Magnetic Control and Optical Imaging of Nanoparticles for Biosensing

0853963S。MajetichIntellectual Merit.拟议的研究计划将开发两种类型的等离子体磁性粒子，并研究在光学成像的同时磁性控制单个粒子运动的能力。虽然这些颗粒小于光学衍射极限，但它们的位置可以通过暗视野光学显微镜通过金涂层的表面等离子体共振来跟踪，或者当荧光团结合到颗粒表面时通过荧光显微镜来跟踪。棒状粒子的旋转将从纵向表面等离子体激元模式的偏振监测。纳米颗粒的磁引导平移具有挑战性，因为粘性拖曳力和随机布朗扩散力对于小尺寸来说都变得很重要。Peclet数分析表明，控制纳米棒的运动应该比相同体积的纳米球更容易，但目前的纳米棒扩散模型在数量上并不一致。另一个复杂因素是水分散体中的聚集体形成。虽然电子显微镜显示高度单分散的颗粒核，但在水或生物介质中的分散体可能含有具有宽尺寸分布的聚集体。对于基于单个粒子的传感以及磁热疗应用，磁响应将取决于聚集体的大小，并且最佳控制需要均匀的样品。 我们将用金涂覆35-50 nm标称球形磁铁矿颗粒，然后用聚合物涂覆以在磷酸盐缓冲盐水（PBS）溶液中形成稳定的分散体。我们的纳米棒样品将基于均匀但非磁性的赤铁矿纳米棒，长约300 nm，直径20 nm，在金和聚合物涂层阶段之前，反应性地涂覆有薄层磁铁矿。在水性分散体和PBS分散体中的团聚体的尺寸将由动态光散射（DLS）确定。 拟议研究的合成部分的目标将是制备高度均匀、最小团聚的颗粒，这些颗粒显示出快速的磁响应，并具有较强的表面等离子体共振。我们将调查的平移和旋转动力学作为施加的磁场和场梯度的函数，首先宏观上由AC磁化率，和纳米棒，等离子体光谱的光学调制。我们还将构建一个光学显微镜细胞与磁性控制的单个纳米粒子和纳米棒的平移和旋转的研究，使用暗场光学显微镜和荧光显微镜。结果将与纳米棒动力学的椭球和圆柱模型的预测进行比较。在拟议工作的最后阶段，这些结果将用于探索新的生物传感方法，其中磁场用于移动粒子并调制其光学响应。我们将研究活细胞内的磁引导平移以探测局部粘度和pH值，以及磁诱导旋转以通过荧光强度对纳米棒表面等离子体的敏感性来监测选择性结合事件。更广泛的影响目标将与拟议计划的研究目标相关联。研究生将由PI共同指导。也将有几个本科研究项目，涉及磁性，光学和光散射测量的颗粒分散。我们已经招募了一名非裔美国大学生来做这个项目。一个关于铁磁流体和磁力的动手实验模块，将被开发用于卡内基梅隆大学的“工程你的未来”计划，该计划针对初中和高中女生，并为匹兹堡公立学校的科学教师提供传播信息的机会。这种联系将被用来招募一名中学教师与我们一起工作，创造适合年龄的课堂材料，演示和活动的基础上胶体稳定力的铁磁流体和等离子体溶胶。

0853963S. MajetichIntellectual Merit. The proposed research program will develop two types of plasmonic magnetic particles, and investigate the ability to control the motion of single particles magnetically while imaging them optically. Though these particles are smaller than the optical diffraction limit, their positions can be tracked by dark field optical microscopy through the surface plasmon resonance of the gold coating, or by fluorescence microscopy when fluorophores are bound to the particle surface. The rotation of rod-shaped particles will be monitored from the polarization of the longitudinal surface plasmon mode. Magnetically guided translation of nanoparticles is challenging because both viscous drag forces and random Brownian diffusion forces become significant for small sizes. Peclet number analysis suggests that it should be easier to control the motion of nanorods than nanospheres of the same volume, but current models of nanorod diffusion do not agree quantitatively. Another complicating factor is aggregate formation in aqueous dispersions. While electron microscopy shows highly monodisperse particle cores, the dispersions in water or biological media may contain aggregates with a broad size distribution. For single particle-based sensing as well as magnetic hyperthermia applications, the magnetic response will depend on the size of the aggregate, and optimal control requires uniform samples. We will coat 35-50 nm nominally spherical magnetite particles with gold, and then with polymers to form stable dispersions in phosphate buffered saline (PBS) solution. Our nanorod samples will be based on uniform but non-magnetic hematite nanorods ~300 nm long and 20 nm in diameter, that are reactively coated with thin layers of magnetite prior to the gold and polymer coating stages. The size of the agglomerates in aqueous and PBS dispersions will be determined from dynamic light scattering (DLS). The objective of the synthetic portion of the proposed research will be to prepare highly uniform, minimally agglomerated particles that show rapid magnetic response and have a strong surface Plasmon resonance. We will investigate the translational and rotational dynamics as a function of the applied field and field gradient first macroscopically by the AC magnetic susceptibility, and for the nanorods, optical modulation of the plasmon spectra. We will also construct an optical microscope cell with magnetic control for single nanoparticle and nanorod translation and rotation studies using dark field optical microscopy and fluorescence microscopy. The results will be compared with the predictions of ellipsoidal and cylindrical models of nanorod dynamics. In the final phase of the proposed work, these results will be used to explore new biosensing approaches where magnetic fields are used to move the particles and modulate their optical response. We will investigate magnetically guided translation within living cells to probe local viscosity and pH, and magnetically induced rotation to monitor selective binding events through the sensitivity of fluorescence intensity to the surface plasmons of the nanorods.The Broader Impact aims will be linked with the research aims of the proposed program. A graduate student will be co-advised by the PIs. There will also be several undergraduate research projects involving magnetic, optical, and light scattering measurements on the particle dispersions. We have already recruited an African-American undergraduate to work on this project. A hands-on experimental module on ferrofluids and magnetic forces that will be developed for use in the Engineering Your Future program at Carnegie Mellon that targets middle school and high school girls, and also provides the opportunity to disseminate information to science teachers in the Pittsburgh Public Schools. This connection will be used to recruit a middle school teacher to work with us in creating age-appropriate classroom materials, demonstrations, and activities based on colloidal stabilization forces in both ferrofluids and plasmonic sols.