Electrochemiluminescence immunoassay using a paper electrode incorporating porous silver and modified with mesoporous silica nanoparticles functionalized with blue-luminescent carbon dots

We have prepared carbon dots (C-dots) by pyrolysis of citric acid. The one-pot synthetic strategy is time-saving and simple and the resulting C-dots display blue luminescence with high quantum yield at an anodic potential of +0.6 V. An electrochemiluminescence (ECL) immunoassay was designed for the sensitive determination of cancer antigen 125 (CA125) by using amino-functionalized mesoporous silica nanoparticles (NH2-MSNs) capped with C-dots. These act as amplification labels on a novel kind of paper working electrode modified with silver nanoparticles (Ag-PWE). This electrode was fabricated by a seed-mediated growth approach and served as a support for the attachment of the antibody. The NH2-MSNs possess higher volume-to-surface ratio than the solid nanoparticles that can carry more C-dots which improves the sensitivity of the immunoassay. The ECL immunoassay was operated by using triethanolamine as a coreactant that is less toxic and more soluble than other popular coreactants. The assay has a linear response over a wide range of 0.01-50 U mL(-1), and the detection limit is 4.3 mU mL(-1). This makes the method one of the most sensitive assays for CA125.