An integrated magnetoimpedance biosensor microfluidic magnetic platform for the evaluation of the cardiac marker cTnI†

An integrated magnetoimpedance (MI) biosensor microfluidic magnetic platform was proposed for the evaluation of the cardiac marker, cardiac troponin I (cTnI). This bioanalyte evaluation platform mainly comprised three external permanent magnets (PMs), one MI element, two peelable SiO₂ film units and a microfluidic chip (MFC). The MI element was made of micro-electro-mechanical system (MEMS)-based multilayered [Ti (6 nm)/FeNi (100 nm)]₅/Cu (400 nm)/[Ti (6 nm)/FeNi (100 nm)]₅ thin films and designed as meander structures with closed magnetic flux. The MFC was fabricated using 3D printing and inverted molding techniques, designed with a solution by mixing the reaction region, magnetic separation region and detection region. Peelable SiO₂ film units with the same size as the MI sensing element were used as the immunoreactivity interface of the bioanalytes. Two large PMs were placed directly below the MI sensing unit to provide a bias magnetic field, and the smaller PM was embedded in MCF for magnetic separation function. Different concentrations of the biological target (cTnI antigen)-, PBS buffer-, and Dynabeads-labeled polyclonal cTnI antibody solution were injected sequentially into the MCF. After immunoreactivity and magnetic separation, a classical sandwich immunoreaction process occurred on the surface of the monoclonal antibody-modified SiO₂ film via self-assembling process in the reaction region of the MFC. The fundamental principle for evaluation of cTnI was based on variations of the MI signal under different concentrations of the biological target coupled with different numbers of Dynabeads. It was demonstrated that the mentioned MI-based magnetic platform could perform quantitative detection analyses over a range of cTnI concentrations (lowest concentration = 0.1 ng mL⁻¹ and highest concentration = 100 ng mL⁻¹). The proposed MI-based magnetic platform provides a sensitive, reliable, stable and reusable bioanalytical platform, and it has potential in future biomedical applications.