unique approach to integrate, automate, parallelize and miniaturize assay formats, ... Keywords: microfluidic platforms, lab-on-a-chip, biomedical diagnostics, ...
Procedia Chemistry Procedia Chemistry 1 (2009) 517–520 www.elsevier.com/locate/procedia
Proceedings of the Eurosensors XXIII conference
Next-generation microfluidic lab-on-a-chip platforms for point-of-care diagnostics and systems biology Jens Ducrée Biomedical Diagnostics Institute, National Centre for Sensor Research, Dublin City University, Glasnevin, Dublin 9, Ireland
Abstract
Lab-on-a-chip technologies have pervaded various fields of the life sciences including nucleic acid testing, immunoassays and cell screening. It has by now been clearly recognized that microfluidic liquid handling offers a unique approach to integrate, automate, parallelize and miniaturize assay formats, thus making it possible to port them from the lab bench to point of care settings. In systems biology, the interaction of cells with micromachined, scale-matched features also offers a new access to the cellular world. This presentation will survey a set of novel microfluidic lab-on-a-chip platforms in the fields of point-of-care diagnostics and systems biology. Important design parameters are low-complexity instrumentation and the amenability of the usually disposable cartridge for high volume polymer microfabrication. Keywords: microfluidic platforms, lab-on-a-chip, biomedical diagnostics, systems biology
Introduction
Microfluidic lab-on-a-chip technologies have emerged over the past decades from a scientific craze to commercially viable solutions and research platforms for biomedical diagnostics and various fields in the life sciences. This invited contribution highlights some novel lab-on-a-chip platforms which have recently been developed at the Biomedical Diagnostics Institute in Dublin, Ireland. The design guidelines were robust liquid handling and amenability to cost-efficient manufacturing as well as high-level system integration, automation and parallelization, thus allowing to perform complex assays in a user friendly fashion. The platforms covered are a “lab-in-a-trench platform using gravity based capturing and convection-diffusion based exchange of reagents, new functionalities such as centrifugo-capillary sample enrichment, sacrificial valving to implement nucleic acid amplification, and total internal reflection (TIR) based optical quality control on a centrifugal “lab-on-a-disk” platforms, as well as a novel systems biology scheme.
1876-6196/09/$– See front matter © 2009 Published by Elsevier B.V. doi:10: 1016/j . proche. 2009. 07. 129
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Lab-in-a-Trench We developped a conceptually very simple microfluidic structure which is based on gravity driven particle sedimentation and propulsion of flow [1]. The structure is composed of a geometric depression of rectangular cross section extending in the direction of the gravity field and oriented transversal to the direction of flow (Fig. 1). In a first step, particles such as cells or beads suspended in the liquid sediment into the trench possessing an aspect ratio adapted to the chosen flow conditions. Now a sequence of other liquids can be provided to the permanently retained particles, e.g. culture medium, wash or lysis buffers, biochemical reagents such as PCR master mix and detection labels. By diffusive mixing, the particles are successively exposed to these liquids. As a pilot application, we implemented a NASBA based nucleic acid test, but also bead based immunoassays can be implemented with the same scheme.
flow
diffusion Fig. 1: Lab-in-a-trench structure with flow velocity distribution [1]. Centrifugal Microfluidic “Lab-on-a-Disk” Platform We expanded the capabilities of established centrifugal microfluidic platforms with several functions. The first is a sample enrichment element based on the centrifugo-capillary recirculation of flow (Fig. 2) [2]. A larger volume of liquid is introduced through the radially inward inlet into a flat hydrophilic chamber segment. Upon rotation, the centrifugal force drives the liquid into an outer reservoir containing a hydrophobized vent to discharge the displaced air. Once the disc is halted, capillary action drives a plug of liquid back towards the axis of rotation. As the centrifugal action very efficiently dries and thus regenerates the hydrophilic character of the surface, the process can be frequently repeated to flow the entire liquid past a capture element in the shallow chamber, which, for instance, features immobilized antibodies.
Immobilized antibodies
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Fig. 2: Centrifugo-capillary recirculation of flow for particle or cell enrichment [2]. Left: Protocol, right: top view also displaying capture zone for enrichment. Also a somatic cell and fat screening structure based on a funnel has been designed for first tier screening of bovine mastitis based on somatic cell count and fat content. The centrifugal microfluidic structure portrayed in Fig. 3 implements sample enrichment, cell lysis, NASBA-based DNA amplification with real-time fluorescent detection [3]. It is based on enrichment of bacteria by centrifugally induced sedimentation in the outer part of the chamber. After this sedimentation, the sacrificial wax valve is opened to remove the excess liquid through the meandering microchannel. Lysis buffer, NASBA mix and an oil film are subsequently added to induce nucleic acid amplification.
