Nanotechnology in medicine : first application of micromosaic immunoassays to human samples

Background: Point-of-care (POC) testing is the idea to measure rapidly
biomarkers near patients. Nanotechnology offers a spectrum of new techniques
that promise to revolutionize medicine. So-called passive microfluidic
networks i.e. miniaturized channels that guide minute amounts of liquids
across a surface are especially promising for a new generation of
immunoassays, as they allow testing of a large number of analytes in a
minimum of time with a minimum amount of reagents. The applicability of
such devices to clinically important disease markers in human plasma samples
has not yet been investigated.
Aim: To investigate the feasibility, sensitivity, reproducibility of the
micromosaic immunoassay (μMIA) to detect biomarkers in spiked human
plasma samples.
Method: We use passive microfluidic networks with 8 channels on a Si wafer
to perform simultaneously up to 64 miniaturized solid phase immunoassays in
a combinatorial fashion (i.e. one μMIA). These assays are distributed on a 180
× 180 μm2 area and are analyzed by fluorescence microscopy.
Results: We optimized the surface chemistry of the wafer, the capture and
detection antibody concentrations, and the analyte incubation time. A μMIA
can be performed within ~8 min. The sample volume required for multiple
analyte detection is only ~2 μL. The detection limit for the cardiac marker C -
reactive protein in human plasma is 0.03 μg mL-1. The intra-assay variance is
4.4%. The quality of the assay pattern was analyzed. We also detected
simultaneously five different cardiac markers in human plasma with one
μMIA.
Conclusions: This is the first experimental demonstration of the feasibility to
detect proteins in human plasma with μMIAs. The reported sensitivity,
reaction time, and intra-assay variance are better or equal to clinical laboratory
testing. The results demonstrate the feasibility of μMIAs to measure
biomarkers in human plasma samples and indicate the potential of μMIAs for
laboratory and POC testing.