MRI: Development of Instrumentation for Direct Measurement of Forces Between a Colloidal Particle and a Surface

dickinson， Richard bababstract胶体粒子和表面之间的作用力直接测量仪器的发展粒子和表面之间的相互作用力对于佛罗里达大学（UF）当前的几个工业和生物医学相关研究项目至关重要。其中包括NSF粒子科学与技术工程研究中心（ERC）的研究工作，该中心专注于将粒子间力与粒子悬浮液的分散和絮凝联系起来。在这个ERC中特别感兴趣的是聚合物诱导的胶体力的作用，如空间和桥接相互作用。ERC也在研究颗粒表面特性在颗粒絮凝和表面沉积中的作用，以开发新的和增强现有的颗粒分离工艺。在UF的其他工作中，正在研究细菌附着在生物材料表面的机制，以便对附着过程中细胞表面大分子的特异性结合的作用有基本的了解。在其他细胞粘附研究中，一个由惠特克基金会资助的生物医学工程项目的合作种子项目正在研究特定细胞粘附到工程生物材料表面的物理化学基础。直接测量胶体粒子和测试表面之间的动态相互作用力的能力将极大地帮助这些当前的项目和类似的设想项目。此外，这样做的仪器的成功开发将对其他地方的类似努力产生广泛的影响。一种能够直接测量单个胶体颗粒和测试表面之间的静态和动态作用力的仪器。该仪器由一个单光束梯度激光陷阱（光学陷阱）组成，用于微操纵测试表面附近的胶体颗粒。利用测试表面上的倏逝波散射光精确测量粒子位置。粒子和表面之间的力是通过粒子从阱中心的偏转来测量的。向表面扫描捕集器位置可以测量作为分离距离函数的静态相互作用力。此外，通过分析粒子位置的布朗涨落，可以测量更复杂的动力，如粘弹性聚合物诱导力，作为分离距离的函数。为了增强这种能力，压电装置将在所需的波形下振荡光阱，以允许分析响应于施加的力函数的力。这种方法的主要新颖之处在于使用单束梯度阱作为力传感器，类似于原子力显微镜中的悬臂，结合倏逝波光散射，精确测量粒子从表面分离的距离。该仪器的原型已经开发出来，并成功地进行了概念验证。该原型能够同时准确地测量静态和动态力，以及大约一微米的胶体颗粒与透明光学平面之间的分离距离。在~ 1 ~ 3 nm的空间分辨率下，样品的灵敏度在0.01 ~ ~5皮牛顿之间。在灵敏度、可测量的颗粒大小和空间分辨率方面，该仪器与其他可用于胶体颗粒直接力测量的技术相比具有显着优势。基于原型的成功表现，计划开发一种更复杂的仪器，供佛罗里达大学多学科研究项目的多名研究人员最终系统使用。提出的仪器将包括一个更强大的捕获激光器和一个压电定位装置，用于对光阱的位置进行更动态的控制。此外，它将能够测量捕获激光产生的后向散射光，这将允许检测陷阱中的亚微观粒子，并提供一种远离表面校准陷阱的方法。冷却的光电倍增管将提高信噪比，并提供更精确的测量。这些特性将大大提高原型的性能。

CTS-9977459Dickinson, Richard BAbstractDevelopment of Instrumentation for Direct Measurement of Forces Between a Colloidal Particle and a Surface The interaction forces between particles and surfaces are of central importance to several current industry and biomedically relevant research projects at the University of Florida (UF). These include research efforts in the NSF Engineering Research Center for Particle Science and Technology (ERC) that focus on relating interparticle forces to dispersion and flocculation of particle suspensions. Of particular interest in this ERC is the role of polymer-induced colloidal forces such as steric and bridging interactions. The ERC is also investigating the role of particle surface properties in particle flocculation and deposition to surfaces in efforts to develop new and enhance existing particle separation processes. In other efforts at UF, the mechanism of bacterial attachment to biomaterial surfaces are being investigated in order to develop fundamental understanding the role of specific binding of cell surface macromolecule in the process of attachment. In other cell adhesion research, a collaborative seed project in the Biomedical Engineering Program funded by the Whitaker Foundation is investigating the physicochemical basis for specific cell adhesion to engineered biomaterial surfaces. Each of these current projects and similar envisioned projects would be greatly aided by the ability to directly measure the dynamic interaction forces between colloidal particle and a test surface. Furthermore, successful development of instrumentation to do so would have a broad impact on similar efforts elsewhere.An instrument that is capable of directly measuring static and dynamic forces between a single colloidal particle and a test surface. The instrument consists of a single-beam gradient laser trap (optical trap), which is used to micromanipulate the colloidal particle near the test surface. The particle position is precisely measured from the light scattered from an evanescent wave at the test surface. The force between the particle and the surface is measured from the deflection of the particle from the trap center. Scanning the trap position toward the surface allows measurement of the static interaction force as a function of separation distance. Furthermore, by analyzing the Brownian fluctuations of the particle position, more complex dynamic forces such asviscoelastic polymer-induced forces can be measured as a function of separation distance. To enhance this capability, a piezoelectric device will oscillate the optical trap at desired waveforms to allow analysis of the forces in response to an applied forcing function. The main novelty of this approach is to use the single beam gradient trap as a force transducer, analogous to a cantilever in atomic force microscopy, in combination with evanescent wave light scattering, which precisely measures the particle separation distance form the surface.A prototype of the instrument has been developed and has successfully demonstrated the proof-of-concept. The prototype is capable of simultaneously and accurately measuring static and dynamic forces vs. separation distance between an approximately one-micron colloidal particle and a transparent, optically flat surface. The sensitivity of the prototype ranges between 0.01 and ~5picoNewtons at ~ 1-3 nm spatial resolution. In terms of sensitivity, measurable particle sizes, and spatial resolution, this instrument has significant advantages over other available techniques for direct force measurement on colloidal particles. Based on the successful performance of the prototype, it is planned to develop a more sophisticated instrument for ultimate systematic use by multiple investigators in multidisciplinary research projects at UF. The proposed instrument will include a much more powerful trapping laser and a piezoelectric position device for more dynamic control on the position of the optical trap. Also, it will be capable of measuring backscattered light form the trapping laser, which will allow detection of submicroscopic particles in the trap and a means to calibrate the trap far from the surface. Cooled photomultiplier tubes will enhance the signal-to-noise ratio and provide more precise measurements. These features will greatly enhance the performance capabilities over the prototype.