Free-Labeled Nanogold Catalytic Detection of Trace UO 2 2+ Based on the Aptamer Reaction and Gold Particle Resonance Scattering Effect

In pH?5.5 2-(N-morpholino)-ethanosulfonic acid buffer solution containing 0.0125?M NaCl at 80?°C, the single-stranded substrate DNA hybrid with enzyme DNA to form double-stranded DNA (dDNA). The substrate chain of dDNA could be cracked catalytically by UO ₂ ²⁺ to produce a short single-stranded DNA (ssDNA) that adsorbed on the nanogold (NG) surface to form stable NGssDNA conjugate, and the unadsorbed NG take place aggregation to produce the NG aggregations in blue color. Both NG and NGssDNA exhibited strong catalytic activity on the gold particle reaction between HAuCl₄ and ascorbic acid that can be monitored by resonance scattering (RS) spectral technique at 620?nm. However, the catalytic effect of NG aggregation was very weak and it cannot be separated from the cracked reaction solution. When the UO ₂ ²⁺ concentration increased, the ssDNA increased, the NGssDNA increased, the formed gold particles increased, and the RS intensity at 620?nm increased. The increased RS intensity ??I _620?nm was linear to UO ₂ ²⁺ concentration in the range of 3.35?C23.45?pM, with a regression equation of ??I _620?nm?=?27.6C?+?29.1, and detection limit of 0.1?pM. This new RS assay was applied to analysis of UO ₂ ²⁺ in water sample with satisfactory results.