Effect of electrolyte and adsorbates on charging rates in mesoporous gold electrodes.

The classical model for porous electrodes reported by De Levie several decades ago (and expanded upon since then) was developed mainly to describe pores with micrometer-scale diameters. Presumably it will break down as pore diameters approach atomic dimensions. Mesoporous gold formed by dealloying is a valuable test platform for this because its 10 nm pores are on the boundary of this expected breakdown and because the electrochemical and surface properties of gold are relatively well understood. The De Levie model works for these electrodes at high salt concentrations, but under dilute conditions, there is not enough salt locally to charge the interface, increasing real impedance on intermediate time scales. Specific adsorption on pore walls can cause a similar increase and also cause an effective mobility decrease, tunable through electrolyte choice and the use of alkanethiol monolayers. These effects are not expected in micrometer-scale pores and are important considerations when designing devices with nanoporous electrodes.

Supercapacitive transport of pharmacologic agents using nanoporous gold electrodes.

In this study, nanoporous gold supercapacitors were produced by electrochemical dealloying of gold-silver alloy. Scanning electron microscopy and energy dispersive X-ray spectroscopy confirmed completion of the dealloying process and generation of a porous gold material with approximately 10 nm diameter pores. Cyclic voltammetry and chronoamperometry of the nanoporous gold electrodes indicated that these materials exhibited supercapacitor behavior. The storage capacity of the electrodes measured by chronoamperometry was approximately 3 mC at 200 mV. Electrochemical storage and voltage-controlled delivery of two model pharmacologic agents, benzylammonium and salicylic acid, was demonstrated. These results suggest that capacitance-based storage and delivery of pharmacologic agents may serve as an alternative to conventional drug delivery methods.

Piezoelectric inkjet printing of a cross-hatch immunoassay on a disposable nylon membrane.

The development of a cost-effective method for manufacturing immunoassays is a key step towards their commercial use. In this study, a piezoelectric inkjet printer and a nylon membrane were used to fabricate a disposable immunoassay. Using a piezoelectric inkjet printer, a cross-hatch pattern of goat anti-mouse antibody (GalphaM) and rabbit anti-horseradish peroxidase (RalphaHRP) antibody were deposited on the nylon membrane. These patterns were subsequently treated with a solution containing rabbit anti-goat antibody labeled with horseradish peroxidase (RalphaG-HRP). The effectiveness of the immobilization process was examined using tetramethylbenzidine (TMB), which oxidizes in the presence of HRP to form a visible precipitate. Optical evaluation of the TMB precipitate was used to assess the precision of the features in the inkjet-printed pattern as well as antibody functionality following inkjet printing. Uniform patterns that contained functional antibodies were fabricated using the piezoelectric inkjet printer. These results suggest that piezoelectric inkjet printing may be used to fabricate low-cost disposable immunoassays for biotechnology and healthcare applications.