Building nanoSPR biosensor systems based on gold magnetic composite nanoparticles.

Composite Fe3O4/Au nanoparticles are attracting considerable interest in developing visual and specific detection of biomolecular due to their unique physical and chemical properties. Here, two localize surface plasmon resonance (LSPR) probes based on Fe3O4/Au nanoparticles (nanoSPR biosensors) were fabricated by exploring 11-mercaptoundecanoic acid (MUA) and poly acrylic acid (PAA) as surface modification agents and subsequently conjugating rabbit IgG with the modified particles' surface. Comparative investigations showed the differences between MUA-particles and PAA-particles, as well as sensitivity of the two as-prepared nanoSPR biosensors when used in target goat anti-rabbit IgG colorimetric detection. Particles coated with PAA were in a better dispersion and showed an ionic independent stability, indicating PAA-particles have a potential application in colorimetric detection. In contrast, the MUA-particle probes revealed a higher sensitivity in SPR detection (50 nmol/L), and further kinetic studies showed the reactions between probes and target followed the second order and the reaction rate of MUA-probes was twice the rate of PAA-probes at the same temperature and condition. Such proof-of concept works reported here demonstrated that the protocol to build nanoSPR biosensors was favored in developing molecular probes, and the novel composite nanoparticles might serve as ideal probes for sensitive, selective and real time detection.