Nils Petersen, PhD




Research in our group is focused on understanding intermolecular interactions in biological membranes and the processing of molecules and nanoparticles as they enter the cell. We study the dynamics and distribution of molecules within the membrane as a means of understanding their function in events such as cell-cell communication, signal transduction, endocytosis and cell differentiation. To this end, we use spectroscopic and microscopic techniques that are suited to study single molecules or molecules at low concentration. There are four major themes:

1. Studies of the distribution and extent of aggregation and interaction of membrane receptors in living cells.

This work is based on analysis of laser scanning confocal microscopy images (Fig 1A) to estimate the density of protein clusters and their sizes. We have developed specific tools - Image Correlation Spectroscopy (Fig 1B) and Image Cross-correlation Spectroscopy for this purpose. 

2. Studies of the dynamics of movement of molecules, clusters, and nanoparticles in living cells.

This work applies fluorescence photobleaching, fluorescence correlation spectroscopy and dynamic image correlation spectroscopy (Fig 2) to study the diffusion and flow of individual molecules or complexes on the surface or within the cell. This provides detailed information of which molecules interact and how the dynamics relates to their function

3. Studies of interactions of nanoparticles with cell membranes

This work aims to understand the mechanism(s) whereby nanoparticles attach to cell surfaces and the pathways whereby they are internalized (endocytosed) in living cells.  We also wish to understand the fate of these nanoparticles as well as the effect they may have on cellular functions, such as growth, division, and differentiation.  The major tools are electron microscopy and fluorescence microscopy, but in the future, we wish to explore other tools, such as secondary ion mass spectrometry.  Figure 3 shows an example of the distribution and colocalization (yellow) of gold nanoparticles (green) and lysosomes (red).

4. Studies of lung surfactants from healthy and dysfunctional animals.

The purpose is to understand how the particular lipids and proteins present in lung surfactants affect the function and malfunction of the surfactant films in lungs. The objective is to establish the phase behaviour of the systems (Fig 4A), to identify the composition and physical characteristics of different phases (Fig 4B) and to establish the mechanism whereby these components create a low surface tension environment dynamically. The program combines imaging by fluorescence, atomic force microscopy (Fig 4A) and secondary ion mass spectrometry (Fig 4B).