Electrochemiluminescence immunosensor for ultrasensitive detection of biomarker using Ru(bpy)32+-encapsulated silica nanosphere labels

Here, we describe a new approach for electrochemiluminescence (ECL) assay with Ru(bpy)32+-encapsulated silica nanoparticle (SiO2@Ru) as labels. A water-in-oil (W/O) microemulsion method was employed for one-pot synthesis of SiO2@Ru nanoparticles. The as-synthesized SiO2@Ru nanoparticles have a narrow size distribution, which allows reproducible loading of Ru(bpy)32+ inside the silica shell and of α-fetoprotein antibody (anti-AFP), a model antibody, on the silica surface with glutaraldehyde as linkage. The silica shell effectively prevents leakage of Ru(bpy)32+ into the aqueous solution due to strong electrostatic interaction between the positively charged Ru(bpy)32+ and the negatively charged surface of silica. The porous structure of silica shell allowed the ion to move easily through the pore to exchange energy/electrons with the entrapped Ru(bpy)32+. The as-synthesized SiO2@Ru can be used as a label for ultrasensitive detection of biomarkers through a sandwiched immunoassay process. The calibration range of AFP concentration was 0.05–30 ng mL−1 with linear relation from 0.05 to 20 ng mL−1 and a detection limit of 0.035 ng mL−1 at 3σ. The resulting immunosensors possess high sensitivity and good analytical performance.