耦合式背光介观荧光分子成像系统设计北大核心CSCD

在生物组织工程的应用中需要有对生物结构标记的三维、纵向评估。一般来说,这些生物组织的结构通常是几毫米厚和浑浊的,因此对图像成像有很大挑战性,且经典荧光显微技术不能满足于其需要。介观荧光分子成像系统是一种新兴的成像系统,该系统基于介观荧光分子层析方法,它填补了显微荧光分子成像技术和宏观荧光分子成像技术之间的空白。为提升介观荧光分子重建的性能,本文主要基于光学原理对光学系统的配置参数进行了优化和改进,包括探测器布局、非耦合或耦合的扫描模式,并对介观荧光分子成像系统的三维成像性能进行了评价和对比。结果表明,本文设计的耦合式背光介观荧光分子层析成像(mesoscopic fluorescence molecular tomography imaging,MFMT)系统能够很好地提升重建性能,获得高质量的重建结果。     

Dispersion in a laser-pumped molecular laser

The dispersion equations are derived for two laser fields of arbitrary intensity interacting with a homogeneously broadened, three-level molecular system. The results obtained apply to laser-pumped molecular lasers and may be used to analyze frequency pulling of the emitting laser and self-focusing or defocusing of the pump laser. The laser fields are allowed to be of arbitrary intensity and to be on or off resonance. The dispersion function for the emitting laserchi'(omega_{s})is evaluated in various limits. The present theory is applied to analyze previous experimental data for cavity frequency pulling in CO2laser-pumped molecular lasers, including a 385-μm D2O laser and a 496-μm CH3F laser. Good agreement is found between theory and experiment.     

Rectifying,giant magnetoresistance,spin-filtering,newgative differential resistance,and switching effects in single-molecule magnet Mn(dmit)2-based molecular device with graphene nanoribbon electrodes

By applying the density functional theory and the nonequilibrium Green’s function formalism, we investigate the spin transport properties of a single-molecule magnet Mn(dmit)₂ sandwiched between two ferromagnetic zigzag-edge graphene nanoribbon electrodes. The results show that the system can present large rectifying, giant magnetoresistance, spin-filtering and negative differential resistance effects with the help of magnetic field modulation. Moreover, an improved switching effect can also be realized by changing the orientation between planes of two dmit ligands. Therefore, the system will provide the possibilities for a multifunctional molecular device design.     

Conductance switching,hysteresis, and magnetoresistance in organic semiconductors

The controllability of charge transport through an organic molecular spin-valve system is theoretically investigated on the basis of a Su–Schrieffer–Heeger model combined with the non-equilibrium Green’s function formalism. We show how the formation of polaron in the organic sub-structure leads to a hysteretic conductance switching, via sweeping either the bias voltage or the electrochemical potential. We further obtain an exponential dependence of the magnetoresistance as a function of the applied bias voltage. The implications of calculated results in relation to experiments and device applications are addressed and commented.     

Thin Functional Zeolite Layer Supported on Infrared Resonant Nano-Antennas for the Detection of Benzene Traces

Infrared absorption spectroscopy is a powerful analytical tool that enables the identification of molecular species. The sensitivity of this technique, that is strongly limited by the small absorption cross-section of molecular vibration, can be greatly improved by resonant interaction with nano-antennas via the surface-enhanced infrared absorption (SEIRA) mechanism. However, most of the examples of SEIRA concern solid-state molecular layers adsorbed on the nano-antennas, while the detection of gas traces still remains elusive due to the spatial extent of the near-field that is used to amplify the molecular vibrations resonantly. Here, a hybrid system composed of a plasmonic nano-antenna array coupled with nanosized zeolite coating for detection of volatile organic compounds in the near field of the resonators is demonstrated. The concerted action of the coating and the nano-antennas enabled the authors to detect record traces of benzene (25 ppb) within 10 min. This approach may ultimately allow the fabrication of a compact system for rapid detection of pharmaceutical and biocompounds with high sensitivity and high selectivity.     

