Surface-enhanced-Raman-scattering-inducing nanoprobe for spectrochemical analysis

This paper describes a new nanoprobe that induces the surface-enhanced Raman scattering (SERS) effect when brought into contact with chemicals on any type of surface. The SERS-inducing probe was fabricated from an optical fiber that was tapered to a tip 100 nm in diameter. A thin layer of silver islands was applied to the tip of the tapered fiber via thermal evaporation to induce the SERS effect. The small scale of the tip may be amenable to localized, nondestructive SERS-based analyses of surfaces with high spatial selectivity. Because the contact probe itself induces the SERS effect, no modification of the sample is required. Direct analysis at submicrometer spatial selectivity is therefore possible for analyte compounds on any type of surface. Various optimization studies and preliminary evaluations were performed. A 10-nm silver thickness was determined to yield the optimum SERS effect. A 25% relative standard deviation in SERS signal was observed for five different probe tips. As a demonstration of the SERS-inducing capability of the probe, Raman spectra were recorded for glass surfaces coated with brilliant cresyl blue and p-aminobenzoic acid before and during contact with the SERS-inducing nanoprobe.     

Ultrahigh-Q nanocavities written with a nanoprobe

High-Q nanocavities have been extensively studied recently because they are considered key elements in low-power photonic devices and integrated circuits. Here we demonstrate that ultrahigh-Q (>10(6)) nanocavities can be created by employing scanning probe lithography on a prepatterned line defect in a silicon photonic crystal. This is the first realization of ultrahigh-Q nanocavities by the postprocess modification of photonic crystals. With this method, we can form an ultrahigh-Q nanocavity with controllable cavity parameters at an arbitrary position along a line defect. Furthermore, the fabricated nanocavity achieves ultralow power all-optical bistable operation owing to its large cavity enhancement effect. This demonstration indicates the possibility of realizing photonic integrated circuits on demand, where various circuit patterns are written with a nanoprobe on a universal photonic crystal substrate.     

Fluorescent magnetic hybrid nanoprobe for multimodal bioimaging

A fluorescent magnetic hybrid imaging nanoprobe (HINP) was fabricated by the conjugation of superparamagnetic Fe3O4 nanoparticles and visible light emitting (～600 nm) fluorescent CdTe/CdS quantum dots (QDs). The assembly strategy used the covalent linking of the oxidized dextran shell of magnetic particles to the glutathione ligands of QDs. The synthesized HINP formed stable water-soluble colloidal dispersions. The structure and properties of the particles were characterized by transmission electron and atomic force microscopy, energy dispersive x-ray analysis and inductively coupled plasma optical emission spectroscopy, dynamic light scattering analysis, optical absorption and photoluminescence spectroscopy, and fluorescent imaging. The luminescence imaging region of the nanoprobe was extended to the near-infrared (NIR) (～800 nm) by conjugation of the superparamagnetic nanoparticles with synthesized CdHgTe/CdS QDs. Cadmium, mercury based QDs in HINP can be easily replaced by novel water-soluble glutathione stabilized AgInS2/ZnS QDs to present a new class of cadmium-free multimodal imaging agents. The observed NIR photoluminescence of fluorescent magnetic nanocomposites supports their use for bioimaging. The developed HINP provides dual-imaging channels for simultaneous optical and magnetic resonance imaging.     

Fluorescence microspectroscopy technique for the study of intracellular protoporphyrin IX dynamics

We describe a technique designed to monitor the fluorescence dynamics of photosensitizers used in photodynamic therapy (PDT) at micrometer-scale locations within individual formalin-fixed cells. The accumulation of protoporphyrin IX (PpIX) within keratinocytes and fibroblasts. following incubation with 5-aminolaevulinic acid (ALA), is shown to be dependent upon both incubation time and cell proliferation status. Also, the process of photobleaching within these cells is demonstrated via the depletion in PpIX fluorescence emission during exposure to 532 nm light. All spectra show a progressive reduction of the 634 nm PpIX peak, following a bi-exponential decay that is consistent with a singlet oxygen mediated process. The rate of photobleaching, when plotted as a function of light dose, increases with reduced incident laser power. The generation of the hydroxyaldehyde-chlorin photoproduct (photoprotoporphyrin), as monitored by the increase in fluorescence emission centered on 672 nm, is also greatest when the lowest laser power is applied. When light is delivered in two fractions, PpIX fluorescence recovers during the dark period and there is an increase in bleaching rate at the onset of the second exposure. These results are qualitatively consistent with measurements performed in vivo, which demonstrate that the photodynamic dose is dependent upon fluence rate and oxygen status.     

