Atomic force microscopy is the only technique that provides sub-nanometer resolution under physiological conditions, needed for imaging biological species like proteins and living cells. This is my view and a summary of techniques for advanced topographical imaging, sensitive force measurements and AFM in combination with optical microscopy.
Having my background in organic chemistry and biological sciences, I wrote a review article for “Nanotoday” a few years ago, that covers a wide range of aspects of using atomic force microscopy (AFM) for biological applications. Until now, this paper still serves as a nice overview for both beginners using AFM for biosamples, but also for experienced users in this field, covering the following topics:
· High resolution imaging of biological species
· Single molecule force measurements
· Topography and recognition imaging
· Combined AFM and optical microscopy
The first part deals with one of the biggest strengths of AFM, requiring the highest art and greatest skills at the same time: the ultimate resolution on imaging biological objects — from single proteins or DNA up to live cells. An important pre-requisite is the tight binding to the substrate, respectively the sample preparation part. Doing this right separates success from failure in many cases.
A somehow neglected field in AFM is sensitive force measurements, ranging from pulling on single complexes, like antigen-antibody or ligand-receptor pairs, up to the unfolding of various protein systems. Only a few groups have pioneered in being able to modify the cantilever tips, making them specific biological sensors down to the single molecule level.
A brilliant method for the localization of specific binding sites with nanometer positional accuracy is “recognition imaging”. It combines dynamic imaging with single molecule recognition force spectroscopy in a much faster and gentle way than off-resonance imaging modes used as an alternative to get this information.
Finally, combining AFM with electromagnetic waves (infrared, Raman, microwaves) opens the path to the spectroscopic discrimination of different species in a biological sample. In particular, fluorescence microscopy has proven to be a powerful tool for selective and specific visualization of labeled molecules down to the single molecule level, rendering it possible to follow cellular processes and monitor the dynamics of living cell components.
And here is the link for this review article in “Nanotoday”, enjoy reading!