Determination of proteins with alpha,beta,gamma,delta-tetrakis(4-sulfophenyl) porphine by measuring the enhanced resonance light scattering at the air/liquid interface

By attaching two right-angled prisms at a quartz cell of a common spectrofluorometer to change the propagation direction of the incident/emission light beams, a novel technique, reflected-light scattering (RFLS), was developed to detect the light scattering signals at the air/liquid interface. At pH 1.86 and ionic strength 0.04, the J- and H-aggregation of alpha,beta,gamma,delta-tetrakis(4-sulfophenyl)porphine that occurred at the interface in the presence of proteins, was assigned by measuring the enhanced resonance light scattering (RLS) signals characterized at 490.2 and 421.6nm, respectively. With the enhanced RLS signals at 490.2nm, a novel assay of proteins was established with the 3sigma limit of detection being 18-70ngml-1. The protein concentrations in synthetic samples and in human serum were determined with satisfactory results.