Sensitivity enhancement for colorimetric glucose assays on whole blood by on-chip beam-guidance
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In this paper, we present a novel concept for optical beam-guidance to significantly enhance the sensitivity of colorimetric assays by extending the optical path length through the detection cell which linearly impacts the resulting attenuation of a probe beam according to the law of Beer-Lambert. In our setup, the incident probe beam is deflected by 90∘ into the chip plane at monolithically integrated V-grooves to pass a flat detection cell at its full width (i.e., with a path length of 10 mm) instead of its usually much smaller height. Afterwards, the attenuated beam is redirected by another V-groove towards an external detector. The general beam-guidance concept is demonstrated by a glucose assay on human whole blood on a centrifugal microfluidic “lab-on-a-disk” platform made of COC. We achieve an excellent linearity with a correlation coefficient (R 2) of 0.997 paired with a lower limit of detection (200 μM) and a good reproducibility with a coefficient of variation (CV) of 4.0% over nearly three orders of magnitude. With an accelerated sedimentation of cellular constituents by centrifugal forces, the sample of whole blood can be analyzed in a fully integrated fashion within 210 s. This time-to-result can even be improved by the numerical extrapolation of the saturation value. Additionally, the direct assay on whole blood also shows a negligible correlation with the hematocrit of the blood sample.
KeywordsGlucose Optical beam-guidance Lab-on-a-disk Colorimetric assay Total internal reflection
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- ABTS (2,2′-Azino-bis(3-ethylbenzthiazoline-6-sulfonic acid), c ABTS = 2 mM, V ABTS = 66.7 μl, Sigma-Aldrich GmbH, Germany, http://www.sigmaaldrich.com, accessed 2005e.
- Accu-Chek, Roche Diagnostics, Switzerland, http://www.roche.com, accessed 2004.
- Cyclic olefin copolymer (Topas®, http://www.ticona.com), accessed 2004.
- J. Ducrée and R. Zengerle, FlowMap–Microfluidics roadmap for the life sciences (Books on Demand GmbH: Norderstedt, Germany, ISBN 3-8334-0744-1, 2004), http://www.microfluidics-roadmap.com, accessed 2004.
- G. Ekstrand, C. Holmquist, A. Örleforn, B. Hellmann, A. Larsson, and P. Andersson, (Proceedings of the μTAS 2000 conference, edited by A. van den Berg, and P. Bergveld, Kluwer Academic Publisher, Dordrecht, NL, 2000), pp. 311–314.Google Scholar
- Examples in clinical diagnostics: Careside Analyzer®, Careside Inc, USA, www.careside.com; Biosite® Biosite Inc., France, www.biosite.com; Pelikan SunTM of Pelikan Technologies Inc., USA, www.pelikantechnologies.com; Chempaq Analyzer, Chempaq A/S, Denmark, www.chempaq.com; i-STAT Portable Clinical Analyzer, i-STAT Corp., USA, http://www.istat.com, (all URLs accessed 2004).
- Fiber Collimation Package F220SMA-A, NA = 0.25, D = 5 mm, http://www.thorlabs.com
- GOD (glucose oxidase), cGOD = 40 units/ml, VGOD = 1.3 μl, Biozyme Laboratories, UK, http://www.biozyme.com, accessed 2005.
- M. Grumann, M. Dube, T. Brefka, J. Steigert, L. Riegger, T. Brenner, K. Mittmann, R. Zengerle, and J. Ducrée, (Proc. Transducers 05 –The 13th conference on Solid State Sensors, Actuators and Microsystems, Seoul, Korea, June 2005c), pp. 1106–1109.Google Scholar
- M. Grumann, I. Moser, J. Steigert, L. Riegger, A. Geipel, C. Kohn, G. Urban, R. Zengerle, and J. Ducrée. Piscataway, NJ: Proc. MEMS 2005, IEEE, USA, (2005a), pp. 108–111.Google Scholar
- M. Grumann, L. Riegger, A. Geipel, R. Zengerle, and J. Ducrée, Vorrichtung und Verfahren zur Umlenkung eines Lichtstrahls, Patent application January 21, 2005b, Document number DE 10 2005 002 348.Google Scholar
- M. Grumann, L. Riegger, T. Nann, J. Riegler, O. Ehlert, K. Mittenbühler, G. Urban, L. Pastewka, T. Brenner, R. Zengerle, and J. Ducrée, Proc. Transducers 05 –The 13 th Conference on Solid State Sensors (Actuators and Microsystems, Seoul, Korea, June 2005d), pp. 1114–1117.Google Scholar
- Horse serum with an initial glucose concentration c 0 of 4.0 mM. Spiking of the sample was achieved by adding glucose, dilution by adding PBS-buffer.Google Scholar
- HRP (horseradish peroxidase), c HRP = 4 units/ml, V HRP = 1.3 μl, Sigma-Aldrich GmbH, Germany http://www.sigmaaldrich.com, accessed 2005.
- S. Lai, S. Wang, J. Luo, L. Lee, S. Yang, and M. Madou Anal. Chem. 76, 1832–1837 (2004).Google Scholar
- Laserdiode LDM650/1LJ, fixfocus, λpeak = 650 nm, 1 mW, Roithner Lasertechnik, Austria, http://www.roithner-laser.com, accessed 2004.
- Z. Liang, N. Chiem, G. Ocvirk, T. Tang, K. Fluri, and D. Harrison Anal. Chem. 68, 1040–1046 (1996).Google Scholar
- M. Madou and G. Kellogg. (Proceedings of SPIE, vol. 3259, 1998, 80–93, 1998).Google Scholar
- M. Madou, Y. Lu, S. Lai, J. Lee, and S. Daunert, (Proceedings of the μTAS 2000 conference, edited by A. van den Berg, P. Bergveld, P. Kluwer Academic Publisher, Dordrecht, NL, 2000), pp. 565–570.Google Scholar
- M. McNeely, M. Spute, N. Tusneem, and A. Oliphjant, (Proc. SPIE –Microfluidic Devices and Systems II, 1999, edited by C. Ahn, and A. Frazier, A. (B.1.2, B.6), 3877, 1999), pp. 210–220.Google Scholar
- R. Oosterbroek and A. van den Berg, Lab-on-a-Chip: Miniaturized systems for (bio)chemical analysis and synthesis (Elsevier Science, Amsterdam, NL, 2003).Google Scholar
- Phosphate buffered saline –PBS (0.1 M phosphate, 0.1 M NaCl, pH = 7.4).Google Scholar
- B. Splawn, F. Lytle, and Anal. Bioanal. Chem. 373, 519–525 (2002).Google Scholar
- Z. Tang, J. Lee, R. Louie, G. Kost, Archives of Pathology and Laboratory Medicine 124, 1135–1140 (2000).Google Scholar
- UV/VIS Microspectrometer, Boehringer Ingelheim MicroParts AG, Germany, http://www.microparts.de, accessed 2004.
- D. Walt, Science 287 (5452), 451–452 (2000).Google Scholar
- J. Zeng, D. Banerjee, M. Deshpande, J. Gilbert, D. Duffy, and G. Kellogg, (Proc. μTAS 2000 conference, Kluwer Academic Publisher, Dordrecht, NL, 2000), pp. 579–582.Google Scholar