Effect of Serum on Electrochemical Detection of Bioassays Having Ag Nanoparticle Labels

The effect of serum on electrochemical detection of bioassays having silver nanoparticle (AgNP) detection labels was investigated. Both a model assay and an antigen-specific sandwich bioassay for the heart failure marker NT-proBNP were examined. In both cases, the AgNP labels were conjugated to a detection antibody. Electrochemical detection was carried out using a galvanic exchange/anodic stripping voltammetry method in which Au³⁺ exchanges with AgNP labels. The assays were carried out using a paper-based electrode platform. The bioassays were exposed to different serum conditions prior to and during detection. There are three important outcomes reported in this article. First, both the model- and antigen-specific assays could be formed in undiluted serum with no detectable interferences from the serum components. Second, to achieve the maximum possible electrochemical signal, the highest percentage of serum that can remain in an assay buffer during electrochemical detection is 0.25% when no washing is performed. The assay results are rendered inaccurate when 0.50% or more of serum is present. Third, the factors inhibiting galvanic exchange in serum probably relate to surface adsorption of biomolecules onto the AgNP labels, chelation of Au³⁺ by serum components, or both. The results reported here provide general guidance for using metal NP labels for electrochemical assays in biofluids.