Paper-Based Sensor for Electrochemical Detection of Silver Nanoparticle Labels by Galvanic Exchange

Here we report a three-dimensional paper fluidic device configured for electrochemical detection of biomolecules labeled with silver nanoparticles (AgNPs). This new sensor, which we call a NoSlip, represents a major improvement of our previously reported oSlip system. Specifically, detection of AgNPs in the NoSlip is based on galvanic exchange rather than a chemical oxidant (bleach or MnO4- in the oSlip). Galvanic exchange is implemented by depositing a very small amount of gold onto the working electrode. Once the AgNP labels are brought into the proximity of the electrode through the use of magnetic force, a fraction of the Au-0 is electrochemically oxidized to Au3+. The Au3+ reacts with the AgNPs to form Ag+ and Au-0. The Ag+ is then detected by anodic stripping voltammetry. This new methodology resolves three shortcomings of the oSlip while simultaneously simplifying the basic sensor form factor. First, the NoSlip resolves an oxidant instability issue because of the inherent stability of the Au0 coating on the electrode that is used to electrogenerate the oxidant (Au3+). Additionally, Au3+ is a milder oxidizing agent than bleach or MnO4-, so it does not attack the major components of the NoSlip. Finally, the NoSlip eliminates the need for a slip layer because the oxidant (Au3+) is electrogenerated on demand. The NoSlip is able to detect AgNP labels down to concentrations as low as 2.1 pM, the time to result is similar to 7 min, and the cost at the laboratory scale, not including application-specific reagents, is $0.30.