Fabrication of Magnetic Conjugation Clusters via Intermolecular Assembling for Ultrasensitive Surface Plasmon Resonance (SPR) Detection in a Wide Range of Concentrations.

Herein, a novel sandwich surface plasmon resonance (SPR) detection assay, which utilizes prion disease-associated isoform (PrPSc) conjugating magnetic nanoparticle clusters (nanoparticle-organic clusters, NOCs) as signal amplification reagents, is constructed for the ultrasensitive detection of PrPSc. Due to the highly specific affinity of aptamer-Fe3O4 nanoparticles (AMNPs) toward PrPSc and the intermolecular assembly behaviors among PrPSc, PrPSc conjugating magnetic nanoparticle clusters were obtained after the incubation of AMNPs and PrPSc and the subsequent concentration processes in an external magnetic field. The conjugation clusters were further injected into the SPR cuvette and captured by the gold sensing film via the Au-S bonding interaction, inducing intense SPR responses. Meanwhile, a traditional sandwich SPR detection format using a gold/PrPSc/AMNPs amplification mode was conducted for the detection of PrPSc as comparison. The results reveal that the synthesized NOCs permitted a 215-fold increase of the SPR signal, while the sandwich format permitted only a 65-fold increase. Moreover, a lower detection limit (1 × 10-4 ng/mL) and a wider quantitation range (1 × 10-4-1 × 105 ng/mL) were demonstrated. The formation of the conjugation clusters and the capture of these clusters were confirmed by high-resolution AFM imaging and molecular simulations. This conjugation-cluster-induced signal amplification strategy has great potential for the detection of small analytes with similar structural characteristics in trace level concentrations with high selectivity and sensitivity by altering the corresponding aptamer labeled to magnetic particles.