Which of the following are optical methods for protein measurement?

• A. Turbidimetry
• B. Refractometry
• C. UV Spectrophotometry
• D. Turbidimetry, Refractometry, and UV Spectrophotometry

Answer: (D)

Light-based approaches are used to measure protein concentrations. Turbidimetry is optical because it analyzes how much light is scattered or blocked as protein particles in suspension pass through the beam, linking turbidity to protein amount. Refractometry is optical since it depends on the refractive index of the solution, which changes with protein concentration and can be calibrated. UV spectrophotometry is optical because it measures the absorption of UV light by protein’s aromatic residues, with higher absorbance indicating more protein. Since all three rely on light interactions to estimate protein content, they are all optical methods for protein measurement.