A Mechanical Competitive Immunosensor Based on Antibody@Fe₂O₃ Magnetic Bead for HSA Detection

The application of competitive immunoassay brings many advantages to the detection of trace biomolecules and has the potential to be applied to urine-based clinical practice. However, this type of detection method has strict requirements for secondary antibody incubation processes and analysis equipment, leading to strong demands for convenient, rapid, and inexpensive detection platforms. In this study, a mechanical competitive immunosensor (MCI) was proposed for the detection of human serum albumin (HSA) based on goat anti-rabbit @Fe2O3 magnetic beads with magnetic sensitization. With the doping of Fe2O3, the conversion layer of MCI responds more accurately and rapidly to stress. In addition, goat anti-rabbit conjugated with animated Fe2O3 nanoparticles were introduced as secondary antibodies for signal amplification. Under the synergistic effect of the magnetic force of magnetic beads and the stress caused by the specific binding of antigen and antibody, the deformation of the film was amplified, which can effectively change the conductive pathway formed by doped carbon nanotubes, resulting in a larger output electric signal. Through competitive immunoassay for HSA, a limit of detection (LOD) of 68 ng/mL was achieved, which was an order of magnitude lower than direct detection methods. With high reproducibility and stability, MCI demonstrated effectiveness in the detection of HSA at a clinically significant concentration range (0.1–<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$50 \; \mu $ </tex-math></inline-formula>g/mL). Moreover, MCI showed excellent specificity and selectivity, which held promise to offer an alternative tool for clinical diagnosis of urine HSA levels in nephrotic patients.