Which test is used to detect the presence of proteins?

The Biuret test is specifically designed to detect the presence of proteins in a sample. When proteins are present, they react with the copper ions in the Biuret reagent, causing a color change to a violet or purple hue. This reaction occurs due to the formation of complex structures between the peptide bonds in proteins and the copper ions, making it an effective and reliable test for protein identification.

Other tests mentioned are aimed at different biomolecules. For example, the Sudan III test is used to identify lipids through their ability to dissolve in nonpolar solvents, resulting in a red-stained area when lipids are present. Benedict's test is utilized to detect reducing sugars, producing a color change when simple carbohydrates with free aldehyde or ketone groups are present. The Diphenylamine test is specifically for detecting nucleic acids, changing color in the presence of DNA or RNA. Thus, the Biuret test is uniquely suited for protein detection among these options.