What kind of microscope should be used to observe bacteria?
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, and animal research need to see the level of bacterial size. What kind of microscope should be used when sorting samples is analyzed in detail in this article.
Answering this question can be discussed in terms of the size of bacteria, the resolution of human eyes and microscopes, etc.
1. The cell size of bacteria is generally on the micron level. Take Escherichia coli as an example: the length is about 1um and the width is about 0.5um.
2. Resolution refers to the minimum distance between two object points that can be clearly distinguished.
The resolution of the microscope refers to the Z minimum distance between two object points that can be clearly distinguished after the microscope zooms in on the image.
The resolution of the instrument refers to the ability of the instrument to provide the microstructure information of the measured object. The higher the resolution, the more detailed the information provided. The magnification beyond the magnification limit is called invalid magnification, and invalid magnification cannot provide more detailed structure information.
3. The resolution of the human eye is 0.1mm, that is, under the condition of sufficient light and a distance of 1 foot, the minimum distance between two points that the general 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 just a small spot. To see its finer structural information, the magnification of the microscope must be increased.
5. The resolution of ordinary optical microscope is limited by the wavelength of visible light (390~770nm,), generally it will not exceed 1000 times, which is the extreme value of magnification of ordinary optical microscope. The magnification of more than 1000 times cannot provide finer structural information, which belongs to the range of invalid magnification.
6. The magnification of the electron microscope can reach 800,000 times. Its basic principle is the same as that of the ordinary optical microscope, which is to generate short-wavelength electron waves through high voltage.
When magnified 400 times (10x, 40x), bacteria can be barely seen, but only the size of a needle tip, like small dots. Generally, we magnify to 1000 times (10x, 100x) to observe. At this time, the appearance of the bacteria can still be seen clearly, even after special dyed flagella. 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 refraction index of cedar oil is higher than that of air, so that a larger magnification can be used.
10x and 40x indicate that the lens is magnified 10 times and 40 times. 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 middle schools can be changed, and the eyepieces are generally 5x and 10x. The eyepiece of a small microscope is generally only 10x, and I have seen Escherichia coli (E.coli), Staphylococcus aureus, Bacillus subtilis, and Bacillus megaterium (used to see spores).
