All-screen-printed graphite sensors integrating permanent bonded magnets. Fabrication, characterization and analytical utility

Abstract

Electrochemical magneto assays have been extremely popular thanks to the facile manipulation of magnetic nanoparticles (MNPs) by a magnetic field. To this end, various related accessories, such as magnetic electrode shafts, electrochemical cells integrating (electro)magnets, magnetic stickers etc. have been developed aiming to attract MNPs on the electrode surface. Herein, we introduce for the first time screen-printed electrodes (SPEs) coupled with screen-printed permanent bonded magnets as a compact, portable, cheap and disposable alternative to aforementioned products. The bonded magnet (3 mm ∅, 56 ± 6 μm thick) consists of micro sized NdFeB particles dispersed in a thixotropic ink, and it was printed on a 100 μm thick polyester film, aligned with the electroactive surface of the SPE, which is printed on the other side of the substrate. Various parameters, such as the composition of the NdFeB/ink blend, the thickness and the pattern (compact or hole-engraved) of the printed magnet, and the thickness of the substrate were investigated by both experimental and theoretical studies. After the magnetization of the bonded magnet with a vibrating sample magnetometer at 2 T, a sufficient magnetic field strength was obtained. The performance is enhanced if a void round area is created in the center of the magnet to introduce a further area of strong field gradient. This pattern allows the development of stronger attracting forces to MNPs, higher MNPs loading and a better distribution of them on the electrode surface. The effective electron transfer between Fe3O4 MNPs and the electrode surface is shown with the electrochemical conversion of surface confined Fe3O4 MNPs to Prussian blue electroactive moieties and the amperometric determination of hydrogen peroxide, while the ultrasensitive determination of riboflavin using Ag/Fe3O4 MNP modified magnet-SPEs is demonstrated.