Modeling and simulation of intracellular dynamics: choosing an appropriate framework

Systems biology is a reemerging paradigm which, among other things, focuses on mathematical modeling and simulation of biochemical reaction networks in intracellular processes. For most simulation tools and publications, they are usually characterized by either preferring stochastic simulation or rate equation models. The use of stochastic simulation is occasionally accompanied with arguments against rate equations. Motivated by these arguments, we discuss in this paper the relationship between these two forms of representation. Toward this end, we provide a novel compact derivation for the stochastic rate constant that forms the basis of the popular Gillespie algorithm. Comparing the mathematical basis of the two popular conceptual frameworks of generalized mass action models and the chemical master equation, we argue that some of the arguments that have been put forward are ignoring subtle differences and similarities that are important for answering the question in which conceptual framework one should investigate intracellular dynamics.     

Two-color photorefractive effect in Mg-doped lithium niobate

The two-color photorefractive response of near stoichiometric lithium niobate (SLN) doped with Mg above a critical threshold has been investigated. Striking differences as compared with non Mg-doped material were observed: The intermediate level in the two-color writing process has approximately a two orders of magnitude longer lifetime in SLN:Mg than in nominally undoped SLN, the grating is written in a shallower level but can be fixed via a simple thermal process and complementary electron-hole gratings are formed. It is proposed that the Fe impurity level moves from below the small-polaron level in nonMgO-doped material to above it, resulting in the increased lifetime of the small polaron. These changes are associated with a shift of the Fe from a Li site to a Nb site. The two-color sensitivity is higher than in the absence of MgO but the dynamic range is much lower.     

Confined dynamics of a single DNA molecule

The effect of a slit-like confinement on the relaxation dynamics of DNA is studied via a mesoscale model in which a bead and spring model for the polymer is coupled to a particle-based Navier-Stokes solver (multi-particle collision dynamics). The confinement is found to affect the equilibrium stretch of the chain when the bulk gyration radius is comparable to or smaller than the channel height and our data are in agreement with the (R(g,bulk)/h)(1/4) scaling of the polymer extension in the wall tangential direction. Relaxation simulation at different confinements indicates that, while the overall behaviour of the relaxation dynamics is similar for low and strong confinements, a small, but significant, slowing of the far-equilibrium relaxation is found as the confinement increases.     

Two-color holography in reduced near-stoichiometric lithium niobate

We explored a number of factors affecting the properties relevant to holographic optical data storage by using a two-color recording scheme in reduced, near-stoichiometric lithium niobate. Two-color, or photon-gated, recording is achieved by use of 852-nm information-carrying beams and 488-nm gating light. Readout at 852 nm is nondestructive, with a gating ratio of ~10(4). Recording sensitivity, gating ratio, dynamic range, and dark decay were measured for crystals of differing stoichiometry, degree of reduction, wavelength of the gating light, temperature, and optical power density. The two-color sensitivity per incident photon is still somewhat less than that of the one-color process at 488 nm for ~1 W/cm(2) of gating light but is essentially the same in terms of absorbed photons. Two-color recording is an attractive way of achieving nondestructive readout in a read-write material, and it allows selective optical erasure.     

