Diameter Polystyrene Research Articles

Single lipid bilayer deposition on polymer surfaces using bicelles.

A lipid bilayer was deposited on a 3 μm diameter polystyrene (PS) bead via hydrophobic anchoring of bicelles containing oxyamine-bearing cholesteric moieties reacting with the aldehyde functionalized bead surface. Discoidal bicelles were formed by mixing dimyristoylphosphatidylcholine (DMPC), dihexanoylphosphatidylcholine (DHPC), dimyristoyltrimethylammonium propane (DMTAP), and the oxyamine-terminated cholesterol derivative, cholest-5-en-3β-oxy-oct-3,6-oxa-an-8-oxyamine (CHOLOA), in the molar ratio DMPC/DHCP/DMTAP/CHOLOA (1/0.5/0.01/0.05) in water. Upon exposure to aldehyde-bearing PS beads, a stable single lipid bilayer coating rapidly formed at the bead surface. Fluorescence recovery after photobleaching demonstrated that the deposited lipids fused into an encapsulating lipid bilayer. Electrospray ionization mass spectrometry showed that the short chain lipid DHPC was entirely absent from the PS adherent lipid coating. Fluorescence quenching measurements proved that the coating was a single lipid bilayer. The bicelle coating method is thus simple and robust, can be modified to include membrane-associated species, and can be adapted to coat any number of different surfaces.

"Sonocytometry" – novel diagnostic method of ultrasonic differentiation of cells in blood flow.

Novel diagnostic method named "sonocytometry", in which streaming blood cell is diagnosed by the reflection of high frequency ultrasound from the cell, is proposed. In the present study, the differentiation of the particle size is performed as a basic study on sonocytometry. Ultrasonic backscatter signal from either 80 or 100 μm diameter polystyrene particles was measured by an ultrasonic transducer with the central frequency of 30 MHz. The spectrum of the reflected signal showed different characteristics according to the particle diameter. Theoretical value of backscatter was calculated by Faran-Hickling model and the correlation coefficient of measured and theoretical value by varying the spherical diameter showed the local maximum value at either 80 or 100 μm diameter. The principle was also validated on the streaming particles in a flow channel. The method successfully classified the particle size. Sonocytometry would be clinically applied for diagnosis of malaria or leukemia.

Poly(ε-caprolactone) scaffolds of highly controlled porosity and interconnectivity derived from co-continuous polymer blends: model bead and cell infiltration behavior.

Porous structures destined for tissue engineering applications should ideally show controlled and narrow pore size distributions with fully interconnected pores. This study focuses on the development of novel poly(ε-caprolactone) (PCL) structures with fully connected pores of 84, 116, 141, and 162μm average diameter, from melt blending of PCL with poly(ethylene oxide) (PEO) at the co-continuous composition, followed by static annealing and selective extraction of PEO. Our results demonstrate a low onset concentration for PEO continuity and a broad region of phase inversion. A novel in vitro assay was used to compare scaffold infiltration by 10-μm diameter polystyrene beads intended to mimic trypsinized human bone marrow stromal cells (hBMSCs). Beads showed a linear increase in the extent of scaffold infiltration with increasing pore size, whereas BMSCs infiltrated 162 and 141μm pores, below which the cells aggregated and adhered near the seeding area with low infiltration into the porous device. While providing a baseline for non-aggregated systems, the beads closely mimic trypsinized cells at pore sizes equal to or larger than 141μm, where optimal retention and distribution of hBMSCs are detected. A cytotoxicity assay using L929 cells showed that these scaffolds were cytocompatible and no cell necrosis was detected. This study shows that a melt blending approach produces porous PCL scaffolds of highly controlled pore size, narrow size distribution and complete interconnectivity, while the bead model system reveals the baseline potential for a homogeneous, non-aggregated distribution of hBMSCs at all penetration depths.

