Fehling's reagent is used to detect reducing sugars.

1. Fehling's reagent: It is prepared from sodium hydroxide solution with a content of 0.1g/mL, copper sulfate solution with a content of 0.05g/mL, and potassium sodium tartrate with a content of 0.2g/mL. into solution. Add Fehling's reagent dropwise into the tissue sample liquid to be tested and place the test tube. Pour into 50-60 degree warm water and heat for 2 minutes. If brick red precipitate appears, it means that the tissue sample fluid contains reducing sugar.

2. Reducing sugars: refers to sugars with reducing properties. Reducing sugars include glucose, fructose, galactose, lactose, maltose, etc. Among sugars, monosaccharides containing free aldehyde or ketone groups and disaccharides containing free aldehyde groups are reducing.

3. Principle of Fehling's reagent: Fehling's reagent is a potassium and sodium tartrate complex of divalent copper ions, which can be reduced to cuprous oxide by aliphatic aldehydes or reducing sugars. Lilin's reagent is a dark blue solution. When heated with aliphatic aldehydes or reducing sugars, "the blue color disappears and a red cuprous oxide precipitate precipitates. During the precipitation process of cuprous oxide, the color of the reaction solution may change." The gradual change from blue → green → yellow → red precipitate. When the reaction is fast, red precipitate is directly observed.

The following are common steps for detecting proteins and some commonly used reagents

1. Sample preparation: Collect the protein samples to be detected, which can be cell extracts, tissue homogenates or serum. The samples need to be stored under low temperature conditions to avoid protein degradation. For cell and tissue samples, protein extraction can be used. The kit lyses the sample and removes the nuclei and cell debris.

2. Protein concentration detection: Use BCA (dithiothreuronic acid method), Lowry or Bradford and other kits to measure protein. Concentration. These reagents will produce color changes after reacting with proteins, which can be measured using a photometer to determine the protein concentration of the sample to be tested.

3 . SDS-PAGE gel electrophoresis: Use polyacrylamide gel for SDS-PAGE electrophoresis separation, separate proteins according to their molecular weight, prepare electrophoresis buffer and sample buffer, and combine the sample to be tested with the gel electrophoresis sample buffer. After mixing, load it into a polyacrylamide gel tank and run electrophoresis to drive the migration of proteins in the gel to separate them according to their molecular weight.

4. Protein transfer (Western blot): Transfer the separated proteins from the gel to a membrane, commonly used are polyvinylidene fluoride (PVDF) and nitrocellulose membranes, to transfer the proteins in the gel to the membrane.

5. Immunological detection: Use specific antibodies to bind to target proteins. Commonly used methods include primary antibodies and secondary antibodies. There are three main methods for antigen-antibody reaction detection: horseradish peroxidase (HRP) labeling system, alkali. Phosphatase (AP) labeling system and luciferase (Fluorescent enzyme) labeling system

6. Imaging and quantitative analysis: Use chemiluminescence detection, Western blot detection system (such as ECL) and other methods or equipment. Image the protein on the membrane and detect the intensity of the signal. Quantify and analyze the protein bands using image analysis software.