Sink/Float Magnetic Immunoassays for In‐Field Bioassays

Abstract

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.

A Wash-Free Spheres-on-Sphere Strategy for On-Site and Multiplexed Biosensing

“…We employed immunoassay as a format to illustrate the principle of the SOS platform, including sandwich/competitive immunoassays, differential sedimentation of spheres with diverse sizes in solution, and Coulter-principle-based analysis of spheres. The PS 1000μm spheres have a high density and abundant surface binding sites, enabling them to sediment and rapidly participate in the reactions . Meanwhile, the PS μm spheres are uniformly dispersed in solution, which increases their collision and separation probability with PS 1000μm spheres.…”

“…The PS 1000μm spheres have a high density and abundant surface binding sites, enabling them to sediment and rapidly participate in the reactions. 31 Meanwhile, the PS μm spheres are uniformly dispersed in solution, which increases their collision and separation probability with PS 1000μm spheres. The presence of targets induces the formation of sandwich complexes, while the addition of NaOH disrupts the antigen−antibody conjugates and releases the PS μm spheres.…”

“…They have garnered considerable interest in various fields owing to their simple structure, easy miniaturization, high sensitivity, and good stability. − One of the classical applications of electrochemical biosensors is the Coulter counter, a device that operates on the principle of resistance counting and can quantify the size and number of particles in the aqueous solution by registering the resistance pulses elicited when the particles traverse to a micropore. , A portable particle counter has the advantages of simultaneously quantifying both the size and number of particles with compactness and portability, offering a promising tool for rapid and on-site detection. Polystyrene microspheres (PS) have advantages in multiple size options, low cost, good dispersion, and accessible surface modification, which can be used as signal probes by immobilizing their surface with recognition molecules. − Consequently, it is feasible to integrate the portable Coulter counter with different sizes of PS spheres to enable simultaneous screening of multiple targets.…”