In this study, the capture efficiency (CE) of magnetic carrier particles at the region of interest (ROI) in a micro-vessel was investigated. A nonuniform magnetic field produced by a Nd-Fe-B magnet was applied to capture the carrier particles at the ROI. The particle–particle and red blood cell (RBC)–carrier particle interactions were taken into account. Other parameters including carrier particle diameter, magnetic force, and non-Newtonian behavior of blood were also considered. The finite element method was used to solve the governing equations. Four cases were considered: (1) Newtonian without interaction forces, (2) Newtonian with interaction forces, (3) non-Newtonian without interaction forces, and (4) non-Newtonian with interaction forces. The results showed that for a particle diameter of 2000 nm, the CE values for the case without interaction force and with interaction force were 70% and 53%, respectively. It was found that by considering the particle–particle and RBC–carrier particle interactions for all magnet–vessel distances, the CE of carrier particles decreased, on average, by nearly 19%. At a magnet–vessel distance of 2.5 cm (d = 2.5 cm), it was seen that the CE values for case 2 and case 3 were nearly 70% and 45%, representing the maximum and minimum CE values, respectively.
