A microfluidic capillary immunoassay platform for rapid and highly sensitive measurement of biomarkers has been developed by the Prof. Urban team at the Bioanalytical Microsystems Laboratory at IMTEK (Institute of Microsystem Technology) of the University of Freiburg, Germany. This micro-ELISA system combines microfluidic capillary channel (immobilization cell) where the primary antibodies are coated covalently, with an electrochemical detection system.
The microassay is based either on a competitive or on sandwich format depending on the biomarker studied. The assay starts by the sequential immobilization of capture antibodies into the capillary micro-vessel, followed by a blocking step and then by the flow injection of serum or other fluids samples. The detection is performed with glucose oxidase (GOD) used as tracer which is either conjugated to the analyte in the case of the competitive assay or to the detection antibody in the sandwich assay (see below figure). After injection of a glucose solution, the GOD converts glucose to gluconolactone and hydrogen peroxide. To accumulate the generated hydrogen peroxide within the channel the flow is stopped for certain time intervals, followed by pumping to the measurement cell for electrochemical quantification.
Figure: Working principle of the immunosensor. Source: Dr. H. Bakirci & Prof. G. Urban
The microfluidic chip-based method is being developed to achieve highly sensitive and fast electrochemical detection of biomarkers. The current prototype allows the signal detection within 2 to 4 minutes with a complete assay execution within few hours. The improvement of the assay sensitivity is still on progress by integrating signal amplification systems which will allow reaching pictogram level of detection limit.
Compared with commercially available ELISA methods, this microdevice assay may be low-cost, simple, easy to handle and requires only minute amount of sample such as whole blood, serum, plasma, saliva, urine, synovial or cerebrospinal fluids.