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Single-entity electrochemistry, which employs electrolysis during the collision of single particles on ultramicroelectrodes, has witnessed significant advancements in recent years, enabling the observation and characterization of individual particles. Information on a single aqueous droplet (e.g., size) can also be studied based on the redox species contained therein. Dopamine, a redox-active neurotransmitter, is usually present in intracellular vesicles. Similarly, in the current study, the electrochemical properties of neurotransmitters in submicron droplets were investigated. Because dopamine oxidation is accompanied by proton transfer, unique electrochemical properties of dopamine were observed in the droplet. We also investigated the electrochemical properties of the adsorbed droplets containing DA and the detection of oxidized dopamine by the recollision phenomenon. [ABSTRACT FROM AUTHOR]

We studied the electrochemical detection of single nanosized water emulsion droplets in organic solution using the electrochemical collision technique on an ultramicroelectrode (UME). In this experiment, the detection system for water droplets does not require any kind of redox species in organic solvent. Only water molecules in the water droplets were considered. When water droplets collided with the UME surface, anodic current spikes were observed in the chronoamperometry, resulting from the electrolysis of water molecules in the water droplets. From the collision frequency and integrated current spike, concentrations and size distributions of water droplets in organic solvent can be determined. [ABSTRACT FROM AUTHOR]

Single nanoparticle (NP) collisions were successfully observed by a potentiometric measurement. The open circuit potential (OCP) of a measuring Au ultramicroelectrode (UME) changes when Pt NPs collide with the UME in a hydrazine solution. The OCP change is related to the redox processes, the concentration of particles, particle size, and electrode size. Compared with the amperometric technique, this approach has several advantages: higher sensitivity, simpler apparatus, fewer problems with NP decomposition, and contamination. [ABSTRACT FROM AUTHOR]

We report the electrochemical detection of single water droplets in an electrolyte-free organic solvent by collision events using a platinum ultramicroelectrode (Pt-UME). Water droplet emulsions were prepared by the ultrasonication of an organic solvent (e.g., dichloroethane) and an aqueous solution containing hydroquinone (H 2 Q) as the redox species and MgSO 4 as an emulsion stabilizer as well as the supporting electrolyte. Under the appropriate potentials, we could observe single water droplet collision phenomena at the Pt-UME by amperometric current-time (I-t) measurements. Water droplets that established contact with the Pt-UME led to amperometric current spikes due to the instantaneous electrolysis of the constituent redox species. The concentration of H 2 Q in the emulsion was adjusted to confirm that the amperometric spike resulted from the electrochemical reaction in the water droplet. As the concentration of H 2 Q increased, the oxidation peak current increased. The size and contact area of the water droplets were also estimated. Based on these single droplet collision results, we could successfully establish a facile water droplet detection system in an organic solvent without the addition of a hydrophobic organic electrolyte. Image 1 [ABSTRACT FROM AUTHOR]