Mirrorless lasing from mesostructured waveguides patterned by soft lithography

Guest aggregation within poly(L-lactic acid)/pluronic P104 thin films

Rhodamine 6G (R6G) doped thin films composed of poly(L-lactic acid) (PLLA) and Pluronic P104 were spin cast onto glass microscope slides and characterized by ultraviolet-visible, steady-state, and time-resolved fluorescence spectroscopy. The results show that R6G aggregation within the film increases as the R6G concentration and P104 loading increases. These results suggest an approach for studying drug distributions (monomers, aggregates) within biodegradable polymer formulations.

Polymer microfluidic chips with integrated waveguides for reading microarrays

A microfluidic chip with an integrated planar waveguide was fabricated in poly(methyl methacrylate), PMMA, using a single-step, double-sided hot-embossing approach. The waveguide was embedded in air on three sides, the solution being interrogated on the fourth. DNA probes were covalently attached to the waveguide surface by plasma activating the PMMA and the use of carbodiimide coupling chemistry. Successful hybridization events were read using evanescent excitation monitored by an imaging microscope, which offered high spatial resolution (2 microm) and a large field-of-view (20 mm diameter field-of-view), providing imaging of the entire array without scanning. The application of the microfluidic/waveguide assembly was demonstrated by detecting low abundant point mutations; insertion C mutations in BRCA1 genes associated with breast cancer were analyzed using a universal array coupled to an allele-specific ligation assay. DNA probes consisting of amine-terminated oligonucleotides were printed inside the microfluidic channel using a noncontact microspotter. Mutant and wild-type genomic DNAs of BRCA1 were PCR (polymerase chain reaction) amplified, with the amplicons subjected to ligation detection reactions (LDRs). LDR solutions were allowed to flow over the microarray positioned on the polymer waveguide with successful ligation events discerned through fluorescence signatures present at certain locations of the array. The microfluidic/waveguide assembly could detect polymorphisms present at <1% of the total DNA content.

Fully integrated microfluidic separations systems for biochemical analysis

Over the past decade a tremendous amount of research has been performed using microfluidic analytical devices to detect over 200 different chemical species. Most of this work has involved substantial integration of fluid manipulation components such as separation channels, valves, and filters. This level of integration has enabled complex sample processing on miniscule sample volumes. Such devices have also demonstrated high throughput, sensitivity, and separation performance. Although the miniaturization of fluidics has been highly valuable, these devices typically rely on conventional ancillary equipment such as power supplies, detection systems, and pumps for operation. This auxiliary equipment prevents the full realization of a "lab-on-a-chip" device with complete portability, autonomous operation, and low cost. Integration and/or miniaturization of ancillary components would dramatically increase the capability and impact of microfluidic separations systems. This review describes recent efforts to incorporate auxiliary equipment either as miniaturized plug-in modules or directly fabricated into the microfluidic device.

Harnessing the sol-gel process for the assembly of non-silicate mesostructured oxide materials

Mesostructured non-silicate oxides, with well-defined organization on the 2-50 nm size scale, may play a pivotal role in advancing vital disciplines such as catalysis, energy conversion, and biotechnology. Herein, we present selected methodologies for utilizing the sol-gel process, in conjunction with organic-directed assembly, to synthesize a variety of mesostructured oxides. The nature of the inorganic precursor is critical for this process. We discuss the development of general routes for yielding stable, nanoscopic, hydrophilic, inorganic precursors compatible with organic co-assembly. In particular, we highlight the use and characterization of organic-acid-modified transition metal oxide sol-gel precursors that allow for the synthesis and processing of designer mesostructured oxides such as titania hybrids for optical applications and porous multicomponent metal oxides useful for catalysis.

Future approaches of nanomedicine in clinical science

Burgeoning applications of nanotechnology are altering practices in traditional medicine. Promoted by the National Institutes of Health, nanomedicinal research is advancing technologies and revolutionizing strategies in clinical science by providing easy access to innovative nanodevices and nanosystems based on the rational design and precise integration of functional nanomaterials. Many long-standing challenges in clinical science could be met through advancement and revolutionization. Nanomedicinal diagnostics could acquire critical information regarding the status of diseased tissues and organs quickly and inexpensively with minimal sampling size and invasion. New strategies in therapeutic and regenerative nanomedicines will enable clinicians to take actions in a timely fashion and patient-friendly manner.

