deflection), the force between the tip and the sample are calculated and derive information about the surface of the sample. The movement of the cantilever is controlled in x, y, and z axis by piezoelectric crystals. A laser-based optical system is used to track the deflection of the cantilever with respect to the sample surface. As the tip encounters surface features, tiny disturbances in z cause the cantilever to bend. This movement is amplified by a laser beam focused on the backside of the cantilever that reflects

**1. Introduction** 

from single molecules to whole cells and tissues.

**2. Fundamentals of atomic force microscopy (AFM)** 

onto a split photodiode, tracing the position of the cantilever.

**Detection of Viruses** 

Benjamín Pineda and Julio Sotelo
