Which protein quantification method has the highest analytical sensitivity?

• A. Direct Ultraviolet Absorption
• B. Folin-Lowry
• C. Refractometry
• D. Turbidimetry

Answer: (B)

Analytical sensitivity in protein assays is about how small an amount can be detected reliably. The Folin-Lowry method yields the strongest colorimetric signal per unit of protein because, after the copper-chelation step, the Folin reagent is reduced by the peptide bonds and certain amino acids, producing a deep blue color whose intensity is proportional to protein amount. This amplification gives a low detection limit and a broad linear range, making it more sensitive than methods that rely on direct optical properties or scattering. Direct ultraviolet absorption depends on aromatic residues and requires fairly concentrated protein, with interference from other absorbing substances. Refractometry measures refractive index changes and is inherently less sensitive for dilute samples. Turbidimetry detects light scattering from particles and is influenced by turbidity and other particulates, reducing reliability at low concentrations. Therefore, Folin-Lowry has the highest analytical sensitivity among these options.