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

Abstract

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 MnO 4 − 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 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 oSlip while simultaneously simplifying the basic sensor form factor. First, the NoSlip 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 NoSlip. Finally, the NoSlip eliminates the need for a slip layer because the oxidant (Au 3+ ) 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 ∼7 min, and the cost at the laboratory scale, not including application-specific reagents, is $0.30. L ateral flow assays (LFAs) were first demonstrated in the 1950s as semiquantitative, colorimetric glucose sensors. 1 Their low cost and simplicity were ideally suited for many applications, and at the present time they dominate the pointof-care (PoC) sensing market. 2,3 LFAs do have limitations that restrict their applications, however. For example, the vast majority provide binary (yes/no) or, at best, semiquantitative output. They are also restricted to simple assays that do not require timed reaction steps, chemical amplification (e.g., polymerase chain reaction), or high degrees of multiplexing. In 2007, Whitesides and co-workers published a seminal paper describing how LFA-like devices could operate in two dimensions. 4 The key insight for that advance was realizing that the tools of photolithography could be used to pattern paper into hydrophilic and hydrophobic domains, thereby directing the flow of aqueous fluids along specified paths in two dimensions and allowing for multiplexed detection. 5−13 The following year the same group showed that this same basic design rule could be expanded to three dimensions, 14 thereby further increasing the number of potential applications. 15−19 Over the past four years, we have expanded on Whitesides' original multidimensional paper sensing ideas by introducing more convenient fabrication methods based on the principles of origami, 20,21 quantitative detection of analytes at subpicomolar concentrations 22 using on-chip electrochemical method...

Managing Heart Failure at Home With Point-of-Care Diagnostics

“…The No Slip technology is a paper-based [18] electrochemical detection platform that provides a quantitative readout. The No Slip platform comprises four wax-printed paper layers, fabricated on a single piece of paper, that are subsequently folded to form the device [19] . As shown in Figure 2 , Layer 1 contains two reservoirs, the inlet and the outlet.…”

Paper-based diagnostic devices

“…As an alternative to colorimetric assays, paper-based assays that rely on electrochemical detection offer many advantages, especially when it comes to performing quantitative tests [53,55,56]. Electrochemical paper-based assays have been demonstrated for a wide range of analytes with high accuracy and precision, and with the ability to detect analytes at femtomolar concentrations [6,69,70]. The electrodes for electrochemical assays are typically printed directly on the microPADs (Figure 2.8), and an external reader is used typically to perform the assay [6].…”

Past, Present and Future Challenges of Biosensors and Bioanalytical Tools in Analytical Chemistry: A Tribute to Professor Marco Mascini

“…5B). The no-slip resolves the KMnO 4 instability as well as the need for layer slipping [45]. Another interesting approach was published on Journal of American Chemical Society in 2014 Figure 4 Examples of colorimetric 3D paper-based analytical devices (PADs) that show the distribution of the fluids.…”

“…The predried blue dye is used to indicate when the flow must be stopped and galvanic exchange detection must be initiated (aec). The mechanism of galvanic exchange is reported in (deg) [45]. (C) Scheme to quantify the laminar flow in hollow-channel PAD.…”