Susanna Aura

Non-Reflecting Silicon and Polymer Surfaces by Plasma Etching and Replication

Constantly increasing demand of renewable and nonpolluting energy production methods has made solar cells one of today’s hottest research areas. Developing more cost-effective fabrication methods that enable production of extremely non-refl ecting surfaces is one of the key issues in solar cell research. [ 1 , 2 ] Many other applications, such as miniaturized chemical analysis systems, would also benefi t greatly from low-cost surfaces with low and uniform refl ectivity. [ 3 ] Typically, suppression of Fresnel refl ection has been achieved by antirefl ective coatings, but they suppress refl ection effi ciently only in a narrow wavelength range. Suppression of refl ection over a broad spectral range can be achieved by using nanotextured surfaces that form a graded transition of the refractive index from air to the substrate. [ 1 , 2 , 4–12 ]

Rapid and sensitive drug metabolism studies by SU-8 microchip capillary electrophoresis-electrospray ionization mass spectrometry

Monolithically integrated, polymer (SU-8) microchips comprising an electrophoretic separation unit, a sheath flow interface, and an electrospray ionization (ESI) emitter were developed to improve the speed and throughput of metabolism research. Validation of the microchip method was performed using bufuralol 1-hydroxylation via CYP450 enzymes as the model reaction. The metabolite, 1-hydroxybufuralol, was easily separated from the substrate (R(s)=0.5) with very good detection sensitivity (LOD=9.3nM), linearity (range: 50-500nM, r(2)=0.9997), and repeatability (RSD(Area)=10.3%, RSD(Migrationtime)=2.5% at 80nM concentration without internal standard). The kinetic parameters of bufuralol 1-hydroxylation determined by the microchip capillary electrophoresis (CE)-ESI/mass spectrometry (MS) method, were comparable to the values presented in literature as well as to the values determined by in-house liquid chromatography (LC)-UV. In addition to enzyme kinetics, metabolic profiling was demonstrated using authentic urine samples from healthy volunteers after intake of either tramadol or paracetamol. As a result, six metabolites of tramadol and four metabolites of paracetamol, including both phase I oxidation products and phase II conjugation products, were detected and separated from each other within 30-35s. Before analysis, the urine samples were pre-treated with on-chip, on-line liquid-phase microextraction (LPME) and the results were compared to those obtained from urine samples pre-treated with conventional C18 solid-phase extraction (SPE, off-chip cartridges). On the basis of our results, the SU-8 CE-ESI/MS microchips incorporating on-chip sample pre-treatment, injection, separation, and ESI/MS detection were proven as efficient and versatile tools for drug metabolism research.

Capillary-driven self-assembly of microchips on oleophilic/oleophobic patterned surface using adhesive droplet in ambient air

This letter describes a capillary-driven self-assembly technique using oleophilic/oleophobic patterned surface and adhesive in ambient air environment. We use a topographical microstructure of porous ormocer functionalized with a fluorinated trichlorosilane for the oleophobic area and gold patterns for the oleophilic area. The resulted oleophilic/oleophobic patterns show significant wettability contrast for adhesive (Delo 18507), with a contact angle of 119° on oleophobic part and 53° on the oleophilic part. Self-alignment of SU-8 microchips on the oleophilic/oleophobic patterns has been demonstrated. The results provide a promising solution for self-alignment of microparts using commercial adhesives in ambient air environment.

Microchip capillary electrophoresis-electrospray ionization-mass spectrometry of intact proteins using uncoated Ormocomp microchips.

We present rapid (<5 min) and efficient intact protein analysis by mass spectrometry (MS) using fully microfabricated and monolithically integrated capillary electrophoresis-electrospray ionization (CE-ESI) microchips. The microchips are fabricated fully of commercial inorganic-organic hybrid material, Ormocomp, by UV-embossing and adhesive Ormocomp-Ormocomp bonding (CE microchannels). A sheath-flow ESI interface is monolithically integrated with the UV-embossed separation channels by cutting a rectangular emitter tip in the end with a dicing saw. As a result, electrospray was produced from the corner of chip with good reproducibility between parallel tips (stability within 3.8-9.2% RSD). Thanks to its inherent biocompatibility and stable (negative) surface charge, Ormocomp microchips enable efficient intact protein analysis with up to ∼10(4) theoretical separation plates per meter without any chemical or physical surface modification before analysis. The same microchip setup is also feasible for rapid peptide sequencing and mass fingerprinting and shows excellent migration time repeatability from run to run for both peptides (5.6-5.9% RSD, n=4) and intact proteins (1.3-7.5% RSD, n=3). Thus, the Ormocomp microchips provide a versatile new tool for MS-based proteomics. Particularly, the feasibility of the Ormocomp chips for rapid analysis of intact proteins with such a simple setup is a valuable increment to the current technology.

