Customized Design of Magnetic Beads for Dynamic Magnetoresistive Cytometry

Spintronic microfluidic chips allied with the magnetic labeling of cells is a newer version of flow cytometry. Here, the commonly used fluorescent tags are replaced by magnetic beads that are excited by a magnetic field and detected by a magnetoresistive (MR) sensor. In addition to the important role played by the sensors, in such systems the magnetic beads can determine the sensitivity, and accuracy of the assay depending on their magnetic moment as well as the specificity defined by their surface functionalization. In this paper, the tailoring of magnetic beads to be used as magnetic labels for magnetic flow cytometrer is reported. Polymeric beads loaded with different contents of magnetite nanoparticles ranging from 14 to 44 wt% and diameters between 120 and 190 nm were prepared and tested in the spintronic microfluidic chip. The objective was to attain a compromise between beads´ magnetic content and signal generated in the MR sensor. The optimal magnetic content was found to be around 30 wt% of magnetite. Further functionalization of the magnetic beads with protein A for antibody conjugation allowed their use in immunomagnetic cell labeling. The final objective is to use these magnetic beads as labels for the detection and counting of circulating tumor cells directly from patient whole blood samples.