Integration of segmented microflow chemistry and online HPLC/MS analysis on a microfluidic chip system enabling enantioselective analyses at the nanoliter scale.

In this work, we introduce an approach to merge droplet microfluidics with an HPLC/MS functionality on a single chip to analyze the contents of individual droplets. This is achieved by a mechanical rotor-stator interface that precisely positions a microstructured PEEK rotor on a microfluidic chip in a pressure-tight manner. The developed full-body fused silica chip, manufactured by selective laser-induced etching, contained a segmented microflow compartment followed by a packed HPLC channel, which were interconnected by the microfluidic PEEK rotor on the fused silica lid with hair-thin through-holes. This enabled the targeted and leakage-free transfer of 10 nL fractions of droplets as small as 25 nL from the segmented microflow channel into the HPLC compartment that operated at pressures of up to 60 bar. In a proof of concept study, this approach was successfully applied to monitor reactions at the nanoliter scale and to distinguish the formed enantiomers.

Method to simulate and analyse induced stresses for laser crystal packaging technologies.

A method to simulate induced stresses for a laser crystal packaging technique and the consequent study of birefringent effects inside the laser cavities has been developed. The method has been implemented by thermo-mechanical simulations implemented with ANSYS 17.0. ANSYS results were later imported in VirtualLab Fusion software where input/output beams in terms of wavelengths and polarization were analysed. The study has been built in the context of a low-stress soldering technique implemented for glass or crystal optics packaging's called the solderjet bumping technique. The outcome of the analysis showed almost no difference between the input and output laser beams for the laser cavity constructed with an yttrium aluminum garnet active laser crystal, a second harmonic generator beta-barium borate, and the output laser mirror made of fused silica assembled by the low-stress solderjet bumping technique.

Optical performance simulation of free-form optics for an eye implant based on a measurement data enhanced model.

This paper describes the application of a modeling approach for precise optical performance prediction of free-form optics-based subsystems on a demonstration model of an eye implant. The simulation model is enhanced by surface data measured on the free-form lens parts. The manufacturing of the free-form lens parts is realized by two different manufacturing processes: ultraprecision diamond machining and microinjection molding. Evaluation of both processes is conducted by a simulation of the optical performance on the basis of their surface measurement comparisons with the nominal geometry. The simulation results indicate that improvements from the process optimization of microinjection molding were obtained for the best manufacturing accuracy.

Real-time adaptive optics testbed to investigate point-ahead angle in pre-compensation of Earth-to-GEO optical communication.

We explore adaptive optics (AO) pre-compensation for optical communication between Earth and geostationary (GEO) satellites in a laboratory experiment. Thus, we built a rapid control prototyping breadboard with an adjustable point-ahead angle where downlink and uplink can operate both at 1064 nm and 1550 nm wavelength. With our real-time system, beam wander resulting from artificial turbulence was reduced such that the beam hits the satellite at least 66% of the time as compared to merely 3% without correction. A seven-fold increase of the average Strehl ratio to (28 ± 15)% at 18 µrad point-ahead angle leads to a considerable reduction of the calculated fading probability. These results make AO pre-compensation a viable technique to enhance Earth-to-GEO optical communication.

Phase topography-based characterization of thermal effects on materials and joining techniques.

There are growing demands to characterize the stability of assemblies of optical components for ultrahigh-precision instruments. In this paper we demonstrate how absolute length measurements by interferometry can be applied to measure the thermal and dimensional stability of connections. In order to enable investigation of common joining techniques, including wringing, screwing, and gluing, as well as specialized, inorganic joining techniques such as silicatic bonding, thin-film soldering, and solderjet bumping, representative connections were fabricated. By using gage blocks or prismatic bodies as joining parts, parallelism and flatness were provided which are needed for precision interferometric length measurements. The stability of connection elements used in ultrahigh-precision instruments was investigated longitudinally and laterally to the connection interface, and also mutual tilting of the parts was detected by analysis of the phase topographies. The measurements have an accuracy level of about 1 nm, and the traditional wringing method was also considered as a reference joining technique. The long-term behavior was studied within a period of about 1 year under constant temperature. Further, the thermal dilatation and the reaction of connections to thermal stress were measured. Results show that screwed connections do not exhibit a significant drift of length or orientation. They also did not show response to temperature variations of ±10°C. This is different for adhesive connections, where dimensional changes of up to 100 nm were observed. The specimens produced by using thin-film soldering as well as silicatic bonding revealed stability of length better than 5 nm per year and angular stability within ±0.1 arcsec. Furthermore, these specimens were shown to be insensitive to a temporary temperature variation in a range from 10°C to 40°C. This situation is slightly different for the sample connections produced by solderjet bumping, which show a positive length change of ∼25 nm and a tilt of ∼1 arcsec. These observations can be explained by creeping of the relatively large solder bumps that bridge a gap of about 100 µm between the connected mirror plates. The thermal expansion of the connections shows a strong correlation with the "layer thickness."

