This project involved investigation and optimization of the chemistry needed to immobilize biorecognition elements (BRE) on gold nanoparticles (AuNPs) to create selective nanoprobes for integration in micro- and nano-fluidic platforms to perform biomarker quantification in biofluids. The AuNPs serve as BRE carriers for analyte pre-concentration to be interfaced with a sensor platform that increases overall sensor sensitivity. Thiol coupling approaches were used in the optimization chemistry to immobilize aptamers and peptides on the AuNP surface. The parameters optimized in this work included reaction times, ligand ratio (PEG-OH vs PEGCOOH) and peptide-AuNP ratio. The first design involving an integrated sensor showed successful cortisol detection at biological levels. A competitive assay involving target recognition at the AuNP surface and release of an electroactive signaling molecule for analyte quantification was realized for cortisol detection. The immobilization protocol was monitored by agarose gel electrophoresis, considering the changes in migration patterns after BRE immobilization as indicators of successful BRE attachment. Peptide coupling was also characterized by dynamic light scattering (DLS) and Zeta potential measurements. The advantage of this approach relies on avoiding surface derivatization on the electrochemical sensor, which can compromise sensitivity and efficiency of signal transduction. Moreover, analyte diffusion to the sensor surface is not required, since the analyte is bound by the AuNPs, which are free in solution, and thus accelerate the detection process.