Determination of nanograms of proteins based on the amplified resonance light scattering signals of Tichromine

A new high-sensitivity detection of protein assay at the nanogram level is developed based on the amplified resonance light scattering signals (RLS) of Tichromine (TCM). In Walpole (NaAc-HCl) buffer (pH 4.05), TCM reacts with proteins to form large particles, which results in remarkable enhanced RLS signals characterized by three peaks at 293 nm, 399 nm and 553 nm. Mechanistic studies showed that the enhanced RLS stems from a large complex of TCM-BSA formed for the electrostatic effect between TCM and BSA. With the enhanced RLS signals at the three wavelengths, the enhanced RLS intensity is proportional to the concentration of proteins in an appropriate range. The lowest limit of determination was 7.4 ng mL−1. The proposed method was successfully applied to determine total protein in human serum samples.