Roland Zengerle

A BIDIRECTIONAL SILICON MICROPUMP

Abstract In this paper we present a bidirectional silicon micropump. It consists of an electrostatically actuated diaphragm and two passive check valves. It differs from other well-known diaphragm pumps, generally referred to as unidirectional pumps, in the layout of the valves. We have designed a flap valve with a first mechanical resonance frequency between 1 and 2 kHz (in the fluid environment). At low actuation frequencies (0.1–800 Hz), the pump works in the forward mode. At higher frequencies (2–6 kHz) the pump operates in the reverse direction. This is due to a phase shift between the response of the valves and the pressure difference that drives the fluid. Investigating different pump layouts, we achieve maximum pump rates of 250 and 850 μl min -1 in the forward direction as well as 400 and 200 μl min -1 in the reverse direction. The maximum back pressure is 31 000 Pa (3.1 m H 2 O) in the forward and 7000 Pa (0.7 m H 2 O) in the reverse direction.

A micro membrane pump with electrostatic actuation

A bulk micromachined membrane pump with outer dimensions of 7 mm*7 mm*2 mm and electrostatic actuation is presented. The micropump consists of four silicon chips, which form two passive check valves, a pump membrane and a counterelectrode for electrostatic actuation. Direct electrostatic forces are used for the deflection of the pump membrane, which has an area of 4 mm*4 mm and a thickness of 25 mu m. The liquid to be pumped is not subjected to any electrical field. The separation between the movable membrane and the electrically isolated stator is 4 mu m.<<ETX>>

Batch-mode mixing on centrifugal microfluidic platforms

We present two novel fluidic concepts to drastically accelerate the process of mixing in batch-mode (stopped-flow) on centrifugal microfluidic platforms. The core of our simple and robust setup exhibits a microstructured disk with a round mixing chamber rotating on a macroscopic drive unit. In the first approach, magnetic beads which are prefilled into the mixing chamber are periodically deflected by a set of permanent magnets equidistantly aligned at spatially fixed positions in the lab-frame. Their radial positions alternatingly deviate by a slight positive and negative offset from the mean orbit of the chamber to periodically deflect the beads inbound and outbound during rotation. Advection is induced by the relative motion of the beads with respect to the liquid which results from the magnetic and centrifugal forces, as well as inertia. In a second approach--without magnetic beads--the disk is spun upon periodic changes in the sense of rotation. This way, inertia effects induce stirring of the liquids. As a result, both strategies accelerate mixing from about 7 minutes for mere diffusion to less than five seconds. Combining both effects, an ultimate mixing time of less than one second could be achieved.

Centrifugal extraction of plasma from whole blood on a rotating disk

We present a centrifugal process for the extraction of plasma from sediment by a decanting structure, terminating with metered plasma which is readily available for subsequent on-disk processing. Our technique supplies 2 microl plasma from 5 microl of whole blood at moderate spinning frequencies of 40 Hz within 20 s, only. The residual cell concentration in the purified plasma amounts to less than 0.11%, independent of the frequency of rotation. A capillary duct connects the extracted plasma to subsequent on-disk processing units.

Cellphone-based devices for bioanalytical sciences

AbstractDuring the last decade, there has been a rapidly growing trend toward the use of cellphone-based devices (CBDs) in bioanalytical sciences. For example, they have been used for digital microscopy, cytometry, read-out of immunoassays and lateral flow tests, electrochemical and surface plasmon resonance based bio-sensing, colorimetric detection and healthcare monitoring, among others. Cellphone can be considered as one of the most prospective devices for the development of next-generation point-of-care (POC) diagnostics platforms, enabling mobile healthcare delivery and personalized medicine. With more than 6.5 billion cellphone subscribers worldwide and approximately 1.6 billion new devices being sold each year, cellphone technology is also creating new business and research opportunities. Many cellphone-based devices, such as those targeted for diabetic management, weight management, monitoring of blood pressure and pulse rate, have already become commercially-available in recent years. In addition to such monitoring platforms, several other CBDs are also being introduced, targeting e.g., microscopic imaging and sensing applications for medical diagnostics using novel computational algorithms and components already embedded on cellphones. This report aims to review these recent developments in CBDs for bioanalytical sciences along with some of the challenges involved and the future opportunities. FigureThe universal Rapid Diagnostic Test (RDT) reader developed at UCLA. It can read various lateral flow assays for point-of-care and telemedicine applications

