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# 6: Experimental Characterization - Mass Spectrometry & Atomic Force Microscopy

• 6.1: Atomic force microscopy (AFM) on Membranes
Atomic force microscopy (AFM) is a technique with multiple applications in biology. This method is a member of the broad family of scanning probe microscopy and was initially developed in 1986 by Binnig et al to overcome the disadvantages of the scanning tunneling microscopy (STM).
• 6.2: Mass spectrometer Ionization Techniques for Membrane Proteins
Mass spectrometry is a technique in which charged particles from a sample are analyzed in order to obtain structural and compositional information about the sample. Mass spectrometry is particularly relevant when studying proteins. With this instrument, the determination of protein structure, function, and interactions is possible. A mass spectrometer can also detect post translational modifications on complex mixtures, perform both quantitative and qualitative analysis, and monitor enzyme react
• 6.3: Electrospray Ionization (ESI) Mass Spectrometry
Electrospray Ionization is a mass spectromentry method where macromolecules are ionized via a “soft” ionization, which does not fragment nor harshly degrade the macromolecules and ionizes by multiple charging. Rather, the macromolecules are ionized into small droplets that are then desolvated further, effectively decreasing the droplet size into molecules with protons. The protonated/desolvated molecules enter the mass analyzer and subsequently the detector to determine the mass/charge ratio.
• 6.4: Mass Analyzer Orbitrap
Mass spectrometry (MS) is an analytic instrument that is used to measure the mass-to-charge ratios (m/z) of samples to obtain qualitative and quantitative information. The development of MS started around 1920 where it was used to study the isotopic abundance of elements. MS capabilities have increased greatly since 1920.
• 6.5: Mass Analyzer Time of Flight
This article will focus on discussing mass spectrometry, time of flight (ToF, mass detector) and time of flight coupled with secondary ion mass spectrometry (ToF-SIMS) as a tool to study membrane lipids. In recent years, mass spectrometry has been a widely used tool to analyze complex biological systems.

Thumbnail: Illustration of a typical result from an AFM scan of a supported lipid bilayer. The bilayer shown here has several defects which appear as pits. By measuring the distance from the top of the bilayer to the substrate it is possible to determine the thickness of the bilayer. (Public Domain; MDougM via Wikipedia).