High Molecular Weights,Polydispersities, and Annealing Temperatures in the Optimization of Bulk‐Heterojunction Photovoltaic Cells Based on Poly(3‐hexylthiophene) or Poly(3‐butylthiophene)

A series of poly(3‐hexylthiophene)s (P3HTs) and poly(3‐butylthiophene)s (P3BTs) with predetermined molecular weights and varying polydispersities are prepared using a simplified Grignard metathesis chain‐growth polymerization. Techniques were elaborated to prepare extremely high molecular weight P3HT (number‐average molecular weight of around 280 000 g mol^–1) with a low polydispersity (< 1.1) without resorting to fractionation. Optimization of the annealing of a series of solar cells based on blends of poly(3‐alkylthiophene)s (P3ATs) and [6,6]‐phenyl C₆₁ butyric acid methyl ester indicates that the polydispersities, molecular weights, and degrees of conjugation of the P3ATs all have an important impact not only on cell characteristics but also on the most effective annealing temperature required. The results indicate that each cell requires annealing treatments specific to the type of polymer and its molecular weight distribution.     

采用温控和碘吸收池技术的发射激光稳频技术

多普勒测风激光雷达通过分析系统回波信号的多普勒频移反演出风速，为提高风场探测精度，从稳频技术方面展开研究。在稳频过程中，分别采取措施消除激光频率的长期漂移和短期抖动。针对激光频率的长期漂移，设计并研制了种子激光器温控箱，通过水浴的控温方式大大减小了激光频率的长期漂移，将激光频率稳定在±50 MHz以内；针对激光频率的短期抖动，采用以碘分子吸收池为核心器件的稳频系统，通过半导体控温方式对碘分子吸收池精确控温，控温精度达0.03 ℃，提高了稳频精度，将激光频率进一步稳定在±8 MHz以内，满足±10 MHz以内的设计精度要求。通过搭建多普勒测风激光雷达系统，对发射激光稳频装置进行系统验证，连续4组风场观测结果表明:系统探测高度为17 km，绝大部分方差在4 m/s以下，满足测风激光雷达测量指标的要求。     

甲醇远红外激光的一条新谱线

甲醇（ＣＨ３ＯＨ）分子是常用的ＦＩＲ激活介质,具有很特别的光谱特征。而小型光泵脉冲亚毫米波激光器是近年来才发展起来的新技术,作者已经成功地研制出管长为１０￣３０ｃｍ的ＣＨ３ＯＨＦＩＲ激光器,并获得谱线。本文利用ＣＨ３ＯＨ分子有表编制成数据库管理程序,对光泵ＣＨ３ＯＨ亚毫米波激光进行计算。代入ＣＯ２－９Ｐ（１６）线振动吸收跃迁的条件及相应的亚毫米波纯转动跃迁所受的跃迁选择条件,将泵频偏限制在±０．０     

Photonics Technology for Molecular Imaging

Recent progress in photonics technologies contributing to the advancements of molecular imaging are reviewed from an industrial point of view. Many imaging modalities have been developed for molecular imaging, and many of these methods rely on the detection of "photons" as a basis for image formation. These include positron emission tomography (PET), near-infrared spectroscopy (NIRS), and fluorescence microscopy. A PET system dedicated to studies of monkeys and a planar imaging system for imaging of plants and small animals have been developed. PET studies on age-related impairment of the serotonin neural functions revealed the mechanism in aged monkeys. The planar imaging system demonstrated the dynamic changes in fluoro-deoxy-glucose distribution in a rat with the time interval of 10 s. Using NIRS, quantitative temporal measurement of an absorber such as hemoglobin in tissues was achieved. The NIRS study on the human brain function suggested the relation between the applied task and the activated area. Diffusion optical tomography is also discussed. A fluorescence microscope has been developed for imaging of molecules in living cells, which is equipped with two image-intensified cooled charge-coupled device cameras having a time-gate function. Preliminary results on mRNA expressions showed the usefulness of the fluorescence resonance energy transfer imaging based on the fluorescence decay time, compared to the conventional intensity imaging method. In the near future, the application of a spatial light modulator and holography, to control the wave front of the light, will produce clearer and more precise images of molecules under microscope. Photonics technologies will provide exciting opportunities for various industries to participate in and contribute to the field of molecular imaging.     

Giant magnetoresistance effect and spin filters in phthalocyanine-based molecular devices

The spin transport properties of molecular devices constructed by hydrogen–phthalocyanine and transition metal (TM)–phthalocyanine molecule with zigzag graphene nanoribbon electrodes are investigated by the Keldysh nonequilibrium Green’s function method in combination with the density functional theory. The results show that there exists giant magnetoresistance in both the hydrogen–phthalocyanine and the TM-phthalocyanine systems. The magnetoresistance ratio is much bigger than that found by Schmaus et al. [S. Schmaus, A. Bagrets, Y. Nahas, T. K. Yamada, A. Bork, M. Bowen, E. Beaurepaire, F. Evers, W. Wulfhekel, Nature Nanotechnology 6 (2011) 185–9] in single hydrogen–phthalocyanine-Co electrodes system. Moreover, it is found that the chromium–phthalocyanine molecular device is a good spin filtering device with nearly 100% spin filtering efficiency at a wide bias voltage region. The mechanisms are proposed for these phenomena.     

