Immunosensor Based on Gold Nanoparticles Encapsulated in Azo-Polymer and Reduced Graphene Oxide for the Detection of the Proinflammatory Molecule Interleukin-6.

Rapid interleukin-6 (IL-6) monitoring is essential for the early diagnosis and management of inflammatory and oncological conditions. This study reports a label-free impedimetric immunosensor based on a ternary poly(azo-BBY)-AuNP/rGO nanocomposite synthesized via a single-step electrochemical process. The platform utilizes dissolved oxygen as an intrinsic redox probe, precluding the need for external mediators. Morphological characterization confirmed a synergistic architecture where gold nanoparticles are encapsulated within the polymeric matrix and covered by a reduced graphene oxide veil, reducing charge-transfer resistance by over 90%. The immunosensor achieved a detection limit of 2.51 pg mL-1 with a linear range between 5 and 30 pg mL-1. A thermodynamic investigation via the Freundlich isotherm revealed a dual-stage adsorption mechanism and a steric "gate effect". Selectivity assays demonstrated high specificity, including the competitive displacement of IL-6 by the IL-1 receptor antagonist (IL-1RA). Practical utility was validated in cell culture, yielding results statistically equivalent to the ELISA gold standard. Operational stability was established for 4 days within a 95% confidence interval (97.2%-115.1%). These findings support the proposed platform as a proof-of-concept label-free immunosensor for IL-6 monitoring.