Lowry’s reagent is used in the Lowry protein assay to measure protein concentration. It contains a combination of copper ions and alkaline tartrate, which reacts with proteins to form a complex, followed by the addition of Folin-Ciocalteu phenol reagent, resulting in a color change. The intensity of the color, typically measured at 750 nm, correlates with the protein concentration in the sample. The Lowry method is sensitive and widely used for protein quantification.