Rapid prototyping of microfluidic chips in COC

We present a novel, cost-efficient process chain for fast tooling and small-lot replication of high-quality, multi-scale microfluidic polymer chips within less than 5 days. The fabrication chain starts with a primary master which is made by well-established cleanroom processes such as DRIE or negative SU-8 resist based surface micromachining. The formation of undercuts in the master which would complicate demolding is carefully avoided. Secondary PDMS masters or epoxy-based masters which are more suitable for common polymer replication schemes such as soft-embossing, hot-embossing or injection molding are subsequently cast from the primary masters. The polymer replica are mainly made of COC and show excellent fidelity with the conventionally micromachined master while displaying no degeneration, even after more than 200 cycles. The use of other polymers such as PMMA is also possible. The process chain further includes surface modification techniques for overall, long-term stable hydrophilic coatings and for local hydrophobic patches as well as a durable sealing based on thermal bonding.

Versatile sample environments and automation for biological solution X-ray scattering experiments at the P12 beamline (PETRA III, DESY)

An integrated environment for biological small-angle X-ray scattering (BioSAXS) at the high-brilliance P12 synchrotron beamline of the EMBL (DESY, Hamburg) allows for a broad range of solution scattering experiments. Automated hardware and software systems have been designed to ensure that data collection and processing are efficient, streamlined and user friendly.

A smartphone-based colorimetric reader for bioanalytical applications using the screen-based bottom illumination provided by gadgets.

A smartphone-based colorimetric reader (SBCR) was developed using a Samsung Galaxy SIII mini, a gadget (iPAD mini, iPAD4 or iPhone 5s), integrated with a custom-made dark hood and base holder assembly. The smartphone equipped with a back camera (5 megapixels resolution) was used for colorimetric imaging via the hood and base-holder assembly. A 96- or 24-well microtiter plate (MTP) was positioned on the gadgets screensaver that provides white light-based bottom illumination only in the specific regions corresponding to the bottom of MTPs wells. The pixel intensity of the captured images was determined by an image processing algorithm. The developed SBCR was evaluated and compared with a commercial MTP reader (MTPR) for three model assays: our recently developed human C-reactive protein sandwich enzyme-linked immunosorbent assay (ELISA), horseradish peroxidase direct ELISA, and bicinchoninic acid protein estimation assay. SBCR had the same precision, dynamic range, detection limit and sensitivity as MTPR for all three assays. With advanced microfabrication and data processing, SBCR will become more compact, lighter, inexpensive and enriched with more features. Therefore, SBCR with a remarkable computing power could be an ideal point-of-care (POC) colorimetric detection device for the next-generation of cost-effective POC diagnostics, immunoassays and diversified bioanalytical applications.

Fully integrated whole blood testing by real-time absorption measurement on a centrifugal platform

We present a novel microfluidic concept to enable a fast colorimetric alcohol assay from a single droplet of whole blood. The reduced turn-around time of 150 seconds is, on the one hand, achieved by a full process integration including metering, mixing with reagents, and sedimentation of cellular constituents. On the other hand, our novel total internal reflection (TIR) scheme allows to monitor the increase of the absorbance values in real-time. Thus, the saturation values can be predicted accurately based on an extrapolation of real-time measurements acquired during a 100 second initial period of rotation. Additionally, we present a metering structure to define nanolitre sample volumes at a coefficient of variation (CV) below 5%.

Frequency-dependent transversal flow control in centrifugal microfluidics.

This work presents a novel flow switch for centrifugal microfluidic platforms which is solely controlled by the Coriolis pseudo force. This Coriolis switch consists of an inverse Y-structure with one common upstream channel and two symmetric outlets on a rotating disk. Above a certain threshold frequency, the Coriolis force becomes dominant that the entire flow is diverted into one of the outlets which is selected by the direction of rotation. The threshold frequency has been measured to be 350 rad s(-1)(approximately 55.7 Hz) for a channel width of 360 microm and a depth of 125 microm. The results are supported by extensive CFD simulations.