This research aims to develop magnetic nanoparticle clusters (MNCs) for separation and detection of Streptococcus mutans (S. mutans). The MNCs were synthesized by a solvothermal method. Poly(acrylic acid) (PAA) was grafted on MNCs by surface-initiated polymerization of acrylic acid via reversible addition-fragmentation chain transfer (RAFT) mechanism. Readily available carboxyl groups on the PAA-grafted MNCs can bind with the cell wall binding domain (CWBD) of automutanolysin, the enzyme that is specific to mutans streptococci using EDC/NHS as coupling reagents. The MNCs both before and after PAA grafting and CWBD conjugation were characterized by Fourier transform infrared spectroscopy (FT-IR), dynamic light scattering (DLS), and transmission electron microscopy (TEM). The CWBD-conjugated MNCs were tested for their ability to separate and detect S. mutans by magnetic separation and selective filtration using cellulose acetate membrane with a diameter of 0.8 μm. Because the size of the CWBD-conjugated MNCs was larger than the pore diameter of the membrane, the CWBD-conjugated MNCs failed to quantitatively distinguish the S. mutans having different concentrations although the counting method confirmed that they can capture the bacteria.
