Current State and Future Prospects of High-Speed AFM

Abstract

Structural biology has solved the atomic structure of many proteins, but all revealed are static snapshots. Single-molecule biophysics has recorded the dynamic action of proteins but only in an indirect way of observing optical markers attached to the molecules. To overcome these limitations, various techniques were developed towards a great speed performance of AFM. Through these efforts, high-speed AFM (HS-AFM) was established a decade ago. HS-AFM enabled for the first time direct observation of protein molecules during their functional activity. A few tens of different protein systems have already been observed with HS-AFM. These imaging studies have demonstrated that HS-AFM can provide deep insights into the functional mechanism of proteins inaccessible with other approaches. This line of imaging studies are now actively carried out. In parallel with this activity, further technical developments have also been performed towards the functional extension of HS-AFM. The targets of HS-AFM is now being expanded from purified molecules to organelles, bacteria, and eukaryotic cells. This review first describes the outline of HS-AFM techniques and its application studies performed so far. Then, it shows remaining technical issues to be solved and proposes ways to overcome these issues.