Synthesis and surface functionalization of silica nanoparticles for nanomedicine

There are a wide variety of silica nanoformulations being investigated for biomedical applications. Silica nanoparticles can be produced using a wide variety of synthetic techniques with precise control over their physical and chemical characteristics. Inorganic nanoformulations are often criticized or neglected for their poor tolerance; however, extensive studies into silica nanoparticle biodistributions and toxicology have shown that silica nanoparticles may be well tolerated, and in some case are excreted or are biodegradable. Robust synthetic techniques have allowed silica nanoparticles to be developed for applications such as biomedical imaging contrast agents, ablative therapy sensitizers, and drug delivery vehicles. This review explores the synthetic techniques used to create and modify an assortment of silica nanoformulations, as well as several of the diagnostic and therapeutic applications.     

Thermal conductivity of nanofluids and size distribution of nanoparticles by Monte Carlo simulations

Nanofluids, a class of solid–liquid suspensions, have received an increasing attention and studied intensively because of their anomalously high thermal conductivites at low nanoparticle concentration. Based on the fractal character of nanoparticles in nanofluids, the probability model for nanoparticle’s sizes and the effective thermal conductivity model are derived, in which the effect of the microconvection due to the Brownian motion of nanoparticles in the fluids is taken into account. The proposed model is expressed as a function of the thermal conductivities of the base fluid and the nanoparticles, the volume fraction, fractal dimension for particles, the size of nanoparticles, and the temperature, as well as random number. This model has the characters of both analytical and numerical solutions. The Monte Carlo simulations combined with the fractal geometry theory are performed. The predictions by the present Monte Carlo simulations are shown in good accord with the existing experimental data.     

Drug nanocrystals for the formulation of poorly soluble drugs and its application as a potential drug delivery system

Formulation of poorly soluble drugs is a general intractable problem in pharmaceutical field, especially those compounds poorly soluble in both aqueous and organic media. It is difficult to resolve this problem using conventional formulation approaches, so many drugs are abandoned early in discovery. Nanocrystals, a new carrier-free colloidal drug delivery system with a particle size ranging from 100 to 1000 nm, is thought as a viable drug delivery strategy to develop the poorly soluble drugs, because of their simplicity in preparation and general applicability. In this article, the product techniques of the nanocrystals were reviewed and compared, the special features of drug nanocrystals were discussed. The researches on the application of the drug nanocrystals to various administration routes were described in detail. In addition, as introduced later, the nanocrystals could be easily scaled up, which was the prerequisite to the development of a delivery system as a market product.     

Optimization of the locations of the loudspeaker and absorption material in a small room

The sound field both in the loudspeaker box and in the room is calculated by an analytical solution of three-dimensional wave equation. It is shown in theory that the amplitude response in small rooms is affected by the following positions: driver position on the front panel of the box, box position in the room, absorption material position in the box and absorption material position on the interior walls of the room. Both our computer prediction and experiments prove that the optimum positions are beneficial to the amplitude response.     

Measurement of the K X-ray absorption jump factors and jump ratios of Gd, Dy, Ho and Er by attenuation of a Compton peak

The X-ray absorption jump factor and jump ratio of Gd, Dy, Ho and Er were measured with a Si(Li) detector by attenuation, with Gd, Dy, Ho and Er foil, a Compton peak produced by the scattering of the Am-241 Gamma rays. Al was chosen as secondary exciter. The experimental absorption jump factors and jump ratios are compared with the theoretical estimates of WinXcom (Radiat. Phys. Chem. 60 (2001) 23), McMaster (Compilation of X-ray cross sections UCRL-50174, 1969; Sec. II. Rev. I), Broll (X-ray Spectrom 15 (1986) 271), Hubbel and Seltzer (NISTIR (1995) 5632) and Budak (Radiat. Meas. accepted for publication). The present results constitute the first measurement for this combination of energy and elements, and good agreement is obtained between experiment and theory.     