Surface assisted laser desorption/ionization on two-layered amorphous silicon coated hybrid nanostructures

Matrix-free laser desorption/ionization was studied on two-layered sample plates consisting of a substrate and a thin film coating. The effect of the substrate material was studied by depositing thin films of amorphous silicon on top of silicon, silica, polymeric photoresist SU-8, and an inorganic-organic hybrid. Des-arg9-bradykinin signal intensity was used to evaluate the sample plates. Silica and hybrid substrates were found to give superior signals compared with silicon and SU-8 because of thermal insulation and compatibility with amorphous silicon deposition process. The effect of surface topography was studied by growing amorphous silicon on hybrid micro- and nanostructures, as well as planar hybrid. Compared with planar sample plates, micro- and nanostructures gave weaker and stronger signals, respectively. Different coating materials were tested by growing different thin film coatings on the same substrate. Good signals were obtained from titania and amorphous silicon coated sample plates, but not from alumina coated, silicon nitride coated, or uncoated sample plates. Overall, the strongest signals were obtained from oxygen plasma treated and amorphous silicon coated inorganic-organic hybrid, which was tested for peptide-, protein-, and drug molecule analysis. Peptides and drugs were analyzed with little interference at low masses, subfemtomole detection levels were achieved for des-arg9-bradykinin, and the sample plates were also suitable for ionization of small proteins.

Hybrid Ceramic Polymers: New, Nonbiofouling, and Optically Transparent Materials for Microfluidics

A new, commercial hybrid ceramic polymer, Ormocomp, was introduced to the fabrication of microfluidic separation chips using two independent techniques, UV lithography and UV embossing. Both fabrication methods provided Ormocomp chips with stable cathodic electroosmotic flow which enabled examination of the Ormocomp biocompatibility by means of microchip capillary electrophoresis (MCE) and (intrinsic) fluorescence detection. The hydrophobic/hydrophilic properties of Ormocomp were examined by screening its interactions with bovine serum albumin and selected amino acids of varying hydrophobicity. The results show that the ceramic, organic-inorganic polymer structure natively resists biofouling on microchannel walls even so that the Ormocomp microchips can be used in intact protein analysis without prior surface modification. With theoretical separation plates approaching 10(4) m(-1) for intact proteins and 10(6) m(-1) for amino acids and peptides, our results suggest that Ormocomp microchips hold record-breaking performance as microfluidic separation platforms. In addition, Ormocomp was shown to be suitable for optical fluorescence detection even at near-UV range (ex 355 nm) with detection limits at a nanomolar level ( approximately 200 nM) for selected inherently fluorescent pharmaceuticals.

Cell adhesion and osteogenic differentiation on three-dimensional pillar surfaces

We hypothesized that when compared with conventional two-dimensional (2D) cultures, substrates containing 3D micropillars would allow cells to grow at levels, activating their cytoskeleton to promote osteogenesis. Fibroblasts, osteoblast-like cells, and mesenchymal stem cells (MSCs) were studied. Planar substrates were compared with 200-nm-, 5-μm-, and 20-μm-high pillars of Ormocomp®, Si, diamond-like carbon, or TiO(2). Scanning electron microscopy and staining of actin cytoskeleton showed 7.5-h adhesion to pillar edges and 5-day stretching between adhesion contacts > 100-μm distances of fibroblast and MSC in 3D networks, whereas SaOS-2 cells adhered flatly and individually on horizontal and vertical surfaces. ERK and ROCK immunostaining at 14 and 21 days confirmed activation of the cytoskeleton. In contrast to expectations, success to induce osteogenesis was dominated by the cytocompatibility of the substrate over the 3D structure. This was shown using early alkaline phosphatase, intermediate osteopontin, and late mineralization markers, together with bone nodule formation, which were seen in planar substrates and low-profile TiO(2) pillars, but were poor in the 20-μm landscape. The lack of intercellular contacts seems to halt the osteogenesis-promoting effects of cytoskeletal organization and tension described earlier.

Porous inorganic–organic hybrid material by oxygen plasma treatment

In this paper, we present the pore formation on inorganic–organic hybrid material, ORMOCER©, by reactive ion etching. ORMOCERs are composed of inorganic backbone where organic side groups are attached by cross-linking. Etching of ORMOCER in oxygen plasma generates porous materials with different pore sizes depending on the etching parameters. In addition to planar films, this pore formation process is applicable to micro and nanostructures. Characteristics of porous materials are evaluated by contact angle measurement, scanning electron microscopy, Fourier transform infrared-attenuated total reflectance spectroscopy, time-of-flight elastic recoil detection analysis and Rutherford backscattering spectrometry. Based on these analyses, it can be concluded that carbon is depleted in the plasma process and oxygen plasma converts the surface of the hybrid film to a more SiO2-like material. Area selective pore formation is also possible by using a metallic etch mask. The porous material is stable enough to allow further processing, e.g. sputtering, plasma-enhanced chemical vapor deposition and atomic layer thin film deposition. This method may thus be used in different applications in fluidics, optics and elsewhere in micro and nanotechnology.

Pore formation in inorganic-organic hybrid material by oxygen plasma treatment

In this work, the use of inorganic-organic hybrid material, ORMOCER (registered trademark of Microresist Technology), is studied. Pores are formed by oxygen plasma which makes the pore formation on pre-patterned surfaces possible. Patterning of porous and non-porous areas on a same substrate can be done by using shadow mask or a deposited thin film as a mask.

Novel Hybrid Material Formicrofluidic Devices

We demonstrate fabrication of microchannels from hybrid material ORMOCER with both conventional UV-lithography and UV-embossing. Enclosed microchannels are produced by ORMOCER- ORMOCER bonding as well as with PDMS cover. A lithographically defined ORMOCER/PDMS capillary electrophoresis (CE) device is fabricated and the electro-osmotic mobility is measured with different buffer conditions. Peptide separation in CE channel is also demonstrated.