Monolithic integration of DUV-induced waveguides into plastic microfluidic chip for optical manipulation

A monolithic polymer optofluidic chip for manipulation of microbeads in flow is demonstrated. On this chip, polymer waveguides induced by Deep UV lithography are integrated with microfluidic channels. The optical propagation losses of the waveguides are measured to be 0.66±0.13dB/mm at a wavelength of λ=808nm. An optimized bead tracking algorithm is implemented, allowing for determination of the optical forces acting on the particles. The algorithm features a spatio-temporal mapping of coordinates for uniting partial trajectories, without increased processing time. With an external laser power of 250mW, a maximum scattering force of 0.84 pN is achieved for 5μm diameter polystyrene beads in water.

Depletion Flocculation Induced by Synergistic Effects of Nanoparticles and Polymers

The depletion flocculation of stable suspensions of charged microparticles (1.2 μm diameter polystyrene) by mixtures of silica nanoparticles (7 nm) and poly(acrylic) acid (PAA, Mn = 24 500) was studied. The experiments revealed a very clear critical flocculation concentration of PAA that was lowered by the addition of the silica nanoparticles. Equilibrium pair potentials between the particles, calculated from force profiles measured between a silica particle and plate using colloid probe atomic force microscopy, showed clear a synergistic effect in that the magnitude of the depletion and structural forces produced in the mixed PAA/nanoparticle system was significantly greater than the sum of the forces in systems containing only PAA or only nanoparticles. This effect arises from adsorption of the PAA onto the nanoparticles, creating much larger charged complexes. Comparing the calculated pair potentials to the observed flocculation results revealed that flocculation occurred once the magnitude of the secondary energy well formed by the attractive depletion force exceeded 5 kT.

Statistical characterization of self-assembled colloidal crystals by single-step vertical deposition

We have statistically characterized the self-assembly of multi-layer polystyrene colloidal crystals, using the technique of vertical deposition, with parameters chosen to produce thick layers of self-assembled crystals in one deposition step. The size distribution of domains produced with this technique was seen to follow a log-normal distribution, hinting that aggregation or fragmentation phenomena play a role. In addition, using a lithographically directed self-assembly method, we have shown that the size of multi-layer, continuous crack-free domains in lithographically defined areas can be many times larger than in the surrounding areas. In a single deposition step, we have produced continuous colloidal crystal films of 260nm diameter polystyrene spheres approximately 30–40 layers thick, with a controllable lateral size of 80–100μm without lithography, and as high as 250μm with the lithographic template. This method allows us to suppress the domain size fluctuations and produces mesoscopically thick colloidal crystals of selected size at a selected location.

Position designated delivery and release of nanospheres using a nanofiber

This work demonstrates a position designated delivery and release of 700-nm diameter polystyrene spheres using a 540nm nanofiber decorated with a flaw. When the optical power increased to 12mW, nanospheres dispersed in the water were trapped by the gradient force, and transported along the nanofiber due to the scattering force. Once they moved to the position of the flaw, they would stop their forward progress, and released at the flaw. Moreover, the designated position can be easily relocated by just moving the nanofiber with the flaw on it. This technique could be employed to deliver drug particles to designated positions.

3D nano-structures for laser nano-manipulation

The resputtering of gold films from nano-holes defined in a sacrificial PMMA mask, which was made by electron beam lithography, was carried out with a dry plasma etching tool in order to form well-like structures with a high aspect ratio (height/width ≈ 3–4) at the rims of the nano-holes. The extraordinary transmission through the patterns of such nano-wells was investigated experimentally and numerically. By doing numerical simulations of 50-nm and 100-nm diameter polystyrene beads in water and air, we show the potential of such patterns for self-induced back-action (SIBA) trapping. The best trapping conditions were found to be a trapping force of 2 pN/W/μm2 (numerical result) exerted on a 50-nm diameter bead in water. The simulations were based on the analytical Lorentz force model.

Volumetric reconstruction of Brownian motion of a micrometer-size bead in water

An effective volumetric measurement and reconstruction scheme for imaging three-dimensional phase objects based on off-axis digital holography is presented. We have experimentally demonstrated the feasibility of our method by observing the Brownian motion of a 3μm diameter polystyrene bead in water. From a single off-axis hologram of a diffracted field by a sample, a series of transverse intensity images for various axial positions were numerically generated. The center position of the bead sample was pinpointed with a nanometer-scale resolution in 3D space and updated with a frame rate of 30 frames/s. Detailed procedures for elimination of virtual images in an off-axis hologram, reduction of background DC noise, and extraction of exact electric fields in an off-axis hologram are described as advantages of our proposed method over conventional in-line holographic 3D measurement schemes.

