A New Era for Lab-on-a-Chip Technologies?

This article discusses the evolution and current applications of lab-on-a-chip technology in chromatography and explores the possibility of a new market for microfluidics in separation science.

Miniaturization has been one of the biggest trends in recent years in all areas of technology. In the analytical and the life sciences it has been a strong driver of academic and industrial developments under the headings "microfluidics", "lab-on-a-chip", or "microTAS" (miniaturized total analytical systems). Historically, the separation sciences have played a significant role in the early stages of the development of this field. A fundamental, but often overlooked work, was carried out by Stephen Terry in Stanford in the mid-1970s, when he integrated a complete gas chromatograph on a silicon wafer.¹ Later, the early works of the pioneering groups involved in lab-on-a-chip technologies - including work by Manz², Harrison², and Ramsey³ - focused on electrophoretic separations but efforts were also made to transfer chromatographic methods onto a microchip. The reasons for this choice can easily be found in the fundamental equations for diffusion and separation efficiency,⁴ indicating a superior performance of chip-based capillary electrophoretic (CE) systems especially with respect to analytical speed. It is therefore not surprising that the first commercial instruments based on lab-on-a-chip technologies were systems which used capillary electrophoretic separation in a microchannel for the analysis of biomolecules (DNA, RNA, proteins), including miniaturized CE instruments from Agilent,⁵ Shimadzu,⁶ and Bio-Rad.⁷

Photo Credit: Stephen Morris/Getty Images

The promise of all these systems was, besides the decrease in "time-to-result", a significant reduction in manual operating steps, a certain amount of process automation, and a better reproducibility of the results. Chip-based capillary electrophoresis is now established as the standard method for the analysis of biomolecules. For chromatographic separations however, the transfer to a chip-based method proved to be significantly more challenging for a variety of reasons. First of all, the maturity of high performance liquid chromatography (HPLC) and gas chromatography (GC) methods meant that the performance level with respect to the quality of separations was already very high and difficult to achieve with compact chip-based devices. Secondly, the overall analytical process in chromatography has not been perceived as being overly cumbersome (in comparison to casting gels in electrophoresis for example), therefore reducing the potential advantages of chip-based methods.

Thirdly, the integration of stationary phases into microchannels posed a significant challenge in the manufacturing process (and still does). And finally, the high pressures required made the interfacing of chips typically made out of silicon or glass problematic. Despite these problems, a fair amount of academic work on chip-based chromatographic methods has been performed.⁸ The coupling of LC with mass spectrometry (MS) has proven to be a particularly attractive area, pioneered in particular by the group of Karger,⁹ because silicon/glass microfabrication technologies allow a very precise and reproducible generation of sharp and narrow structures suitable to generate a stable Taylor-cone configuration for subsequent injection into a mass spectrometer. Furthermore, the integration of sample purification and other functionalities into a single device made for a reduction in size, which allows for a better integration into a coupled system.

On a commercial level, work performed by Killeen¹⁰ at Agilent used laser-ablation as a microfabrication technology to generate an integrated microfluidic chip as a front end for a mass spectrometer. This was developed into a commercial HPLC-Chip–MS system.

Waters Corp later developed a UHPLC nano device which uses a microfabricated ceramic substrate to perform HPLC prior to MS coupling.

In the field of GC, the developments were noticeably fewer. On the academic side, it was work by Yu at Lawrence Livermore Lab¹¹ as well as the group of Kostiainen at the University of Helsinki¹² that demonstrated feasibility for GC.

On the commercial side, the Dutch company C2V had developed a GC system based on a silicon microchip during the mid-2000s, which was launched in 2010 by Thermo Fisher, however this product was discontinued.

Despite these developments, it should be noted that the progress and uptake of miniaturization technologies in the chromatographic sciences has been slower than in other disciplines. In my opinion, this is the result of several factors: Firstly, it should be noted that the areas in which microfluidics makes the fastest commercial advances are areas in which complex protocols are commonplace. A typical example of such a field is molecular diagnostics, which is currently experiencing a dramatic increase in the number of integrated, microfluidics-based cartridge solutions. The driver here is that in the conventional workflow, a large number of protocol steps have to be performed, either manually or by complex laboratory robotics. Both approaches increase the time-to-result and increase the risk of errors as well as the need for a suitable infrastructure to perform these protocols. A further example can be found in biology, where complex cellular assays can be performed in an integrated microfluidics device without human interaction.

