Mediator and label free estimation of stress biomarker using electrophoretically deposited Ag@AgO-polyaniline hybrid nanocomposite

Cortisol, a steroid hormone, is an important biomarker for psychological stress and its detection is gaining prominence for personalized health monitoring. In present work, electrophoretically deposited nanocomposite films of polyaniline (PANI) and core-shell Ag@AgO nanoparticles (NP similar to 5 nm) have been explored as an electro-active nanostructured platform for Anti-cortisol antibody (Anti-C-ab) immobilization for electrochemical immunosensing of cortisol. Covalent binding of Anti-C-ab onto Ag@AgO-PANI nanocomposite was achieved using EDC/NHS chemistry, which results in the amide bond formation between amino groups of PANI and COOH groups of anti-C-ab. Nonspecific binding sites on the immunosensing electrodes were blocked using bovine serum albumin (BSA). The uniform distribution of electro-active and surface charged Ag@AgO NP in PANI matrix results in a nanoporous granular morphology (roughness similar to 10 nm) that provides a functionalized conductive microenvironment for Anti-C-ab immobilization. The BSA/Anti-C-ab/Ag@AgO-PANI/Au bioelectrodes have been characterized using electrochemical impedance technique (EIS), cyclic voltammetric (CV) technique and atomic force microscopic (AFM) technique, respectively. In CV studies nanocomposite exhibited characteristic response current peak corresponding to AgO NP (0.25 V) with large magnitude of current response and resulted in high electron transport at the electrode-electrolyte interface without a mediator. Electrochemical response studies via CV for the fabricated BSA/Anti-C-ab/Ag@AgO-PANI/Au immunosensor as a function of cortisol concentration exhibited a wide linear detection range of 1 PM-1 mu M, a detection limit of 0.64 pM mL(-1)(lower than ELISA), and high sensitivity 66 mu A M-1 with a regression coefficient of 0.998. The findings of present work may explore the application of Ag@AgO-PANI hybrid nanocomposite to detect cortisol and other biomarkers for point-of-care application. (C) 2013 Elsevier B.V. All rights reserved.