Transparent Microspheres Research Articles

A Color-Changeable “Pearl” for Visually Displaying Chemical Complexation Reactions

An experimental design by combining hydrogel and ethylenediaminetetraacetic acid disodium salt (EDTA) for visually displaying chemical complexation reactions is developed. The Na+ ions on the α-l-guluronic acid (G) unit of the sodium alginate molecule undergo an ion exchange with a divalent cation, so that the G units are stacked to create a cross-linked network, forming a hydrogel. EDTA is inserted into the as-prepared hydrogel, producing transparent hydrogel microspheres containing EDTA, which are considered to be color-changeable pearls on the basis of the chelation of EDTA when reacting with several metal ions. By using different stability constants of the same typed coordination complexes, the color of pearls is changeable. The process and mechanism of the complex reaction are investigated by using elemental mapping, Fourier transform infrared reflection (FTIR) and Raman spectra. Moreover, all the instruments and chemicals for this experiment are included in one single portable experimental kit. The kit is small, easy to carry, cheap, and safe, and it enables easy display of related chemical reactions. By using the developed kit, the students’ hands-on experience can be improved. The experimental operation is simple, green, safe, and interesting, which enables the engineering of color-changeable pearls to be broadly used including the chemical experiment courses in universities, experimental teaching in schools, and the chemical popularization activities for the public.

Synthesis of transparent silica microspheres with mesopores to encapsulate dye molecules for the fluorescence enhancement

Transparent mesoporous silica microspheres were successfully synthesized via sol-gel method followed by calcination. The prepared microspheres consisted of sub-micrometer particles embedded in a gel matrix, which was the main product of the fast hydrolysis and condensation of TEOS in the octylamine-containing medium. The continuous gel network gave light transparency of these microspheres. The microspheres were statically immersed in rhodamine 6 G (R6G) dye solutions with different concentrations. The guest R6G molecules loaded in the microspheres exhibited significantly enhanced fluorescence performance compared with the correspondent dye solutions. The localization and dispersion of dye molecules in the nanopores of microspheres reduced the aggregation of dye molecules which otherwise quenched the luminescence. A comparative study on the loading of the same dye within another transparent and an opaque silica gel with larger pore sizes indicated that the transparency and the smaller pore size of the transparent microspheres explained its larger fluorescence enhancement effect.

Assembly method of biological lens array based on maskless lithography

<p indent="0mm">In the field of micro and nano optics, transparent dielectric microspheres and living biological cells have attracted more and more attention due to their optical imaging capabilities. However, it is difficult to integrate them directly onto optical systems because of their size and bioactivity limitations. Although multi-physics field methods based on optical tweezers and acoustic tweezers can manipulate microspheres and cells for imaging, they tend to have specific requirements for imaging samples. Here, we proposed a method for the preparation of microsphere/cellular lens array modules based on maskless lithography. Natural sedimentation principle is utilized to form microlens arrays by assembling SiO₂ microspheres and MCF-7 cells on the hydrogel microporous module. The experimental and simulation results show that the SiO₂ microsphere array embedded in the hydrogel still maintains its super-resolution imaging capability, and the MCF-7 cells can achieve the image magnification. As a result of the arrayed imaging, a larger viewing field can be obtained than that of individual microspheres or cells. The modular imaging method proposed in this paper is expected to be applied in the field of biophotonic devices and <italic>in vivo</italic> optical imaging.

Chalcogenide Microsphere‐Assisted Optical Super‐Resolution Imaging

AbstractMicrosphere‐assisted optical imaging has been proved straightforward and cost‐effective for super‐resolution imaging in material science and biomedical research. Optically transparent microspheres with a high refractive index are critical for achieving superior super‐resolution capabilities yet remain to be further exploited. Here, the use of As2S3 (an optically transparent chalcogenide glass) microspheres, with a refractive index as high as 2.31 (at 600 nm) and diameters ranging from 10 to 215 µm, for optical super‐resolution imaging is reported. Under white‐light illumination (peaked at 646 nm), As2S3 microspheres full‐immersed in polymethyl methacrylate or immersion oil generate super‐resolved virtual images of nanostructures (≈90 nm in minimum feature size) with a magnification up to 8×. The lateral resolution of full‐immersed microspheres, which can be as low as ≈172 nm for a 19 µm diameter As2S3 microsphere, is also investigated. Moreover, super‐resolved real imaging of nanostructures with semi‐immersed As2S3 microspheres is demonstrated for the first time. Compared with the full‐immersion approach (e.g., for a 30 µm diameter microsphere, the image plane is ≈30 µm underneath the specimen with a magnification of 4.3×), the semi‐immersion approach provides an obvious improvement in the magnification (6.6×) and a much longer operation distance to the objective (the image plane is ≈140 µm above the specimen).

