Single Microsphere Research Articles

Photoacoustic Spectrum Analysis for Microstructure Characterization in Biological Tissue: Analytical Model

Photoacoustic spectrum (PA) analysis (PASA) has been found to have the ability to identify the microstructures in phantoms and biological tissues. PASA adopts the procedures in ultrasound spectrum analysis, although the signal generation mechanisms related to ultrasound backscatter and PA wave generation differ. The purpose of this study was to theoretically validate PASA. The analytical solution to the power spectrum of PA signals generated by identical microspheres following discrete uniform random distribution in space was derived. The simulation and experiment validation of the analytical solution include: (i) the power spectrum profile of a single microsphere with a diameter of 300 μm, and (ii) the PASA parameters of the PA signals generated by randomly distributed microspheres 100, 200, 300, 400 and 500 μm in diameter, at concentrations of 30, 60, 120, 240, 480 per 1.53 cm3 in the observation range 0.5–13 MHz.

A simple method for encapsulating single cells in alginate microspheres allows for direct PCR and whole genome amplification.

Microdroplets are an effective platform for segregating individual cells and amplifying DNA. However, a key challenge is to recover the contents of individual droplets for downstream analysis. This paper offers a method for embedding cells in alginate microspheres and performing multiple serial operations on the isolated cells. Rhodobacter sphaeroides cells were diluted in alginate polymer and sprayed into microdroplets using a fingertip aerosol sprayer. The encapsulated cells were lysed and subjected either to conventional PCR, or whole genome amplification using either multiple displacement amplification (MDA) or a two-step PCR protocol. Microscopic examination after PCR showed that the lumen of the occupied microspheres contained fluorescently stained DNA product, but multiple displacement amplification with phi29 produced only a small number of polymerase colonies. The 2-step WGA protocol was successful in generating fluorescent material, and quantitative PCR from DNA extracted from aliquots of microspheres suggested that the copy number inside the microspheres was amplified up to 3 orders of magnitude. Microspheres containing fluorescent material were sorted by a dilution series and screened with a fluorescent plate reader to identify single microspheres. The DNA was extracted from individual isolates, re-amplified with full-length sequencing adapters, and then a single isolate was sequenced using the Illumina MiSeq platform. After filtering the reads, the only sequences that collectively matched a genome in the NCBI nucleotide database belonged to R. sphaeroides. This demonstrated that sequencing-ready DNA could be generated from the contents of a single microsphere without culturing. However, the 2-step WGA strategy showed limitations in terms of low genome coverage and an uneven frequency distribution of reads across the genome. This paper offers a simple method for embedding cells in alginate microspheres and performing PCR on isolated cells in common bulk reactions, although further work must be done to improve the amplification coverage of single genomes.

In Situ Surface‐Enhanced Raman Spectroscopy Study of Plasmon‐Driven Catalytic Reactions of 4‐Nitrothiophenol under a Controlled Atmosphere

AbstractWe demonstrate the plasmon‐driven catalytic reactions of 4‐nitrothiophenol (4NTP) on a single Ag microsphere by an in situ surface‐enhanced Raman spectroscopy (SERS) technique. The highly SERS‐active hierarchical Ag structures served as an ideal platform to study plasmon‐driven catalytic reactions. This single‐particle surface‐enhanced Raman spectroscopy (SP‐SERS) technique coupled with inbuilt apparatus allow us to study the impact of reaction atmospheres and laser power on the rate of dimerization and reduction of 4NTP. Contrary to that found in previous studies, 4NTP could be transformed into 4‐aminothiophenol under H2O or H2 atmosphere. The broadening and splitting of the ν(CC) band during the reaction results from the frequency shift of the ν(CC) band that arises from different products. Our results suggest that the SP‐SERS technique is ideally suited to study plasmon‐driven catalytic reactions because of the possibility to monitor the reaction under controlled atmospheres in real time.

