Synchronizing the chemical composition of silver nanoparticle surfaces

非技术性总结：银纳米颗粒（尺寸约为1 - 100 nm，比人类头发的宽度小1000倍以上）用于广泛的应用，包括抗菌涂层，化妆品，电子，化学和生物传感器以及催化。 然而，银是高反应性材料，特别是当收缩到纳米级尺寸时，并且容易发生不希望的副反应，例如当银珠宝或器皿暴露于周围环境时形成的公知的失泽。 这些不需要的副反应会影响银纳米材料在关键应用中的性能和再现性。 即使从同一个瓶子中取出的银纳米颗粒在第1天与第100天的表现也不同，并且由于表面上发生的反应的程度和化学性质，可能存在显著的批次间异质性。 本提案的目的是确定是否可以清洁已经经历这些不需要的反应的银纳米颗粒的表面，并将它们恢复到更均匀、可再现的银表面。 为了实现这一点，银纳米颗粒将暴露于各种化学和电化学条件下，其表面的变化将通过跟踪其光学性质的时间依赖性变化来监测。 通过跟踪大量单个纳米颗粒的行为，这些研究将确定产生从显著的表面异质性转变为纳米颗粒群体中改善的均匀性的特定条件。 该提案还将支持研究生和本科生的培训，所有这些学生都参加了Willets实验室的社区外展活动（包括由该小组开发的银高中化学实验室的冒险），以及支持PI正在进行的专业发展工作，这些工作侧重于改善科学交流以及在化学领域创造一个更加公平和包容的环境。金属纳米颗粒广泛用于许多应用，包括传感，纳米医学和催化，但其表面化学的动态变化会影响其重现性。 而不是试图在合成过程中控制纳米颗粒的表面，该提案旨在开发策略，以同步合成后的纳米颗粒的表面化学，从而在集成到设备中并用于应用时创造更多的可再现行为。 为了使整个银纳米颗粒群的表面化学同步，将化学地或电化学地引入牺牲壳，其胜过纳米颗粒表面上的不需要的污染物。然后通过电化学剥离去除壳，理想地恢复原始银表面。 该提案将测试各种化学和电化学壳，以评估它们改善纳米颗粒群内表面均匀性的能力。 为了量化该方法的成功，暗场散射显微镜将用于跟踪整个壳生长和剥离周期中单个纳米颗粒的散射强度、光谱分布和空间起源。 单个纳米颗粒电溶解的动力学将用作确认所得银表面的质量的度量，快速电溶解表明接近原始的银，而缓慢的电溶解动力学表明高水平的表面杂质。 这些研究不仅将产生用于改善银纳米颗粒中的合成后/储存表面均匀性的策略，这将改善关键应用中的再现性，而且还将允许直接比较纳米颗粒在暴露于各种扰动时的动力学和界面行为如何变化。 推广项目介绍高中学生从当地少数民族服务学校的银纳米粒子合成和光谱补充拟议的工作，沿着与PI领导的专业发展活动的研究生。这个奖项反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的智力价值和更广泛的影响审查标准的支持。

Non-technical Summary:Silver nanoparticles (~1 – 100 nm in size, more than 1000x smaller than the width of a human hair) are used in a wide range of applications, including antibacterial coatings, cosmetics, electronics, chemical and biological sensors, and catalysis. However, silver is a highly reactive material, particularly when shrunk down to nanoscale dimensions, and is susceptible to unwanted side reactions, such as the well-known tarnish that forms when silver jewelry or utensils are exposed to the ambient environment. These unwanted side reactions can impact the performance and reproducibility of silver nanomaterials in critical applications. Even silver nanoparticles taken from the same bottle will perform differently on day 1 vs. day 100, and there can be significant batch-to-batch heterogeneity, due to the extent and chemical nature of the reactions that have happened on the surface. The objective of this proposal is to determine whether it is possible to clean the surface of silver nanoparticles that have undergone these unwanted reactions and restore them to a more uniform, reproducible silver surface. To accomplish this, silver nanoparticles will be exposed to a variety of chemical and electrochemical conditions, and the change in their surface will be monitored by following time-dependent changes in their optical properties. By tracking the behavior of large numbers of single nanoparticles, these studies will determine specific conditions that produce a shift from significant surface heterogeneity to improved homogeneity across a nanoparticle population. The proposal will also support the training of graduate and undergraduate students, all of whom participate in community outreach with the Willets lab (including the Adventures in Silver high school chemistry lab developed by the group), as well as support the ongoing professional development efforts of the PI, which focus on improving scientific communication as well as creating a more equitable and inclusive environment within chemistry.Technical Summary:Metal nanoparticles are widely used across a number of applications, including sensing, nanomedicine, and catalysis, yet dynamic changes in their surface chemistry can affect their reproducibility. Rather than attempt to control the surface of nanoparticles during synthesis, this proposal seeks to develop strategies to synchronize the surface chemistry of nanoparticles post-synthesis, thereby creating more reproducible behaviors when integrated into devices and used in applications. To synchronize the surface chemistry across a population of silver nanoparticles, sacrificial shells will be introduced, either chemically or electrochemically, which outcompete unwanted contaminants on the surface of the nanoparticles. The shells will then be removed via electrochemical stripping, ideally recovering pristine silver surfaces. This proposal will test a variety of chemical and electrochemical shells, in order to assess their ability to improve the surface homogeneity within a nanoparticle population. To quantify the success of the approach, dark field scattering microscopy will be used to track the scattering intensity, spectral profile, and spatial origin of single nanoparticles throughout the shell growth and stripping cycle. The kinetics of single nanoparticle electrodissolution will be used as a metric to confirm the quality of the resulting silver surfaces, with fast electrodissolution indicating near-pristine silver and sluggish electrodissolution kinetics suggesting high levels of surface impurities. These studies will not only yield strategies for improving the post-synthesis/storage surface homogeneity in silver nanoparticles, which will improve reproducibility in critical applications, but will also allow for direct comparisons in how the kinetics and interfacial behaviors of nanoparticles change when exposed to various perturbations. Outreach projects introducing high school students from a local minority-serving school to silver nanoparticle synthesis and spectroscopy complement the proposed work, along with PI-led professional development activities for graduate students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.