Interfacial Microrheology of Protein Layers using Magnetic Nanowire Probes

Leheny/Johns Hopkins/0651666蛋白质吸附在空气-水或油-水界面并产生坚硬界面层的趋势对许多当前和开发中的技术至关重要，特别是与食品、生物医学和制药行业相关的技术。此外，蛋白质层的形成过程为蛋白质变性、蛋白质相互作用和凝胶转变等问题提供了独特的视角。这项建议描述了一种新的、高灵敏度的实验方法，通过使用限制在界面上的磁性纳米线作为活跃的微观流变学探针来表征蛋白质层的界面剪切流变学。智能优点：吸附在界面上的蛋白质与传统小分子表面活性剂之间的一个关键区别是蛋白质形成粘弹性很强的层的倾向。在许多情况下，这种机械行为可以产生优异的性能，例如在稳定乳液和泡沫方面。因此，了解蛋白质层的流变性对于了解其形成和稳定性的基本方面以及将其应用于技术应用都是至关重要的。基于几何考虑，所提出的使用线状探针的微观流变学方法自然适合于测量纳米级流体薄膜的剪切流变性，并且纳米线应该比现有的界面剪切流变学技术更灵敏。该方法的基础包括表征限制在空气-水界面的纳米线所经历的阻力，当纳米线在精确的磁力矩的作用下旋转时，蛋白质层就会在那里形成。最近的理论预测，当各向异性物体被限制在这样的薄膜中时，它的流体动力学行为将发生根本性的变化，例如线状粒子。从实验上澄清这些预测的有效性及其适用范围将具有深远的影响。这样的澄清对于对拟议的蛋白质层界面流变学实验进行适当的定量解释也是必要的。磁性纳米线是研究这些理论想法的理想系统，该项目将包括实验来验证预测。在了解了膜中纳米线的旋转阻力后，该方法将被应用于两个蛋白质层体系的界面剪切流变学研究：(I)低浓度的溶菌酶溶液，其成层的特征是诱导期延长；(Ii)由乳球蛋白和小分子表面活性剂的溶液形成的薄膜，其蛋白质层的机械性能对表面活性剂的存在高度敏感。选择这些系统是因为它们提出了引人注目的科学问题，并有机会通过拟议的实验方法发现重大的新现象。然而，拟议实验的另一个目标是建立更普遍的微观流变学技术，将磁性纳米线作为研究界面系统机械特性的重要工具。广泛影响：作为该项目的一部分，将从约翰霍普金斯大学的一个推广倡议--女性科学与工程计划(WISE)招募一名女高中生参与这项研究。该项目的更广泛影响还将包括对研究生和本科生的研究、培训和教育。此外，这项工作将对界面蛋白质层的研究和基于界面蛋白质层的技术产生潜在的重大影响，特别是对于具有中尺度异质性的系统，而现有技术无法获得这些系统，以及目前样本量小是限制因素的材料。坚硬的界面层对许多当前和发展中的技术至关重要，特别是与食品、生物医学和制药行业相关的技术。

Leheny / Johns Hopkins / 0651666The tendency for proteins to adsorb at air-water or oil-water interfaces and to create stiffinterfacial layers is vital to many current and developing technologies, particularly those related to the food, biomedical, and pharmaceutical industries. Further, the process of protein-layer formation provides a unique perspective on issues of protein denaturation, protein-protein interactions, and the gel transition. This proposal describes experiments to apply a new, high sensitivity approach to characterizing the interfacial shear rheology of protein layers by employing magnetic nanowires confined at the interface as active microrheology probes.Intellectual Merit: A key difference between proteins adsorbed at interfaces and conventional small-molecule surfactants is the propensity of the proteins to form layers that are strongly viscoelastic. In many circumstances, this mechanical behavior can lead to superior properties, such as in stabilizing emulsions and foams. Consequently, knowledge of the rheological properties of protein layers is crucial both for understanding fundamental aspects of their formation and stability as well as for adopting them for technological application. Based on geometric considerations, the proposed microrheology approach using wire-shaped probes is naturally suited for measuring the shear rheology of nanometer-scale fluid films, and the nanowires should be significantly more sensitive than existing interfacial shear rheology techniques. The basis of the approach involves characterizing the drag experienced by nanowires confined to the air-water interface at which protein layers form as the wires are rotated by precise magnetic torques. Recent theory has predicted fundamental changes to the hydrodynamic behavior of an anisotropic object, such as a wire-shaped particle, when it is confined to such a thin film. Clarifying experimentally the validity of these predictions and their range of applicability would have far-reaching implications. Such clarification will also be necessary for a proper quantitative interpretation of the proposed interfacial rheology experiments on protein layers. The magnetic nanowires are an ideal system to investigate these theoretical ideas, and the project will include experiments to test the predictions. With the rotational drag on nanowires in films understood, the approach will then be applied to interfacial shear rheology studies of two protein layer systems (i) lysozyme solutions at low concentration for which layer formation is characterized by an extended induction period and (ii) films formed from solutions of lactoglobulin and small molecule surfactants for which the mechanical properties of the protein layer are highly sensitive to the presence of the surfactant. These systems are selected for thecompelling scientific problems they present and for the opportunities to uncover significant new phenomena through the proposed experimental approach. However, an additional objective of the proposed experiments will be to establish more generally the technique of microrheology with magnetic nanowires as an important tool for studying the mechanical properties of interfacial systems.Broader Impacts: As part of this project, a female high school student will be recruited from the Women in Science and Engineering (WISE) Program, a Johns Hopkins outreach initiative, to participate in the research. The broader impacts of the project will also include research training and education for a graduate student and an undergraduate student. In addition, the work will provide potentially significant impact to both the research on and the technology based on interfacial proteins layers, particularly with regard to systems with mesoscale heterogeneity that cannot be accessed with current techniques and to materials for which small sample quantity is currently a limiting factor. Stiff interfacial layers are vital to many current and developing technologies, particularly those related to the food, biomedical, and pharmaceutical industries.