Development of video atomic force microscopy for in vivo bioimaging of biological processes

The ability to image biological entities is crucial to many key developments in science. Atomic force microscopy allows visualisation of living cells and systems without labels, in real time, with good spatial and temporal resolution. However a drawback of this technology, in order for it to be widely applicable to be used in high-throughput and for study of dynamics, is the time taken for image capture. We are at the forefront of development of VideoAFM, which will increase the speed of imaging by 1000 fold. This will revolutionise the use of the technology in many biological applications. This unique project will fully integrate technology development with addressing real biological problems in the area of microbial cell surfaces. In particular we will examine the surface properties of the major pathogen Staphylococcus aureus, which allow it to interact so successfully with its human host. A direct collaboration between the investigators and a commercial manufacturer of the technology will allow practical outcomes to be converted into real products within a short timespan. Thus the project will overcome existing limitations to give a widely useful technology for biological science, which will be exemplified by the applications carried out during the project.

The recent development of VideoAFM has provided a 1000 fold increase in frame-rate compared to conventional AFM technology. However, to bypass the limitations of the standard approach to AFM, we have had to completely reappraise the way in which the sample is scanned and the way in which the AFM tip tracks the sample surface. This has introduced several issues for the application of the technology to biological systems, and it is the purpose of the current application to address these issues and test the technology through application to several key areas in our understanding of the human pathogen S. aureus. Imaging in liquid is central to bio-applications. We will develop VideoAFM for stable use in liquid, and methods for the rapid control of sample environment to facilitate the in-situ observation of processes with nanometre spatial and sub-second temporal resolution. This will allow direct, real-time imaging of processes such as the action of antibiotics on living cells. Imaging with chemical specificity is one of the strengths of conventional AFM, but is currently beyond the capabilities of VideoAFM. We will develop a technique for rapidly monitoring the frictional force component, and apply this to the in-situ mapping of cell-surface physical properties at the molecular scale. We will also develop a combined video-rate and conventional AFM approach to the measurement of surface interaction forces, using VideoAFM scan rates to find areas/times of interest and automated switching to conventional AFM to then locally probe the functionalised tip / surface interaction. High throughput methods require large areas to be rapidly imaged with molecular resolution. We will combine conventional and resonant scanners to allow macroscopic areas to be imaged with VideoAFM through a tiling process, so that hundreds of microns can be imaged in tens of seconds at nanometre resolution, allowing comparison of surface structure over large populations of bacteria.