Dielectric spectroscopy of concentrated colloidal suspensions

A comparison between experimental measurements and theoretical calculations of the permittivity and conductivity of concentrated colloidal suspensions is presented. Dielectric spectroscopy measurements for 100nm and 200nm diameter polystyrene spheres at volume fractions between ϕ=0.01−0.18 and electrolyte concentrations 0.01–1mM KCl (P.J. Beltramo, E.M. Furst, Langmuir 28 (2012) 10703–10712) are compared to cell-model calculations that account for the hydrodynamic and electrokinetic interactions between particles (F. Carrique, F.J. Arroyo, M.L. Jimenez, A.V. Delgado, J. Chem. Phys. 118 (2003) 1945–1956). Under most conditions, there is good agreement between experiment and theory. At low ionic strengths, the dielectric increment exhibits a low-frequency plateau in the experimental spectroscopy and cell model calculations. However, at the highest ionic strengths, the cell model predicts a low frequency plateau that is not observed experimentally. The conductivity increments qualitatively agree over all volume fractions, ionic strengths and frequencies.

Ordering of Polystyrene Nanoparticles on Substrates Pre-Coated with Different Polyelectrolyte Architectures

Adjusting the inter-particle distances in ordered nanoparticle arrays can create new nano-devices and is of increasing importance to a number of applications such as nanoelectronics and optical devices. The assembly of negatively charged polystyrene (PS) nanoparticles (NPs) on Poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) brushes, quaternized PDMAEMA brushes and Si/PEI/(PSS/PAH)2, was studied using dip- and spin-coating techniques. By dip-coating, two dimensional (2-D), randomly distributed non-close packed particle arrays were assembled on Si/PEI/(PSS/PAH)2 and PDMAEMA brushes. The inter-particle repulsion leads to lateral mobility of the particles on these surfaces. The 200 nm diameter PS NPs tended to an inter-particle distance of 350 to 400 nm (center to center). On quaternized PDMAEMA brushes, the strong attractive interaction between the NPs and the brush dominated, leading to clustering of the particles on the brush surface. Particle deposition using spin-coating at low spin rates resulted in hexagonal close-packed multilayer structures on Si/PEI/(PSS/PAH)2. Close-packed assemblies with more pronounced defects are also observed on PDMAEMA brushes and QPDMAEMA brushes. In contrast, randomly distributed monolayer NP arrays were achieved at higher spin rates on all polyelectrolyte architectures. The area fraction of the particles decreased with increasing spin rate.

A method for detecting forward scattering signals on-chip with a photonic-microfluidic integrated device.

A photonic integrated microfluidic device is demonstrated to perform optical excitation and forward scatter collection all on-chip in a planar format. Integrated on-chip optics formed a tailored beam geometry for optimal excitation of particles while a special design modification allowed for on-chip forward collection with the beam shaping capabilities. A notch was placed in the lens system that caused a dark spot on the facet of a collection waveguide while not affecting the beam geometry at the point of interrogation. The modified device with the ability to form a 10 μm beam geometry was demonstrated to detect the forward scatter from blank 5 μm diameter polystyrene beads. Free-space collection of side scatter signals was performed simultaneously with the on-chip collection and the designs demonstrated and enhanced SNR while the reliability of detection was determined to be appropriate for many applications. Excellent performance was confirmed via a false positive rate of 0.4%, a missed events rate of 6.8%, and a coincident rate of 96.3% as determined between simultaneously performed free-space and on-chip detection schemes.

