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In this study, we report a convenient analytical method for a full-range quantification of the C-reactive protein (CRP), a blood biomarker of infection and cardiovascular events. We determine CRP over the entire diagnostically relevant concentration range in undiluted human blood serum in a single test, using a tandem giant magnetoresistance (GMR) sensor. The tandem principle combines a sandwich assay and a competitive assay, which allows for the discrimination of the concentration values resulting from the multivalued dose-response curve ("Hook" effect), which characterizes the one-step sandwich assay at high CRP concentrations. The sensor covers a linear detection range for CRP concentration from 3 ng/mL to 350 μg/mL, the detection limit (s/n = 3) is 1 ng/mL. The prominent features of the chip-based method are its expanded dynamic range and low sample volume (50 μL), and the need for a short measurement time of 15 min. These figures of merit, in addition to the low detection limit equal to the established assay instrumentation, make it a viable candidate for use in point-of-care diagnostics.

We report a microfluidic sandwich immunoassay constructed around a dual-giant magnetoresistance (GMR) sensor array to quantify the heart failure biomarker NT-proBNP in human plasma at the clinically relevant concentration levels between 15 pg/mL and 40 ng/mL. The broad dynamic range was achieved by differential coating of two identical GMR sensors operated in tandem, and combining two standard curves. The detection limit was determined as 5 pg/mL. The assay, involving 53 plasma samples from patients with different cardiovascular diseases, was validated against the Roche Cobas e411 analyzer. The salient features of this system are its wide concentration range, low detection limit, small sample volume requirement (50 μL), and the need for a short measurement time of 15 min, making it a prospective candidate for practical use in point of care analysis.

A kind of easily assembly self-driving test card was developed for the rapid detection and quantification of heart-type fatty acid binding protein (H-FABP) utilizing time-resolved fluorescence microspheres as signal probes. It was easy to make microfluidic channel structures with double-sided adhesive and cut out of test card substrate and cover based on polymethyl methacrylate (PMMA) material by the laser cutting technique. The membrane of polystyrene containing maleic anhydride functional groups was coated on PMMA plate surface by dip-coating method. Furthermore, the capture antibody was immobilized effectively on PMMA surface by covalent binding with maleic anhydride groups. The cover was treated with plasma treatment to improve the hydrophilic ability, so that the liquid could flow smoothly in the microchannel. The whole analysis process could be completed within 10 min. There was a very good linear correlation between response and H-FABP concentration in the range of 0.5−100 ng mL−1 (R2 = 0.9966), and the detection limit was 0.1 ng mL−1 (S/N = 3). The intra-assay precision was less than 10% and the inter-assay precision was less than 15%. This detection method has the advantages such as high sensitivity, fast detection and good accuracy.

By integrated magnetic sensors and microfluidic system, a microfluidic magnetic bioprocessor was developed for the rapid detection of multi-target biomarkers. Three digestive system tumor makers, α-fetoprotein (AFP), carcinoembryonic antigen (CEA) and carbohydrate antigen 19-9 (CA 19-9) were simultaneously detected in immune reactions in the microchannel as a model system to evaluate this multi-target detection system performance. The experiment parameters including injecting flow velocity, immune reaction time and rinsing rate for each step were optimized. The standard curves were established for three tumor markers detection in serum samples, with the detection limits of 0.1 ng mL −1 (CEA), 0.1 ng mL −1 (AFP), 30 U mL −1 (CA19-9) and the dynamic ranges spanning four orders of magnitude. Multi-biomarker analysis could be completed within 30 min, and good linear relations were obtained between the results of magnetic bioprocessor and ELISA method, otherwise, the former had the advantages such as fast detection and high sensitivity.