Nanogold (NG) particles in size of 5 nm were prepared by a NaBH₄-trisodium citrate procedure. The aptamer was used to modify the 5 nm nanogold to obtain a resonance scattering (RS) spectral probe (aptamer-NG) for Pb^2＋. In the medium of pH 7.0 Na₂HPO₄-NaH₂PO₄ and in the presence of 30 mmol•L^－1 NaCl, the probe was stable and did not aggregate. The Pb^2＋ interacted with aptamer in the probe to form very stable G-quadruplex and release the nanogold particles. Under the action of the salt, the nanogold particles could aggregate to larger nanogold clusters, which led to the increase of resonance scattering peak intensity at 552 nm. The increased RS intensity (ΔI) was linear to Pb^2＋ concentration (c) in the range of 0.07～42 nmol•L^－1, with a regression equation of ΔI＝12.0c＋9.2, a coefficient of 0.9965 and a detection limit of 0.03 nmol•L^－1. The proposed method was applied to detect Pb^2＋ in water samples, with satisfactory results.

Key words: Pb^2＋, aptamer, nanogold, resonance scattering spectral probe