Triple signal amplification strategy based on size and shape transformation of ultrasmall sub-10 nm gold nanoparticles tag towards sensitivity improvement of electrochemical immunosensors

Triple signal amplification strategy was designed to enhance the electrochemical detection sensitivity of immunosensing platform based on gold nanoparticles (AuNP) tagging. The strategy described herein includes the stepwise enlargement of AuNP tag. The first step was achieved by reducing gold chloride ion in presence of AuNP acting as nucleation seeds. In this step, size of AuNP was increased by the growth of gold shell over small AuNP tag. The second step was accomplished by initiating the growth of spiky AuNP. This particular step will offer a large increase of AuNP size and surface area due to the change of nanoparticles shape. Finally, the silver enhancement step was used to provide an electroactive layer for electrochemical detection. The sandwich immunoassay was carried out using prostate specific antigen (PSA), as a model analyte. Precursors and enhancement process, which were commonly used for spiky AuNP synthesis, were adapted and optimized to achieve the highest electrochemical signal. Since the spiky AuNP enhancement step is established and reported here for the first time, the effect of relevant experimental conditions, i.e. concentration and ratio of Au and Ag ions, reducing agents, and reaction time, were thoroughly examined. Size of AuNP tag and enhancing steps were also confirmed to have the most influence on the successful enhancement process. By understanding the valuable insight of this approach, detection sensitivity of applicable AuNP-tagged immunoassay can be significantly improved. Based on an electrochemical immunosensor demonstrated here, the triple signal amplification leads to over 260-fold of signal increase in comparison with conventional silver enhancement process. Therefore, this approach would be promising strategy for improving detection limit of AuNP-tagged sensing platform. (C) 2016 Elsevier B.V. All rights reserved.