A LABEL-FREE DEOXYRIBOZYMES RESONANCE RAYLEIGH SCATTERING ASSAY FOR TRACE LEAD(II) BASED ON NANOGOLD CATALYSIS OF CHLOROAURIC ACID-VITAMIN C PARTICLE REACTION

In pH 7.2 Tris-HCl buffer solution, the substrate strand DNA (SDNA) was hybridized to the enzyme strand DNA (EDNA) forming a double strand DNA (dsDNA). The SDNA in dsDNA could be cleaved by lead(II) to release a cleavaged single-stranded (ssDNA) that prevented the gold nanoparticles (AuNPs) from forming a stable AuNPs-ssDNA conjugate. The unconjugated AuNPs were aggregated to form AuNP aggregation (AuNPsA) that appeared as a resonance Rayleigh scattering (RS) peak at 532 nm. When the lead(II) concentration increased, the AuNPs-ssDNA increased, the AuNPsA decreased, the color changed from blue to red, and the RS intensity at 532 nm decreased. The decreased RS intensity Delta I-532 nm was linear to the lead(II) concentration in the range of 0.67-60 nmol/L, with a detection limit of 0.3 nmol/L. The AuNPs-ssDNA exhibited a strong catalytic effect on the reaction between chloroauric acid and vitamin C (VC) that can be detected by an RS method at 620 nm. When the lead(II) concentration increased, the intensity at 620 nm increased, and the increased intensity Delta I-620 nm was linear to the lead(II) concentration in the range of 1.33-120 pmol/L, with a detection limit of 0.5 pmol/L. The proposed method was applied to detect lead(II) in water samples, with satisfactory results.