Transfection ability and intracellular DNA pathway of nanostructured gene-delivery systems

Considerable efforts have been devoted to the design of structured materials with functional properties. Polyelectrolyte multilayer films are now a well-established nanostructured concept with numerous potential applications, in particular as biomaterial coatings. This technique allows the preparation of nanostructured architectures exhibiting specific properties for cell-activation control and local drug delivery. In this study, we used a multilayered system made of poly-(l-lysine)/hyaluronic acid (PLL/HA) as a reservoir for active DNA complexes with nonviral gene-delivery vectors, PLL, beta-cyclodextrin (CD), and PLL-CD. When embedded into the multilayered films, the transfection efficiencies of the DNA complexes and the cell viability were improved. The highest transfection efficiency was obtained with the PLL-CD/plasmid DNA (pDNA) complexes. We found that this high transfection efficiency was related to an efficient internalization of the complexes in the cell cytoplasm and selected nuclei domains through a nonendocytotic pathway. For the first time, we report the intracellular pathway of the pDNA in complexes incorporated into the multilayered system.     

Two-color planar laser-induced fluorescence thermometry in aqueous solutions

We demonstrate a two-color planar laser-induced fluorescence technique for obtaining two-dimensional temperature images in water. For this method, a pulsed Nd:YAG laser at 532 nm excites a solution of temperature-sensitive rhodamine 560 and temperature-insensitive sulforhodamine 640. The resulting emissions are optically separated through filters and detected via a charged-couple device (CCD) camera system. A ratio of the two images yields temperature images independent of incident irradiance. An uncertainty in temperature of +/- 1.4 degrees C is established at the 95% confidence interval.     

Optical and MRI multifunctional nanoprobe for targeting gliomas

A multifunctional nanoprobe capable of targeting glioma cells, detectable by both magnetic resonance imaging and fluorescence microscopy, was developed. The nanoprobe was synthesized by coating iron oxide nanoparticles with covalently bound bifunctional poly(ethylene glycol) (PEG) polymer, which were subsequently functionalized with chlorotoxin and the near-infrared fluorescing molecule Cy5.5. Both MR imaging and fluorescence microscopy showed significant preferential uptake of the nanoparticle conjugates by glioma cells. Such a nanoprobe could potentially be used to image resections of glioma brain tumors in real time and to correlate preoperative diagnostic images with intraoperative pathology at cellular-level resolution.     

二色调相式双折射系统的设计及其应用

以二色氩离子激光作光源,采用相调制技术设计了用于同时实时测量流场双折射及取向角的二色调相式流动双折射实验装置。由于采用了二色光源,避免了在计算过程中运用二阶贝塞尔函数以及在信号处理时分析二次谐波,简化了实验装置及结果计算。装置通过低通滤波电路和锁相放大器分别测量入射光和出射光中基频成分的光强度,并把它们转换成数字信号,由此计算出待测流场的双折射和取向角。实验证明,应用该装置同步测量了双折射及取向角,最大测量误差控制在0.5%~1%。     

Two-color excitation fluorescence microscopy through highly scattering media

We study the performance of two-color excitation (2CE) fluorescence microscopy [Opt. Lett. 24, 1505 (1999)] in turbid media of different densities and anisotropy. Excitation is achieved with two confocal excitation beams of wavelengths lambda(1) and lambda(2), which are separated by an angular displacement theta, where lambda(1) not equal lambda(2), 1/lambda(e) = 1/lambda(1) + 1/lambda(2), and lambda(e) is the single-photon excitation wavelength of the sample. 2CE fluorescence is generated only in regions of the sample where the two excitation beams overlap. The 2CE fluorescence intensity is proportional to the product of the two excitation intensities and could be detected with a large-area photodetector. The requirement of spatiotemporal simultaneity for the two excitation beams makes 2CE fluorescence imaging a promising tool for observing microscopic objects in a highly scattering medium. Optical scattering asymmetrically broadens the excitation point-spread function and toward the side of the focusing lens that leads to the contrast deterioration of the fluorescence image in single- or two-photon (lambda(1) = lambda(2)) excitation. Image degradation is caused by the decrease in the excitation energy density at the geometrical focus and by the increase in background fluorescence from the out-of-focus planes. In a beam configuration with theta not equal 0, 2CE fluorescence imaging is robust against the deleterious effects of scattering on the excitation-beam distribution. Scattering only decreases the available energy density at the geometrical focus and does not increase the background noise. For both isotropic and anisotropic scattering media the performance of 2CE imaging is studied with a Monte Carlo simulation for theta = 0, pi/2, and pi, and at different h/d(s) values where h is the scattering depth and d(s) is the mean-free path of the scattering medium.     

