In pH 5.5 2-(N-morpholine)-ethyl sulfonic acid buffer solution and in the presence of NaCl, the substrate single stranded DNA hybridized with the DNA enzyme to form double stranded DNA (dsDNA) at 80 ℃. can cleaved the substrate strand of the dsDNA to produce short single stranded DNA that adsorbed on the surface of the gold nanoparticle to prevent its aggregation, and the uncombined gold nanoparticles aggregate to big particles that exhibited a resonance scattering (RS) peak at 610 nm. When the concentration increased, the short single stranded DNA increased, the combined gold nanoparticles increased, and the aggregated gold nanoparticles decreased, the RS intensity at 610 nm decreased. Under the selected conditions, the decreased RS intensity (ΔI_{610 nm}) is linear to concentration in the range of 0.67～60.3 nmol/L, with a regression equation of ΔI_{610 nm}＝11.9C＋6.1, a correlation coefficient of 0.9972, and a detection limit of 0.09 nmol/L . This method has been applied to determination of in wastewater, with satisfactory results.

Key words: aptamer, double stranded DNA, nanogold, resonance scattering spectral assay