Surface design for precise control of spatial growth of a mesostructured inorganic/organic film on a large-scale area

A microfabrication technique is presented to fabricate a mesostructured inorganic/organic composite film, i.e., silica/cetyltrimethylammonium chloride (CTAC) film, with near-perfect site-selectivity on a large surface area based on a spatially regulated growth method. To precisely regulate the site-selective growth of this mesocomposite film at the solid/liquid interface, we designed a novel microtemplate consisting of a "dual-component" self-assembled monolayer (SAM) with alternating hydrophobic trifluorocarbon (CF3) and cationic amino (NH2) groups. First, (heptadecafluoro-1,1,2,2-tetrahydrodecyl)trimethoxysilane (FAS)-SAM was formed onto Si substrate covered with native oxide (SiO2/Si) from vapor phase. The substrate was then photolithographically micropatterned using 172 nm vacuum UV light. Finally, the micropatterned FAS-SAM was immersed in a solution of 1 vol % (aminoethylaminomethyl)phenethyltrimethoxysilane (AEAMPS) in absolute toluene. Due to these treatments, a dual-SAM microtemplate with CF3- and NH2-terminated surfaces was fabricated, as evidenced by lateral force microscopy, ellipsometry, and X-ray photoelectron spectroscopy. Using this template, the microfabrication of a mesocomposite film was demonstrated. As a control, the micropatterned hydrophobic FAS-SAM template (composed of CF3- and OH-terminated surfaces) was also treated under the same conditions. Optical microscopy and atomic force microscopy confirmed that the formation of the continuous mesocomposite film proceeded only on the FAS-SAM-covered regions, while the AEAMPS-SAM-covered regions remained free of deposits. This shielding effect also remained constant regardless of the pattern's geometry, i.e., the interval distance between the FAS-SAM-covered areas in the pattern. Through this approach, we were able to obtain well-defined 5-, 10-, and 20-mum wide mesocomposite microlines over the entire 10 x 10 mm2 area with high area-selectivity. On the other hand, when the SiO2 regions were not terminated with the cationic NH2 groups, cluster formation proceeded not only on the hydrophobic CF3 regions but also on the SiO2 regions, particularly with an increase in the pattern interval distance, resulting in lower final pattern resolution.

Highly oriented tunable wrinkling in polymer bilayer films confined with a soft mold induced by water vapor

The authors report the formation of highly oriented wrinkling on the surface of the bilayer [polystyrene (PS)/poly(vinyl pyrrolidone) (PVP)] confined by a polydimethylsiloxane (PDMS) mold in a water vapor environment. When PVP is subjected to water vapor, the polymer loses its mechanical rigidity and changes to a viscous state, which leads to a dramatic change in Young's modulus. This change generates the amount of strain in the bilayer to induce the wrinkling. With a shape-controlled mold, they can get the ordered wrinkles perfectly perpendicular or leaned 45 degrees to the channel orientation of the mold because the orientation of the resultant force changes with the process of water diffusion which drives the surface to form the wrinkling. Additionally, they can get much smaller wrinkles than the stripe spacing of PDMS mold about one order. The wrinkle period changes with the power index of about 0.5 for various values of the multiplication product of the film thicknesses of the two layers, namely, lambda approximately (h(PS)h(PVP))(1/2).

Designed synthesis of mesoporous solids via nonionic-surfactant-templating approach

The continual needs for improved performances in applications derived by diversified compositions and mesostructures have pushed forward the development of mesoporous solids. The nonionic-surfactant-templating approach has been a critical route in this advancement. A large number of nonionic surfactants widely used in industries and featured with low cost, low toxicity, bio-degradation and ordered microdomains can be utilized as effective templates to the design and synthesis of abundant mesoporous solids. This feature article provides recent reports on the use of nonionic surfactant self-assembly as examples to fabricate high-quality ordered mesoporous solids which illustrates advances in synthesis and understanding of formation mechanisms. It includes the selection of surfactants, a summary of the effects of synthetic parameters, the current understanding of the synthetic pathways and related mechanisms with some emphasis on evaporation induced self-assembly (EISA), as well as the design and synthesis on the microscale (atomic and molecular compositions) and mesoscale (mesostructures). Preliminary applications of mesoporous solids particularly in optical devices, electrodes and biomaterials are also presented.

Mesoporous bragg stack color tunable sensors

Herein we report a novel self-assembly synthesis, structural and optical characterization of mesoporous Bragg stacks (MBS) composed of spin-coated multilayer stacks of mesoporous TiO(2) and mesoporous SiO(2). Investigation of the optical response of MBS to the infiltration of alcohols and alkanes into its pores reveals better sensitivity and selectivity than conventional Bragg reflectors. Furthermore, we demonstrate that the chemical sensing ability can be tuned via layer thickness, composition and surface properties.

Deposition of thin mesoporous silica films on glass substrates from basic solution

Transparent thin (ca. 100 nm) films of silica-surfactant mesostructured materials were deposited on borosilicate glass plates and soda-lime glass tubes from aqueous solutions containing tetraethoxysilane, alkyltrimethylammonium chloride, ammonia, and methanol. By calcination in air, the films became mesoporous (BET surface area of 700-900 m2 g-1) with pore diameter 2.0-2.8 nm.

