In a citrate containing solution, anion of citrate self-assembled on Au nanoparticle surface with positive charge, making Au nanoparticle become a supermolecular compound with negative charge surrounded by citrate. In a weak acid medium of pH 4.4～6.8, the supermolecular compound can combine with kanamycin by the virtue of electrostatic and hydrophobic interaction, forming aggregate with bigger diameters (average diameter increased from 12 to 20 nm ). The aggregate made plasmon absorption band of glod nanoparticle show evident bathochromic effect (Δλ＝102 nm), resonance Rayleigh scattering (RRS) in- tensity be enhanced greatly and the resonance nonlinear scattering such as frequency double scattering (FDS) and second order scattering (SOS) be increased markedly as well. The maximum scattering peaks are at 280 nm for RRS, 310 nm for FDS and 480 nm for SOS respectively. In optimum conditions, there was a linear relationship between scattering intensity ΔI and the concentration of kanamycin, and the highest sensitivity was RRS. So gold nanoparticle could be the RRS probe of high sensitivity for kanamycin with the detection limits of kanamycin being 10.52 ng•mL^－1. The method has good selectivity and has been successfully applied to the detection of kanamycin in clinic serum samples. In addition, the reaction mechanism and the reasons for the enhancement of RRS were discussed.

Key words: gold nanoparticle, resonance Rayleigh scattering spectrum, kanamycin