Relaxation of biofunctionalized magnetic nanoparticles in ultra-low magnetic fields

In this work, the spin-spin relaxation rate, 1/T₂, and spin-lattice relaxation rate, 1/T₁, of protons' spins induced by biofunctionalized magnetic nanoparticles and ferrofluids are investigated using a high-T_c superconducting quantum interference device-detected magnetometer in ultra-low fields. The biofunctionalized magnetic nanoparticles are the anti-human C-reactive protein (antiCRP) coated onto dextran-coated superparamagnetic iron oxides Fe₃O₄, which is labeled as Fe₃O₄-antiCRP. The ferrofluids are dextran-coated iron oxides. It was found that both 1/T₂ and 1/T₁ of protons in Fe₃O₄-antiCRP are enhanced by the presence of magnetic nanoparticles. Additionally, both the 1/T₁ and 1/T₂ of Fe₃O₄-antiCRP are close to that of ferrofluids, which are dextran-coated Fe₃O₄ dispersed in phosphate buffer saline. Characterizing the relaxation of Fe₃O₄-antiCRP can be useful for biomedical applications.