Identification of new silk-like protein from B. magister and development of functional materials based on it

Tandem repeat proteins have composite structure and unique properties, which allow them to be used in multiple fields, such as soft photonics, drug delivery and textile industry. The recent discovery of squid ring teeth (SRT) proteins have expanded the existing repertoire of repetitive polypeptides. We chose previously unexplored squid B. magister for our research, isolated and analyzed a new protein forming its ring teeth and hooks, and amplified the corresponding gene. Finally, we used this new isolated SRT protein to fabricate transparent thin films and microspheres.

Dynamic blood flow phantom for in vivo liquid biopsy standardization

In vivo liquid biopsy, especially using the photoacoustic (PA) method, demonstrated high clinical potential for early diagnosis of deadly diseases such as cancer, infections, and cardiovascular disorders through the detection of rare circulating tumor cells (CTCs), bacteria, and clots in the blood background. However, little progress has been made in terms of standardization of these techniques, which is crucial to validate their high sensitivity, accuracy, and reproducibility. In the present study, we addressed this important demand by introducing a dynamic blood vessel phantom with flowing mimic normal and abnormal cells. The light transparent silica microspheres were used as white blood cells and platelets phantoms, while hollow polymeric capsules, filled with hemoglobin and melanin, reproduced red blood cells and melanoma CTCs, respectively. These phantoms were successfully used for calibration of the PA flow cytometry platform with high-speed signal processing. The results suggest that these dynamic cell flow phantoms with appropriate biochemical, optical, thermal, and acoustic properties can be promising for the establishment of standardization tool for calibration of PA, fluorescent, Raman, and other detection methods of in vivo flow cytometry and liquid biopsy.

Wavelength-tunable focusing via a Fresnel zone microsphere.

In this Letter, a novel, to the best of our knowledge, structural configuration on a transparent microsphere is proposed to engineer the focusing light field. By patterning a hybrid diffractive Fresnel zone plate structure on a partially milled microsphere using a focused ion beam, wavelength-dependent switching between mono-focal and multi-focal functionalities can be achieved. Generation of on-axis tri-foci and mono-focus light fields under high numerical-aperture (${\rm NA}\gt {0.67}$NA>0.67) conditions at two working wavelengths (405 nm and 808 nm) have been demonstrated both numerically and experimentally.

From 2D to 3D super-resolution imaging through glass microspheres -INVITED

Microsphere-assisted microscopy is a new imaging technique which allows the diffraction limit to be overcome using transparent microspheres. It makes it possible to reach a resolution of up to 100 nm in air while being label-free and full-field. An overview of the imaging technique is presented showing the influence of the photonic jet on the image nature and the unconventional behaviour of the magnification factor. Moreover, interferometry through microspheres is demonstrated for the 3D reconstruction of nanoelements.

Super-resolution imaging system based on integrated microsphere objective lens

White-light super-resolution imaging, proposed in 2011, has been achieved by combining the transparent microspheres of the micron scale with an ordinary optical microscope. At present, in most of the researches employed is the way of spreading microspheres directly onto the surface of sample, which causes the randomness and discontinuity of microspheres. It is impossible to achieve the complete imaging of specific regions, which greatly limits the application scope of this technology. Such an issue can be solved by using microprobes or micro-cantilevers to precisely transfer the location of microsphere, but for doing so, a sophisticated controlling system is required, which is costly and not user-friendly. In this paper, a robust, controllable, easy-to-use integrated design which can efficiently consolidate microsphere and objective together is demonstrated for super-resolution imaging. The PDMS and customized metal sleeve are used to encapsulate the microsphere semi-submerged on the ordinary objective lens to achieve an integrated design. In this system, the distances among the microsphere, objective lens and the sample are controlled accurately by building a side-view imaging and position feedback system. With the help of a universal microscopic imaging system, the super-resolution imaging of specific controlled areas is realized. Based on theoretical analysis, the semi-submerged structure of the 100-μm-diameter BaTiO&lt;sub&gt;3&lt;/sub&gt; microsphere has a strong focusing effect, which can form the so-called ‘photonic nanojet’ on a micro-scale in length and on a sub-diffraction scale in waist to possess the ability to break through the diffraction limit within the range of focal length. At the same time, experiments are carried out for investigating imaging performances at various working distances in the air. According to the experimental results, the system can clearly distinguish between the CPU lattice features of 200 nm and the Blu-ray disc fringe of 100 nm, which means that the resolution of the ordinary microscopic objective lens (40×, NA 0.6) is significantly enhanced by 4.78×. In addition, with the increase of working distance, the magnification factor increases gradually, but the image contrast becomes worse, and the super-resolution effect fades. The integrated design which can match with ordinary optical microscope to achieve super resolution imaging has universality of installation and operation, and greatly conduces to super-resolution imaging of sub-diffraction limit samples.

