Novel ultrasensitive immunosensor based on magnetic particles for direct detection of transferrin in blood

A novel immunosensor for transferrin (Tf) detection in blood samples has been developed. The stable layer of carbon-encapsulated magnetic nanoparticles containing carboxylic groups anchored with the monoclonal antibody ensured good electric contact for direct electron exchange between transferrin and the electrode surface. The interactions of the immobilized antibody with transferrin (at various concentration) were monitored via various responses, i.e.: voltammetric (reduction current of Tf), gravimetric (amplitude of frequency oscillations) and impedance (charge transfer resistance). For the determination of transferrin in blood samples the best procedure is the gravimetric one that gave the highest sensitivity. The obtained results show excellent linear response in the Tf concentration range between 5 × 10−7 and 5 × 10−2 g dL−1 (5 × 10−3 ÷ 500 μg mL−1) with the detection limit of ca. 12.0 ± 1.8, 15.0 ± 2.4 and 24.0 ± 5.2 ng dL−1 for gravimetric, impedance and voltammetric analysis, respectively. The functionality of the electrochemical immunosensor has been also demonstrated during the analysis of the Tf level in rat blood samples.