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 No Slip, represents a major improvement of our previously reported o Slip system. Specifically, detection of AgNPs in the No Slip is based on galvanic exchange rather than a chemical oxidant (bleach or MnO 4 – in the o Slip). 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 Au 3+ . The Au 3+ 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 o Slip while simultaneously simplifying the basic sensor form factor. First, the No Slip resolves an oxidant instability issue because of the inherent stability of the Au 0 coating on the electrode that is used to electrogenerate the oxidant (Au 3+ ). Additionally, Au 3+ is a milder oxidizing agent than bleach or MnO 4 –, so it does not attack the major components of the No Slip. Finally, the No Slip eliminates the need for a slip layer because the oxidant (Au 3+ ) is electrogenerated on demand. The No Slip is able to detect AgNP labels down to concentrations as low as 2.1 pM, the time to result is ∼7 min, and the cost at the laboratory scale, not including application-specific reagents, is $0.30.