We present a novel design for an electrochemical cell with a thickness of approximately 30 µm. The design incorporates a carbon fiber electrode (with a diameter of 10 µm) inserted through a bubble wall or stable surfactant film, which serves as the electrochemical medium. To establish a stable surfactant film, we utilized a solution filled with non-ionic Triton-X100 surfactants. This medium was employed for both electrochemical sensing and electrodeposition purposes.

For microelectroanalysis, a modified carbon microelectrode coated with nanosheet graphene oxide (serving as the sensing electrode) was positioned across a soap bubble wall. A 1 mm diameter silver wire was used as the counter/reference electrode, while the soap bubble contained dissolved nitrite ions. This approach enabled the proposed sensing system to successfully detect NO2-, both when present on a hand and when dissolved in the Triton-X100 surfactant film. This technique holds particular significance in criminal investigations, as the presence of NO2- ions on the hand indicates gunshot residue and can aid in suspect identification. Therefore, this sensing strategy offers rapid analysis with a low detection limit of 28 µM. It proves functional for on-site sensing, making it suitable for efficient police and criminal investigations. Notably, compared to the current method, it is simple, cost-effective, involves only one step, and eliminates the need for any sample preparation steps.

In the second part of the study, we evaluated the micro-electrodeposition process within a bubble wall. For electrodeposition, various ions, such as silver and palladium ions, were dissolved within the bubble film. A bare carbon microelectrode was positioned within the bubble wall, and an appropriate cathodic potential was applied. The resulting metallic film was analyzed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy. The images obtained from the analysis revealed that the thickness of the bubble wall or electrochemical cell imposes limitations on the electrodeposition area at the microscale level. Furthermore, the lifespan of the bubble wall played a crucial role in controlling the duration and thickness of the deposited film, ranging from the nanoscale to the microscale.

Finally, we believe that this novel work can open new approaches in sensing and synthesis in electrochemical science.