Dynamic ACE₂-Functionalized Magnetic Micromotors for Electrochemical Protein S Detection from SARS-CoV-2: Toward...

Inspired by the diagnostic potential of micromotor technology, this study presents a novel magnetic micromotor-based electrochemical biosensing approach for the sensitive detection of spike (S) protein in microliter-scale sample volumes. Tubular MoS₂/Ni magnetic micromotors are externally modified with gold nanoparticles (AuNPs) to enable the covalent immobilization of angiotensin-converting enzyme 2 (ACE₂) as the capture probe, leveraging its intrinsic recognition capability and resilience to viral mutations for future-proof detection. The inner Ni layer provides biocompatible magnetic propulsion while simplifying washing and handling steps. The resulting ACE₂/Au/MoS₂/Ni micromotors are actively navigated for 20 min to efficiently capture the S protein/anti-S IgG/HRP-labeled secondary antibody immunocomplex. After capture, the micromotors are deposited onto a screen-printed electrode for chronoamperometric detection at -0.1 V using 3,3',5,5'-tetramethylbenzidine (TMB) as a redox mediator. Micromotor motion is shown to be crucial, enhancing the amperometric signal by approximately 50% in confined sample microenvironments. This clearly demonstrates the active role of micromotor propulsion in promoting target-receptor interactions and improving analytical performance. The biosensing platform achieves a low limit of detection (53 pg/mL) and high selectivity, with negligible cross-reactivity toward protein N and influenza A HA1. Importantly, validation in nasopharyngeal and plasma samples demonstrates the reliable classification of positive and negative cases, highlighting the suitability of the method for rapid screening applications. Overall, this micromotor-based strategy provides a robust, mutation-resilient, and decentralized approach for precision biosensing of respiratory infections, with strong potential for future point-of-care development.