Arrays Of Microparticles Research Articles

A photo-defined membrane for precisely patterned cellular and microparticle arrays

The ability to pattern particles in well-defined arrays enhances microfluidic devices. A low-fluorescence optically transparent photo-curable resist (1002F) was characterized for use as a mechanical sieve in a microfluidic chip. Films of thickness 10 μm and 25 μm were created containing pores 6–10 μm in diameter with pitches ranging from 5–300 μm. The uniform photo-defined pores had diameters with standard deviations of 3%. Integrated with microfluidic devices, the films were used to trap polystyrene microspheres, and in a different experiment, MCF7 human epithelial adenocarcinoma cells (ATCC HTB-22). A mechanical sieve was used to trap two types of fluorescent particles and, separately MCF7 cells with NIH/3T3 murine fibroblast cells (ATCC CRL-1658) as a proof-of-concept for striated cellular co-culture.

Parallel near-field optical micro/nanopatterning on curved surfaces by transported micro-particle lens arrays

Although laser surface nanopatterning by particle lens arrays (PLA), utilizing near-field enhancement, has been extensively utilized previously, a suitable technique for the deposition of PLA on the curved surface of a cylinder was not available. In this paper, a novel technique for nanopatterning on curved surfaces using PLA is demonstrated. In the proposed technique, a hexagonal closed pack monolayer of SiO2 spheres is first formed by self-assembly on a flat glass surface. The formed monolayer of particles is then picked up by a flexible optically transparent sticky surface and placed on the substrate to be patterned. A 532 nm wavelength Nd : YVO4 laser was used to irradiate the substrate with the laser passing through the flexible, transparent surface and the particles. Experimental investigations are made to ascertain the properties of the patterns. In addition, the optical near-field distribution around the particles is numerically simulated. The proposed technique is validated for nanopatterning of the curved surface of a cylinder.

The Determination of Methanol Using an Electrolytically Fabricated Nickel Microparticle Modified Boron Doped Diamond Electrode

AbstractA nickel modified boron doped diamond (Ni‐BDD) electrode and nickel foil electrode were used in the determination of methanol in alkaline solutions. The Ni‐BDD electrode was electrodeposited from a 1 mM Ni(NO3)2 solution (pH 5), followed by repeat cycling in KOH. Subsequent analysis utilised the Ni(OH)2/NiOOH redox couple to electrocatalyse the oxidation of methanol. Methanol was determined to limits of 0.3 mM with a sensitivity of 110 nA/mM at the Ni‐BDD electrode. The foil electrode was less sensitive achieving a limit of 1.6 mM and sensitivity of 27 nA/mM. SEM analysis of the electrodes found the Ni‐BDD to be modified by a quasi‐random microparticle array.

High-resolution spectroscopy with microparticle arrays

High-resolution spectroscopy with microparticle arrays

Laser-controlled microscale fluid flows near the air-liquid interface of suspension droplets

We investigate microscale flows of microparticles driven by a laser beam focused near the air-liquid interface of a suspension droplet. Three distinct regimes, convection, a linear flow, and a nonflow, are found by controlling both the position of the beam focus relative to the air-liquid interface and the laser power. They are governed by the most dominant of two effects exerted by a focused laser beam, i.e., local heating and radiation pressure. We find that in the nonflow regime two-dimensional close-packed arrays of microparticles are formed on the air-liquid interface, and spin on the beam axis. We show that micron-sized polystyrene beads can be bonded into a long chain structure by taking advantage of the linear flow.

Manufacture and characterisation of agarose microparticles

The mechanical properties of agarose microparticles formed by shearing bulk gels dispersed in cold water using a high speed rotor/stator device were investigated. The influence of agarose concentration on bulk gel texture (Young’s modulus, stress and strain at failure) and microparticle size (Sauter mean diameter and size distribution) was assessed. Results obtained showed that bulk gels from 1 to 8% (w/w) showed a linear increase in Young’s modulus with concentration, while the true strain values at failure levelled at high concentrations (>3%). High speed shearing of the bulk gels yielded final particle sizes for the l% and 2% w/w microgel suspensions significantly lower than for the more concentrated gels (3–8% w/w) which are statistically identical ( p < 0.005) at 103 ± 2 μm, irrespective of concentration. Rheological investigation of the microparticle suspensions, over a range of bulk gel concentrations, showed that microparticles form a solid like suspension at high volume fractions, becoming fluid like above a well defined yield stress. Overall, a simple and low-cost procedure has been developed to produce an array of agarose microparticles that can confer a range of textural functionalities to beverages from liquids to fluid gels.

Suspension arrays of hydrogel microparticles prepared by photopatterning for multiplexed protein-based bioassays

Suspension arrays for protein-based assays have been developed using shape-coded poly(ethylene glycol) (PEG) hydrogel microparticles to overcome the problems with current systems which use color-coded rigid microparticles as protein supports. Various shapes of hydrogel microparticles were fabricated by a two-step process consisting of photopatterning and flushing using a poly(dimethylsiloxane) (PDMS) channel as a molding insert. Hydrogel microparticles with lateral dimensions ranging from 50 to 300 micrometers were fabricated using different molecular weights of PEG (700, 3,400, and 8,000 Da), by which the water content and swelling behavior of the hydrogel microparticles could be controlled. Protein-entrapped hydrogel microparticles were prepared in a suspension array format, and PEG hydrogel could encapsulate proteins without deactivation for a week due to its high water content and soft nature. The sequential bienzymatic reaction of hydrogel-entrapped glucose oxidase (GOX) and peroxidase (POD) was successfully investigated using fluorescence detection, demonstrating one possible application of suspension arrays. Furthermore, a mixture of two different shapes of hydrogel microparticles containing GOX/POD and alkaline phosphatase (AP), respectively, was prepared and the shape-coded suspension array was used for simultaneous characterization of two different enzyme-catalyzed reactions.

