Ultrasensitive Enzyme-free Biosensor by Coupling Cyclodextrin Functionalized Au Nanoparticles and High-Performance Au-Paper Electrode

Microfluidic paper-based analytical device (μPAD), originally developed for improving healthcare in developing countries, presents a simple yet powerful platform for performing low-cost and portable diagnostic devices. Here, we report an enzyme-free μPAD for the detection of two tumor markers. First, a porous structure of gold nanoparticle (AuNP)-modified paper working electrode (Au-PWE), with a feature of all-round conductivity and plenty of active sites favoring biological ligand attachment, was fabricated as a sensor substrate. Next, cyclodextrin functionalized AuNPs (CD@AuNPs) as dual mimicking enzyme were prepared to load secondary antibodies or peptide. On one sample zone, in the presence of carcinoembryonic antigen (CEA), CD@AuNPs could be introduced into the Au-PWE through a sandwich immunoreaction, boosting the electrochemical signal of o-phenylenediamine (o-PD) via the trigger of a cascade catalysis reaction toward glucose and o-PD, eventually resulting in the sensitive detection of CEA. On another working zone, with the introduction of another target prostate-specific antigen (PSA), peptide cleavage took place, which further led to CD@AuNPs being released from Au-PWE, and then, the variation of electrochemical signals was recorded for the detection of PSA. We demonstrated, using the device, that the detection of CEA and PSA clinically had high sensitivity, wide linear ranges, and low detection limits. We believe that our work provides a promising platform for point-of-care testing, especially in resource-limited regions.