Microscopes: why seeing smaller is not always better

Why are researchers working on a new type of microscope that has a lower resolution than those which already exist?

Antonie Van Leeuwenhoek first saw and described cells and bacteria through one of the first microscopes in the 17th century.

Since then we have wanted to know about biology in smaller and smaller scale. The first microscopes consisted of nothing more than a tube with a plate for the object in one end and a magnifying glass in the other. In the 18th century the resolution was improved by the development of lenses of bigger curvature resulting in greater magnification, and through combining several lenses together. It wasn't until the 20th century that new scientific theories and technologies allowed the creation of different types of microscopes altogether.

New technologies and methods in fluorescence microscopy will make it possible to understand cellular processes in a scale never seen before. Besides broadening our understanding of how life works, it will open endless new possibilities for the development of new treatments in fields such as cancer research, immunology and cardiovascular diseases. With these microscopes resolution of 20-50 nm should be commonly achievable.

What will fluorescence microscopes enable us to see?

Most microscopes ever invented have been 'optical'. That is they bounce light off an object in order to study it. However, light microscopy suffers from one weakness: limited resolution. Due to the wave nature of light, different waves in a beam of light interfere with each other, i.e. they diffract. Because of this, when a beam of light is focused using a lens, it forms a spot that is about 200 nm wide in the x- and y-directions and 500 nm long in the z-direction, depending on the wavelength of the light and the angle of which the lens can collect light.

Since the 1930's various types of electron microscopes have been invented and while remaining expensive, have come into fairly common usage. The development of the electron microscope, where a beam of electrons is used instead of a beam of light, greatly increased the resolution due to the smaller wavelength of electrons compared to photons. Photons are the particle which light is made of.

While electron microscopes revealed an entirely new world of detail never before observed they are generally not compatible with biological imaging. Samples need to be held in an airless vacuum in order to be viewed with an electron microscope. Also, techniques for the preparation of samples involve cutting the material to be observed into thin slices , use of metals such as uranium, lead or coating the sample with a variety of conductive metals. In any case, biological material viewed through an electron microscope is no longer alive.

There are many applications in biology and medicine where it would be desirable to have the resolution of an electron microscope without killing the sample. Although human and other animal cells are big enough to be observed with a light microscope, the functioning of the cells is regulated by the synthesis and transportation of proteins that often interact or bind together to perform specific functions. For example, our immunologic reactions are based on the ability of cells to produce proteins that target foreign objects. Also the death of a cell is regulated by proteins; the inability of cells to die in a controlled manner leads to cancer. However, with the typical resolution of a light microscope of about 200 nm it is not possible to tell if and how the proteins interact, how they are transported to specific parts of the cell and why they are needed there. Understanding these mechanisms is essential in medical research and the development of new treatments.

How do fluorescence microscopes work?