The UCB/MPE cassegrain submillimeter heterodyne spectrometer

The UCB/MPE Submillimeter Heterodyne Spectrometer is a system for ascronomical spectroscopy in the high-frequency atmospheric windows from 500 to 1000 GHz. It contains a molecular laser local oscillator, a cooled Schottky open structure mixer, a quasi-optical coupling system, and an acousto-optical spectrometer. The compact receiver mounts at the Cassegrain focus of large infrared astronomical telescopes. The receiver noise temperature on the telescope is approximately 3500 K (DSB) during observations of the CO J=7→6 line at 806.652 GHz. The spectrometer's frequency resolution and instantaneous bandwidth (<2 MHz resolution across 1.1 GHz) are well suited for observations of molecular emission lines from a variety of astronomical sources.     

基于多普勒测风激光雷达的锁频系统与激光测速系统的设计与实现

在非相干多普勒测风激光雷达系统中,激光的线宽与频率的稳定性是影响测量结果准确性的两个重要因素。研制的激光雷达系统采用种子注入方法产生窄线宽脉冲激光,采用碘分子饱和吸收稳频的方法,利用VB语言基于PID算法编写仪器控制程序,将种子激光器的频率锁定在碘分子吸收线1 109线的高波数边缘上,长时间(4 h)锁频的精度0.5 MHz,频率的长期稳定度为3.5510-9。设计了连续光测速系统,得出多普勒频移测得的实验值与实际斩波盘的速度值曲线,速度误差小于0.4 m/s。由此也说明,所设计的连续光测速系统可以对整个锁频系统进行校准。该实验也为测风激光雷达的建设提供指导意义。     

Effect of molecular bending and foreign molecules on electronic properties of molecular junctions

We have investigated the charge transport properties of molecular junction using density functional theory in combination with the non-equilibrium Green's function. The charge transport behaviour and change in electronic properties of the molecular junctions formed by bending CNTs is explained by analysing molecular projected self-consistent Hamiltonian, projected density of state, transmission eigen channel, and transmission spectra. The system we used for investigation is consisting of CNTs (3, 3), & (3, 0) with conducting electrodes of Au. Because of the gradual loss in overlapping of the molecular orbitals due to bending processes the conductance decreases. The work also reveals that H₂O significantly affects the conductance of the bent CNTs by interacting with the orbitals of the CNTs and shifting orbital energies, closer to the Au Fermi energy.     

An ab initio approach to the calculation of current-voltage characteristics of programmable molecular devices

Molecular electronics can be developed if we are able to program a random arrangement of molecules or a field-programmable molecular random array. The ansatz that small molecules can be programmed needs to be demonstrated; this means characterizing the smallest molecular system with programmable features. We demonstrate that even two molecules in a series conformation can have multivalued responses and, thus, is able to be programmed; we also indicate how to extend this programmability to other molecular circuit conformations. Current programs for the calculation of current-voltage characteristics of electronic circuits, needed for such demonstrations, are only capable of predicting single-valued characteristics. We present results from our ab initio procedures that couple the molecular approaches with a practical analysis of molecular circuits having strong nonlinearities.     

Hybrid small animal imaging system combining magnetic resonance imaging with fluorescence tomography using single photon avalanche diode detectors

The high sensitivity of fluorescence imaging enables the detection of molecular processes in living organisms. However, diffuse light propagation in tissue prevents accurate recovery of tomographic information on fluorophore distribution for structures embedded deeper than 0.5 mm. Combining optical with magnetic resonance imaging (MRI) provides an accurate anatomical reference for fluorescence imaging data and thereby enables the correlation of molecular with high quality structural/functional information. We describe an integrated system for small animal imaging incorporating a noncontact fluorescence molecular tomography (FMT) system into an MRI detector. By adopting a free laser beam design geometrical constraints imposed by the use of optical fibers could be avoided allowing for flexible fluorescence excitation schemes. Photon detection based on a single-photon avalanche diode array enabled simultaneous FMT/MRI measurements without interference between modalities. In vitro characterization revealed good spatial accuracy of FMT data and accurate quantification of dye concentrations. Feasibility of FMT/MRI was demonstrated in vivo by simultaneous assessment of protease activity and tumor morphology in murine colon cancer xenografts.     

