Laboratory for Physical Chemistry, ETH Zurich, Wolfgang-Pauli Strasse 10, Zurich, Switzerland.
Nat Nanotechnol. 2012 Jun 24;7(7):448-52. doi: 10.1038/nnano.2012.99.
Measuring the size and charge of objects suspended in solution, such as dispersions of colloids or macromolecules, is a significant challenge. Measurements based on light scattering are inherently biased to larger entities, such as aggregates in the sample, because the intensity of light scattered by a small object scales as the sixth power of its size. Techniques that rely on the collective migration of species in response to external fields (electric or hydrodynamic, for example) are beset with difficulties including low accuracy and dispersion-limited resolution. Here, we show that the size and charge of single nanoscale objects can be directly measured with high throughput by analysing their thermal motion in an array of electrostatic traps. The approach, which is analogous to Millikan's oil drop experiment, could in future be used to detect molecular binding events with high sensitivity or carry out dynamic single-charge resolved measurements at the solid/liquid interface.
测量悬浮在溶液中的物体（如胶体或大分子的分散体）的大小和电荷是一项重大挑战。基于光散射的测量方法本质上偏向于较大的实体，例如样品中的聚集体，因为小物体散射的光强度与其尺寸的六次方成正比。依赖于物种对外部场（例如电场或流场）的集体迁移的技术存在包括低准确性和分散限制分辨率在内的困难。在这里，我们通过分析它们在静电陷阱阵列中的热运动，展示了通过直接测量单个纳米物体的热运动，以高通量的方式对其大小和电荷进行直接测量。这种方法类似于密立根的油滴实验，将来可用于以高灵敏度检测分子结合事件，或在固/液界面进行动态单电荷分辨测量。
