Microdroplet-Based Potentiometric Redox Measurements on Gold Nanoporous Electrodes

Abstract

Potentiometric redox measurements were made in subnanoliter droplets of solutions using an optically transparent nanoporous gold electrode strategically mounted on the stage of an inverted microscope. Nanoporous gold was prepared via dealloying gold leaf with concentrated nitric acid and was chemisorbed to a standard microscope coverslip with (3-mercaptopropyl)trimethoxysilane. The gold surface was further modified with 1-hexanethiol to optimize hydrophobicity of the surface to allow for redox measurements to be made in nanoscopic volumes. Time traces of the open-circuit potential (OCP) were used to construct Nernst plots to evaluate the applicability of the droplet-based potentiometric redox measurement system. Two poised one-electron transfer systems (potassium ferricyanide/ferrocyanide and ferrous/ferric ammonium sulfate) yielded Nernstian slopes of -58.5 and -60.3 mV, respectively, with regression coefficients greater than 0.99. The y-intercepts of the two agreed well to the formal potential of the two standard oxidation-reduction potential (ORP) calibrants, ZoBell's and Light's solution. The benzoquinone and hydroquinone redox couple was examined as a representative two-electron redox system; a Nernst slope of -30.8 mV was obtained. Additionally, two unpoised systems (potassium ferricyanide and ascorbic acid) were studied to evaluate the system under conditions where only one form of the redox couple is present in appreciable concentrations. Again, slopes near the Nernstian values of -59 and -29 mV, respectively, were obtained. All experiments were carried out using solution volumes between 280 and 1400 pL with injection volumes between 8 and 100 pL. The miniscule volumes allowed for extremely rapid mixing (<305 ms) as well. The small volumes and rapid mixing along with the high accuracy and sensitivity of these measurements lend support to the use of this approach in applications where time is a factor and only small volumes are available for testing.

Nanoporous Gold Electrodes with Tuneable Pore Sizes for Bioelectrochemical Applications

“…Nanoporous gold (NPG) has been the focus of many electrochemical investigations, such as the effect of residual Ag in the alloy on the electrocatalytic properties , the electrochemical properties of NPG in biofouling solutions or more recently the potentiometric responses of microdroplet redox compounds on NPG .…”

Nanobiotechnology as a platform for the diagnosis of COVID-19: a review

“…Nanoparticles exhibit distinct properties such as large surfaces, many active sites, and high adsorption capacities compared to bulk materials. Thus, they have been applied for several applications such as analytical chemistry [17][18][19][20][21][22][23][24][25][26], proteomics [27], sensing/biosensing [28][29][30][31][32][33][34][35], biotechnology [36][37][38][39][40][41][42][43][44][45], nanomedicine [46][47][48][49][50][51][52][53], drug delivery [54][55][56], gene transfer [57][58][59][60], wound healing [61], energy-based applications [62][63][64]…”

Flexible Nanoporous Gold Electrodes for Electroanalysis in Complex Matrices

“…It is also possible to capture the dealloyed leaf on glass modified with a mercaptosilane. [12][13] In this case, the electrode is optically transparent and can be used with an optical microscope. The challenge lies in the electrical connection to the fragile nanoporous gold.…”

“…It involves chemical dealloying commercially obtained white gold leaf in nitric acid for a set period of time and capturing the dealloyed gold leaf on a conducting substrate (e. g., a gold coated slide; tin or indium oxide) in order to make the electrode. It is also possible to capture the dealloyed leaf on glass modified with a mercaptosilane . In this case, the electrode is optically transparent and can be used with an optical microscope.…”