Fluorescent plasma nanocomposite thin films containing nonaggregated rhodamine 6G laser dye molecules

This letter reports a novel methodology for the synthesis of dye-containing nanocomposite thin films containing fluorescent rhodamine 6G (Rh6G) laser dye molecules. The nanocomposites are deposited in one step at room temperature in a downstream microwave plasma operating at low pressure and power. By controlling the plasma chemistry, it is possible to reduce the formation of dye dimers and higher aggregates that quench the fluorescence of the dye molecules. The films are intensely absorbent and fluorescent, insoluble in water, mechanically stable, and present good adhesion to the substrate. Besides, the method is compatible with the present silicon technology and therefore particularly interesting for the fabrication of integrated optoelectronic devices.

Colloidal woodpile structure: three-dimensional photonic crystal with a dual periodicity

With planar photolithography and self-assembly techniques, multilayer colloidal crystals with a woodpile structure were fabricated. They represent a new kind of photonic crystals, that is, three-dimensional (3D) photonic crystals with a dual periodicity; one comes from the face-centered cubic (fcc) structure within the colloidal crystal strips and the other one results from the periodic arrangement of the colloidal crystal strips.

Synthesis, characterization and optical properties of silver and gold nanowires embedded in mesoporous MCM-41

Uniform nanowires of silver and gold inside the channels of MCM-41 were prepared by controlled reduction of their respective metal salts with sodium borohydride (NaBH4). Presence of nanowires of silver and gold in MCM-41 were confirmed by high angle X-ray diffraction (XRD) data (peaks between 2ϑ = 30 − 60°) and transmission electron microscopy (TEM) confirmed the diameter of the nanowires. Diameter of nanowires is found to be ∼ 2.8 nm which is coincident with channel diameter of MCM-41. Optical properties of these heterostructured materials Ag-MCM-41 and Au-MCM-41 reveals the presence of surface plasmon absorption peaks of silver and gold respectively, and the shift in the absorption bands are associated to agglomeration of clusters inside the channels. Room temperature photoluminescence spectra exhibits interesting optical properties as observed for direct band gap semiconductors. Non-linear optical properties (NLO) corresponding to second harmonic generation (SHG) values were also recorded for self supported films of these heterostructured materials. Enhanced optical non-linearity was found to be arising from a corresponding increase of local field near the surface plasmon resonance. Further enhancement in SHG was found with poling due to an induction of orientation order.

Fluorescent Hydroxyflavone-Zeolite Nanoparticles: Ship-in-a-Bottle Synthesis and Photophysical Properties

3-Hydroxyflavone (3-OHF) was incorporated in zeolite micropores by ship-in-a-bottle synthesis. This strategy consists of constructing the molecule by reaction of small precursors within the cavity. 3-OHF molecules exhibit excited-state intramolecular proton transfer (ESIPT) and a tautomeric equilibrium between the 3-OHF-excited structures N* and T*exists. This equilibrium is strongly affected by the protic nature and polarity of the surrounding medium. The textural and spectroscopic characterization of the dye-loaded zeolite colloids enabled the study of the correlation between the optical properties of the dye and the zeolite micropore environment.

Highly efficient enrichment and subsequent digestion of proteins in the mesoporous molecular sieve silicate SBA-15 for matrix-assisted laser desorption/ionization mass spectrometry with time-of-flight/time-of-flight analyzer peptide mapping

Based on a previous study of protein digestion inside the nanoreactor channels of the mesoporous molecular sieve silicate SBA-15 (Chem. Eur. J. 2005, 11: 5391), we have developed a highly efficient enrichment and subsequent tryptic digestion of proteins in SBA-15 for matrix-assisted laser desorption/ionization mass spectrometry with time-of-flight/time-of-flight analyzer (MALDI-TOF/TOF) peptide mapping. The performance of the method is exemplified with myoglobin and cytochrome c. First, protein adsorption isotherms for two standard proteins with a range of initial concentration of proteins were investigated at room temperature. The results revealed that the kinetic adsorption rate of a protein within SBA-15 was independent of initial protein concentration, and a 15-min protein enrichment within SBA-15 could be enough for protein identification in biological samples. It was noticed that no washing steps were needed to avoid protein loss due to desorption from the mesochannels into solution. Second, protein digestion inside the channels of SBA-15 was also optimized. After adsorption of proteins into SBA-15 in 15 min, the trypsin solution (pH 8) was directly added to the SBA-15 beads with immobilized proteins by centrifugation, and then the digestion was performed for 15 min at 37 degrees C. It was observed that a higher peptide sequence covering of 98% for myoglobin was obtained by MALDI-TOF/TOF analysis, compared to in-solution digestion. So the protein digestion inside SBA-15 was proved to be significantly faster and yielded a better sequence coverage. The new procedure allows for rapid protein enrichment and digestion inside SBA-15, and has great potential for protein analysis.

