Silver nanoparticles were prepared by NaBH₄ reduction procedure. An aptamer-modified Ag nanoprobe (AgSH-ssDNA) for thrombin was prepared. In the media of pH 7.0 Tris-HCl and KCl, the AgSH-ssDNA specifically combined with thrombin to form G-quadruplex and Ag cluster, which resulted in the resonance scattering intensity at 480 nm (I_{480 nm}) increasing. As the amount of thrombin increased, the amount of Ag clusters increased, and the I_{480 nm} value increased. At the same time, Ag/Au nanoparticles of different Ag/Au molar ratio were also prepared for the thrombin RS analysis. The results showed the Ag system had some advantages such as high sensitivity, wide linear range, low-cost, and the simplicity of nanoparticles preparation. Its increased intensity ΔI_{480 nm} was linear to the thrombin concentration in the range of 0.14～11.5 nmol/L, with a regression equation of ΔI_{480 nm}＝19.1C＋2.2, a correlation coefficient of 0.9833, and a detection limit of 17 pmol/L. This method was applied to detect thrombin in human plasma samples with satisfactory results.

Key words: nanosilver, aptamer, thrombin, resonance scattering spectral assay