Sensitivity enhancement for colorimetric glucose assays on whole blood by on-chip beam-guidance.
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.
Grumann
M
M
Lab for MEMS Applications, IMTEK-University of Freiburg, Georges-Koehler-Allee 106, 79110 Freiburg, Germany. grumann@imtek.de
Steigert
J
J
Riegger
L
L
Moser
I
I
Enderle
B
B
Riebeseel
K
K
Urban
G
G
Zengerle
R
R
Ducrée
J
J
D001774:Blood Chemical Analysis / Q000295:instrumentation* / Q000379:methods; D001786:Blood Glucose / Q000032:analysis*; D004867:Equipment Design; D006801:Humans; D008832:Microchemistry / Q000295:instrumentation* / Q000379:methods; D044085:Microfluidics / Q000295:instrumentation* / Q000379:methods; D012680:Sensitivity and Specificity
D001786:Blood Glucose