Improving direct immunoassay response by layer-by-layer films of gold nanoparticles - Antibody conjugate towards label-free detection

The conjugation of nanoparticles with antibodies has been successfully applied in sandwich immunoassays for detecting cancer biomarkers. However, two antibodies are necessary to perform such experiment, being one of them functionalized with a signal label for optical or electrochemical assay. This approach is time and cost consuming compared to direct label-free immunoassays. In this study, we propose the synthesis of gold nano particles conjugated to anti-PSA antibody to produce a label-free impedimetric inununosensors based on nanostructured Layer-by-Layer (LbL) films. Prostate-specific antigen (PSA) detection was performed by electro-chemical impedance spectroscopy demonstrating a detection mechanism governed by Langmuir-Freundlich adsorption model. This strategy provided a significant sensitivity using 10-fold less antibody than conventional inununosensors, i.e. decreasing costs using a simple approach, with a limit of detection of 0.17 ng mL(-1) and an analytical range of 0.1-20 ng mL(-1) indicating that our sensor is potentially useful for clinical applications.