Super-resolution imaging within reach

Although several optical techniques have been developed to overcome the resolution limit in microscopy, the optical imaging of subwavelength features is still a real challenge (difficulty to build, or risks of phototoxicity). Microsphere-assisted microscopy has recently made super-resolution imaging accessible to scientists. An easy-to-implement optical setup to perform full-field and contactless super-resolution measurements using transparent microspheres is presented. We show that this rather simple imaging system (in comparison with the usual optical nanoscopes) makes it possible to achieve a lateral resolution of 200 nm in air and, thus, to visualize nanostructured media and biological elements.

High Resolution Microsphere‐Assisted Interference Microscopy for 3D Characterization of Nanomaterials

Nanoscale materials are nowadays widely used in many different modern technologies. Special attention is thus required for their characterization in order to optimize fabrication processes. However, current characterization systems which can achieve nanometric resolution over a large area and in three dimensions are few. Classical optical microscopy presents a resolving power limited by diffraction, making impossible the visualization of elements with a size under half the wavelength. Recently, several methods have thus been developed to overcome this limitation, among them microsphere‐assisted microscopy. Indeed, using a transparent microsphere, a full‐field image of the sample can be retrieved with a higher resolution than the diffraction‐limit. In this paper, this new imaging technique is combined with phase‐shifting interferometry in order to reconstruct the 3D surface of nanostructures. An enhancement of a factor of 4.0 in the lateral resolution is demonstrated while combining this with the nanometric axial sensitivity of interferometry. Results are shown of the topography of reference gratings as well as periodic Ag nano‐dots on silicon and laser induced ripples in steel, spaced by a few hundred nanometres. A comparison of these results is made with those from SEM and atomic force microscopy.

Transparent Silk Fibroin Microspheres from Controlled Droplet Dissolution in a Binary Solution.

Silk is a natural polymer with a broad range of potential applications in textiles, advanced materials, biomedical devices, and drug delivery. The ability to control the morphology and assembly of silk fibroin is essential for the fabrication of silk-based structured materials. Here, we report an effective and simple approach based on droplet dissolution for weaving silk fibroin into spheres of several hundred micrometers in diameter. The spheres possess regular wrinkled microstructures on the surface and switchable transparency for visible light. To produce these silk spheres, we immersed a sessile microdrop of the silk fibroin aqueous solution in a surrounding phase of ethanol in toluene at low concentration (<10%). The droplet experienced a two-phase process: the first phase of volume expansion due to the intake of organic solvents from the surrounding phase and the second phase of droplet dissolution. The dissolution rate is closely related to the dynamics of the droplet, while the resulting microstructure of the silk microsphere is simply adjusted by the composition of the surrounding solution. At high concentrations of ethanol, silk fibroin formed a thin shell around the droplet during the initial expansion of the droplet in volume. As the droplet shrank at a later stage, the shell around the droplet wrinkled and crumpled, leading to regular ridges and crevices on the microsphere surface. This work demonstrates that controlled droplet dissolution may be explored as a novel and effective way to tailor microstructures of silk assemblies. The as-prepared silk microspheres may be potentially used as optical units or microcarriers.

Colloidal crystals with diamond symmetry at optical lengthscales

Future optical materials promise to do for photonics what semiconductors did for electronics, but the challenge has long been in creating the structure they require—a regular, three-dimensional array of transparent microspheres arranged like the atoms in a diamond crystal. Here we demonstrate a simple approach for spontaneously growing double-diamond (or B32) crystals that contain a suitable diamond structure, using DNA to direct the self-assembly process. While diamond symmetry crystals have been grown from much smaller nanoparticles, none of those previous methods suffice for the larger particles needed for photonic applications, whose size must be comparable to the wavelength of visible light. Intriguingly, the crystals we observe do not readily form in previously validated simulations; nor have they been predicted theoretically. This finding suggests that other unexpected microstructures may be accessible using this approach and bodes well for future efforts to inexpensively mass-produce metamaterials for an array of photonic applications.

Concentration nonlinearity of a suspension of transparent microspheres under the action of a gradient force in a periodically modulated laser field

Based on a one-dimensional Smoluchowski equation we have developed the theory of concentration nonlinearity of a suspension of transparent microspheres under the action of a gradient force in an interference laser field. The numerical solution of a system of recurrence equations resulting from the Smoluchowski equation after expansion of the microsphere concentration in the harmonic series has allowed us to determine the dependence of the concentration nonlinearity settling time on the intensity of the incident radiation. In the diffusion limit, we have derived the expression for the optical Kerr coefficient, which is found to be for an aqueous suspension of latex microspheres with a radius of and a concentration of . Diffraction of a probe wave on a light-induced concentration grating is considered as a method for studying a nonlinear concentration response of an artificial highly efficient nonlinear medium for laser radiation of long pulse duration.

