Department of Materials Science and Engineering, ‡Department of Chemistry, and §Department of Physics and Astronomy, Northwestern University , Evanston, Illinois 60208, United States.
ACS Nano. 2013 Dec 23;7(12):11301-9. doi: 10.1021/nn405109z. Epub 2013 Nov 23.
The radial distribution of monovalent cations surrounding spherical nucleic acid-Au nanoparticle conjugates (SNA-AuNPs) is determined by in situ small-angle x-ray scattering (SAXS) and classical density functional theory (DFT) calculations. Small differences in SAXS intensity profiles from SNA-AuNPs dispersed in a series of solutions containing different monovalent ions (Na(+), K(+), Rb(+), or Cs(+)) are measured. Using the "heavy ion replacement" SAXS (HIRSAXS) approach, we extract the cation-distribution-dependent contribution to the SAXS intensity and show that it agrees with DFT predictions. The experiment-theory comparisons reveal the radial distribution of cations as well as the conformation of the DNA in the SNA shell. The analysis shows an enhancement to the average cation concentration in the SNA shell that can be up to 15-fold, depending on the bulk solution ionic concentration. The study demonstrates the feasibility of HIRSAXS in probing the distribution of monovalent cations surrounding nanoparticles with an electron dense core (e.g., metals).
通过原位小角 X 射线散射（SAXS）和经典密度泛函理论（DFT）计算，确定了单价阳离子在球形核酸-金纳米粒子缀合物（SNA-AuNPs）周围的径向分布。测量了分散在一系列含有不同单价离子（Na(+)、K(+)、Rb(+)或 Cs(+)）的溶液中的 SNA-AuNPs 的 SAXS 强度曲线的微小差异。使用“重离子替换”SAXS（HIRSAXS）方法，我们提取了与 SAXS 强度相关的阳离子分布依赖性贡献，并表明它与 DFT 预测相符。实验与理论的比较揭示了 SNA 壳中阳离子的径向分布以及 DNA 的构象。分析表明，SNA 壳中的平均阳离子浓度增强，最高可达 15 倍，具体取决于本体溶液的离子浓度。该研究证明了 HIRSAXS 在探测具有电子密集核（例如金属）的纳米粒子周围单价阳离子分布的可行性。
