Size-Controllable Magnetic Iron Oxide Nanorods for Biomarker Targeting and Improving Microfluidic Mixing

Anisotropic nanoparticles, especially gold (Au) nanocubes and nanorods, exhibit unique physical and biological properties compared with their spherical-shaped counterparts, attracting increased attention and effort in developing such a class of nanomaterials for enhanced biomedical applications. Here, we report the dimension-controlled preparation of aqueously stable iron oxide nanorods (IONRs) with tunable dimensions (lengths ranging from 25 to 85 nm and diameters from 5 to 16 nm) and varied saturation magnetization values (from 50 to 79 emu·g^-1). Subsequently, the prepared IONRs were evaluated for cell uptake and tested for different biomedical applications that can take advantage of strong magnetic properties of IONRs. In immunomagnetic capturing of biofluidic biomarkers, transferrin-conjugated IONRs demonstrated substantial improvement in efficiency (88%) of capturing transferrin receptor overexpressed pediatric brain tumor medulloblastoma cells (D556) compared with that (47.5%) of commonly used commercial magnetic separation agents, micron-sized Dynabeads. In detecting Aβs and tau proteins, known as Alzheimer's disease biomarkers, antibody-conjugated IONRs showed high sensitivity (91.3%) and specificity (88%). Prepared IONRs also demonstrated rotational movement under the controllable alternating magnetic field. By varying the strength and frequency of an alternating magnetic field, IONRs can be driven as nanoscaled "stirring bars" in the fluid sample in the biofluidic chamber, leading to enhanced liquid mixing for rapid magnetic separations (completed within 106 s).