An integrated microfluidic chip enabling control and spatially resolved monitoring of temperature in micro flow reactors.

A strength of microfluidic chip laboratories is the rapid heat transfer that, in principle, enables a very homogeneous temperature distribution in chemical processes. In order to exploit this potential, we present an integrated chip system where the temperature is precisely controlled and monitored at the microfluidic channel level. This is realized by integration of a luminescent temperature sensor layer into the fluidic structure together with inkjet-printed micro heating elements. This allows steering of the temperature at the microchannel level and monitoring of the reaction progress simultaneously. A fabrication procedure is presented that allows for straightforward integration of thin polymer layers with optical sensing functionality in microchannels of glass-polydimethylsiloxane (PDMS) chips of only 150 µm width and 29 µm height. Sensor layers consisting of polyacrylonitrile and a temperature-sensitive ruthenium tris-phenanthroline probe with film thicknesses of about 0.5 to 6 µm were generated by combining blade coating and abrasion techniques. Optimal coating procedures were developed and evaluated. The chip-integrated sensor layers were calibrated and investigated with respect to stability, reproducibility, and response times. These microchips allowed observation of temperature in a wide range with a signal change of around 1.6 % per K and a maximum resolution of around 0.07 K. The device is employed to study temperature-controlled continuous micro flow reactions. This is demonstrated exemplarily for the tryptic cleavage of coumarin-modified peptides via fluorescence detection.

Rapid isoelectric point determination in a miniaturized preparative separation using jet-dispensed optical pH sensors and micro free-flow electrophoresis.

Herein, the fabrication, characterization, calibration, and application of integrated microfluidic platforms for fast isoelectric point (pI) determinations via free-flow electrophoresis with integrated inkjet-printed fluorescent pH sensor microstructures are presented. These devices allow one to determine the pI of a biomolecule from a sample mixture with moderately good precision and without addition of markers in typically less than 10 s total separation and analysis time. Polyhydroxyethyl methacrylate (pHEMA) hydrogels were covalently coupled with fluorescein and hydroxypyrene trisulfonic acid (HPTS)-based pH probes. These were piezoelectrically jet-dispensed onto acrylate-modified glass as pH sensor microarrays with a diameter of 300-600 µm and thicknesses of 0.4-2.4 µm with high spatial accuracy. Microchip fabrication and integration of these pH sensor arrays was realized by multistep liquid-phase photolithography from oligoethylene glycol precursors resulting in glass-based microfluidic free-flow isoelectric focusing (µFFIEF) chips with integrated pH observation capabilities. The microchips were characterized with regard to pH sensitivity, response times, photo-, and flow stability. Depending on the sensor matrix, they allowed IEF within a pH range of roughly 5.5-10.5 with good sensitivity and fast response times. These microchips were used for FFIEF of small molecule markers and several protein mixtures with simultaneous monitoring of local pH. This allowed the determination of their pI via multispectral imaging of protein and pH sensor fluorescence without addition of external markers. Obtained pI's were generally in good agreement with known data, demonstrating the applicability of the method for pI determination in micropreparative procedures within a time frame of a few seconds only.

Fabrication of microinjection-molded miniature freeform Alvarez lenses.

Microinjection molding is a mass production method to fabricate affordable optical components. However, the intense nature of this process often results in part deformation and uneven refractive index distribution. These two factors limit the precision of replicated optics. In order to understand the influences of injection molding on freeform optical devices, in this study, finite element method (FEM) was employed to investigate the miniature microinjection-molded Alvarez lenses. In addition, an innovative metrology setup was proposed to evaluate the optical wavefront patterns in the molded lenses using an interferometer-based wavefront measurement system. This measurement setup utilized an optical matching liquid to reduce or eliminate the lenses' surface power such that the wavefront pattern with large deviation from the freeform lenses can be measured by a regular wavefront setup. The FEM simulation results were also used to explain the differences between the nominal and experimentally measured wavefront patterns of the microinjection-molded Alvarez lenses. In summary, the proposed method combining simulation and wavefront measurements is shown to be an effective approach for studying injection molding of freeform optics.