A second reason is the inherent structure of the analytical tasks addressed by the current analytical laboratories. While many technologies (HPLC, MS etc.) are high-performance methods requiring comparatively complex instrumentation, skilled personnel, and a laboratory infrastructure, the main thrust in the development of microfluidics-based devices is oriented towards a decentralized application at the point-of-interest or point-of-care. In these cases, the ultimate analytical performance might not be needed, or may not be achievable. However, there could be be a need (and a market) for moderately priced, fast "time-to-result" compact systems with limited analytical resolution that are easy to use by moderately skilled personnel to complement the current "high-end" market of analytical instrumentation.

Microfluidics-enabled systems might prove to be the technological answer to these challenges. In particular the ability to integrate complex workflows into a single device is very appealing.

Typical for microfluidics-based solutions, especially in life science or diagnostic applications, is the use of the microfluidic device as a disposable tool, which is in contrast to the model of reusable chips or on-chip columns used in the current commercial systems. The reason for this can be found in the cost structure, because it is cheaper to use a new device each time rather than to develop and apply a validated cleaning procedure.

Although challenging, a business model based on disposable consumables could also provide an alternative to the current situation, providing a revenue stream that is not so heavily dependent on instrumentation. This would certainly require a significant system and business model development but again could enable new approaches and markets.

In conclusion, the advances in technology and commercialization of microfluidics-enabled products do currently happen more readily in fields other than the separation sciences, despite the fact that much of the early ground-breaking work took place in this field.

Lab-on-a-chip technology could enable new markets in addition to the currently served analytical markets. The science, knowledge, and supplier infrastructure are all available, it only takes a bold move to open up new opportunities. Microfluidics is moving into the mainstream in many scientific and technological fields¹³ and it would be a shame if separation science misses out on this opportunity.

References

1. S.C. Terry, J.H Jermann, and J.B. Angell, IEEE Trans. Electron. DevicesED-26, 1880–1886 (1979).

2. D.J. Harrison, K. Fluri, K. Seiler, Z. Fan, C.S. Effenhauser, and A. Manz, Science261(5123), 895–897 (1993).

3. Stephen C. Jacobson, Roland Hergenroder, Lance B. Koutny, and J. Michael Ramsey, Anal. Chem.66(7), 1114–1118 (1994).

4. C.S. Effenhauser, in Microsystem Technology in Chemistry and Life Science A. Manz and H. Becker, Eds. (Topics in Current Chemistry Vol. 194, Springer-Verlag, Heidelberg, Germany, 1998), pp. 51–82.

5. A. Masotti and T. Preckel, Nature Methods August 2006 (http://www.nature.com/nmeth/journal/v3/n8/pdf/nmeth908.pdf)

6. H. Nagata, M. Tabuchi, K. Hirnao, and Y. Baba, Chromatography26(1), 23–28 (2005).

7. http://www.bio-rad.com/webroot/web/pdf/lsr/literature/Bulletin_5286.pdf

8. J.P. Kutter, Journal of Chromatography A1221, 72–82 (2012).

9. Iulia M. Lazar, Lijuan Li, Yu Yang, and Barry L Karger, Electrophoresis24(21), 3655–62 (2003).

10. H. Yin, K. Killeen, R. Brennen, D. Sobek, M. Werlich, and T. van de Goor, Anal Chem.77(2), 527–33 (2005).

11. C.M. Yu, Hand-held multiple system gas chromatograph, US Patent 6306200 B1, (2001).

12. M. Haapala, L. Luosujärvi, V. Saarela, T. Kotiaho, R.A. Ketola, S. Franssila, and R. Kostiainen, Anal Chem. 79(13), 4994–9 (2007).

13. H Becker, Lab on a Chip9(15), 2119–2122 (2009).

Holger Becker, PhD, FRSC, is co-founder and Chief Scientific Officer of microfluidic ChipShop GmbH. He obtained his PhD in physics from Heidelberg University, Heidelberg, Germany, in 1995 with a paper on surface acoustic wave chemical sensors. He then worked with Andreas Manz as a research associate at Imperial College, London, UK. He has held several positions in the microsystem industry before founding microfluidic ChipShop in 2002. His research interests lie in the application of micro- and nanotechnologies in chemistry and the life sciences.

E-mail: hb@microfluidic-chipshop.com

Website: www.microfluidic-chipshop.com

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