What kind of microscope should be used for bacterial observation?
Optical microscope is a precise instrument for magnifying and observing objects. Different optical microscopes can observe different kinds of samples. Users in industries such as microbiology research, plant research and animal research need to see the grade of bacteria size. So what kind of microscope should be used when observing such samples? This paper analyzes in detail.
The answer to this question can be discussed from the aspects of the size of bacteria, the resolution of human eyes and microscopes.
1. The cell size of bacteria is generally micron-scale. Take E.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 objects that can be clearly distinguished.
The resolution of microscope refers to the minimum distance between two objects that can be clearly distinguished after the microscope enlarges and images.
The resolution of the instrument refers to the ability of the instrument to provide the micro-structure information of the measured object. The higher the resolution, the more detailed the information provided. The magnification beyond the amplification limit is called invalid amplification, which can not provide more information about the fine structure.
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 small distance between two points that the human eye can distinguish is 0.1 mm..
4. To sum up: In order to see the existence of bacteria, the magnification should be at least: 0.1mm ÷ 0.5um = 1000 ÷ 5 =200 times. However, at this magnification, the bacteria (Escherichia coli) seen is only a small point. In order to see its more subtle structural information, the magnification of the microscope must be improved.
5. The resolution of ordinary optical microscope is limited by the wavelength of visible light (390~770nm), which is generally not more than 1000 times, which is the amplification extreme value of ordinary optical microscope. Magnification of more than 1000 times cannot provide more subtle structural information, which belongs to the scope of invalid amplification.
6. The magnification of electron microscope can reach 800,000 times, and its basic principle is the same as that of ordinary optical microscope, which generates short-wavelength electron waves through high voltage.
You can barely see the bacteria when you zoom in 400 times (10x, 40x), but it is only the size of a needle tip, just like dots. Generally, we still zoom in to 1000 times (10x, 100x) for observation. At this time, the appearance of bacteria can still be seen clearly, even after specially dyed flagella. Zoom in 1000 times and you'll need an oil mirror. The so-called oil mirror is to drop a drop of fragrant tar between the objective lens and the cover glass. The light refractive index of fragrant tar is higher than that of air, so that a larger magnification can be used.
10x and 40x indicate that this lens is magnified by 10x and 40x. The magnification of the eyepiece is multiplied by the magnification of the objective lens to get the total magnification of this microscope. The eyepiece and objective lens of the microscope used in middle school can be changed, and the eyepiece is generally 5x and 10x. The eyepiece of a better microscope is generally only 10x, and I have seen Escherichia E.coli, Staphylococcus aureus, Bacillus subtilis, and Bacillus megaterium (used to see spores).
