Sensitivity enhancement for colorimetric glucose assays on whole blood by on-chip beam-guidance

University of Freiburg, Freiburg, Baden-Württemberg, Germany
Biomedical Microdevices (Impact Factor: 2.88). 10/2006; 8(3):209-14. DOI: 10.1007/s10544-006-8172-x
Source: PubMed


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( composite function) 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 microM) 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.

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    • "Some of these use passive working principles [3–5], others apply dielectrophoresis [6,7], acoustic standing waves [8–11], segmented flow [12–14], or magnetophoresis [15,16]. Applying centrifugal force is one of the most powerful candidates for the passive steady-non pulsatile-flow in microfluidic systems [17] for continuous fully automated processing such as cell arrangement [18], DNA concentration [19], biomolecular separation [20], and also a compact disc (CD) microfluidic chip based enzyme-linked immunosorbent assay (ELISA) [21], whole blood glucose analysis [22], and hybridization assay for phenylketonuria (PKU) screening [23]. Especially, extraction of plasma from whole blood exploiting microfluidic pathways with centrifugal pumping [24] and cell trapping exploiting reagent-impregnated agarose-made micro holes with centrifugal liquid pumping [25] were examined for practical applications. "
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    • "In performing glucose concentration detection, the most commonly used biorecognition element is immobilized glucose oxidase (Ivnitski et al. 2008; Ammam and Fransaer 2009). Glucose detection is generally performed using either electrochemical methods (Garcia and Henry 2004) or optical absorbance methods (Grumann et al. 2006). Suzuki and Kumagai (2003) developed a disposable glucose sensor in which the glucose concentration was visualized directly in a manner similar to that of a mercury-or alcohol-loaded thermometer. "
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