The spectrophotometer is a laboratory routine analysis device consisting mainly of a light source, a monochromator, a sample chamber, a detector, a signal processor, and a display and storage system. It uses spectral analysis methods to qualitatively and quantitatively analyze samples, and is commonly used in modern molecular biology laboratories for nucleic acid, protein quantification, and quantification of bacterial growth concentrations. A spectrophotometer, also known as a spectrometer, uses a light source that can generate multiple wavelengths to generate a specific wavelength of light through a series of spectroscopic devices. After the light source passes through the tested sample, some of the light source is absorbed, and the sample is absorbed. The value is thus converted to the concentration of the sample. The absorbance of the sample is proportional to the concentration of the sample. The measurement range generally includes a visible light region with a wavelength range of 380 to 780 nm and an ultraviolet region with a wavelength range of 200 to 380 nm. Different light sources have their own specific emission spectra, so different illuminants can be used as the light source of the instrument.

Quantification of nucleic acids <br> Quantification of nucleic acids is the most frequently used function of the spectrophotometer. Oligonucleotides, single-stranded, double-stranded DNA, and RNA can be quantified in buffer. The absorption peak of the highest absorption peak of nucleic acid is 260 nm. The molecular composition of each nucleic acid is different, so the conversion factor is different. To quantify different types of nucleic acids, select the corresponding coefficients in advance.

Direct quantification of proteins (UV method)
This method is to directly test the protein at a wavelength of 280 nm. Select the Warburg formula, the photometer can directly display the concentration of the sample, or select the appropriate conversion method to convert the absorbance to the sample concentration. This method is suitable for testing relatively pure, relatively single-component proteins. Compared with the colorimetric method, the ultraviolet direct quantitative method is fast and easy to operate; but it is easily interfered by parallel substances, such as DNA interference; in addition, the sensitivity is low, and the protein concentration is required to be high.

Colorimetric Protein Quantitative <br> Colorimetric assays are based on protein constituents: amino acids (such as tyrosine, serine) react with additional chromogenic groups or dyes to produce colored materials. The concentration of the colored substance is directly related to the number of amino acids reacted by the protein, thereby reacting the protein concentration. Colorimetric methods generally include BCA, Bradford, Lowry and other methods.

Bacterial cell density (OD 600)
OD600 is the standard method for tracking microbial growth in liquid cultures. The culture solution containing no bacterial solution was used as a blank solution, and then the culture-containing culture solution after the culture was quantitatively determined. In order to ensure proper operation, the cell count must be performed with a microscope for each microorganism and each instrument to make a calibration curve. It should be noted that the sample tested cannot be centrifuged to maintain the bacterial suspension.

The spectrophotometer is a precision instrument and should be properly kept and carefully maintained to ensure long-term use of the spectrophotometer, long-term stability and reliability, and high measurement accuracy.

Spectrophotometer use precautions
1. Before using the instrument, the user should first understand the structure and working principle of the instrument, as well as the functions of each control knob. The safety performance of the instrument should be checked before the power is turned on.
2. When the pointer instrument has not been powered on, the meter pointer must be on the zero scale. If this is not the case, you can use the calibration screw on the meter to zero.
3. The instrument should be stored in a room with an ambient temperature of 5 ° C ~ 35 ° C and a humidity of 85% under the original packaging conditions of the manufacturer, and there should be no harmful substances in the air that cause corrosion.
4. The working environment of the instrument should be in a dry room. When used, it should be placed on a firm and stable workbench. The indoor lighting should not be too strong.
5. After using the cuvette, rinse it off with distilled water and wipe off the water with a clean soft gauze to prevent the surface finish from being damaged and affect the light transmittance of the cuvette.
6. The matching problem of the cuvette. The cuvette must be used together, otherwise the test results will be meaningless.
7. Since the instrument has been debugged to the best condition before leaving the factory, the user can't adjust it without authorization. It is not allowed to open the case to remove the parts (except for replacing the light source), especially to remove the monochromator, not to hurt or wipe the optics. Original mirror.
8. In case of failure, it is urgent to self-repair. Under the guidance of the technical personnel of the factory, please have the qualified personnel to carry out inspection, adjustment and maintenance, and recommend repair.

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