Outlining the different types of microscopes and their uses in cell biology.
The microscope has been around for centuries, and there are various people credited with its invention. Over the years, many different types of microscopes have been invented, all with their own benefits towards furthering our understanding of the cells which build up every living organism. The simplest of all the microscopes is the common light microscope, which was the first to be invented, and most will have used during science lessons at school to view various slides. Modern light microscopes usually have a highest resolution of 0.2μm, and can be used to view the overall structure of cells, whilst only being able to define some of the larger organelles. Different views can be obtained by manually switching the optical components such as the lense, for example phase-contrast and interference-contrast optics, which can allow for a clearer view of the specimen. The microscope works by shining a bright light through the specimen, which must be thin enough to allow the light to pass through, and chemically fixed.
However, this is not the only type of microscope available for observing cells. A fluorescent microscope can be used to view specific parts of a specimen, by using fluorescent dyes which bind to relating proteins in the parts of the substance you wish to view. It works similarly to a light microscope, except it works using two colour filters before the light hits the eye, one before the specimen and one after. The first ensures only light which will excite the dye reaches the specimen, and the second filters out this light, allowing the wavelengths of light emitted by the fluorescent dye to pass through. This makes the dyed objects appear bright on a dark background, and can be used to observe specific things without background noise and images, for example watching the movement of chromosomes during mitosis.
A specific type of fluorescent microscope exists, and is known as a confocal microscope. This works along the same principles as fluorescent microscopy, but uses a laser to illuminate the specimen instead of light. The laser is focused on one pinhole region of the specimen at a specific depth, allowing a crisp clear image of the fluorescent dye at that point. The laser then be scanned across the image, building up a clear 2D image of the specimen which might not be achieved using a simple fluorescent microscope due to dyes at different depths.
The most powerful type of microscope currently available is an electron microscope, of which there exists two types. A transmission electron microscope can resolve up to 2 nm of detail. It uses a beam of electrons hitting the image and then being detected, then processed to appear on a screen, using heavy metal stains to increase the contrast. The specimen must be extremely thin, and placed in a vacuum, therefore studying living specimens is an impossibility. However, the level of detail it provides allows us to observe the workings of organelles themselves. A scanning electron microscope takes things a step further, scanning the electron beam across the specimen and using the information to construct a high detail 3D rendition of the specimen’s surface. Though this can only be viewed at a resolution of 3-20nm, the 3D aspect of the imaging is incredibly useful when studying specific types of cells.