厚朴酚近红外光谱的2D-COS解析及其在藿香正气口服液模型中应用

以氘代氯仿为溶剂,以中药化学标准品厚朴酚为载体,采用二维相关光谱(Tow-dimensional correlation spectroscopy, 2D-COS)技术,采集近红外光谱(near infrared spectroscopy, NIR),由氘代氯仿纯溶剂与厚朴酚原始光谱的二维相关同步谱可知,厚朴酚在1 365～1 455, 1 600～1 720, 2 000～2 181和2 275～2 465 nm处有特征吸收,其中1 440 nm为酚基O—H伸缩振动基频的一级倍频谱带,1 679 nm为芳基C—H及与芳基相连的甲基C—H伸缩振动一级倍频谱带,2 117, 2 304, 2 339和2 370 nm为芳基C—H伸缩振动、弯曲振动和变形振动的组合频,2 445 nm为芳基相连的甲基C—H弯曲振动基频二级倍频谱带,这些波段为厚朴酚的特征归属。以藿香正气口服液复杂体系为载体,以厚朴酚光谱解析的特征波段与间隔偏最小二乘(interval partial least squares, iPLS)和组合间隔偏最小二乘(synergy interval partial least squares, SiPLS)筛选的特征波段分别建立偏最小二乘(partial least squares, PLS)定量模型,模型的决定系数R2_cal 和R2_pre均大于0.99,校正均方根误差(root mean of square error of calibration, RMSEC),交叉验证均方根误差(root mean of square error of cross validation, RMSECV)和预测均方根误差(root mean of square error of prediction, RMSEP)均较小。结果表明,2D-COS技术解析厚朴酚所得波段建立的定量模型与iPLS和SiPLS波段筛选的模型均相对稳定,这使定量模型的波段选择更具有解释性。该研究为中药化学成分NIR光谱解析特征波段的归属提供方法参考,同时为NIR建模波段筛选提供借鉴和指导。     

Optical and optoacoustic measurements of the absorption properties of spherical gold nanoparticles within a highly scattering medium

In the present paper the requirements for optical parameter characterization of absorbing materials located within a highly scattering medium has been addressed. The measurement scheme incorporates the optoacoustic technique where a single acoustic transducer is used to detect ultrasonic transients generated from laser irradiation. The absorbing medium is based on different concentrations of spherical gold nanoparticles (SGNP’s), these are currently being considered as non-toxic targeted optical contrast agents for both medical imaging and cancer therapeutics. In this paper we present results which demonstrate the two main advantages the optoacoustic technique has over other measurement schemes. These are the possibility to obtain information on the position and dimensions of absorbing bodies using a time of flight analysis (TOF) and secondly, the higher sensitivity of the optoacoustics compared to optical transmission techniques. The former advantage is of particular interest for imaging applications and the latter for detection and characterization of absorbing materials surrounded by high levels of high scattering mediums. We present for the first time the characterization of SGNP within a highly scattering medium. To further demonstrate the feasibility of the optoacoustic technique, the scattering coefficient of the surrounding medium has also been characterized.     

Transport and crystallization of colloidal particles in a thin nematic cell

In a thin planar nematic cell, the application of an AC electric field induces a macroscopic transport of micrometer-sized colloidal particles along the nematic director. We have analyzed the dependence of particle velocities on the electric-field amplitude and frequency and found that it decreases exponentially with increasing frequency. Using specially designed electrodes we have observed that colloidal particles could be pumped and accelerated across the field-no-field interface, and measured the structural force and the corresponding potential, which is of the order of 10000 k_BT for 4μm particles. We demonstrate that spatially periodic close-packed crystalline colloidal structures can be obtained, which are thermodinamically metastable for many days after turning off the electric field and slowly decay into linear chains. Above the nematic-isotropic phase transition, such crystalline structures are non-stable and decay in few minutes.     

