Silica Nanoparticle Tags for Capacitive Affinity Sensors

Capacitive affinity sensors have shown great promise for disposable biosensors but have poor sensitivity as a direct sensor if the analyte molecule is small. In this paper, we report an indirect capacitive affinity sensor with silica nanoparticle tags to enhance the sensitivity for sandwich type of immunoassays. In these experiments, the anti-body-antigen-antibody complex (as in the standard indirect sandwich immunoassay) is simulated by a human-IgG-anti-human-IgG complex. Silica nanoparticles were synthesized by controlled hydrolysis of TEOS in alcohol and anti-human IgG antibodies were immobilized on them. The capacitive immunosensor comprised of a deposited gold electrode on oxidized silicon with human IgG immobilized on it. After the immunocomplexation process, the nanoparticles manifest by a significant decrease of capacitance compared to when only anti-human-IgG is incubated