Ultramicro spectrophotometer is a very important analytical instrument. Whether in the scientific research fields of physics, chemistry, biology, medicine, material science, environmental science, or in modern production management departments such as chemical industry, medicine, environmental detection, metallurgy, etc., ultraviolet-visible spectrophotometer has a wide and important application. Spectrophotometer is a very important analytical instrument. No matter in the scientific research fields of physics, chemistry, biology, medicine, material science and environmental science, or in the modern production and management departments of chemical industry, medicine, environmental detection and metallurgy, ultraviolet-visible spectrophotometer has a wide and important application. Spectrophotometer is an instrument for quantitative and qualitative analysis of substances by spectrophotometry, which is often used for quantitative analysis of nucleic acid, protein and bacterial growth concentration. Ultramicro spectrophotometer has become a routine instrument in modern molecular biology laboratory. It is usually used to quantify the growth concentration of nucleic acid, protein and bacteria. The laboratory determines the growth density and growth period of bacteria, and infers the growth density of bacteria according to experience and visual inspection. When encountering demanding experiments, it is necessary to accurately determine the bacterial cell density with a spectrophotometer. OD600 is a standard method for tracking microbial growth in liquid culture. Taking the culture solution without bacteria solution as blank solution, and then quantifying the cultured culture solution with bacteria. In order to ensure the correct operation, it is necessary to count the cells of each microorganism and each instrument with a microscope and make a calibration curve. Occasionally, the OD value of bacterial liquid is negative in the experiment, because the colored medium is used, that is, after the bacteria are cultured for a period of time, they react with the medium and change color. In addition, it should be noted that the tested samples cannot be centrifuged, and the bacteria are kept in suspension.