A coupled reagent of o-phthalaldehyde and sulfanilic acid for protein detection based on the measurements of light scattering signals with a common spectrofluorometer

A rapid and sensitive method for the determination of proteins is proposed with a coupled reagent of o-phthalaldehyde and sulfanilic acid by measuring the light scattering (LS) signals with a common spectrofluorometer. Mechanism investigations showed that o-phthalaldehyde couples at first with sulfanilic acid with fast speed and forms a new synthesized Schiff base dye, which then interacts with protein rapidly on acidic condition, resulting in greatly enhanced LS signals with the maximum peak located at 344 nm. Based on the linear relationship between enhanced LS intensities and concentrations of proteins, a novel assay of HSA and BSA is established in the linear range of 0.1–25.0 μg ml−1 with the limits of detection (3σ) being 13 ng ml−1 depending on the concentration of the reagent. Results for sample detections of our method were consistent with the documented spectrophotometric method with CBB G250 assay.