Morphology of single picosecond pulse subsurface laser-induced modifications of sapphire and subsequent selective etching.

The effect of 1030nm single picosecond pulsed laser-induced modification of the bulk of crystalline sapphire using a combined process of laser amorphization and selective wet chemical etching is studied. Pulse durations of more than 1 picosecond are not commonly used for this subsurface process. We examine the effect of 7 picosecond pulses on the morphology of the unetched, as well as etched, single pulse modifications, showing the variation of shape and size when varying the pulse energy and the depth of processing. In addition, a qualitative analysis of the material transformation after irradiation is provided as well as an analysis of cracking phenomena. Finally, a calculated laser intensity profile inside sapphire, using the Point Spread Function (PSF), is compared to the shape of the modifications. This comparison is employed to calculate the intensity threshold leading to amorphization, which equals 2.5⋅1014 ± 0.4⋅1014 W/cm2.

Fluorescent cyanine dyes for the quantification of low amounts of dsDNA.

In this research six cyanine fluorophores for the quantification of dsDNA in the pg-ng range, without amplification, are compared under exactly identical conditions: EvaGreen, SYBR Green, PicoGreen, AccuClear, AccuBlue NextGen and YOYO-1. The fluorescence intensity as a function of the amount of dsDNA is measured at the optimal wavelengths for excitation and emission and for each dye the limit of detection and the response linearity at low levels of dsDNA are determined. No linear range was found for SYBR Green and YOYO-1 for pg-ng quantities of dsDNA. EvaGreen, PicoGreen, AccuClear and AccuBlue NextGen show good linearity in the pg-ng range. AccuClear exhibits the widest linear range of 3 pg-200 ng, whereas AccuBlue NextGen turned out to have the highest sensitivity of the tested dyes with a limit of detection of 50 pg.

Bacterial viability on chemically modified silicon nanowire arrays.

The global threat of antimicrobial resistance is driving an urgent need for novel antimicrobial strategies. Functional surfaces are essential to prevent spreading of infection and reduce surface contamination. In this study we have fabricated and characterized multiscale-functional nanotopographies with three levels of functionalization: (1) nanostructure topography in the form of silicon nanowires, (2) covalent chemical modification with (3-aminopropyl)triethoxysilane, and (3) incorporation of chlorhexidine digluconate. Cell viability assays were carried out on two model microorganisms E. coli and S. aureus over these nanotopographic surfaces. Using SEM we have identified two growth modes producing distinctive multicellular structures, i.e. in plane growth for E. coli and out of plane growth for S. aureus. We have also shown that these chemically modified SiNWs arrays are effective in reducing the number of planktonic and surface-attached microorganisms.

Characterization of porous silicon integrated in liquid chromatography chips.

Properties of porous silicon which are relevant for use of the material as a stationary phase in liquid chromatography chips, like porosity, pore size and specific surface area, were determined with high-resolution SEM and N(2) adsorption-desorption isotherms. For the anodization conditions investigated, porosity is between 20 and 60%, pore sizes between 2 and 5 nm and specific surface area between 130 and 410 m(2)/cm(3). It was established that under identical anodization conditions, porous layer formation is 10-15% slower on micromachined pillars than on flat substrates, and depends on geometrical parameters like pillar diameter and height and interpillar spacing. In microchannels containing pillars with a porous silicon shell, chromatographic experiments on a coumarin dye mixture were performed, which in comparison with non-porous pillars showed a significant increase of the retention factors, resulting from the large internal surface of the porous pillars. The increased relative retention of one of the coumarin dyes, C480, could be correlated quantitatively with the measured internal surface of the porous layer. Due to the small pore size, these porous shell columns are particularly suitable for analytical or preparative separation of low-molecular weight molecules, with applications in metabolomics, food quality control, or medical diagnostics.

Substantial rate enhancements of the esterification reaction of phthalic anhydride with methanol at high pressure and using supercritical CO2 as a co-solvent in a glass microreactor.

The esterification reaction of phthalic anhydride with methanol was performed at different temperatures in a continuous flow glass microreactor at pressures up to 110 bar and using supercritical CO(2) as a co-solvent. The design is such that supercritical CO(2) can be generated inside the microreactor. Substantial rate enhancements were obtained, viz. a 53-fold increase was obtained at 110 bar and 60 degrees C. Supercritical CO(2) as a co-solvent gave rise to a 5400-fold increase (both with respect to batch experiments at 1 bar at the same temperature).

Fabrication and characterization of high-temperature microreactors with thin film heater and sensor patterns in silicon nitride tubes.

In this paper the fabrication and electrical characterization of a silicon microreactor for high-temperature catalytic gas phase reactions, like Rh-catalyzed catalytic partial oxidation of methane into synthesis gas, is presented. The microreactor, realized with micromachining technologies, contains silicon nitride tubes that are suspended in a flow channel. These tubes contain metal thin films that heat the gas mixture in the channel and sense its temperature. The metal patterns are defined by using the channel geometry as a shadow mask. Furthermore, a new method to obtain Pt thin films with good adhesive properties, also at elevated temperatures, without adhesion metal is implemented in the fabrication process. Based on different experiments, it is concluded that the electrical behaviour at high temperatures of Pt thin films without adhesion layer is better than that of Pt/Ta films. Furthermore, it is found that the temperature coefficient of resistance (TCR) and the resistivity of the thin films are stable for up to tens of hours when the temperature-range during operation of the microreactor is below the so-called "burn-in" temperature. Experiments showed that the presented suspended-tube microreactors with heaters and temperature sensors of Pt thin films can be operated safely and in a stable way at temperatures up to 700 degrees C for over 20 h. This type of microreactor solves the electrical breakdown problem that was previously reported by us in flat-membrane microreactors that were operated at temperatures above 600 degrees C.

A light detection cell to be used in a micro analysis system for ammonia.

This paper describes the design, realization and characterization of a micromachined light detection cell. This light detection cell is designed to meet the specifications needed for a micro total analysis system in which ammonia is converted to indophenol blue. The concentration of indophenol blue is measured in a light detection cell. The light detection cell was created using KOH/IPA etching of silicon. The KOH/IPA etchant was a 31 wt.% potassium hydroxide (KOH) solution with 250 ml isopropyl alcohol (IPA) per 1000 ml H(2)O added to it. The temperature of the solution was 50 degrees C. Etching with KOH/IPA results in 45 degrees sidewalls ({110} planes) which can be used for the in- and outcoupling of the light. The internal volume of the realized light detection cell is smaller than 1 mul, enabling measurements on samples in the order of only 1 mul. Measurements were performed on indophenol blue samples in the range of 0.02 to 50 muM. In this range the measurements showed good reproducibility.