Highly conductive and transparent Ag honeycomb mesh fabricated using a monolayer of polystyrene spheres

We describe the design principles and fabrication of Ag honeycomb mesh as a transparent conductive electrode using a polystyrene (PS) sphere template. Monolayers of PS spheres with different diameters, such as 600 nm, 3 μm, and 10 μm, are studied as templates to form Ag mesh with high transmittance. Since the parasitic Ag islands degrade the transmittance, both heat pretreatment and wet etching are used to control the area covered by parasitic Ag islands. The trade-off between transmittance and conductivity forces us to use larger diameter PS spheres. Ten-micron PS spheres are chosen as the template for the PS sphere monolayer, and heat pretreatment and Ag wet etching are used to demonstrate that the Ag honeycomb mesh transparent electrodes have high performance. The transmittance and the sheet resistance are 83% and 20 Ω/sq, which are comparable to commercial ITO electrodes.

Cross-Sectional Tracking of Particle Motion in Evaporating Drops: Flow Fields and Interfacial Accumulation

The lack of an effective technique for three-dimensional flow visualization has limited experimental exploration of the "coffee ring effect" to the two-dimensional, top-down viewpoint. In this report, high-speed, cross-sectional imaging of the flow fields was obtained using optical coherence tomography to track particle motion in an evaporating colloidal water drop. This approach enables z-dimensional mapping of primary and secondary flow fields and changes in these fields over time. These sectional images show that 1 μm diameter polystyrene particles have a highly nonuniform vertical distribution with particles accumulating at both the air-water interface and the water-glass interface during drop evaporation. Particle density and relative humidity are shown to influence interfacial entrapment, which suggests that both sedimentation rate and evaporation rate affect the dynamic changes in the cross-sectional distribution of particles. Furthermore, entrapment at the air-water interface delays the time at which particles reach the ring structure. These results suggest that the organization of the ring structure can be controlled based on the ratio of different density particles in a colloidal solution.

Wafer-Scale Fabrication of Plasmonic Crystals from Patterned Silicon Templates Prepared by Nanosphere Lithography

By combining nanosphere lithography with template stripping, silicon wafers were patterned with hexagonal arrays of nanowells or pillars. These silicon masters were then replicated in gold by metal evaporation, resulting in wafer-scale hexagonal gratings for plasmonic applications. In the nanosphere lithography step, two-dimensional colloidal crystals of 510 nm diameter polystyrene spheres were assembled at the air-water interface and transferred to silicon wafers. The spheres were etched in oxygen plasma in order to define their size for masking of the silicon wafer. For fabrication of metallic nanopillar arrays, an alumina film was grown over the nanosphere layer and the spheres were then removed by bath sonication. The well pattern was defined in the silicon wafer by reactive ion etching in a chlorine plasma. For fabrication of metal nanowell arrays, the nanosphere monolayer was used directly as a mask and exposed areas of the silicon wafer were plasma-etched anisotropically in SF6/Ar. Both techniques could be used to produce subwavelength metal replica structures with controlled pillar or well diameter, depth, and profile, on the wafer scale, without the use of direct writing techniques to fabricate masks or masters.

Demonstration of Efficient On-Chip Photon Transfer in Self-Assembled Optoplasmonic Networks

Plasmonic nanoantennas facilitate the manipulation of light fields on deeply sub-diffraction-limited length scales, but high dissipative losses in metals make new approaches for an efficient energy transfer in extended on-chip integrated plasmonic circuits mandatory. We demonstrate in this article efficient photon transfer in discrete optoplasmonic molecules comprising gold nanoparticle (NP) dimer antennas located in the evanescent field of a 2 μm diameter polystyrene bead, which served as an optical microcavity (OM). The optoplasmonic molecules were generated through a guided self-assembly strategy in which the OMs were immobilized in binding sites generated by quartz (SiO2) or silicon posts that contained plasmonic nanoantennas on their tips. Control of the post height facilitated an accurate positioning of the plasmonic antennas into the evanescent field of the whispering gallery modes located in the equatorial plane of the OM. Cy3 and Cy5.5 dyes were tethered to the plasmonic antennas through oligonucleotide spacers to act as on-chip light sources. The intensity of Cy3 was found to be increased relative to that of Cy5.5 in the vicinity of the plasmonic antennas where strongly enhanced electric field intensity and optical density of states selectively increase the excitation and emission rates of Cy3 due to spectral overlap with the plasmon. The fluorescent dyes preferentially emitted into the OM, which efficiently trapped and recirculated the photons. We experimentally determined a relative photon transfer efficiency of 44% in non-optimized self-assembled optoplasmonic molecules in this proof-of-principle study.

