Magnetic Beads for DNA isolation

How magnetic beads work [1]

Early magnetic beads consisted of an iron-oxide core coated with silane. The surface of these beads was bound with molecules containing a free carboxylic acid. This functional group bound to DNA or RNA. Environmental salt concentration was varied to control the strength of the bonds between functional groups and nucleic acid. This allowed for controlled reversible binding. Different functional groups such as -COOH, -OH or -NH2 are used. For specific compounds some beads are functionalize with immobilized affinity ligands, hydrophobic ligands, or ion-exchange groups.

Recyclable magnetic beads [2]

Recyclable magnetic beads fall into 3 categories. core–shell structure particles, matrix-dispersed structure particles and hollow structure particles. These are regarding the structure of the beads. Each bead can be recycled in various ways. These methods could be classified into four types: direct reuse, washing treatment, chemical treatment and high-temperature calcination.

     1.“Direct reuse means that recyclable magnetic particles are reused directly after magnetic separation without extra processing. This method is suitable for applications in which the remnants do not affect the next cycle… this includes enzyme immobilization and pathogenic bacterial inactivation.”
     2.Washing treatment shows a wider range of applications, such as enzyme immobilization, bacterial immobilization, protein extraction, and DNA adsorption. However, washing treatments may affect binding ability 
     3.Example for a desorption experiment: “NaOH solution was added to weaken the electrostatic interaction between the polyaniline chains and dsDNA. Afterward, the recovered particles were washed with deionized water and HCl, bringing their fully active form (positively charged) to the next adsorption–desorption cycle. The adsorption efficiency was 90% after three cycles. However, acid and base solutions may destroy the secondary structure and affect the subsequent use of DNA.”
     4.High-temperature calcination also presents the risk of denaturing the secondary structure of the beads. Typically used when the other three methods fail. 

(1) Safarik, I.; Safarikova, M. Magnetic Techniques for the Isolation and Purification of Proteins and Peptides. Biomagn Res Technol 2004, 2, 7. https://doi.org/10.1186/1477-044X-2-7.

(2) Liu, Z.; Liu, Y.; Shen, S.; Wu, D. Progress of Recyclable Magnetic Particles for Biomedical Applications. J. Mater. Chem. B 2018, 6 (3), 366–380. https://doi.org/10.1039/C7TB02941A.