Two-color antibunching from band-gap engineered colloidal semiconductor nanocrystals

Photon antibunching is ubiquitously observed in light emitted from quantum systems but is usually associated only with the lowest excited state of the emitter. Here, we devise a fluorophore that upon photoexcitation emits in either one of two distinct colors but exhibits strong antibunching between the two. This work demonstrates the possibility of creating room-temperature quantum emitters with higher complexity than effective two level systems via colloidal synthesis.     

Aptamer-mediated nanoparticle-based protein labeling platform for intracellular imaging and tracking endocytosis dynamics

Although nanoparticles have been widely used as optical contrasts for cell imaging, the complicated prefunctionalized steps and low labeling efficiency of nanoprobes greatly inhibit their applications in cellular protein imaging. In this study, we developed a novel and general strategy that employs an aptamer not only as a recognizer for protein recognition but also as a linker for nanoreporter targeting to specifically label membrane proteins of interest and track their endocytic pathway. With this strategy, three kinds of nanoparticles, including gold nanoparticles, silver nanoparticles, and quantum dots (QDs), have been successfully targeted to the membrane proteins of interest, such as nucleolin or prion protein (PrP(C)). The following investigations on the subcellular distribution with fluorescent immunocolocalization assay indicated that PrP(C)-aptamer-QD complexes most likely internalized into cytoplasm through a classical clathrin-dependent/receptor-mediated pathway. Further single-particle tracking and trajectory analysis demonstrated that PrP(C)-aptamer-QD complexes exhibited a complex dynamic process, which involved three types of movements, including membrane diffusion, vesicle transportation, and confined diffusion, and all types of these movements were associated with distinct phases of PrP(C) endocytosis. Compared with traditional multilayer methods, our proposed aptamer-mediated strategy is simple in procedure, avoiding any complicated probe premodification and purification. In particular, the new double-color labeling strategy is unique and significant due to its superior advantages of targeting two signal reporters simultaneously in a single protein using only one aptamer. What is more important, we have constructed a general and versatile aptamer-mediated protein labeling nanoplatform that has shown great promise for future biomedical labeling and intracellular protein dynamic analysis.     

Development of a dedicated ion injector for accelerator-based nanoprobe facilities

The paper discusses possible ways of increasing beam brightness in ion injectors. The argon/helium ion injector comprising a newly designed RF ion source and, a Wien filter has been designed for use in accelerator-based nanoprobe facilities. The phase set degradation due to aberrations in the injector ion-optic system was simulated with allowance for multipole and fringing fields. The RF ion sources with different permanent magnet systems were tested. Experiments were performed with argon and helium. A plasma density of up to 3×10¹¹ cm⁻³ and beam brightness of ∼100 A/(m² rad² eV) were obtained. The ion current density inside an extracting electrode in the source was 10 mA/cm² for an emission hole diameter of 0.6 mm. Measurements of the current value and emittance were performed with ion source testing equipment permitting measurements of the ion beam current, emittance, mass composition, and RF power input into the plasma.     

Study of DNA internal dynamics by quasi-elastic light scattering

We have studied the large-scale internal fluctuations in DNA coils by using quasi-elastic light-scattering spectroscopy. We have measured the angular dependence of the first cumulant of the scattered-light autocorrelation function. Within the q (3) domain of this dependence, we observed the transition from the asymptotic behavior predicted for good solvents to the asymptotic behavior predicted for ? conditions. This allowed us to determine the screening length of volume interactions in DNA chains. Analysis of the autocorrelation functions by a regularization procedure allowed us to reconstruct the mode composition of the scattered light and to determine the relaxation time of the fluctuations in the coil size.