Felix von Stetten

... Prototyping is organized in rapid prototyping chains for polymer fabrication, sealing and assembly in a rapid prototyping workshop. ... of multiple fluidic components onto a single system with the ability of a well defined fabrication process to fabricate cost efficient devices. ...

ABSTRACT We present an infrared (IR) thermocycler with closed loop temperature control for performing fast polymerase chain reactions (PCR) in centrifugal microfluidics. It consists of an IR ring heater and an on-disk wireless temperature sensor module with a resolution of 0.1 K. The closed loop system enables to precisely control the temperature of the reagents even at varying conditions e.g. manufacturing tolerances of the polymer film disks, different locations of the cavities, ambient temperature changes. Due to the direct heating of the reagents by IR absorption we achieve fast average heating gradients of up to 4 K/s. Average cooling gradients so far are limited to 1.3 K/s. Our system is superior in terms of energy efficiency, temperature accuracy and overall reproducibility and robustness.

We present a new method for aliquoting liquids on the centrifugal microfluidic platform. Aliquoting is an essential unit operation to perform multiple parallel assays (“geometric multiplexing”) from one individual sample, such as genotyping by real-time polymerase chain reactions (PCR), or homogeneous immunoassay panels. Our method is a two-stage process with an initial metering phase and a subsequent transport phase initiated by switching a centrifugo-pneumatic valve. The method enables aliquoting liquids into completely separated reaction cavities. It includes precise metering that is independent on the volume of pre-stored reagents in the receiving cavities. It further excludes any cross-contamination between the receiving cavities. We characterized the performance for prototypes fabricated by three different technologies: micro-milling, thermoforming of foils, and injection molding. An initial volume of ~90 μl was split into 8 aliquots of 10 μl volume each plus a waste reservoir on a thermoformed foil disk resulting in a coefficient of variation (CV) of the metered volumes of 3.6%. A similar volume of ~105 μl was split into 16 aliquots of 6 μl volume each on micro-milled and injection-molded disks and the corresponding CVs were 2.8 and 2.2%, respectively. Thus, the compatibility of the novel aliquoting structure to the aforementioned prototyping and production technologies is demonstrated. Additionally, the important question of achievable volume precision of the aliquoting structure with respect to the production tolerances inherent to each of these production technologies is addressed experimentally and theoretically. The new method is amenable to low cost mass production, since it does not require any post-replication surface modifications like hydrophobic patches.

We present a novel microfluidic platform using laminar-flow magnetophoresis for combined continuous extraction and purification of DNA. All essential unit operations (DNA binding, sample washing and DNA elution) are integrated on one single chip. The key function is the motion of magnetic beads given by the interplay of laminar flow and time-varying magnetic field. The time for extraction was 1 minute. The device is a central part of a complete biochemical system for continuous monitoring of cell-growth in bioreactors. The novel platform allows continuous purification of DNA, but is also applicable to purification of RNA, proteins or cells, including their subsequent real-time analysis in general.

We present the operational concept, microfabrication, and electrical performance of an enzyme-less direct glucose fuel cell for harvesting the chemical energy of glucose from body fluids. The spatial concentrations of glucose and oxygen at the electrodes of the one-compartment setup are established by self-organization, governed by the balance of electro-chemical depletion and membrane diffusion. Compared to less stable enzymatic and immunogenic microbial fuel cells, this robust approach excels with an extended life time, the amenability to sterilization and biocompatibility, showing up a clear route towards an autonomous power supply for long-term medical implants without the need of surgical replacement and external refueling. Operating in physiological phosphate buffer solution containing 0.1 wt% glucose and having a geometrical cathode area of 10 cm2, our prototype already delivers 20 µ W peak power over a period of 7 days.

Abstract: We present an abiotically catalyzed glucose fuel cell and demonstrate its application as energy harvesting power source for a cardiac pacemaker. This is enabled by an optimized DC-DC converter operating at 40% conversion efficiency, which surpasses commercial ...

This paper describes a method for the quantitative detection of biochemical binding events onto microstructured and functional surfaces on a truly single molecular level. The classic Streptavidinbiotin system is used to provide the last detection step and the binding is visualized via gold-nanoparticles in a SEM. We showed that this allows a spatial resolution down to the nanometer scale. It also allowed us to proof the spot size dependence of binding kinetics according to the theorem of Ekins in one single experiment. The method allows to analyze any binding event on a planar surface and is enabling to measure surface densities of functional groups like the amount of BSA molecules on a blocked glass surface.

