The centrifugo-pneumatic Lab-on-a-Disk (LoaD) platform: towards robust flow control for larger-scale functional integration

This work shows for the first time how unavoidable tolerances in manufacturing and experimental input parameters have a decisive influence on the reliability of flow control in Lab-on-a-Disk (LoaD) platforms and must therefore be considered towards larger scale fluidic integration (LSI)

Microfluidics: an enabling technology for the life sciences

During the last year we have investigated existing and future markets, products and technologies for microfluidics in the life sciences. Within this paper we present some of the findings and discuss a major trend identified within this project: the development of microfluidic platforms for flexible design of application specific integrated microfluidic systems. We discuss two platforms in detail which are currently under development in our lab: microfluidics on a rotating CD ("Lab-CD") as well as a platform to realized customized "nanoliter & picoliter dispensing systems"

A centrifugo-magnetically actuated gas micropump

This paper describes a novel gas micropump on a centrifugal microfluidic platform. The pump is integrated on a passive and microstructured polymer disk which is sealed with an elastomer lid featuring paramagnetic inlays. The rotational motion of this hybrid disk over a stationary magnet induces a designated sequence of volume displacements of the elastic lid, leading to a net transport of gas. The pumping pressure scales linearly with the frequency, with a maximum observable pressure of 4.1 kPa. The first application of this rotary device is the production of gas-liquid flows by pumping ambient air into a continuous centrifugal flow of liquid. The injected gas volume segments the liquid stream into a series of liquid compartments. Apart from such multi-phase flows, the new pumping technique supplements a generic air-to-liquid sampling method to centrifugal microfluidic platforms

A simple opto-fluidic switch detecting liquid filling in polymer-based microfluidic systems

A novel detection scheme for detection of liquid levels and bubbles in microfluidic systems, using the principle of total internal reflection (TIR) is presented. A laser beam impinges on the side walls of a channel which are inclined at 45deg. In an unfilled channel of such a "V-groove", TIR deflects the beam by 90deg into a simple light detector. Upon the presence of liquid, the refractive index in the channel changes, thus eliminating deflection by TIR. The detection principle is robust, requiring no calibration, and tolerating alignment errors of the laser larger than the width and depth of the microfluidic channels. The machining of the V-groves can seamlessly be integrated into common polymer microfabrication schemes such as injection molding

Droplet mixer based on siphon-induced flow discretization and phase shifting

We present a novel mixing principle for centrifugal microfluidic platforms. Siphon structures are designed to disrupt continuous flows in a controlled manner into a sequence of discrete droplets, displaying individual volumes as low as 60 nL. When discrete volumes of different liquids are alternately issued into a common reservoir, a striation pattern of alternating liquid layers is obtained. In this manner diffusion distances are drastically decreased and a fast and homogeneous mixing is achieved. Efficient mixing is demonstrated for a range of liquid combinations of varying fluid properties such as aqueous inks or saline solutions and human plasma. Volumes of 5 muL have been mixed in less than 20 s to a high mixing quality. One-step dilutions of plasma in a standard phosphate buffer solution up to 1:5 are also demonstrated

Concentration of white blood cells from whole blood by dual centrifugo-pneumatic siphoning with density gradient medium

Due to the pervasiveness of HIV infections in developing countries there exists a need for a low-cost, user-friendly point-of-care device which can be used to monitor the concentration of T-lymphocytes in the patient’s blood expressing the CD4+ epitope. As a first step towards developing a microfluidic “lab-on-a-disc” platform with this aim we present the concentration of white blood cells from whole blood using a density medium in conjunction with centrifugo-pneumatic siphon valves [1]. Two such valves are actuated simultaneously, removing the bulk of plasma through the upper valve and the bulk of WBCs through the lower valve while leaving the vast majority of red blood cells in the centrifugal chamber

Hybrid integrated platform of PDMS microfluidics and silica capillary for effective CE and ESI-MS coupling

We present an effective hybrid integration of PDMS microfluidic devices and fused silica capillaries. These hybrid microfluidic integrated PDMS and silica capillary (iPSC) modules exhibit a novel architecture and method for leakage free CE sample injection requiring only a single high voltage source. Use of the iPSC devices is based on a modular approach which allows the capillary to be reused over 1,000 times whilst replacing the fluidics below it for different experiments. Integrating fused silica capillaries with PDMS microfluidics allows the direct application of a wide variety of well established conventional CE protocols for complex analyte separations and ESI-MS coupling, allowing users to focus on the sample analysis rather than the development of new separation protocols. The iPSC fabrication method is simple (3 steps) and quick (7 min)

Alginate micro-bead fabrication on a centrifugal microfluidics platform

We present a novel method for the direct, centrifugally induced fabrication of small alginate beads displaying adjustable diameters between 180 mum and 800 mum by polymer-tube micronozzles. The size distribution features a CV of 7 - 16 % for the main peak. Up to 600 beads per second and channel are issued from the micronozzle through an air gap towards a standard lab tube ("Eppi") attached to the rotor spinning and containing a curing agent. At spinning frequencies between 5 Hz and 28 Hz, the tubes align horizontally under rotation and return to a vertical position as soon as the rotor is at rest. The hardened beads are collected within the tube for further processing or characterization. This method is considered as a low cost technology for micro encapsulation technologies

Robust lumped-element modelling of centrifugo-pneumatic and siphon valving towards highly predictive simulation of large-scale integrated microfluidic networks

Drastic parameter reduction by lumped-element modelling by descriptors for flow control elements such as hydrodynamic resistance (“resistor”) pressure head (“voltage”) and flexible parts (“capacitance”) is the method of choice for simulating complex centrifugal microfluidic networks. As all liquid on such “Lab-on-a-Disc” (LoaD) systems are subject rotationally induced field, valving techniques are absolutely essential to orchestrate the serial release and processing of on-board samples and reagent

TIR-based dynamic liquid-level and flow-rate sensing and its application on centrifugal microfluidic platforms

For the first time we present a technique for the spatio-temporally resolved localization of liquid-gas interfaces on centrifugal microfluidic platforms based on total internal reflection (TIR) at the channel wall. The simple setup consists of a line laser and a linear image sensor array mounted in a stationary instrument. Apart from identifying the presence of (usually unwanted) gas bubbles, the here described online meniscus detection allows to measure liquid volumes with a high precision of 1.9%. Additionally, flow rates and viscosities (range: 1-10.7 mPa s) can be sensed even during rotation at frequencies up to 30 Hz with a precision of 4.7% and 4.3%, respectively