Johnson Alexis, Welsher Kevin D
Department of Chemistry, Duke University, Durham, NC 27708, USA.
bioRxiv. 2024 Aug 4:2024.07.08.602591. doi: 10.1101/2024.07.08.602591.
Nanoparticles (NP) are versatile materials with widespread applications across medicine and engineering. Despite rapid incorporation into drug delivery, therapeutics, and many more areas of research and development, there is a lack of robust characterization methods. Light scattering techniques such as dynamic light scattering (DLS) and electrophoretic light scattering (ELS) use an ensemble-averaged approach to the characterization of nanoparticle size and electrophoretic mobility (EM), leading to inaccuracies when applied to polydisperse or heterogeneous populations. To address this lack of single-nanoparticle characterization, this work applies 3D Single-Molecule Active Real-time Tracking (3D-SMART) to simultaneously determine NP size and EM on a per-particle basis. Single-nanoparticle EM is determined by using active feedback to "lock on" to a single particle and apply an oscillating electric field along one axis. A maximum likelihood approach is applied to extract the single-particle EM from the oscillating nanoparticle position along the field-actuated axis, while mean squared displacement is used along the non-actuated axes to determine size. Unfunctionalized and carboxyl-functionalized polystyrene NPs are found to have unique EM based on their individual size and surface characteristics, and it is demonstrated that single-nanoparticle EM is a more precise tool for distinguishing unique NP preparations than diffusion alone, able to determine the charge number of individual NPs to an uncertainty of less than 30. This method also explored individual nanoparticle EM in various ionic strengths (0.25-5 mM) and found decreased EM as a function of increasing ionic strength, in agreement with results determined via bulk characterization methods. Finally, it is demonstrated that the electric field can be manipulated in real time in response to particle position, resulting in one-dimensional electrokinetic trapping. Critically, this new single-nanoparticle EM determination and trapping method does not require microfluidics, opening the possibility for the exploration of single-nanoparticle EM in live tissue and more comprehensive characterization of nanoparticles in biologically relevant environments.
纳米颗粒（NP）是用途广泛的材料，在医学和工程领域有着广泛的应用。尽管已迅速应用于药物递送、治疗以及更多的研发领域，但仍缺乏可靠的表征方法。诸如动态光散射（DLS）和电泳光散射（ELS）等光散射技术采用总体平均方法来表征纳米颗粒的大小和电泳迁移率（EM），应用于多分散或异质群体时会导致不准确。为解决这种缺乏单纳米颗粒表征的问题，本研究应用三维单分子主动实时追踪（3D-SMART）在逐个颗粒的基础上同时测定NP的大小和EM。通过使用主动反馈“锁定”单个颗粒并沿一个轴施加振荡电场来确定单纳米颗粒的EM。应用最大似然法从沿场驱动轴的振荡纳米颗粒位置提取单颗粒EM，而沿非驱动轴使用均方位移来确定大小。发现未功能化和羧基功能化的聚苯乙烯NP基于其各自的大小和表面特性具有独特的EM，并且证明单纳米颗粒EM是比单独扩散更精确的区分独特NP制剂的工具，能够将单个NP的电荷数确定到不确定性小于30。该方法还研究了各种离子强度（0.25 - 5 mM）下的单个纳米颗粒EM，发现EM随离子强度增加而降低，这与通过体相表征方法确定的结果一致。最后，证明可以根据颗粒位置实时操纵电场，从而实现一维电动捕获。至关重要的是，这种新的单纳米颗粒EM测定和捕获方法不需要微流体技术，为在活组织中探索单纳米颗粒EM以及在生物相关环境中更全面地表征纳米颗粒开辟了可能性。
