Cells are the smallest unit of life. They are intricate, complex nanomachines that perform a large variety of complex tasks that, taken together, result in the living organisms we see around us. Cells do all this with a minimal set of building blocks that make up all organic molecules. To still perform all these complex functions, cells arrange the organic molecules with tremendous precision. Inside a cell is a complex arrangement of building-blocks that all interact with each other. Some of these building-blocks only have a size of a few hundred atoms. Yet, together they arrange into intricate assemblies that make up the parts of this nanoscale machine. Slight deviations from this arrangement can lead to catastrophic failure and subsequently to diseases in the whole organism. Therefore, one of the critical challenges for life science is understanding the detailed arrangement of the structures on and inside cells.
Cells are "alive," and life is always associated with change. For cells to perform their function, they continuously change their outer and inner structures. They do this to respond to changes in the environment, perform essential metabolic tasks, fight off invaders, or duplicate themselves. Seeing how the cells' components change during these processes is equally or even more important than just knowing how the structure is at any given point in time. However, observing change is challenging since many individual building blocks and structures are so small that one cannot see them with conventional light microscopes. More powerful microscopes are needed that can "see" objects much smaller than the wavelength of light exist, however, to achieve this level of detail, the cells need to be killed, fixed, and put in a vacuum.
A specialty type of microscope, the atomic force microscope (AFM), is the only technique capable of continuously observing living cells with nanometre resolution without killing them. It achieves this by gently tracing the cell's surface with a sharp needle called the AFM cantilever sensor. The signal from this cantilever needle is then used to reconstruct a 3D representation of the sample surface. One of AFM's main advantages is that it can image a sample in almost any environment and does not require any harsh sample preparation. Continuous high-resolution imaging of the outside surface of living cells for hours on end is possible. However, many of the important cellular processes happen on the inside of the cell. These processes are not addressable with AFM without breaking the cell open and thereby killing it.
This project aims to enable AFM imaging of the inside of the cell without killing it. For this, we only make a small incision in the cell membrane through which we insert the cantilever tip we can enter the cells without killing them. Using precise control of the needle's position, we can "feel our way" around inside the cell without breaking the fragile inner structures. Optimizing all components of our "InCell" microscope will help us obtain the necessary resolution and imaging speed to "film" some of the fundamental processes that are going on inside the cells.
The project has achieved spectactular results which have been published in high impact journals. We have successfully penetrated living cells with the AFM cantilever without killing them, making way for a new field of imaging inside cells. The InCell AFM as well as the InCell cantilevers have become a vital resource for our research as well as those of others who have already adopted the technology.
