Rotating magnetic nanochain-based biosensor enables 6-minute ultrasensitive quantification of heart-type fatty...

Rapid, quantitative measurement of heart-type fatty acid-binding protein (H-FABP) at the point of care is important to rule in acute myocardial infarction, yet remains challenging due to insufficient sensitivity and speed of current rapid tests. Here, we present a lateral flow immunoassay (LFIA) that integrates antibody-functionalized iron oxide nanochains with a rotating magnetic field and magnetic particle quantification (MPQ) technique. Under a low-frequency rotating magnetic field (200 Oe, 3 Hz), anisotropic nanochains were observed to act as nanoscale stirrers, significantly accelerating antigen-antibody interactions. Maintaining magnetic rotation during lateral flow appears to enable a dynamic cooperative capture mechanism at the test line, where previously bound nanochains may magnetically recruit new labels, locally enriching signal by 5-fold. Additionally, rotational agitation resulted in a 2-fold reduction in nonspecific background signals, due to shear-induced disruption of weak aggregates. Volumetric MPQ detection, based on readout of the labels' nonlinear magnetization, interrogates the entire membrane thickness rather than only the surface, increasing both sensitivity and dynamic range. Using a single 6-min step and 50 μL of untreated human serum, the assay achieves an ultrasensitive detection limit of 21 pg/mL (45-fold improvement over an LFIA employing non-rotating spherical magnetic nanoparticles) and a broad dynamic range of 0.02-50 ng/mL. The MPQ reader eliminates the need for optics, cameras, or complex fluidics, enabling rapid, portable, and reagent-efficient point-of-care testing. By delivering picogram-level sensitivity in a simple 6-min protocol, this magnetically actuated LFIA with volumetric detection has the potential to enable bedside decision-making in cardiovascular emergencies.