In this paper, we propose the development of microfluidic disposables that can be processed with standard laboratory instruments. The use of prevalent processing devices could significantly reduce existing market entry barriers for lab-on-a-chip solutions and support the market uptake of microfluidic products. We demonstrate the concept with the following applications: •microfluidic chips for DNA-purification operated on a standard laboratory centrifuge

Self-containing, ready-to-use cartridges are essential for mobile Lab-on-a-Chip (LoaC) systems intended for Point-of-Care (POC) use. Up to now, a common weak point in many LoaC developments is the need to dispense liquid reagents into the test cartridge before or during processing of the assay. To address this issue we have developed an efficient method for fusing liquid reagents into glass ampoules, which are then sealed into a centrifugally operated cartridge. For on-demand reagent release, the ampoules are disrupted through the flexible lid of the cartridge. Upon centrifugation, 98.7 microL out of 100 microL (CV = 2.5%) of the pre-stored contents are released into the microfluidic system. No liquid loss is observed for ethanol and H(2)O stored for 300 days at room temperature. Frozen storage is possible without damage to the ampoules. Applicability of this concept is demonstrated by performing a LoaC integrated DNA extraction after 140 days of reagent pre-storage. DNA yield from 32 microL of whole blood was up to 199 ng, which is 77% of an off-chip reference extraction. The presented approach allows the improvement of existing LoaC cartridges where pre-storage of liquid reagents was not implemented yet.

We demonstrate controlled transport of superparamagnetic beads in the opposite direction of a laminar flow. A permanent magnet assembles 200 nm magnetic particles into about 200 μm long bead chains that are aligned in parallel to the magnetic field lines. Due to a magnetic field gradient, the bead chains are attracted towards the wall of a microfluidic channel. A rotation of the permanent magnet results in a rotation of the bead chains in the opposite direction to the magnet. Due to friction on the surface, the bead chains roll along the channel wall, even in counter-flow direction, up to at a maximum counter-flow velocity of 8 mm s−1. Based on this approach, magnetic beads can be accurately manoeuvred within microfluidic channels. This counter-flow motion can be efficiently be used in Lab-on-a-Chip systems, e.g. for implementing washing steps in DNA purification.

Enzymes are powerful catalysts for biosensor and biofuel cell electrodes due to their unique substrate specificity. This specificity is defined by the amino acid chain's complex three-dimensional structure based on non-covalent forces, being also responsible for the very limited enzyme lifetime of days to weeks. Many electrochemical applications, however, would benefit from lifetimes over months to years. This mini-review provides a critical overview of strategies and ideas dealing with the problem of short enzyme lifetime, which limits the overall lifetime of bioelectrochemical electrodes. The most common approaches aim to stabilize the enzyme itself. Various immobilization techniques have been used to reduce flexibility of the amino acid chain by introducing covalent or non-covalent binding forces to external molecules. The enzyme can also be stabilized using genetic engineering methods to increase the binding forces within the protein or by optimizing the environment in order to reduce destabilizing interactions. In contrast, renewing the inactivated catalyst decouples overall system lifetime from the limited enzyme lifetime and thereby promises theoretically unlimited electrode lifetimes. Active catalyst can be supplied by exchanging the electrolyte repeatedly. Alternatively, integrated microorganisms can display the enzymes on their surface or secrete them to the electrolyte, allowing unattended power supply for long-term applications.

Two microfluidic cartridges intended for upgrading standard laboratory instruments with automated liquid handling capability by use of centrifugal forces are presented. The first microfluidic cartridge enables purification of DNA from human whole blood and is operated in a standard laboratory centrifuge. The second microfluidic catridge enables genotyping of pathogens by geometrically multiplexed real-time PCR. It is operated in a slightly modified off-the-shelf thermal cycler. Both solutions aim at smart and cost-efficient ways to automate work flows in laboratories. The DNA purification cartridge automates all liquid handling steps starting from a lysed blood sample to PCR ready DNA. The cartridge contains two manually crushable glass ampoules with liquid reagents. The DNA yield extracted from a 32 μl blood sample is 192 +/- 30 ng which corresponds to 53 +/- 8% of a reference extraction. The genotyping cartridge is applied to analyse isolates of the multi-resistant Staphyloccus aureus (MRSA) by real-time PCR. The wells contain pre-stored dry reagents such as primers and probes. Evaluation of the system with 44 genotyping assays showed a 100% specificity and agreement with the reference assays in standard tubes. The lower limit of detection was well below 10 copies of DNA per reaction.