Detection of Pb²⁺ at attomole levels by using dynamic light scattering and unmodified gold nanoparticles

Lead ion (Pb²⁺) accumulation in nature can affect the environment and human health severely. Thus, rapid and sensitive detection is of great importance. One-step detection of Pb²⁺ at attomole levels was realized by using dynamic light scattering (DLS) technique coupled with unmodified gold nanoparticles (AuNPs). Pb²⁺-dependent DNAzyme was double-stranded and could not adsorb on the surface of AuNPs, while the substrate strand could be cleaved into ssDNA fragments on addition of Pb²⁺. The ssDNA fragments could adsorb on the surface of AuNPs and prevent them from aggregating in the presence of NaCl. Therefore, the disperse state of AuNPs changed on addition of Pb²⁺ in the presence of DNAzyme and NaCl, which was estimated with an average hydrodynamic diameter by using DLS. Under optimum conditions, the average diameter of the solution decreased linearly with the concentration of Pb²⁺ over the range from 10 to 300 pM, with a detection limit of 6.2 pM. Moreover, satisfactory results were obtained when the proposed method was applied in the detection of Pb²⁺ in water samples.