光泵NH3分子亚毫米波频谱特性的理论计算

本文从密度矩阵方程出发,分别采用三能级和多组独立三能级迭加的近似方法对光泵NH_3分子亚毫米激光器的输出光强进行了理论研究.同时根据NH_3分子能级结构对TEA-CO_2激光器的10R(6)谱线泵浦NH_3分子亚毫米波频谱特性进行了数值计算,理论计算结果与实验符合较好.     

Clocked molecular quantum-dot cellular automata

Quantum-dot cellular automata (QCA) is an approach to computing that eliminates the need for current switches by representing binary information as the configuration of charge among quantum dots. For molecular QCA, redox sites of molecules serve as the quantum dots. The Coulomb interaction between neighboring molecules provides device-device coupling. By introducing clocked control of the QCA cell, power gain, reduced power dissipation, and computational pipelining can be achieved. We present an ab initio analysis of a simple molecular system, which acts as a clocked molecular QCA cell. The intrinsic bistability of the molecular charge configuration results in dipole or quadrupole fields that couple strongly to the state of neighboring molecules. We show how clocked control of the molecular QCA can be accomplished with a local electric field.     

The Photo-Hall Effect in High-Mobility Organic Semiconductors

High-mobility crystalline organic semiconductors are important for applications in advanced organic electronics and photonics. Photogeneration and transport of mobile photocarriers in these materials, although very important, remain underexplored. The photo-Hall effect can be used to address the fundamental charge transport properties of these functional molecular materials, without the need for fabricating complex transistor devices or chemical doping. Here, a photo-Hall effect is demonstrated in organic semiconductors, using a benchmark molecular system rubrene as an experimental platform. It is shown that this technique can be used to directly measure the charge carrier mobility and photocarrier density, decouple the surface and bulk transport phenomena, and thus significantly deepen the understanding of the mechanism of photoconductivity in these high-performance molecular materials.     

Impedance characterization of microarray recording electrodes in vitro

The mechanisms underlying performance degradation of chronically implanted silicon microelectrode arrays in the central nervous system (CNS) remain unclear. Humoral and cellular components of the brain foreign body response were evaluated to determine whether their presence on the electrode surface results in increased electrical impedance. Iridium oxide microelectrode recording arrays were electrically characterized in saline, culture media with 10% fetal bovine serum, and coated with various CNS cell types isolated from rat brain. Electrochemical impedance spectroscopy and cyclic voltammetry were performed using a three-electrode system. Potential cycling caused an immediate decrease in electrical impedance, which increased with time toward precycling values, with the effect of cycling remaining significant for several days. The addition of serum caused a significant increase in impedance of up to 28% relative to the saline control. Microelectrodes coated with various cell types known to participate in the foreign body response caused a 20%-80% increase in impedance immediately after contact that remained constant or gradually increased for several weeks. Our findings suggest that the attachment of molecular and cellular species following microelectrode implantation into brain tissue likely contribute to increases in impedance, but do not appear sufficient to hinder recording performance.     

Tuning Molecular Adhesion via Material Anisotropy

Cell adhesion with extracellular matrix depends on the collective behaviors of a large number of receptor‐ligand bonds at the compliant cell‐matrix interface. While most biological tissues and structures, including cells and extracellular matrices, exhibit strongly anisotropic material properties, existing studies on molecular adhesion via receptor‐ligand bonds have been largely limited to isotropic materials. Here the effects of transverse isotropy, a common form of material anisotropy in biological systems, in modulating the adhesion behavior of a cluster of receptor‐ligand bonds are investigated. The results provide a theoretical basis to understand cell adhesion on anisotropic extracellular matrices and to explore the possibility of controlling cell adhesion via anisotropy design in material properties. The combined analysis and simulations show that the orientation of material anisotropy strongly affects the apparent softness felt by the adhesive bonds, thereby altering their ensemble lifetime by several orders of magnitude. An implication of this study is that distinct cellular behaviors can be achieved through remodeling of material anisotropy in either extracellular matrix or cytoskeleton. Comparison between different loading conditions, together with the effects of material anisotropy, yields a rich array of out‐of‐equilibrium behaviors in the molecular interaction between reactant‐bearing soft surfaces, with important implications on the mechanosensitivity of cells.