Engineering of Au/Ag Nanostructures for Enhanced Electrochemical Performance

Abstract

The effect of nanostructuring on the electrochemical activity of a series of Au/Ag electrocatalysts, with and without graphene nanoplatelets (G) as carbon matrix support and β-cyclodextrin as capping agent, was systematically investigated using the ferri/ferrocyanide redox probe. A series of Au/Ag nanostructures with different morphologies were synthesized and characterized using a combination of spectroscopy, electron microscopy, and electroanalytical methods. Evaluation of the cyclic voltammograms obtained from the ferri/ferrocyanide redox probe using electrodes modified with the different Au/Ag nanostructures revealed significant enhancement in peak currents upon using hollow Au/Ag nanobox and porous-hollow Au/Ag nanocage analogs in comparison to conventional solid spherical Au nanoparticles. The observed improvements in electrochemical activities can be attributed to the nanoreactor cage and edge effects in the hollow cubic nanostructures. Moreover, the dispersion of the nanostructures in G and their surface modification with β-cyclodextrin further enhanced their electrochemical performance. The best performing Au/Ag nanostructure that was modified with β-cyclodextrin and G was used to fabricate an electrochemical sensor for the stress biomarker cortisol. The resulting electrochemical sensor exhibited good linear response to cortisol in the concentration range of 1 pM to 100 nM, making it a promising platform technology for monitoring the physiological stress indicator. Nanoparticle based electrochemical sensors have received considerable attention in recent years due to their exceptional attributes including high sensitivity, good reliability, and stability.1-4 Moreover, engineered electrocatalytic nanomaterials provide a means to develop simple-to-contruct 5 electrochemical sensors that can be used for routine point-of-care health monitoring and diagnostics.6,7 However, for most biomedical applications, a next generation sensor platform technology will require significant improvements in the nanomaterials' properties to facilitate lower detection limits and higher sensitivities under lower costs for mass production. 8,9 An effective electrochemical sensor relies heavily on the surface architecture of the working electrode in order to allow the recognition process to occur under short response time, achieve good signal-tonoise (S/N) ratio, and detect the analyte of interest at low limits of detection (LOD) with high selectively.9-11 For these purposes, Au nanoparticles have been heavily explored for their use as modifiers of the electrochemical sensor's interface due to their unique attributes such as high conductivity, 12 stability, 13 ease of enabling surface chemical modifications, 13,14 and their large surface-to-volume ratios. 15,16Moreover, Au nanoparticles are less susceptible to suffer from surface poisoning compared to other commonly used electrocatalytic nanometals. 17 Due to the many promising attributes of Au-based nanostructures, this nanomaterial has become a good scaffold for different electr...

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