Simulation of Thermal Behavior in Hollow-glass-microsphere-filled Cement Composites

In this paper, thermal behavior in cement composites filled with hollow glass microspheres was modeled by finite element method based on heat conduction theory. According to experimental observation of the microsphere distribution in the cement matrix material by the scanning electron microscope, a twodimensional unite cell including single hollow glass microsphere and cement material phase is chosen as the computational model, in which the specified temperature conditions are applied on the opposite edges of the cell to model heat transfer in the cell by finite element simulation. The effects of volume content and wall thickness of the microsphere, thermal conductivities of the wall and the cement on the effective thermal conductivity of the composite are investigated. Numerical results demonstrate that the developing lightweight cement-based composite can have significant lower thermal conductivity than the cement matrix itself by introducing the hollow glass microsphere.

Analysis of diffraction imaging in non-conjugate configurations.

Diffraction imaging of scattered light allows extraction of information on scatterer's morphology. We present a method for accurate simulation of diffraction imaging of single particles by combining rigorous light scattering model with ray-tracing software. The new method has been validated by comparison to measured images of single microspheres. Dependence of fringe patterns on translation of an objective based imager to off-focus positions has been analyzed to clearly understand diffraction imaging with multiple optical elements. The calculated and measured results establish unambiguously that diffraction imaging should be pursued in non-conjugate configurations to ensure accurate sampling of coherent light distribution from the scatterer.

3D-technology of the formation and maintenance of single dormant microspheres from 2000 human somatic cells and their reactivation in vitro.

We developed an original reproducible 3D-technology for preparation of single dormant microspheres consisting of 2000 somatic cells. The dynamics of microsphere assembly from mesenchymal and epithelial cells of retinal pigment epithelium was traced using time-lapse microscopy: formation of a loose aggregate over 24 h followed by its gradual consolidation and formation of a compact viable microsphere with a diameter of 100-150 μ by day 7. The cell number in the formed microspheres remains unchanged. Reactivation observed upon fusion of epithelial and/or mesenchymal microspheres results in the formation of a united compact microtissue. The fusion dynamics reproduces spherogenesis irrespective of the initial amount of co-cultured microspheres. Reactivation via two-step induced angiogenesis opens new prospects for production of vascularized microspheres and microtissues.

Near-field probing of Mie resonances in single TiO2 microspheres at terahertz frequencies.

We show experimentally that poly-crystalline TiO2 spheres, 20-30 μm in diameter, exhibit a magnetic dipole Mie resonance in the terahertz (THz) frequency band (1.0-1.6 THz) with a narrow line-width (<40 GHz). We detect and investigate the magnetic dipole and electric dipole resonances in single high-permittivity TiO2 microspheres, using a near-field probe with a sub-wavelength (~λ/50) size aperture and THz time-domain spectroscopy technique. The Mie resonance signatures are observed in the electric field amplitude and phase spectra, as well as in the electric field distribution near the microspheres. The narrow line-width and the sub-wavelength size (λ/10) make the TiO2 microspheres excellent candidates for realizing low-loss THz metamaterials.

Photorefractive tuning of whispering gallery modes of a spherical resonator integrated inside a microstructured optical fibre

We demonstrate the photorefractive tuning of the whispering gallery modes of a single BaTiO3 microsphere resonator integrated inside a grapefruit-shaped microstructured optical fibre, upon CW laser irradiation at 532 nm while using irradiation intensities up to 5.5 W/cm2. Temporal evolution results of the WGM spectra are provided with respect to the illumination and relaxation conditions applied.

Self-assembled conjugated polymer spheres as fluorescent microresonators.

Confinement of light inside an active medium cavity can amplify emission. Whispering gallery mode (WGM) is one of mechanisms that amplifies light effectively by confining it inside high-refractive-index microstructures, where light propagates along the circumference of a sphere via total internal reflection. Here we show that isolated single microspheres of 2–10 μm diameter, formed from self-assembly of π-conjugated alternating copolymers, display WGM photoemission induced by laser pumping. The wavelengths of the emission peaks depend sensitively on the sphere size, position of the excitation spot and refractive index of each polymer. The Q-factor increases with increasing sphere diameter and displays a linear correlation with the reciprocal radius, indicating that the small curvature increases the efficacy of the total internal reflection. WGM photoemission from π-conjugated polymer microspheres is unprecedented and may be of high technological impact since the microspheres fulfill the role of fluorophores, high-refractive-index media and resonators simultaneously, in addition to their simple fabrication process.