Near and far-wall effects on the three-dimensional motion of bacteria-driven microbeads

Bio-hybrid microrobots have been heavily studied due to their potential applications as minimally invasive medical microdevices. Though most researchers have focused on two-dimensional and near-wall motion, this letter uses a defocused optical tracking method to quantify the three-dimensional motion of 5 μm diameter polystyrene beads driven by attached Serratia marcescens bacteria. Away from walls the beads trace out helical trajectories, demonstrating kinematics produced by near-constant forces and torques. Near-wall motion is observed to be more stochastic. The motion of beads driven by single bacteria is analyzed in detail, providing an understanding of the forces and torques on the beads.

Generation of scalable quasi-3D metallo-dielectric SERS substrates through orthogonal reactive ion etching

We combined two orthogonal reactive ion etching strategies on monolayers of 4 μm diameter polystyrene (PS) microspheres assembled on a planar glass substrate to create geometrically diverse but highly regular quasi-3D nano-structured arrays with centimeter length scales. Reactive ion etching (RIE) with O2/CF4 was used to selectively etch PS and, thus, to adjust the morphology of the PS mask, and CHF3 RIE was then used to etch the SiO2 substrate. The dynamic combination of these two etching procedures facilitated the realization of a wide variety of 3D-corrugated surface morphologies, including pedestals, bowls, honeycombs and blossom bud like arrays. The generated structures were then evaporated with Au films of defined thicknesses to generate metallo-dielectric arrays with tunable surface roughness. Hexagonal diffraction patterns from the fabricated structures confirm the successful realization of extended periodic hexagonal structures and the optical transmission spectra showed an efficient trapping of incident light in these ultra-rough metallo-dielectric arrays. The metallo-dielectric substrates were finally optimized for the detection of the pesticide methyl parathion in a concentration as low as 1 × 10−10 M through surface enhanced Raman spectroscopy (SERS).

SERS detection of polycyclic aromatic hydrocarbons on a bowl-shaped silver cavity substrate

Trace detection of polycyclic aromatic hydrocarbons (PAHs) by surface-enhanced Raman scattering (SERS) on a metal sandwich substrate bridged by 1,10-decanedithiolis is reported in this work. The bowl-shaped silver cavity (BSSC) thin film bottom layer was prepared by electrodeposition using a closely packed monolayer of 500 nm diameter polystyrene spheres as a template. The as-prepared silver cavity array has proven to be a SERS-active substrate with excellent performance and reproducibility when using p-aminothiophenol (PATP) as the probe molecule. A 1,10-decanethiol monolayer was then assembled on the silver film to concentrate PAHs within the hot-spot of SERS detection. The top layer of silver was introduced by an S–Ag bond between the thiols of the 1,10-decanethiol and the silver nanoparticles. The proposed structure was employed to perform the SERS-based PAH detection. The measured SERS spectra enabled the easy detection of anthracene and pyrene; the two PAH compounds can be detected over a wide concentration range and the detection limit of anthracene and pyrene was 8 and 40 nM, respectively. The results demonstrate that the new SERS substrate is suitable for the quantitative identification of non-polar organic pollutants like PAHs.

Sequence-Specific Nucleic Acid Detection from Binary Pore Conductance Measurement

We describe a platform for sequence-specific nucleic acid (NA) detection utilizing a micropipet tapered to a 2 μm diameter pore and 3 μm diameter polystyrene beads to which uncharged peptide nucleic acid (PNA) probe molecules have been conjugated. As the target NAs hybridize to the complementary PNA-beads, the beads acquire negative charge and become electrophoretically mobile. An applied electric field guides these NA-PNA-beads toward the pipet tip, which they obstruct, leading to an indefinite, electrically detectable, partial blockade of the pore. In the presence of noncomplementary NA, even to the level of single base mismatch, permanent pore blockade is not seen. We show application of this platform to detection of the anthrax lethal factor sequence.