The enzyme linked immunosorbent substrate reagent is a very important reagent, which is widely used in the fields of biomedicine and molecular biology. In experiments, we often use DAOS linked enzyme immunoassay substrate reagent, which is fully known as N-ethyl-N - (2-hydroxy-3-sulfopropyl) -3,5-dimethoxyaniline sodium salt in Chinese, with CAS number 83777-30-4. This reagent has the characteristics of small molecular weight and high sensitivity. DAOS is widely used in various immune detection methods, such as ELISA, immunoblotting, immunohistochemistry, etc. It has been adopted by many research institutions and hospital laboratories, and can be used for protein detection in various biological samples, such as blood, urine, cerebrospinal fluid, etc. The use of DAOS reagent is extremely convenient, and fluorescence detection can be carried out by adding DAOS reagent and hydrogen peroxide substrate. DAOS reagents have high detection sensitivity and can detect extremely small protein concentrations, making them widely used in many biomedical and molecular biology studies. DAOS reagent, as a relatively new type of chromogenic substrate reagent, mainly converts the substrate into fluorescent products through enzymatic reactions, and quantitatively analyzes the fluorescent products using fluorescence spectroscopy analysis during the detection process. DAOS reagent is different from other substrate reagents in that it has excellent durability and is not easily affected by environmental factors, thus ensuring the stability and accuracy of the detection results.