Incubation-Free Electrochemical Immunosensor Using a Gold-Nanocatalyst Label Mediating Outer-Sphere-Reaction-Philic and Inner-Sphere-Reaction-Philic Species

Abstract

We reprots a new nanocatalytic scheme based on the facts that the redox reaction between a highly outer-sphere-reaction-philic (OSR-philic) species and a highly inner-sphere-reaction-philic (ISR-philic) species is slow that an OSR- and ISR- philic Au-nanocatalyst label can mediate the two different types of redox species. This scheme allows highly sensitive and incubation free detection of creatine kinase-MB (CK-MB). Outer-sphere to inner-sphere redox cycling occurs in the sequence of a highly OSR-philic ITO electrode, highly OSR-philic Os(bpy)2Cl2 +/Os(bpy)2Cl2, OSR- and ISR-philic AuNC, and highly ISR-philic hydrazine. Ultimately, using outer-sphere to inner-sphere electrochemical-nanocatalytic (ENc) redox cycling that allows high signal amplification. When the ENc redox cycling was applied to a sandwich-type immunosensor for the detection of CK-MB, the calculated detection limit was approximately 20 fg mL-1 for mouse IgG, reconfirming that the ENc redox cycling allowed ultrasensitive detection. In the case of another cardiac target (myoglobin), the chronocoulometric signal was similar to that of zero CK-MB, indicating that the immunosensor is selective. The results for clinical serum samples showed that the charge increased with increasing concentration of CK-MB with good reproducibility, indicating that the immunosensor is practically appealing.