Ultrasensitive protein detection: a case for microfluidic magnetic bead-based assays.

We review the use of magnetic micro- and nanoparticles ('magnetic beads') in microfluidic systems for ultrasensitive protein detection. During recent years magnetic beads have been used frequently in immunoassays, either as mobile substrates on which the target antigen is captured, as detection labels, or simultaneously as substrates and labels. The major part of the reviewed work has as application the detection of antibodies or disease biomarkers in serum or of biotoxins from food samples. Several of the most sensitive assays allow protein detection down to fg mL(-1) concentrations. We benchmark the performance of these microfluidic magnetic bead-based assays with the most promising earlier work and with alternative solutions.