Defined Ion-Transfer Voltammetry of a Single Microdroplet at a Polarized Liquid/Liquid Interface

Abstract

A strategy for the fast analysis of ion transfer/facilitated ion transfer toward a tiny (femtoliter) water-in-oil droplet has been established. This scenario is embodied by the fusion of a w/o microdroplet at the micro liquid/liquid (L/L) interface, with the use of Fourier transform fast-scan cyclic voltammetry (FT-FSCV) to express the apparent half-wave potentials of anions or cations encapsulated inside the w/o microdroplet. First, the half-wave potential is in strict accordance with the transfer Gibbs free energy of either cations or anions. Second, the half-wave potential has been found to be positively proportional to the logarithmic concentration of ions, shedding thermodynamic insight into ion transfer. Third, as an instance of multivalent biopolymers, the transfer of protamine inside the single w/o microdroplet has been investigated. Obvious discrepancies in the behaviors of the fusion impacts at different pH, as well as in the absence and presence of the cationic surfactant DNNS–, are revealed. The internal mechanism of protamine transfer has been thoroughly investigated. This work proposes a strategy to sensitively and quickly determine the transfer Gibbs energy and the concentration of ions encapsulated in a single microdroplet, and it provides the possibility of analyzing the interfacial transfer properties of trace biomacromolecules inside an aqueous micro- or nanoscale droplet.

Mass Transfer from Ion-Sensing Component-Loaded Nanoemulsions into Ion-Selective Membranes: An Electrochemical Quartz Crystal Microbalance and Thin-Film Coulometry Study

“…Thin-film coulovoltammetry (TFCV) can also be used to visualize the uptake of neutral ionophores as shown in Figure . Based on earlier research, ,,− ion–ionophore interactions give rise to a peak shift for the outward cation transfer inhibited by the ionophore relative to the uncomplexed ion, requiring a more positive potential. The relative charge from these two peaks can be used to monitor ionophore uptake if the cation-exchanger in the PVC membrane is kept at a sufficiently high concentration (here at 100 mmol kg –1 ).…”

Disposable-micropipette tip supported electrified liquid–organogel interface as a platform for sensing acetylcholine

“…Miniaturization of ITIES has been mainly classified based on the fabrication methods used to obtain the interfaces: namely pulled glass pipettes, thin polymer or silicon membranes and micro-cavity. [22][23][24][25][26][27][28] Numerous analytical opportunities have been offered by electrified ITIES, especially in the development of chemical and biochemical sensing applications. [29][30][31] From our knowledge, electrified soft/liquid-liquid interfaces have been potential platforms for sensing applications.…”

Galvani Potential-Dependent Single Collision/Fusion Impacts at Liquid/Liquid Interface: Faradic or Capacitive?

“…Stochastic collision of single entities by electrochemical methods (so-called nano-impacts) has emerged as a successful alternative for the study of so-called “hard” particles (metal, − metal oxide, − carbonaceous, , polymeric, core–shell structure, , etc.) particles and “soft” particles (microdroplets, − liposomes, micelles, vesicles, cells, etc.). In particular, the nano-impact experiments of “hard” or “soft” entities at the micro-interface between two immiscible electrolyte solutions (micro-ITIES) have become a research hotspot. − ,− On the one hand, ITIESs are generally more uniform (defect-free), reproducible, and easily renewable than electrode-solution interfaces.…”