Voltammetry at Nanoparticle and Microparticle Modified Electrodes: Theory and Experiment

Electrodes modified with random arrays of nanoparticles and/or microparticles find significant application in electroanalysis. Theory is developed for the diffusional current at nanoparticle-modified electrodes via the diffusion domain approach which is used to model the electrode surface as a randomly distributed assembly of spherical particles. Experiments are reported for the electrocatalytic reduction of protons at a palladium particle modified electrode and shown to behave as predicted theoretically.

Visualization of optical binding of microparticles using a femtosecond fiber optical trap

At the microscopic level, light-matter interactions can organize colloidal matter via a process known as optical binding. Optical binding refers to the creation of arrays of microparticles formed in the presence of laser fields, the inter-particle spacing being determined by the refocusing and/or scattering of the laser fields by the microparticles. In this paper we investigate one-dimensional optically bound arrays of microparticles using a femtosecond dual-beam optical fiber trap, and develop a means to visualize the field intensity distributions responsible for the optical binding using two-photon fluoresence imaging from fluorescein added to the host medium. The experimental intensity distributions are shown to be in good agreement with numerical simulations, thereby validating our new approach to visualizing the fields responsible for optical binding, and the physical model of optical binding as due to refocusing of the fields by the microparticles.

Rotation of two-dimensional arrays of microparticles trappedby circularly polarized light

We investigate the creation and the rotation of the array of microparticles trapped by circularly polarized light. We find that a smooth rotation requires two-dimensional structure having a rotational symmetry along the light beam axis. We show that it is possible to control smoothly both the rate and the sense of rotation not only by varying the handedness and the power of the incident beam but also by varying the position of the beam focus.

Multianalyte immunoassay with self-assembled addressable microparticle array on a chip

This paper describes the random fluidic self-assembly of metallic particles into addressable two-dimensional microarrays and the use of these arrays as a platform for constructing a biochip useful for bioassays. The basic units in the assembly were the microfabricated particles carrying a straightforward visible code and the corresponding array template patterned on a glass substrate. The particles consisted of a hydrophobic and magnetic Ni-polytetrafluoroethylene (PTFE) composite layer on one face, and on the other face a gold layer that was modified for biomolecular attachment. An array template was photoresist-patterned with spatially discrete microwells in which an electrodeposited Ni-PTFE hydrophobic composite layer and a hydrophobic photo-adhesive coating were deposited. The particles, after biomaterial attachment and binding processes in bulk, were self-assembled randomly onto the lubricated bonding sites on the chip substrate, driven by a combination of magnetic, hydrophobic, and capillary interactions. The encoding symbol carried by the particles was used as the signature for the identification of each target/assay attached to the particle surface. We demonstrate here the utility of microfabricated-encoded particle arrays for conducting multianalyte immunoassays in a parallel fashion with the use of imaging detection.

Polymer microparticle arrays from electrodynamically focused microdroplet streams

We describe instrumentation for forming two-dimensional arrays of polymer microparticles produced from electrodynamically focused microdroplet streams. A single-stage linear quadrupole was used to focus droplets/particles onto silanated glass slides mounted on a computer-driven two-dimensional translation stage. Center-to-center position stability was on the order of 1 μm. Applications to molecular sorting with polymer particles as host carriers are discussed.

Lens functions of polymer microparticle arrays

Lens functions of an array of polymer microparticles, whose particle size distribution is monodispersion, are investigated. It was demonstrated that the formation of single or double layered microparticle arrays can be controlled. The double layered array showed a characteristic lens function which can be explained by the Moiré pattern formation between the two lens sheets adjacent to each other. The image showing up on the second lens sheet could be varied by controlling the rotation angle of the second sheet, corresponding to the variation of the Moiré pattern. A spherically curved sheet of microlens array (SMLA) was prepared as an analogy to the compound eye of an insect. The lens function of the double layered SMLA was also investigated and discussed in terms of the image-forming mechanism as an analogue to the compound eye. The mechanisms of the lens functions could be theoretically explained and the phenomena were regenerated by computational simulation.

Microparticle Raman spectroscopy

The instrumentation and techniques used to explore the chemistry of microparticles (with dimensions of order 1 μm and masses of order 1 pg) via Raman spectroscopy are surveyed, and recent applications are presented. The method features electrodynamic levitation of single microparticles and arrays of microparticles, so the most commonly used electrodynamic balances are described. Several examples of microparticle spectroscopy are given, including salt particle phase transition, chemical reaction between microparticles of Na 2CO 3 and (NH 4) 2SO 4, the effects of morphology-dependent resonances on Raman spectra for organic droplets, and spectroscopic measurements during evaporation of a binary component microdroplet.