Fig. 3: Structure performing an integrated NASBA assay on a centrifugal microfluidic platform [3]. One important issue in lab-on-a-chip systems is quality control. We developed a simple means to check channel filling levels and the presence of (usually unwanted) gas bubbles by means of total internal reflection (TIR) in Fig. 4 [4]. This can even be done “online”, i.e. under rotation, The setup features a liquid carrying and an auxiliary air channel featuring a segment with triangular cross section. Similar to a pickup head in optical disk drives, a line laser and a linear detector investigate the system from the upper side. In empty, i.e. gas filled channels, the geometry is chosen to allow TIR on both channels, i.e. a beam emitted from the laser is deflected at the first auxiliary channel into the plane of the substrate and at the second channel back toward the detector. In liquid filled segments, the beam is not returned to the detector. Hence, only those parts of the line detector corresponding to channel segments which are not filled with liquid will record the laser signal. The intensity distribution of the linear detector therefore maps the liquid-gas distribution in the channel and can therefore detect filling levels and gas bubbles.
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Fig. 4: Setup for TIR-based online detection of liquid levels and gas bubbles [4]. Systems Biology Platform We developped a systems biology platform incorporating functions such as cell capture, culturing, treatment with drugs, optical inspection, lysis and electrophoresis. Figure 5 illustrates a chip where suspended cells are captured by mechanical barriers in a meandering channel [5]. Small gaps between the top of the barriers and the lid ensure favorable flow lines and liquid supply. After culturing and treatment of the cells, a lysis buffer carries the lysate in a sequential, segment-wise fashion into the central electrophoresis capillary for analysis. Two novel methods are presented to establish stable CE conditions in polymeric or elastomeric microfluidic chips. The first relies on the integration of a glass capillary into a PDMS chip [6], the second on the plasma enhanced vapor-phase deposition (PECVD) of a glassy surface in already sealed PDMS or polymeric channels [7]. Out-flow
Out-flow
In-flow
2 μm gap Flow lines
Fig. 5: Capturing of cells by mechanical barriers in a meandering channel [5]. Acknowledgements This work was supported by Science Foundation Ireland under Grant No. 05/CE3/B754. References [1] Ivan K. Dimov and Luke P. Lee. Integrated NASBA array for drug screening and expression profiling. In Proceedings of μTAS 2008, October 12-16, San Diego, USA, pages 640-642. [2] J. L. Garcia-Cordero, L. Basabe-Desmonts, J. Ducrée, and A. J. Ricco. Liquid recirculation in microfluidic channels by the interplay of capillary and centrifugal forces. In Proceedings of Transducers 2009, June 21-25, Denver, Colorado, USA, 2009. status: accepted. [3] José L. García-Cordero, Ivan K. Dimov, Jens Ducrée, Justin O'Grady, Thomas Barry, and Antonio J. Ricco. Monolithic centrifugal microfluidic platform for bacteria capture and concentration, lysis, nucleic-acid amplification, and real-time detection. In Proceedings of MEMS 2009, January 26-29, Sorrento, Italy, p. 356-359. [4] J. Hoffmann, L. Riegger, D. Mark, F. von Stetten, R. Zengerle, and J. Ducrée. TIR-based dynamic liquid-level and flow-rate sensing and its application on centrifugal microfluidic platforms. In Proceedings of MEMS 2009, January 26-29, Sorrento, Italy, pages 539-542. [5] Asif Riaz, Ivan Dimov, Lorcan Kent, Claus R. Poulsen, Antonio J. Ricco, and Luke P. Lee. Integrated microfluidic systems biology platform: Cell culture, drug treatment, lysis, separation and detection. In Laurie E. Locascio, editor, Proceedings μTAS 2008, October 12-16, San Diego, USA, pages 1193-1195. [6] Ivan K. Dimov, Asif Riaz, Jens Ducrée, and Luke P. Lee. Microfluidic reusable plug and play capillary electrophoresis module. In Proceedings of the 15th International Conference on Solid-State Sensors, Actuators & Microsystems (Transducers'09), June 21-25, Denver, Colorado, USA. pages 1281-1284. [7] Asif Riaz, Ram P. Gandhiraman, Ivan K. Dimov, Lourdes B. Desmonts, Antonio J. Ricco, Jens Ducrée, Stephen Daniels, and Luke P. Lee. Thin film barrier formation in PDMS microcavities. In Proceedings Transducers 2009, June 21-25, Denver, Colorado, USA. pages 1051-1054.
