Size-Controlled Synthesis of Carboxyl-Functionalized Magnetite Particles: Effects of Molecular Weight of the Polymer and Aging

Magnetic particles (MPs) are of great interest in many varied applications in the fields of biotechnology, biomedicine, and environmental remediation. To accommodate different applications, size-control synthesis of MPs is of particular interest. Here, we report a simple synthesis of MPs in the range of nano to microsize (23 nm to 1.2 μm). Specifically, the particle size of MPs was tuned by the (i) molecular weight (Mw) of poly­(acrylic acid) (PAA) and (ii) aging process. Three different hydrothermal procedures using different Mw of PAA were compared, namely, one-step hydrothermal, two-step hydrothermal, and coating-after hydrothermal methods. The Mw of PAA used was 1.8k, 30k, 50k, and 100k g/mol. The resulted particle sizes of the one-step hydrothermally synthesized 1.8k, 30k, 50k, and 100k MPs were 1202 ± 359, 447 ± 156, 418 ± 88, and 247 ± 34 nm, respectively, and those of the two-step ones were 23 ± 3, 100 ± 14.1, 116 ± 26, and 78 ± 6 nm, respectively. The crystal composition, ζ-potentials, magnetic properties, magnetic separation efficiencies, and protein conjugation properties were studied systematically. The results showed that MPs synthesized via one-step hydrothermal synthesis demonstrated the highest yield and the highest magnetic separation efficiency. Bovine serum albumin, lysozyme, and enhanced green fluorescent protein as protein models were successfully conjugated with the MPs, and the application of antibody-conjugated PAA-MPs for bacterial capture was demonstrated