Which of the following methods can be used to measure protein concentration in a sample, utilizing the principles of both spectrophotometry and enzymatic assays?

Both spectrophotometric and enzymatic techniques can determine protein levels. The Bradford and BCA assays use a dye that binds protein; the resulting color change is measured by absorbance at 595 nm or 562 nm, giving a direct protein‑dependent signal. Enzymatic methods, such as the Enzyme‑Linked Immunosorbent Assay (ELISA), employ a protein‑specific antibody linked to an enzyme that converts a substrate into a colored product, whose absorbance is read spectrophotometrically. By comparing the absorbance to a standard curve, the protein concentration is calculated. For example, a 1 µg/mL protein sample might give an absorbance of 0.