Miniaturized continous glucose sensing system using microdialysis in adipose tissue
Byeong-Ui Moon 1,2, Ben H.C. Westerink1, Elisabeth Verpoorte 2
1 Biomonitoring and Sensoring
2 Pharmaceutical Analysis
Department of Pharmacy
University of Groningen
The long-term goal of this project is to realize an autonomous, portable sensing system for continuous in vivo glucose monitoring , based on microfluidics technology coupled to microdiaysis sampling. Detection of glucose in microdialysate is based on the reaction in solution of glucose oxidase (GOD) with glucose to produce H2O2.
A c ontinuous in vivo glucose monitoring system should provide clinically relevant information in real time over longer periods (days) for better control of glucose levels  . To date, systems have commonly relied on electrochemical detection (ECD), with GOD immobilized directly onto the electrode to minimize enzyme consumption and facilitate detection of the H 2 O 2 produced. However, immobilization of enzyme layers which are robust enough to perform over many days continues to be difficult. Enzyme activity diminishes over time, and sensing layers are prone to fouling. Additionally, monitoring systems are still bulky and uncomfortable to wear. We have adopted an alternative microfluidic approach, in which nL amounts of sample and enzyme are rapidly reacted in a microreactor comprising a channel for chaotic mixing, as first presented by Stroock et al. . Integrated Pt electrodes (uncoated) detect the H 2 O 2 produced. The use of microfluidics has several advantages, including fast response times (fast reactions), flowrates which are compatible with microdialysis sampling, economic use of enzyme and possibilities for overall system miniaturization. ECD instrumentation can also be made small and portable.
An alternative approach using optical detection is also being investigated. The H2O2 produced by the reaction of glucose and GOD reacts with luminol to produce light in the form of chemiluminescence (CL).
The microchannels were replicated in poly(dimethylsiloxane) (PDMS), and sealed with a glass wafer. A thick photoresist (PR 4562) mold was made on a silicon wafer using two steps of standard photolithography to make a chaotic mixing channel with an array of grooves . For ECD, a thin-film Pt electrode was positioned at the end of the fluidic channel as an on-chip detector. For CL, a PDMS channel and a commercially available silicon photodiode were reversibly bonded to each other .
Results and Discussion
Measurement of amperometric response as a function of glucose concentration in channels with no grooves or slanted grooves yielded linear calibration curves for concentrations up to 10 mM glucose.
The CL sensing system has two flow-through microreactors, the first one for the reaction of GOD and glucose, and the second for the reaction of H2O2 and luminol. The length of the first reactor was 21 mm, while the length and volume of the second reactor were 16 cm and 1.2 µL, respectively.
The ECD system can also be used for other applications/analytes by simply introducing other enzymes (e.g. glutamate oxidase). The CL system will be further developed by optimizing the reaction conditions e.g. the pH and concentrations of luminol and catalyst.
FOR MORE INFORMATION
See the PDF files of contributions to the following conferences:
PDF file: 2009 Microsystems in Medicine and Biology Abstract Continuous Glucose Monitoring Moon
Moon, B.-U., Schoonen, A.J.M., Westerink, B.H.C., Verpoorte, E., Development of microreactors for continuous glucose monitoring, The 5th International Conference on Microtechnologies in Medicine and Biology (MMB 2009), Quebec City, Canada, April 1-3, 2009 (poster).
PDF file: µTAS2008_Proceedings_Abstract_Enzymatic_Microreactor
Moon, B.-U., Schoonen, A.J.M., Westerink, B.H.C., Verpoorte, E., An enzymatic microreactor for continuous glucose monitoring, The 12th International Conference on Miniaturized Systems for Chemistry and Life Sciences (µTAS 2008 Conference), San Diego, California, October 12-16, 2008 (poster).
D.C. Klonoff, “Perspectives Continuous Glucose Monitoring: Roadmap for 21st Century Diabetes Therapy”, Diabetes Care, vol. 28, pp. 1231-1239, 2005.
A.D. Stroock, S.K.W. Dertinger, A. Ajdari, I. Mezic, H.A. Stone, and G.M. Whitesides, “Chaotic Mixer for Microchannels”, Science, vol. 295, pp. 647-651, 2002.
B.-U Moon, A.J.M. Schoonen, B.H.C. Westerink, E.M.J. Verpoorte, “An Enzymatic Microreactor for Continuous Glucose Monitoring”, Proceedings of µ TAS 2008 , San Diego, October 12-16, 2008, pp. 1093-1095.
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