Crystal growth and design of a facile synthesized uniform single crystalline football-like anatase TiO2 microspheres with exposed {001} facets

Uniform football-like anatase TiO2 particles exposed by {0 0 1} facets were successfully synthesized by an environment-friendly, facile and low-temperature hydrothermal method in water solution without any additional capping agent. The crystallographic structure and the growth mechanism of anatase TiO2 particles were investigated systematically by X-ray diffraction pattern (XRD), field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectra (XPS), respectively. The formation mechanism of football-like anatase TiO2 particles exposed by {0 0 1} facets is investigated. It was found that there existed a selective adsorption of F− ions on different facets by analyzed with the density functional theory (DFT) computer simulation results, and it would lead to a selective nucleation and crystal growth of anatase football-like TiO2 particles. Additionally, this type of exposed {0 0 1} facets football-like TiO2 microspheres were used as a scattering overlayer on a transparent P25 film for fabrication of photoanodes for dye-sensitized solar cells (DSSCs). The results showed that an overall light conversion efficiency of this film was 6.31%, which is higher than that of the overall efficiency (5.13%) obtained from the P25 photoanode owing to the superior light scattering effect of microspheres and excellent light reflecting ability of the mirror-like plane {0 0 1} facets.

Ultraviolet electroluminescence from hetero p-n junction between a single ZnO microsphere and p-GaN thin film.

We report ultraviolet electroluminescence from a hetero p-n junction between a single ZnO microsphere and p-GaN thin film. ZnO microspheres, which have high crystalline quality, have been synthesized by ablating a ZnO sintered target. It was found that synthesized ZnO microspheres had a high-optical property and exhibit the laser action in the whispering gallery mode under pulsed optical pumping. A hetero p-n junction was formed between the single ZnO microsphere/ p-GaN thin film, and a good rectifying property with a turn-on voltage of approximately 6 V was observed in I-V characteristic across the junction. Ultraviolet and visible electroluminescence were observed under forward bias.

Preparation of uniform magnetic recoverable catalyst microspheres with hierarchically mesoporous structure by using porous polymer microsphere template

Merging nanoparticles with different functions into a single microsphere can exhibit profound impact on various applications. However, retaining the unique properties of each component after integration has proven to be a significant challenge. Our previous research demonstrated a facile method to incorporate magnetic nanoparticles into porous silica microspheres. Here, we report the fabrication of porous silica microspheres embedded with magnetic and gold nanoparticles as magnetic recoverable catalysts. The as-prepared multifunctional composite microspheres exhibit excellent magnetic and catalytic properties and a well-defined structure such as uniform size, high surface area, and large pore volume. As a result, the very little composite microspheres show high performance in catalytic reduction of 4-nitrophenol, special convenient magnetic separability, long life, and good reusability. The unique nanostructure makes the microspheres a novel stable and highly efficient catalyst system for various catalytic industry processes.

Optical clearing at cellular level

Strong light scattering in tissues and blood reduces the usability of many optical techniques. By reducing scattering, optical clearing enables deeper light penetration and improves resolution in several optical imaging applications. We demonstrate the usage of optical tweezers and elastic light scattering to study optical clearing [one of the major mechanisms-matching of refractive indices (RIs)] at the single particle and cell level. We used polystyrene spheres and human red blood cells (RBCs) as samples and glycerol or glucose water solutions as clearing agents. Optical tweezers kept single microspheres and RBCs in place during the measurement of light scattering patterns. The results show that optical clearing reduces the scattering cross section and increases g. Glucose also decreased light scattering from a RBC. Optical clearing affected the anisotropy factor g of 23.25-μm polystyrene spheres, increasing it by 0.5% for an RI change of 2.2% (20% glycerol) and 0.3% for an RI change of 1.1% (13% glucose).

Optical Fabrication of Semiconductor Single-Crystalline Microspheres in Superfluid Helium

ABSTRACTWe successfully fabricated semiconductor microspheres of ZnO, ZnSe, etc., by laser ablation in superfluid helium and investigated their morphology and optical properties. Time-resolved photoluminescence spectroscopy in ultraviolet region of single ZnO microspheres shows luminescence spectra with mode structures and remarkable reduction of the luminescence decay time compared to that of polycrystals or non-spherical microparticles. This indicates strong light-matter interaction due to efficient light-confinement in the ZnO microspheres. In addition, the fabricated ZnSe microspheres also show the photoluminescence spectra with typical mode structures indicating their high sphericity.

