Interface between Two Immiscible Electrolyte Solutions Electrodes for Chemical Analysis.

The interface between two immiscible electrolyte solutions (ITIES) plays vital roles in various fields, such as neuroscience, environmental science, analytical chemistry, separation, catalysis, and nanoparticle synthesis. ITIES emerges as a unique approach in chemical analysis due to its sensitivity to both redox-active and redox-inactive analytes. Neurotransmitters, metal ions, drug molecules, and other complex molecules such as proteins have been detected using ITIES. The detection of redox-inactive species at the ITIES has opened a door to understanding a wide range of complex systems that are less suited to probing by solid electrodes. In this feature article, we present the history of electrochemistry at the ITIES; charge transfer reactions, thermodynamics, and kinetics at the ITIES; electrode-solution interfacial structure; and a diverse range of applications enabled by ITIES.

Detection of Acetylcholine at Nanoscale NPOE/Water Liquid/Liquid Interface Electrodes.

The interface between two immiscible electrolyte solutions (ITIES) has become a very powerful analytical platform for sensing a diverse range of chemicals (e.g., metal ions and neurotransmitters) with the advantage of being able to detect non-redox electroactive species. The ITIES is formed between organic and aqueous phases. Organic solvent identity is crucial to the detection characteristics of the ITIES [half-wave transfer potential (E1/2), potential window range, limit of detection, transfer coefficient (α), standard heterogeneous ion-transfer rate constant (k0), etc.]. Here, we demonstrated, for the first time at the nanoscale, the detection characteristics of the NPOE/water ITIES. Linear detection of the diffusion-limited current at different concentrations of acetylcholine (ACh) was demonstrated with cyclic voltammetry (CV) and i-t amperometry. The E1/2 of ACh transfer at the NPOE/water nanoITIES was -0.342 ± 0.009 V versus the E1/2 of tetrabutylammonium (TBA+). The limit of detection of ACh at the NPOE/water nanoITIES was 37.1 ± 1.5 µM for an electrode with a radius of ∼127 nm. We also determined the ion-transfer kinetics parameters, α and k0, of TBA+ at the NPOE/water nanoITIES by fitting theoretical cyclic voltammograms to experimental voltammograms. This work lays the basis for future cellular studies using ACh detection at the nanoscale and for studies to detect other analytes. The NPOE/water ITIES offers a potential window distinct from that of the 1,2-dichloroethane (DCE)/water ITIES. This unique potential window would offer the ability to detect analytes that are not easily detected at the DCE/water ITIES.

Chiral Plasmons: Au Nanoparticle Assemblies on Thermoresponsive Organic Templates.

Template-assisted strategies are widely used to fabricate nanostructured materials. By taking these strategies a step forward, herein we report the design of two chiral plasmonic nanostructures based on Au nanoparticle (NP) assemblies organized in clockwise and anticlockwise directions, having opposite response to circularly polarized light. The chiral plasmonic nanostructures are obtained by growing Au NPs on chiral templates based on d- and l-forms of alanine functionalized phenyleneethynylenes. Interestingly, Au NP assemblies show mirror symmetrical electronic circular dichroism (ECD) bands at their surface plasmon frequency originating through their asymmetric organization. Upon increasing the temperature, the chiral templates dissociate as evident from the disappearance of their ECD signal. The profound advantage of the thermoresponsive nature of the templates is employed to obtain free-standing chiral plasmonic nanostructures. The tilt angle high-resolution transmission electron microscopic measurements indicate that the NP assemblies, grown on a template based on the d-isomer, organize in clockwise direction ( P-form) and on l-isomer in anticlockwise direction ( M-form). The inherent chirality prevailing on the surface of the template drives the helical growth of the Au NPs in opposite directions. Experimental results are rationalized by a model which accounts for the large polarizability of Au NPs. The large polarizability leads to large oscillating dipole moments whose effects become prominent when interparticle distances are comparable to the particle size.