In this study a novel antibody conjugated chitosan-gold nanoparticles (Ab-CS-GNPs) was engineered by the green synthesized method for detection of the target antigen (Ag) by three different types of optical biosensing system (colorimetric, localized surface plasmon resonance (LSPR) and paper-based dot-blot). Colloidal GNPs was synthesized by chitosan as reducer and stabilizer agent. For paper-based dot-blot detection, antibodies were conjugated to CS-GNPs surface and applied as nanobioprobe to

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... he detection of spotted Ag on nitrocellulose (NC) membrane by the naked eye. Dot-blot assay results showed that the limit of detection (LOD) of the nanobioprobe is 1 μg/ml without any signal enhancement. In colorimetric and glasslide-based LSPR detections no significant response to antigen binding was observed due to the high thickness of chitosan layer on GNPs surface. Therefore, this engineered system could be used as nanobioprobe for optical detection of Ag in sandwich-like immunoassay systems that apply GNPs as a label of Ab.