Role of synthesis variables on controlled nucleation and growth of hexagonal molybdenum oxide nanocrystals: investigation on thermal and optical properties

Solution based chemical precipitation route has been utilized for the controlled synthesis of novel and single phase 3Dhierarchical flower-like microspheres of hexagonal molybdenum oxide nanocrystals.

Measuring the Force Gradient Acting on a Magnetic Microsphere above a Micro-Magnet Array

The attractive action exerted by an array of micro-magnets on a single polystyrene microsphere containing superparamagnetic iron oxidenanoparticles, the microsphere constituting a model for cells functionalised with such nanoparticles, have been studied in air by using magnetic force microscopy. For this purpose, the method of gluing a magnetic microsphere to an AFM tip has been developed. Using this custom-made colloidal probe, the regions of the micro-magnet array that act as magnetic traps for the magnetic microsphere have been localized and the long-range trap-sphere interactions have been recorded, measured and compared with simulations.

Study of the focusing effect of silica microspheres on the upconversion of Er3+–Yb3+ codoped glass ceramics

• Silica microspheres have been located on the surface of glass and glass ceramics samples codoped with Er and Yb. • Microspheres act as microlens of the 950 nm excitation light resulting in focalized excited regions in the samples with sizes under the micron. • Intense red upconversion is achieved in the focalized areas. • Microspheres collect the upconversion emission light, scoping with the together microlensing properties an enhancement of the detected signal in a 3x factor. • Performed Finite-Difference Time-Domain simulations predict the size of the focalized regions in good agreement with the experimental measurements. The upconversion emission properties of Er 3+ –Yb 3+ codoped glass and glass ceramic samples with different Si/Al ratios and thermal treatments were analyzed by covering their surfaces with silica microspheres (3.8 μm diameter). A 950 nm laser beam is focused by the microspheres producing a set of photonic nanojets near the surface of the samples. After the upconversion processes of the Er 3+ ions located in each microsphere focus area, these ions emit light in the green and red regions. The red emission from each sample was measured, yielding an upconversion intensity in the focal areas three times higher than the emission from the bare substrate. To estimate the real size of the red emission area under a single microsphere, a deconvolution of the measured focal spots with the Point Spread Function of the experimental setup was performed, resulting in a Full Width at Half Maximum of 330 nm. The results obtained by Finite-Difference Time-Domain simulations are in good agreement with the experimental values.

Multiple versus single injections of fluorescent microspheres for the determination of regional organ blood flow in septic sheep

Determination of regional blood flow by the injection of microspheres in sepsis models is crucial for the experimental evaluation of the influence of experimental treatment strategies on organ perfusion. However, multiple injections may critically increase the total quantity of microspheres, thereby restricting regional microcirculation and altering the results of blood flow measurements. This study was designed to compare the results of multiple versus single injections of microspheres in an established ovine sepsis model. Injury was induced by smoke inhalation and instillation of Pseudomonas aeruginosa into the lungs. Twenty sheep were studied for 4, 8, 12, 18, or 24 h, respectively. Microspheres were injected at the end of the study period and the animals were euthanized and organ tissues were harvested. Another four sheep were studied for 24 h and multiple microsphere injections were performed at the above indicated time points in the same animals. Tracheal blood flow significantly increased and blood flow to the pancreas and ileum significantly decreased versus baseline in both groups (P < 0.05 each). Blood flow to the ileum, renal cortex and skin did not significantly change versus baseline in both groups (P > 0.05). Blood flow was higher to the trachea in the multiple injection group at 18 h (P = 0.048) and to the ileum at 12 h (P = 0.049), and lower to the skin at 18 h (P = 0.015). In conclusion, the results indicate that multiple versus single microsphere injections induced no or negligible alterations during ovine sepsis. This finding may help reduce the quantity of animals needed in future experiments.

