Sink/Float Magnetic Immunoassays for In‐Field Bioassays

Analytical tests/devices that are used outside laboratory settings are required to have a very simple analytical protocol to get clearance by regulatory authorities. This study describes sink/float magnetic immunoassays, a new type of rapid, mix‐and‐observe, instrument‐free tests for the detection of biomarkers in untreated biological samples that are very simple and might meet the simple‐to‐use criterion of authorities to be used in the field. These tests can tell whether an analyte is above or below a predetermined level within 25–45 minutes based on the sinking or floating of a mm‐sized sphere on the surface of which an immunoassay that uses reporter antibodies conjugated to superparamagnetic nanoparticles is performed. This manuscript describes the theory and proof‐of‐concept applications of sink/float magnetic immunoassays for the detection of C‐Reactive Protein, anti‐Treponema pallidum antibodies and E. coli bacteria. Sink/float magnetic immunoassays detect proteins, antibodies, and bacteria in samples using a simple mix‐and‐observe protocol that uses a biofunctionalized small sphere, some liquid reagents and a small permanent magnet. A simple sink/float test of the sphere identifies if the analyte is above or below a predetermined level; the sphere sinks only if the analyte is above the concentration level.