The absorption spectrum of water between 13 540 and 14 070 cm: ICLAS detection of weak lines and a complete line list

The absorption spectrum of water vapor has been investigated by Intracavity Laser Absorption Spectroscopy (ICLAS) between 13 540 and 14 070 cm⁻¹. This spectrum is dominated by relatively strong transitions of the 4δ polyad of vibrational states. The achieved sensitivity - on the order of α_min ∼ 10⁻⁹ cm⁻¹ - has allowed one to newly measure 222 very weak transitions with intensities down to 5 × 10⁻²⁸ cm/molecule at 296 K. Fifty new or corrected H₂¹⁶O energy levels belonging to a total of 13 vibrational states could be determined from the rovibrational analysis based on variational calculations by Schwenke and Partridge. The previous investigations in the region by Fourier Transform Spectroscopy were critically evaluated and used to construct the best to date set of energy levels accessed by transitions in the considered region. All the rovibrational transitions reaching these upper energy levels and having intensities larger than 4.0 × 10⁻²⁸ cm/mol were calculated. In the resulting line list, the positions at the level of experimental accuracy were augmented with variational intensities leading to the most complete line list for water in normal isotopic abundance in the 13 500-14 100 cm⁻¹ region.     

Two-photon absorption and nonlinear optical properties of a new organic dye PSPI

Trans-4-[p-(pyrrolidinyl)styryl]-N-methylpyridinium iodide (abbreviated as PSPI thereafter) is a two-photon absorption (TPA) dye newly synthesized by our research group. It possesses much larger TPA cross-section and much stronger upconversion fluorescence emission than those of common organic dye (such as rhodamine) when excited with near infrared (IR) radiation. TPA spectrum and upconversion efficiency spectrum of HEASPI solution at various wavelengths were measured. There is 34 nm blue shift for the central wavelength of the TPA induced absorption peak compared with two times of the linear absorption peak. The biggest molecular TPA cross-section σ₂^′ is 2.85×10⁻⁴⁷ cm⁴ s/photon at 930 nm. At 1064 nm, σ₂^′ is 3.12×10⁻⁴⁸ cm⁴ s/photon. The highest efficiency is 3.9% at 1010 nm, whereas 2.9% at 1064 nm. Its optical power limiting properties at 930 nm have also been illustrated.     

Quasinormal modes and absorption of a massless scalar field for the magnetic Gauss–Bonnet black hole

We study the massless scalar quasinormal frequencies of an asymptotically flat static and spherically symmetric black hole with a nonzero magnetic charge in four-dimensional extended scalar-tensor-Gauss–Bonnet theory. The results show that the real part of the quasinormal frequency becomes larger and the imaginary part becomes smaller with increasing the magnetic charge or the angular harmonic index. The existence of magnetic charges will reduce the damping of scalar perturbation, but increase the frequency. We also study the absorption cross-section of the scalar field in this black hole. We find that its curve will become lower as the magnetic charge increases, i.e. the magnetic charge will weaken the absorption capacity of the black hole. Meanwhile, the high-frequency limit of the total absorption cross-section is just the area of black hole shadow.     

Radial distribution of temperature in a thin lens due to absorption of light and heat conduction

We consider the stationary radial distribution of temperature in a lens. For a thin lens, i.e. a two-dimensional model problem, we give an analytical approximation for the distribution of temperature, a quantity of great importance for the prediction of the performance of the lens. We compare this formula with the numerical solution of the heat equation for several examples. Finally, we discuss the incorporation of the heat-transfer to the environment in principle and give prospects for further generalizations of this theory.     

Novel photonic technique creates micrometer resolution protein arrays and provides a new approach to coupling of genes, peptide hormones and drugs to nanoparticle carriers

We demonstrate that ultraviolet light can be used to make sterically oriented covalent immobilization of a large variety of protein molecules onto either thiolated quartz, gold or silicon. The reaction mechanism behind the reported new technology involves light-induced breakage of disulphide bridges in proteins upon UV illumination of nearby aromatic amino acids, resulting in the formation of free, reactive thiol groups that will form covalent bonds with thiol reactive surfaces. In general, the protein molecules retain their function. The size of the immobilization spot is limited to the focal point of illumination being as small as a few micrometers. This new technology allows for dense packing of different bio-molecules on a surface, allowing the creation of multi-potent functionalised new materials, such as nano-biosensors. We have developed the necessary technology for preparing large protein arrays of enzymes and fragments of monoclonal antibodies. Dedicated image processing software has been developed for making quality assessment of the protein arrays. This novel technology is ideal to couple drugs and other bio-molecules to nanoparticles which can be used as carriers into cells for therapeutic purposes.     

