High-Contrast Imaging of Nano-Channels Using Reflection Near-Field Scanning Optical Microscope Enhanced by Optical Interference

We demonstrated a contrast enhancement in a near-field scanning optical microscope (NSOM) by optical interference with an aperture probe in reflection (illumination-collection) mode operation. We observed a NiO film deposited on a sapphire substrate and clearly visualized 2-nm-deep nano-channel structures on the surface of the film. The reflection NSOM enhanced by optical interference is quite a promising instrument for high-resolution optical detection and estimation of low-contrast nanostructures.     

Scanning Near-Field Optical Microscopy and Microspectroscopy of Green Fluorescent Protein in Intact Escherichia coli Bacteria

Scanning near-field optical microscopy (SNOM) yields high-resolution topographic and optical information and constitutes an important new technique for visualizing biological systems. By coupling a spectrograph to a near-field microscope, we have been able to perform microspectroscopic measurements with a spatial resolution greatly exceeding that of the conventional optical microscope. Here we present SNOM images of Escherichia coli bacteria expressing a mutant green fluorescent protein (GFP), an important reporter molecule in cell, developmental, and molecular biology. Near-field emission spectra confirm that the fluorescence detected by SNOM arises from bacterially expressed GFP molecules.     

Resolution of Internal Total ReflectionScanning Near-field Optical Microscopy

In this paper, the probe-sample interaction equation based on Mie's scattering theory is derived, and the resolution of scanning near field optical microscopy is calculated numerically. The results show that the offset of far-field component to near-field component in total field plays an important role in the resolution and the size of samples also has influence on resolution.     

近场显微干涉成像中的探测角度和偏振问题研究

用偶极子耦合系统来模拟近场干涉测量中的探针样品关系,并利用各电场分量之间的组合方程组精确计算出其可能探测到的强度和相位像。结果显示,近场干涉所测量到的近场像的分辨力和探测器的方位及参考光的偏振方向之间有较强的依赖关系,随着探测器位置不同或者参考光偏振方向的变化,同一样品在同一照明条件下所得到的图像也会发生明显的改变。在倏逝波照明的情况下,近场像的精确度随着探测器相对于样品视角的增大而改善,且在不同偏振方向的近场像中,只有偏振方向垂直于样品表面的像能真实反映样品的细节分布,且同时具有足够的强度分布。     

Resolution of Internal Total Reflection Scanning Near-field Optical Microscopy

In this paper, the probe-sample interaction equation based on Mie′s scattering theory is derived, and the resolution of scanning near field optical microscopy is calculated numerically. The results show that the offset of far-field component to near-field component in total field plays an important role in the resolution and the size of samples also has influence on resolution.     

扫描近场光学显微镜探针与光场相互作用的分析

采用时域有限差分方法对镀金属膜光纤探针在近场光探测中对光场产生的扰动和相互作用过程进行了数值分析。选择纳米孔径的隐失场光场和镀金属膜光纤探针建立了近场光探测的理论模型,讨论了探针孔径尺寸、扫描高度等因素对光场探测的影响,以及测量光场与初始光场之间的关系等。研究结果表明,当探针孔径尺寸与待测纳米孔径尺寸相当,探针扫描高度在接近探针孔径尺寸的一半时,测量得到的光场分布数据能够准确描述初始光场分布。     

拉直的单个DNA分子的全内反射荧光实时成像研究

全内反射荧光(TIRF)成像技术利用穿透深度仅200 nm左右的隐失波来激发诱导荧光,探测灵敏度和图像信噪比大大提高,成为单分子研究的有力工具。分子梳技术利用DNA末端与固体表面的结合力和周围流体流动产生的侧向力将DNA分子拉伸并平铺在表面上。结合这两种技术,对分子梳拉直的单个DNA分子进行了清晰的实时荧光成像,发现TIRF成像条件下DNA分子与荧光探针YOYO-1组成的复合体可自然避免发生光敏断裂现象;实时监测了单个DNA-YOYO-1复合体的光漂白过程,通过对激发光照射时间与探测器曝光时间进行同步控制,可大幅降低光漂白程度,为拉直的单个DNA分子的长时间实时观察和成像研究优化了实验条件,为实时、可视化地研究其与蛋白质相互作用的动力学过程奠定了基础。     

Surface chemistry and catalysis of oxide model catalysts from single crystals to nanocrystals

Fundamental understandings of surface chemistry and catalysis of solid catalysts are of great importance for the developments of efficient catalysts and corresponding catalytic processes, but have been remaining as a challenge due to the complex nature of heterogeneous catalysis. Model catalysts approach based on catalytic materials with uniform and well-defined surface structures is an effective strategy. Single crystals-based model catalysts have been successfully used for surface chemistry studies of solid catalysts, but encounter the so-called “materials gap” and “pressure gap” when applied for catalysis studies of solid catalysts. Recently catalytic nanocrystals with uniform and well-defined surface structures have emerged as a novel type of model catalysts whose surface chemistry and catalysis can be studied under the same operational reaction condition as working powder catalysts, and they are recognized as a novel type of model catalysts that can bridge the “materials gap” and “pressure gap” between single crystals-based model catalysts and powder catalysts. Herein we review recent progress of surface chemistry and catalysis of important oxide catalysts including CeO₂, TiO₂ and Cu₂O acquired by model catalysts from single crystals to nanocrystals with an aim at summarizing the commonalities and discussing the differences among model catalysts with complexities at different levels. Firstly, the complex nature of surface chemistry and catalysis of solid catalysts is briefly introduced. In the following sections, the model catalysts approach is described and surface chemistry and catalysis of CeO₂, TiO₂ and Cu₂O single crystal and nanocrystal model catalysts are reviewed. Finally, concluding remarks and future prospects are given on a comprehensive approach of model catalysts from single crystals to nanocrystals for the investigations of surface chemistry and catalysis of powder catalysts approaching the working conditions as closely as possible.