Wojciech Nogala

Atomic Force Microscopy of Electrochemical Nanoelectrodes

Nanometer-sized electrodes have recently been used to investigate important chemical and biological systems on the nanoscale. Although nanoelectrodes offer a number of advantages over macroscopic electrochemical probes, visualization of their surfaces remains challenging. Thus, the interpretation of the electrochemical response relies on assumptions about the electrode shape and size prior to the experiment and the changes induced by surface reactions (e.g., electrodeposition). In this paper, we present first AFM images of nanoelectrodes, which provide detailed and unambiguous information about the electrode geometry. The effects of polishing and cleaning nanoelectrodes are investigated, and AFM results are compared to those obtained by voltammetry and SEM. In situ AFM is potentially useful for monitoring surface reactions at nanoelectrodes.

Voltammetric pH Nanosensor.

Nanoscale pH evaluation is a prerequisite for understanding the processes and phenomena occurring at solid-liquid, liquid-liquid, and liquid-gas interfaces, e.g., heterogeneous catalysis, extraction, partitioning, and corrosion. Research on the homogeneous processes within small volumes such as intracellular fluids, microdroplets, and microfluidic chips also requires nanometer scale pH assessment. Due to the opacity of numerous systems, optical methods are useless and, if applicable, require addition of a pH-sensitive dye. Potentiometric probes suffer from many drawbacks such as potential drift and lack of selectivity. Here, we present a voltammetric nanosensor for reliable pH assessment between pH 2 and 12 with high spatial resolution. It consists of a pyrolytic carbon nanoelectrode obtained by chemical vapor deposition (CVD) inside a quartz nanopipette. The carbon is modified by adsorption of syringaldazine from its ethanolic solution. It exhibits a stable quasi-reversible cyclic voltammogram with nearly Nernstian dependency of midpeak potentials (-54 mV/pH). This sensor was applied as a probe for scanning electrochemical microscopy (SECM) in order to map pH over a platinum ultramicroelectrode (UME), generating hydroxide ions (OH(-)) by the oxygen reduction reaction (ORR) at a diffusion-controlled rate in aerated phosphate buffered saline (PBS). The results reveal the alkalization of the electrolyte close to the oxygen reducing electrode, showing the insufficient buffer capacity of PBS to maintain a stable pH at the given conditions.

Processes at nanopores and bio-nanointerfaces: general discussion

Hassan Alzahrani, Christophe Antoine, Lane Baker, Sebastien Balme, Gourav Bhattacharya, Paul W. Bohn, Qiong Cai, Chrys Chikere, Richard M. Crooks, Naren Das, Martin Edwards, Cyril Ehi-Eromosele, Niklas Ermann, Lei Jiang, Frederic Kanoufi, Christine Kranz, Yitao Long, Julie MacPherson, Kim McKelvey, Michael Mirkin, Richard Nichols, Wojciech Nogala, Juan Pelta, Hang Ren, Jennifer Rudd, Wolfgang Schuhmann, Zuzanna Siwy, Zhongqun Tian, Patrick Unwin, Liping Wen, Henry White, Katherine Willets, Yanfang Wu and Yilun Ying