Synthesis, vibrational and optical properties of a new three-layered organic-inorganic perovskite (C4H9NH3)4Pb3I4Br6

An organic-inorganic hybrid perovskite (C₄H₉NH₃)₄Pb₃I₄Br₆ was synthesized and studied by X-ray diffraction, Raman and infrared spectroscopies, optical transmission and photoluminescence. The title compound, abbreviated (C₄)₄Pb₃I₄Br₆, crystallises in a periodic two-dimensional multilayer structure with P2₁/a space group. The structure is built up from alternating inorganic and organic layers. Each inorganic layer consists of three sheets of PbX₆ (X=I, Br) octahedra. Raman and infrared spectra of the title compound were recorded in the 100-3500 and 400-4000 cm⁻¹ frequency ranges, respectively. An assignment of the observed vibration modes is reported. Optical transmission measurements, performed on thin films of (C₄)₄Pb₃I₄Br₆, revealed two absorption bands at 474 and 508 nm. Photoluminescence measurements have shown a green emission peak at 519 nm.     

一种新型有机染料HEASPS在不同波长时的双光子吸收和频率上转换性质研究

报道了一种新型双光子吸收染料 ,即反式 - 4- [4′- (N-羟乙基 - N-乙基胺基 )苯乙烯基 ]- N-甲基吡啶对甲苯磺酸盐的非线性光学性质 ;测试了染料在 72 0～ 110 0 nm波段的非线性透过率曲线。结果发现 :双光子吸收最强波长相对线性吸收峰波长的两倍处有明显蓝移 ;计算出的相应波长的双光子吸收截面在 930 nm处染料有最大双光子吸收截面(2 .0 6× 10 - 4 7cm4·s/ photon) ;测量了染料在 90 0～ 110 0 nm波段的上转换效率 ,在 10 2 0 nm处有最高效率 (5 .1% ) ,最高激射效率的波长相对最强双光子吸收的波长有明显红移     

Disorder and superconductivity: a new phase of bi-particle localized states

We study the two-dimensional, disordered, attractive Hubbard model by the projector quantum Monte Carlo method and Bogoliubov-de Gennes mean-field theory. Our results for the ground state show the appearance of a new phase with charge localization in the metallic regime of the non-interacting model. Contrary to the common lore, we demonstrate that mean-field theory fails to predict this phase and is unable to describe the correct physical picture in this regime. Received 2 July 2001     

Scattering and absorption of light by ice particles: Solution by a new physical-geometric optics hybrid method

A new physical-geometric optics hybrid (PGOH) method is developed to compute the scattering and absorption properties of ice particles. This method is suitable for studying the optical properties of ice particles with arbitrary orientations, complex refractive indices (i.e., particles with significant absorption), and size parameters (proportional to the ratio of particle size to incident wavelength) larger than ∼20, and includes consideration of the edge effects necessary for accurate determination of the extinction and absorption efficiencies. Light beams with polygon-shaped cross sections propagate within a particle and are traced by using a beam-splitting technique. The electric field associated with a beam is calculated using a beam-tracing process in which the amplitude and phase variations over the wavefront of the localized wave associated with the beam are considered analytically. The geometric-optics near field for each ray is obtained, and the single-scattering properties of particles are calculated from electromagnetic integral equations. The present method does not assume additional physical simplifications and approximations, except for geometric optics principles, and may be regarded as a “benchmark” within the framework of the geometric optics approach. The computational time is on the order of seconds for a single-orientation simulation and is essentially independent of the size parameter. The single-scattering properties of oriented hexagonal ice particles (ice plates and hexagons) are presented. The numerical results are compared with those computed from the discrete-dipole-approximation (DDA) method.     

Jump of the minimal site and a new correlation function in the Bak-Sneppen model

A new type of spatio-temporal correlation function for the process approaching the self-organized criticality is investigated within the Bak-Sneppen model for biological evolution. In terms of the “directional shorter distance” between the two sites with minimum fitness at two successive updates, the correlation function is defined and studied numerically for the nearest- and random-neighbor versions of the model. Qualitatively different behaviors of the jump of the minimal site in the two models are presented, and the behaviors of the correlation functions are shown also different. Received 14 April 2001 and Received in final form 28 June 2001