Functional Membrane-Implanted Lab-on-a-Chip for Analysis of Percent HDL Cholesterol

A functional lab-on-a-chip has been developed for simultaneous quantitative analyses of highdensity lipoprotein (HDL) cholesterol (HDL-C) and total cholesterol (total-C) in a submicroliter plasma sample. The analytical device was fabricated by placing commercial membranes, traditionally used for rapid diagnostics, within microfluidic channels engraved on the surface of a plastic chip. The concentration of HDL-C was measured using enzymatic reactions to produce a colorimetric signal after separation of the single plasma lipoprotein from a mixture. Two small pieces of different membrane pads were used to provide each group of reagents, for HDL separation and enzyme reactions, deposited within their tiny pores in a dry state. To maintain a connection toward the capillary action of the medium, the pads were arranged in a sequence within the fluidic channel that controlled the inlet and outlet of the flow. Upon the addition of a sample, the fluid was delivered through the pads of the chip and a color signal was subsequently generated in proportion to the concentration of HDL-C. The level of total-C was concurrently determined by following identical processes, except absent HDL separation. The two signals were simultaneously determined by employing optical detectors based on transmittance of a light. Such total analyses were completed within 2 min, and the sample sizes were able to be reduced to 0.4 L for HDL-C and 0.1 L for total-C, enough to cover the clinically required dynamic ranges.