Single-Molecule Interactions at a Surfactant-Modified H₂ Surface Nanobubble

Abstract

In schematics and cartoons, the gas–liquid interface is often drawn as solid lines that aid in distinguishing the separation of the two phases. However, on the molecular level, the structure, shape, and size of the gas–liquid interface remain elusive. Furthermore, the interactions of molecules at gas–liquid interfaces must be considered in various contexts, including atmospheric chemical reactions, wettability of surfaces, and numerous other relevant phenomena. Hence, understanding the structure and interactions of molecules at the gas–liquid interface is critical for further improving technologies that operate between the two phases. Electrochemically generated surface nanobubbles provide a stable, reproducible, and high-throughput platform for the generation of a nanoscale gas–liquid boundary. We use total internal reflection fluorescence microscopy to image single-fluorophore labeling of surface nanobubbles in the presence of a surfactant. The accumulation of a surfactant on the nanobubble surface changes the interfacial properties of the gas–liquid interface. The single-molecule approach reveals that the fluorophore adsorption and residence lifetime at the interface is greatly impacted by the charge of the surfactant layer at the bubble surface. We demonstrate that the fluorescence readout is either short- or long-lived depending on the repulsive or attractive environment, respectively, between fluorophores and surfactants. Additionally, we investigated the effect of surfactant chain length and salt type and concentration on the fluorophore lifetime at the nanobubble surface.

The new era of high throughput nanoelectrochemistry

“…22 SMLM was used to monitor the dynamics of molecular adsorption and electrochemical or catalytic processes at various nanoscale interfaces, such as NPs or nanobubbles. [330][331][332][333][334][335][336] Removal of the background incident light is usually achieved through oblique incidence illumination (e.g., in dark-field illumination). Total internal reflection (TIR) incidence allows observation, with higher sensitivity, of the few 200-300 nm adjacent to the illuminated interface.…”

“…409 Optical microscopies are ideal for monitoring dynamically and under operating conditions the dynamics of formation and growth of nanobubbles on surfaces. 410,411 Nanobubbles were imaged by single molecule fluorescence microscopy using fluorescent probes that are trapped at the liquid-gas interface, 334 even forming molecular aggregates. 336 Using this methodology, the group of Zhang imaged the hydrogen spill-over occurring at gold nanoplates supported on ITO electrodes during OER 332 and the delayed production of H2 nanobubbles at AuPd electrode during HER that could be explained by the ability of palladium to store hydrogen.…”

The New Era of High-Throughput Nanoelectrochemistry

“…Single fluorescent molecular probe sensitivity is reached by FM, in what is known as single-molecule localization microscopy (SMLM) . SMLM was used to monitor the dynamics of molecular adsorption and electrochemical or catalytic processes at various nanoscale interfaces, such as NPs or nanobubbles. − …”

“…It has been proposed that those bubbles act as nanoreporters of catalytic activity, and therefore, it has been argued that mapping these nucleation sites reveals the most active region of the electrode . Optical microscopies are ideal for monitoring dynamically and under operating conditions the dynamics of formation and growth of nanobubbles on surfaces. , Nanobubbles were imaged by single-molecule fluorescence microscopy using fluorescent probes that are trapped at the liquid–gas interface, even forming molecular aggregates . Using this methodology, the Zhang group imaged the hydrogen spillover occurring at gold nanoplates supported on ITO electrodes during OER and the delayed production of H 2 nanobubbles at AuPd electrode during HER that could be explained by the ability of palladium to store hydrogen …”

Operando imaging in electrocatalysis: insights into microstructural materials design

“…Nanobubble‐based fluorescence microscopy was employed to study various gas evolution reactions, providing valuable insights through this technique [119,146–148] . Utilizing Rhodamine 6G as a dye molecule, H 2 nanobubbles were labelled with a single dye molecule, enabling the elucidation of their intricate interfacial dynamics (Figure 10a).…”