Planar tripods of platinum: formation and self-assembly

This communication describes a synthesis of planar tripods of platinum and their assembly into two-dimensional (2D) nano-structures using the Langmuir-Blodgett (LB) technique.

Pore size distribution analysis of selected hexagonal mesoporous silicas by grand canonical Monte Carlo simulations

We combine here a regularization procedure with individual adsorption isotherms obtained from grand canonical Monte Carlo simulations in order to obtain reliable pore size distributions. The methodology is applied to two hexagonal high-ordered silica materials: SBA-15 and PHTS, synthesized in our laboratory. Feasible pore size distributions are calculated through an adaptable procedure of deconvolution over the adsorption integral equation, with two necessary inputs: the experimental adsorption data and individual adsorption isotherms, assuming the validity of the independent pore model. The application of the deconvolution procedure implies an adequate grid size evaluation (i.e., numbers of pores and relative pressures to be considered for the inversion, or kernel size), the fulfillment of the discret Picard condition, and the appropriate choice of the regularization parameter (L-curve criteria). Assuming cylindrical geometry for both porous materials, the same set of individual adsorption isotherms generated from molecular simulations can be used to construct the kernel to obtain the PSD of SBA-15 and PHTS. The PSD robustness is measured imposing random errors over the experimental data. Excellent agreement is found between the calculated and the experimental global adsorption isotherms for both materials. Molecular simulations provide new insights into the studied systems, pointing out the need of high-resolution isotherms to describe the presence of complementary microporosity in these materials.

Surfactant Removal and Silica Condensation during the Photochemical Calcination of Thin Film Silica Mesophases

The evolution of photochemical surfactant removal and silica condensation from organically templated thin film silica nanocomposites with mesoscopic ordering has been probed using a combined application of Fourier transform infrared (FT-IR) spectroscopy and single wavelength ellipsometry. Thin films of silica nanocomposites were prepared by a previously reported evaporation-induced self-assembly process. Specifically, oxidized silicon and gold substrates were withdrawn at 25 mm/min from a subcritical micelle concentration solution containing an ethylene oxide surfactant as a structure-directing agent and tetraethyl orthosilicate as a silica precursor. Real-time grazing incidence difference FT-IR spectra of the nanocomposite films on gold taken during exposure to short-wavelength ultraviolet light (184-257 nm) show that surfactant removal and silica condensation occur gradually and concomitantly. Surfactant removal and silica reconstructions were found to be nearly complete after 90 min of exposure. Further, a transient feature was observed in the FT-IR spectra around 1713 cm(-1) during the UV exposure process and was assigned to a carbonyl (C=O) stretching mode absorption, reflecting the transient formation of a partially oxidized surfactant intermediate. From these data we propose a stepwise model for surfactant removal from the nanocomposite films. Ellipsometrically determined index of refraction values collected as a function of UV exposure are also shown to support such a stepwise mechanism of surfactant removal from the ordered nanocomposite silica thin film mesophases studied here.

Ordered surfactant-templated poly(3,4-ethylenedioxythiophene) (PEDOT) conducting polymer on microfabricated neural probes

Ordered conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) was electrochemically fabricated using a self-assembled medium of surfactant molecules as a template. The morphology and microstructure were extensively investigated by optical and electron microscopy, and results show that the coated films were composed of anisotropic domains having a characteristic size of 15-150 nm. The surfactant-templated ordered PEDOT films were electrochemically deposited on microfabricated neural probes with an electrode site area of 1,256 microm(2). The electrical properties were studied by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). EIS showed a lowered magnitude of 35 kOmega (from an initial approximately 800 kOmega) at the biologically relevant frequency of 1 kHz. CV results show that the film has higher charge capacity and is more electrochemically stable than either nodular PEDOT or PPy. Furthermore, we have begun to probe the biological response to such a material intended to define the tissue-material interface. Results show that minute concentrations of the non-ionic surfactant are enough to kill all nearby cells in culture. It is possible however, to create surfactant-templated ordered PEDOT such that SH-SY5Y survive on the conductive polymer.

Current Understanding of Formation Mechanisms in Surfactant-Templated Materials

Surfactant-templated materials are created through self-assembly in solutions containing both surfactant micelles and an inorganic species. The resulting materials are composites containing an organized surfactant micelle array encapsulated in the inorganic material. Removal of the surfactants generates nanoscale pores which replicate the highly organized micelle phase, producing high surface area materials with uniform pores that have applications in catalysis, molecular separation, encapsulation for sensors and slow release, and thin films for optoelectronics and photoelectrochemical devices. This review looks at recent work aimed at understanding how these materials self-assemble from dilute surfactant solutions to form intricate nanoscale configurations, which also often show complex and highly ordered structures on longer length scales.