逐层沉积过程中单个亚微米气泡的微观表征：创建智能代理
Microscopic Characterization of Individual Submicron Bubbles during the Layer-by-Layer Deposition: Towards Creating Smart Agents
摘要：
我们研究了各种聚离子涂层的气泡的平均直径范围从300到500 nm的个别属性。暗视野显微镜允许跟踪由阳离子和阴离子聚电解质（PE）的逐层（LbL）沉积封装的亚微米气泡（SB）的单个颗粒。我们的重点是两个步骤的电荷反转的PE-SB复合物：第一个是从带负电荷的裸SB没有PE添加到正SB封装的聚阳离子（单层沉积），和第二个是过度充电到带负电荷的PE-SB复合物由于随后添加的聚阴离子（双层沉积）。这些现象的细节已经通过分析经历布朗运动或电泳的各种PE-SB复合物的一些轨迹而得到澄清。从分析中得到的对比结果如下：超过化学计量比的阳离子聚合物的量是所需的第一电荷反转，而聚阴离子的化学计量添加导致的PE-SB复合物颗粒的电中和。双层沉积中化学计量的恢复为制造仅用阴离子和阳离子PE封装的多层SB铺平了道路，这提供了一种简单的协议来创建用于药物递送或超声造影成像的智能试剂。
英文摘要：
We investigated the individual properties of various polyion-coated bubbles with a mean diameter ranging from 300 to 500 nm. Dark field microscopy allows one to track the individual particles of the submicron bubbles (SBs) encapsulated by the layer-by-layer (LbL) deposition of cationic and anionic polyelectrolytes (PEs). Our focus is on the two-step charge reversals of PE-SB complexes: the first is a reversal from negatively charged bare SBs with no PEs added to positive SBs encapsulated by polycations (monolayer deposition), and the second is overcharging into negatively charged PE-SB complexes due to the subsequent addition of polyanions (double-layer deposition). The details of these phenomena have been clarified through the analysis of a number of trajectories of various PE-SB complexes that experience either Brownian motion or electrophoresis. The contrasted results obtained from the analysis were as follows: an amount in excess of the stoichiometric ratio of the cationic polymers was required for the first charge-reversal, whereas the stoichiometric addition of the polyanions lead to the electrical neutralization of the PE-SB complex particles. The recovery of the stoichiometry in the double-layer deposition paves the way for fabricating multi-layered SBs encapsulated solely with anionic and cationic PEs, which provides a simple protocol to create smart agents for either drug delivery or ultrasound contrast imaging.
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