DNA Adsorption by ZnO Nanoparticles near Its Solubility Limit: Implications for DNA Fluorescence Quenching and DNAzyme Activity Assays

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• 作者：Lingzi Ma ; Biwu Liu ; Po-Jung Jimmy Huang ; Xu Zhang ; Juewen Liu
• 刊名：Langmuir
• 出版年：2016
• 出版时间：June 7, 2016
• 年：2016
• 卷：32
• 期：22
• 页码：5672-5680
• 全文大小：492K
• 年卷期：0
• ISSN：1520-5827

文摘

Zinc oxide (ZnO) is a highly important material, and Zn²⁺ is a key metal ion in biology. ZnO and Zn²⁺ interconvert via dissolution and hydrolysis/condensation. In this work, we explore their interactions with DNA, which is important for biointerface, analytical, and bioinorganic chemistry. Fluorescently labeled DNA oligonucleotides were adsorbed by a low concentration (around 5 μg/mL) of ZnO nanoparticles, near the solubility limit. Right after mixing, fluorescence quenching occurred, indicating DNA adsorption. Then, fluorescence recovered, attributable to ZnO dissolution. The dissolution rate followed A₅ > T₅ > C₅. Dissolution was slower with longer DNA. The adsorption affinity was also measured by a displacement assay to be G₅ > C₅ > T₅ > A₅, suggesting that tightly adsorbed DNA can retard ZnO dissolution. Electrostatic interactions are important for DNA adsorption because ZnO is positively charged at neutral pH, and a high salt concentration inhibits DNA adsorption. Next, in situ formation of ZnO from Zn²⁺ was studied. First, titrating Zn²⁺ into a fluorescently labeled oligonucleotide at pH 7.5 resulted in an abrupt fluorescence quenching beyond 0.2 mM Zn²⁺. At pH 6, quenching occurred linearly with the Zn²⁺ concentration, suggesting the effect of Zn²⁺ precipitation at pH 7.5. Second, a Zn²⁺-dependent DNA-cleaving DNAzyme was studied. This DNAzyme was inhibited at higher than 2 mM Zn²⁺, attributable to Zn²⁺ precipitation and adsorption of the DNAzyme. This paper has established the interplay between DNA, Zn²⁺, and ZnO. This understanding can avoid misinterpretation of DNA assay results and adds knowledge to DNA immobilization.