Strategies for optimal biological imaging

If members of public are asked which two areas of science and engineering will have the most dramatic impact in the next decade, it is a fair bet to say that many people would mention either information technology or bioscience, possibly the human genome project, maybe Dolly the sheep.This project functions at the junction between these vitally important areas. Future developments in biology are highly dependent on imaging technologies. Nowadays, imaging means far more than taking a picture, it involves making accurate maps of different properties of cells and organisms. A related trend is the shift from simply imaging the structure of cells to imaging their function. In other words, can we see where specific biochemical reactions are taking place? Or can we observe changes in the electrical activity at the surface of a firing neuron? Measurement of these processes gives great insight into biological functions. Fluorescent markers are usually used for functional imaging. These attach to different parts of the cell, often with great specificity. When illuminated with light of one wavelength (colour) they emit photons (light) of a different wavelength, this allows the presence of the fluorescent tags and the part of the cell to which they are associated to be precisely located. Fluorescence microscopy has been enormously important in enabling biologists to elucidate many subtle chemical processes in cells and colonies of cells.Unfortunately, this is not enough because biological processes are very complicated and are heavily interrelated, we therefore need a lot of information to understand the different processes. We need to image on ever smaller scales (high spatial resolution), with better localization in time (temporal resolution) over longer periods. There is, thus, a need to acquire vast amounts of information.Nature, in general, and fluorescent molecules, in particular, are not generous in giving up information. A phenomenon called 'photobleaching' means that on average each fluorescent molecule can only be excited a finite number of times before it becomes exhausted and can no longer be used as a label. Even worse photobleaching is associated with toxicity thus damaging the samples we are trying to observe. In short photons are precious and must be used wisely.This is where the science of communication is so important because it defines laws that say how much information may be transmitted for a given photon budget. Adapting and developing these ideas to study new microscope techniques allows one to compare different methods as well as developing new optimized methods. This is particularly important when we develop so called superresolution methods that enable us to see objects smaller than the limits of conventional microscopy. These are potentially enormously significant but they are generally very expensive in photons.Another approach is to use labels such as gold nanoparticles, down to 5nm in diameter, that do not suffer from photobleaching. We will also examine the use of sound waves which at very high frequencies can, potentially, image even smaller objects than light. Another theme is development of novel customized optical detectors in response to the fact that many of these alternative optical techniques are not well served by existing light detectors. Although admirable for many purposes, they are not ideally suited for detecting small changes on a large background, that can arise when nanoparticles are used. Combining optical microscopy with other techniques, such as probe microscopies gives a great deal of complementary information that will greatly ease the demands on data gathering.This project is very broad ranging from theoretical analysis, novel optical system design through to electronics and signal processing. The project will deliver many important results and should spawn new projects that will enable us and others to generate new applicable technologies.