To observe bacteria, what type of microscope should I use?
As a precision instrument for magnifying and observing objects, optical microscopes can observe different types of samples. Users in industries such as microbial research, plant research, animal research, etc. need to see the size level of bacteria. Therefore, what kind of microscope should be used when observing such samples? 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 smallest 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 the microscope magnifies the image.
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. Exceeding the amplification limit is called ineffective amplification, which cannot provide more information about subtle structures.
3. The resolution of the human eye is 0.1mm, which means that under sufficient lighting and a distance of 1 foot, the smallest distance that the human eye can distinguish between two points is 0.1mm.
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 small dots, and in order to see more detailed structural information, it is necessary to increase the magnification of the microscope.
5. The resolution of ordinary optical microscopes is limited by the wavelength of visible light (390-770nm), and generally does not exceed 1000 times, which is the maximum magnification of ordinary optical microscopes. Magnification exceeding 1000 times cannot provide finer structural information and 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 voltage.
By zooming in 400 times (10x, 40x), you can barely see the bacteria, but they are only the size of a needle tip, like small dots. We usually zoom in to 1000 times (10x, 100x) to observe, and at this time, the appearance of the bacteria can still be seen quite clearly. After special staining, the flagella can also be seen clearly. To magnify 1000 times, you need to use a magnifying glass. The so-called oil mirror is to drop a drop of tar between the objective lens and the cover glass. The refractive index of tar is higher than that of air, so that a larger magnification can be used.
10x and 40x indicate that this lens is magnified 10x and 40x. The magnification of the eyepiece multiplied by the magnification of the objective lens gives the total magnification of the microscope. The eyepiece and objective of the microscope used in middle school can be replaced, and the eyepiece is usually 5x or 10x. The eyepiece of a small microscope is usually only 10x, which can be used to observe Escherichia coli, Staphylococcus aureus, Bacillus subtilis, and Bacillus subtilis (used to observe spores).
