Highly-sensitive electrochemical detection of proteins using aptamer-coated gold nanoparticles and surface enzyme reactions

Gold nanoparticle (NP) enhanced surface sandwich assays for the detection of proteins is developed in conjunction with a surface enzyme reaction. As a model protein, immunoglobulin E (IgE) possessing two different epitopes for anti-IgE and IgE specific aptamer is used. A surface sandwich was first formed via the adsorption of IgE onto IgE aptamer coated Au NP-modified gold electrodes followed by the specific interaction of alkaline phosphatase (ALP) conjugated anti-IgE onto the surface IgE complex. The selective electrochemical signal was then achieved by measuring released electrons from the reaction of the substrate, 4-aminophenylphosphate (APP) with the surface IgE-aptamer-NPs/IgE/anti-IgE-ALP complex. The signal enhancement effect of NPs in ALP amplified assays was also studied using the IgE aptamer/IgE/antiIgE-ALP complex. The use of aptamer coated NPs with the enzymatically amplified sandwich assay resulted in an excellent enhancement for IgE detection and a significant reduction of non-specific adsorption events.