Glass heating through submicron spots produced with silica microspheres

The emission spectra of phosphate glasses doped with different concentrations of Nd3+ ions have been measured and the dependence of the emission intensity on the concentration of doping ions has been explained using energy transfer models. Thus, the optimum concentration in order to obtain the maximum heating of the glass has been theoretically estimated. The glass sample doped with a Nd3+ concentration closest to the optimum was covered with silica transparent microspheres with different diameters (2, 7, and 25μm). The incident laser light at 532nm was focused through the microspheres producing submicron spots (known as photonic nanojets) that excite the doping ions in the glass and heat the matrix due to non-radiative processes. From this, the heating as a function of the microsphere diameter has been analysed.

Characteristics of photonic nanojets from ordered microassemblies of dielectric spheres

Spatially localised light structures (photonic nanojets) formed in the near field of light scattering from an ordered ensemble of single-layer clusters of transparent glass microspheres have been theoretically studied. The main parameters of photonic nanojets (length, width, focal distance and intensity) are calculated based on numerical solution of Maxwell equations, and their behaviour under conditions of interference between neighbouring microparticles is analysed. The degree of manifestation of collective effects during the formation of a nanojet array is found to depend on the spatial structure of the ensemble of microspheres, their size and repetition period. It is found that in some cases, having chosen an appropriate configuration of a microsphere ensemble, one can improve significantly the characteristics of the photonic nanojets formed by this ensemble.

Fabrication of silicon nanowire arrays by near-field laser ablation and metal-assisted chemical etching

We present an elegant route for the fabrication of ordered arrays of vertically-aligned silicon nanowires with tunable geometry at controlled locations on a silicon wafer. A monolayer of transparent microspheres convectively assembled onto a gold-coated silicon wafer acts as a microlens array. Irradiation with a single nanosecond laser pulse removes the gold beneath each focusing microsphere, leaving behind a hexagonal pattern of holes in the gold layer. Owing to the near-field effects, the diameter of the holes can be at least five times smaller than the laser wavelength. The patterned gold layer is used as catalyst in a metal-assisted chemical etching to produce an array of vertically-aligned silicon nanowires. This approach combines the advantages of direct laser writing with the benefits of parallel laser processing, yielding nanowire arrays with controlled geometry at predefined locations on the silicon surface. The fabricated VA-SiNW arrays can effectively transfect human cells with a plasmid encoding for green fluorescent protein.

Sintering and piezoelectric properties of K0.5Na0.5NbO3 glass microspheres

Laser-fused K0.5Na0.5NbO3 (KNN) powder of 75% transparent fraction has been sintered by pressureless sintering, spark plasma sintering (SPS), and hot isostatic pressing (HIP). The laser-fused KNN has a fictive temperature of 503°C and an onset crystallization temperature of around 529°C. The results have shown that sintering of the laser-fused KNN powder utilizing the viscous flow of the transparent microspheres (amorphous content)–at the kinetic window (26°C)–is possible. The highest yield relative density is around 83% at a sintering temperature of 525°C and at a sintering pressure of 280MPa. Limited density has been reached because of formation of crystalline surface layers around the amorphous areas. The samples hipped at 525°C have low piezoelectric coefficient d33 of 5 pC/N because of the residual porosity that led to early dielectric breakdown during the polarization. The sintering behavior, the resulting microstructure as well as the measured properties will be discussed.

Spectrum analysis of liquid immersion to transparent microsphere based optical nanoscopy

Recently, it was experimentally shown that barium titanate (BaTiO3) glass microsphere immersed in the liquid can be used for super-resolution imaging. However the inherent physical mechanism is still not clear. In this paper, spectrum analysis method is adopted to investigate the effect of liquid immersion to microsphere based optical super-resolution imaging. By tracking the propagation of part of the evanescent wave of the object's spectrum, the range of immersed-liquid's refractive index to achieve super resolution can be derived. To verify this analysis, we theoretically model the imaging process with finite-difference time-domain (FDTD) and angular spectrum propagation method. The result shows that only the BaTiO3 microsphere immersed in the liquid with moderate refractive index, the super-resolution can be achieved. And the lower refractive index of liquid corresponds to larger magnification.

Widefield scanning imaging with optical super-resolution

An economical, pollution-free microsphere-based widefield scanning imaging method is presented. This system is able to visualize the surface pattern of the sample through a transparent dielectric microsphere stuck onto a glass probe. The microsphere endows the system with super-resolution capability, while the field of view can easily be expanded by scanning and image stitching. The feasibilities and advantages of this method have been verified experimentally.