Sheung Janet Y, Ge Pinghua, Lim Sung Jun, Lee Sang Hak, Smith Andrew M, Selvin Paul R
Department of Physics, University of Illinois at Urbana-Champaign, Champaign, Illinois 61801, United States.
Department of Physics and Astronomy, Vassar College, Poughkeepsie, New York 12604, United States.
J Phys Chem C Nanomater Interfaces. 2018;122(30):17406-17412. doi: 10.1021/acs.jpcc.8b02516. Epub 2018 Jul 11.
Quantum dots are fluorescent nanoparticles with narrow-band, size-tunable, and long-lasting emission. Typical formulations used for imaging proteins in cells are hydrodynamically much larger than the protein targets, so it is critical to assess the impact of steric effects deriving from hydrodynamic size. This report analyzes a new class of quantum dots that have been engineered for minimized size specifically for imaging receptors in narrow synaptic junctions between neurons. We use fluorescence correlation spectroscopy and transmission electron microscopy to calculate the contributions of the crystalline core, organic coating, and targeting proteins (streptavidin) to the total hydrodynamic diameter of the probe, using a wide range of core materials with emission spanning 545-705 nm. We find the contributing thickness of standard commercial amphiphilic polymers to be ~8 to ~14 nm, whereas coatings based on the compact ligand HS-(CH) (OCHCH)-OH contribute ~6 to ~9 nm, reducing the diameter by ~2 to ~5 nm, depending on core size. When the number of streptavidins for protein targeting is minimized, the total diameter can be further reduced by ~5 to ~11 nm, yielding a diameter of 13.8-18.4 nm. These findings explain why access to the narrow synapse derive primarily from the protein functionalization of commercial variants, rather than the organic coating layers. They also explain why those quantum dots with size around 14 nm with only a few streptavidins can access narrow cellular structures for neuronal labeling, whereas those >27 nm and a large number of streptavidins, cannot.
量子点是具有窄带、尺寸可调谐和持久发光特性的荧光纳米颗粒。用于细胞内蛋白质成像的典型制剂在流体动力学上比蛋白质靶点大得多，因此评估流体动力学尺寸产生的空间位阻效应的影响至关重要。本报告分析了一类新型量子点，这类量子点经过专门设计，尺寸最小化，用于神经元之间狭窄突触连接中受体的成像。我们使用荧光相关光谱和透射电子显微镜，通过使用发射波长范围为545 - 705 nm的多种核心材料，来计算晶体核心、有机涂层和靶向蛋白（链霉亲和素）对探针总流体动力学直径的贡献。我们发现标准商业两亲聚合物的贡献厚度约为8至14纳米，而基于紧密配体HS-(CH) (OCHCH)-OH的涂层贡献约为6至9纳米，根据核心尺寸，直径可减少约2至5纳米。当用于蛋白质靶向的链霉亲和素数量减至最少时，总直径可进一步减少约5至11纳米，产生的直径为13.8 - 18.4纳米。这些发现解释了为什么能够进入狭窄突触主要源于商业变体的蛋白质功能化，而非有机涂层。它们还解释了为什么那些尺寸约为14纳米且只有少数链霉亲和素的量子点能够进入狭窄的细胞结构进行神经元标记，而那些直径大于27纳米且有大量链霉亲和素的量子点则不能。
