What type of microscope should be used for bacterial observation
Optical microscope is a precision instrument for magnifying and observing objects. Different optical microscopes can observe different types of samples. Users in industries such as microbial research, plant research, animal research and other industries need to see the level of bacterial size, then observe this. What kind of microscope should be used when classifying samples is analyzed in detail in this article.
The answer to this question can be discussed in terms of bacterial cell size, human eye and microscope resolution.
1. The size of bacteria is generally micron. Take Escherichia coli as an example: the length is about 1um and the width is about 0.5um.
2. Resolution refers to the smallest distance between two object points that can be clearly distinguished.
The resolution of a microscope refers to the minimum distance between two object points that can be clearly distinguished after the microscope is enlarged and imaged.
The resolution of the instrument refers to the ability of the instrument to provide information on the fine structure of the measured object. Higher resolutions provide more detailed information. The magnification beyond the magnification limit is called invalid magnification, and invalid magnification cannot provide more information on the fine structure.
3. The resolution of the human eye is 0.1mm, that is, under the conditions of sufficient light and a distance of 1 foot, the minimum distance between two points that the human eye can distinguish is 0.1mm.
4. To sum up: To see the existence of bacteria, the magnification must be at least: 0.1mm ÷ 0.5um = 1000 ÷ 5 = 200 times. However, at this magnification, the bacteria (Escherichia coli) seen is only a small dot, and the magnification of the microscope must be increased in order to see its finer structural information.
5. The resolution of ordinary optical microscopes is limited by the wavelength of visible light (390~770nm,), generally not more than 1000 times, which is the magnification limit of ordinary optical microscopes. The magnification of more than 1000 times cannot provide more detailed structural information, which belongs to the range of invalid magnification.
6. The magnification of the electron microscope can reach 800,000 times. The basic principle is the same as that of the ordinary optical microscope, which generates short-wavelength electron waves through high voltage.
At 400x magnification (10x, 40x), you can barely see the bacteria, but they are only the size of the tip of a needle, like small dots. Generally, we still magnify to 1000 times (10x, 100x) for observation. At this time, the appearance of bacteria can still be seen clearly, and the flagella can be seen clearly after special dyeing. To magnify 1000 times, you need to use an oil lens. The so-called oil lens is to drop a drop of cedar oil between the objective lens and the cover glass. The light refractive index of cedar oil is higher than that of air, so that a larger magnification can be used.
10x, 40x means the lens is magnified 10x, 40x. The magnification of the eyepiece is multiplied by the magnification of the objective to obtain the total magnification of the microscope. The eyepieces and objective lenses of the microscopes used in secondary schools can be replaced, and the eyepieces are generally 5x and 10x. The eyepieces of a little microscope are generally only 10x, and have seen Escherichia coli (E.coli), Staphylococcus aureus, Bacillus subtilis, and Bacillus megaterium (for viewing spores).
