Enhanced Stability of Gold Magnetic Nanoparticles with Poly(4-styrenesulfonic acid-co-maleic acid): Tailored Optical Properties for Protein Detection.

Gold magnetic nanoparticles (GoldMag) have attracted great attention due to their unique physical and chemical performances combining those of individual Fe3O4 and Au nanoparticles. Coating GoldMag with polymers not only increases the stability of the composite particles suspended in buffer but also plays a key role for establishing point-of-care optical tests for clinically relevant biomolecules. In the present paper, poly(4-styrenesulfonic acid-co-maleic acid) (PSS-MA), a negatively charged polyelectrolyte with both sulfonate and carboxylate anionic groups, was used to coat the positively charged GoldMag (30 nm) surface. The PSS-MA-coated GoldMag complex has a stable plasmon resonance adsorption peak at 544 nm. A pair of anti-D-dimer antibodies has been coupled on this GoldMag composite nanoparticle surface, and a target protein, D-dimer was detected, in the range of 0.3-6 μg/mL. The shift of the characteristic peak, caused by the assembly of GoldMag due to the formation of D-dimer-antibody sandwich bridges, allowed the detection.