What type 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 microbial research, plant research, animal research and other industries need to see the size level of bacteria, so when observing this What kind of microscope should be used when analyzing samples? This article analyzes it in detail.
The answer to this question can be discussed from aspects such as the size of bacterial cells and the resolution of the human eye and microscope.
1. The size of bacterial cells is generally in the micron level. Taking 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 a microscope refers to the minimum distance between two object points that can be clearly distinguished after the microscope magnifies the image.
The resolution of the instrument refers to the ability of the instrument to provide information on the fine structure of the object being measured. Higher resolution provides more detailed information. Magnification that exceeds the amplification limit is called ineffective amplification, and ineffective amplification cannot provide more detailed structural information.
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 general human eye can distinguish is 0.1mm.
4. In summary: If you want 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 (E. coli) seen are only a small dot. To see its more detailed structural information, the magnification of the microscope must be increased.
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 extreme magnification of ordinary optical microscopes. Magnification exceeding 1000 times cannot provide more detailed structural information and falls into the range of ineffective amplification.
6. The magnification of an electron microscope can reach 800,000 times. Its basic principle is the same as that of an ordinary optical microscope. It 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 a pinhead, like small dots. Generally, we still magnify to 1000 times (10x, 100x) for observation. At this time, the appearance of the bacteria can still be seen quite clearly, and the flagellum can also 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 refractive index of cedar oil is higher than that of air, so that greater magnification can be used.
10x and 40x indicate that the lens magnifies 10 times and 40 times. The magnification of the eyepiece multiplied by the magnification of the objective lens gives the total magnification of the microscope. The eyepieces and objective lenses of microscopes used in middle schools are interchangeable. The eyepieces are usually 5x and 10x. The eyepieces of some microscopes generally only have 10x, which is used to see Escherichia coli (E.coli), Staphylococcus aureus, Bacillus subtilis, and Bacillus megaterium (used to see spores).
