In pH 1.8～2.5 Britton-Robinson (BR) buffer medium, negatively charged chondroitin sulfate A (CSA) can react with positively charged proteins, such as human serum albumin (HSA), bovine serum albumin (BSA), chymotrypsin (Chy), lysozyme (Lyso) and α-amylase (α-Amy), via electrostatic attraction, hydrogen bonding and hydrophobic interaction. This lead to the enhancement of resonance Rayleigh scattering (RRS) and resonance non-linear scattering (RNLS), including second order scattering (SOS) and frequency doubling scattering (FDS), and appearance of new spectra. The scattering intensities (ΔI_RRS, ΔI_SOS and ΔI_FDS) are directly proportional to the concentrations of protein in certain ranges. Each method has high sensitivity and the detection limits (3() are 4.5～12.0 (RRS), 8.9～15.8 (SOS) and 13.4～31.5 (FDS) (g/L for proteins. The CSA-BSA system is the most sensitive which the detection limit for BSA is 4.5 (g/L. In this article, the spectral characteristics, optimum conditions of the reaction and influencing factors have been investigated. The reaction mechanism and binding mode are discussed. Take RRS method of CSA-BSA system for example, the effects of coexisting substances on the reaction are investigated. The method can be applied to the determination of protein in serum and urine samples with satisfactory results.

Key words: chondroitin sulfate A, protein, resonance Rayleigh scattering, second order scattering, frequency doubling scattering