Fabrication of Magnetic-Antimicrobial-Fluorescent Multifunctional Hybrid Microspheres and Their Properties

Novel magnetic-antimicrobial-fluorescent multifunctional hybrid microspheres with well-defined nanostructure were synthesized by the aid of a poly(glycidyl methacrylate) (PGMA) template. The hybrid microspheres were fully characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), X-ray diffraction (XRD) and digital fluorescence microscope. The as-synthesized microspheres PGMA, amino-modified PGMA (NH2-PGMA) and magnetic PGMA (M-PGMA) have a spherical shape with a smooth surface and fine monodispersity. M-PGMA microspheres are super-paramagnetic, and their saturated magnetic field is 4.608 emu·g−1, which made M-PGMA efficiently separable from aqueous solution by an external magnetic field. After poly(haxemethylene guanidine hydrochloride) (PHGH) functionalization, the resultant microspheres exhibit excellent antibacterial performance against both Gram-positive and Gram-negative bacteria. The fluorescence feature originating from the quantum dot CdTe endowed the hybrid microspheres with biological functions, such as targeted localization and biological monitoring functions. Combination of magnetism, antibiosis and fluorescence into one single hybrid microsphere opens up the possibility of the extensive study of multifunctional materials and widens the potential applications.

Modeling lasing of a chalcogenide glass microcylinder

Theoretical modeling of the interaction between electromagnetic radiation and microresonators in the shape of homogeneous microcylinders has shown that the morphology of the microresonators affects the transformation of optical radiation in the microlaser modes. We established that in a laser with microresonators of cylindrical symmetry made from chalcogenide glass, two-mode lasing regimes can be realized in modes of different orders for gain-to-loss ratios <1. The region of existence for two-mode lasing is determined by the gain-to-loss ratio and the magnitude of the electromagnetic fi eld for the spatial structure of morphological resonances. Introduction. Currently microresonators have been at the center of extensive research due to the possibility of using them as a convenient object for realization of miniature devices based on single dielectric microspheres and microfi bers. This is connected with the fact that weakly absorbing dielectric microparticles act as optical resonators, and morphological resonances are realized in them. A microresonator based on a dielectric microparticle of a certain symmetry (spherical, cylindrical, ellipsoidal, etc.) has additional advantages, including signifi cant lowering of the threshold for realization of various nonlinear phenomena, strong focusing of radiation, low sensitivity to fracture and overheating due to the strength scale effect, and convenient matching between microspheres or microcylinders and optical fi bers. One of the fi rst investigations of modes in a dye-impregnated cylindrical microlaser and their use for measuring the parameters of microresonators are described in (1, 2). Microfi bers enable nearly lossless excitation of high-Q modes in optical cavities, which are extremely sensitive to a change in the environment and can also be used as sensors (3, 4). Optical processes in cylindrical microresonators are the object of active experimental studies (5-8). However, these papers basically just demonstrate potential ways such systems may be used. At the same time, optical phenomena observed in this case need theoretical substantiation; in particular, the characteristic features of the effect of the spatial structure of the electromagnetic fi eld on the process of low-threshold stimulated emission have not yet been suffi ciently studied. Fabrication of chalcogenide glass microcylinders is of special interest (9). This material is widely used in spectroscopy for fast processing of optical signals in fi ber-optic communication lines, video camera tubes, and also for recording holograms. The high refractive index of chalcogenide glass (2.2-2.7) lets it be used for fabrication of microresonators, strongly concentrating the radiation within the microcylinders. This is why the corresponding theoretical studies were done using microcylinders made of chalcogenide glass. Theoretical Model. In microresonators of cylindrical symmetry, certain sets of eigenmodes are realized. Each mode is characterized by a certain frequency and Q factor, which depend both on the diffraction parameter (ρ = 2πR/λ, R is the radius of the microcylinder, λ is the wavelength of the laser radiation) for the microcylinder and on the optical constants of the microcylinder material. Along with the Q factor, an important electrodynamic characteristic of a microresonator is the spatial structure of the electromagnetic fi eld inside it, which is formed by summing the spatial structures of the fi elds for the eigenmodes. Methods for obtaining and solving the equations for determining the frequencies of the eigenmodes are well known and discussed in detail in (10). We should point out that each equation has an infi nite number of solutions. Each solution is characterized by the mode number l, which determines the number of peaks in the intensity distribution of the internal fi eld as the polar angle j varies from 0 to 180°, and the order s, equal to the number of peaks in the fi eld intensity distribution for