Which microscope should be used to view bacterial cells?
As a precision instrument for magnifying and observing objects, different optical microscopes can observe different types of samples. Users in industries such as microbiology, plant research, and animal research need to see the size level of bacteria. Therefore, when observing such samples, what kind of microscope should be used? This article provides a detailed analysis.
The answer to this question can be discussed from the aspects of bacterial cell size, human eye and microscope resolution.
1. The size of bacterial cells is generally in the micrometer range, taking Escherichia coli as an example: the length is about 1um and the width is about 0.5um.
2. Resolution refers to the small distance between two objects that can be clearly distinguished.
The resolution of a microscope refers to the minimum distance between two objects that can be clearly distinguished after magnification and imaging.
The resolution of an instrument refers to its ability to provide information on the microstructure of the object being measured. The higher the resolution, the more detailed the information provided. The amplification factor that exceeds the amplification limit is called invalid amplification, which cannot provide more information about the fine structure.
3. The resolution of the human eye is 0.1mm, which means that under sufficient light and a distance of 1 foot, the average human eye can distinguish a small distance of 0.1mm between two points.
4. In summary, to see the presence 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 are only a small dot, and in order to see more detailed structural information, it is necessary to increase the magnification of the microscope.
5. The resolution of a regular optical microscope is limited by the visible light wavelength (390-770nm) and generally does not exceed 1000 times, which is the amplification limit of a regular optical microscope. Magnification beyond 1000 times cannot provide more detailed structural information, which falls within the scope of ineffective amplification.
6. The magnification of an electron microscope can reach 800000 times, and its basic principle is the same as that of a regular optical microscope, which generates short wavelength electron waves through high pressure.
By zooming in at 400 times (10x, 40x), you can barely see the bacteria, but they are only the size of a needle tip, like small dots. Usually, we still zoom in to 1000 times (10x, 100x) for observation, and at this time, the appearance of the bacteria can still be clearly seen, even after special staining of flagella. To magnify 1000 times, you need to use an oil mirror. The so-called oil mirror is to drop a drop of cedar oil between the objective lens and the cover glass. The refractive 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 10x and 40x. The magnification of the eyepiece is multiplied by the magnification of the objective lens to obtain the total magnification of this microscope. The eyepiece and objective of a microscope used in middle school can be replaced, and the eyepiece is generally 5x or 10x. The eyepiece of a small microscope is usually only 10x, and it can examine Escherichia coli, Staphylococcus aureus, Bacillus subtilis, and Bacillus megalobus (used to observe spores).
