Category Archives: Microscopy

Understanding the Diffraction Limit in Microscopy

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Basic light microscopy can only resolve objects that are larger than 100 nm which means that while it can visualize animal cells (~10,000nm), organelles and bacteria (~1,000nm), it cannot visualize viruses (<100nm), proteins (<10nm) or small molecules(~1nm) (see post summarizing Biological Scales). This limitation is known as the “diffraction limit” and is caused by the fact light only interacts differently with objects separated by more than one wavelength (λ). Intuitively, its helpful to think of each of these wavelengths as “a minimum pixel size” for a computer image where: infrared light (λ ~ 10.0μm) has pixels 100 times larger than ultraviolet light (λ ~ 0.1μm).

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The “Spectrum” of Microscopic and Spectroscopic Techniques

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Electromagnetic (EM) radiation is our main source of information about the world (i.e. “seeing is believing”). Most scientific techniques rely on some form of imaging/visualization (“microscopy”) and/or measurement of energy absorption or emission (“spectroscopy”) or both (for instance: fluorescence microscopy). In the figure above we outline the spectrum of electromagnetic radiation from x-rays to microwaves and the different scientific techniques that each type of radiation supports.

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