Ferrocene (Fc)-encapsulated cucurbit[7]uril (CB[7]) supramolecular host–guest complex (Fc@CB[7]) as a synthetic recognition pair has been widely adapted for coupling biomolecules and nanomaterials due to its ultrahigh binding affinity. In this paper, we have explored the binding of CB[7] on binary ferrocenylundecanethiolate/octanethiolate self-assembled monolayer on gold (FcC11S-/C8S-Au), a model system to develop our understanding of host–guest chemistry at molecular interfaces. It has been shown that upon incubation with CB[7] solution the redox behavior of FcC11S-/C8S-Au changes remarkably; i.e., a new pair of peaks appeared at more positive potential with narrowed widths. The ease of quantitation of surface bound-redox species (Fc+/Fc and Fc+@CB[7]/ Fc@CB[7]) enabled us to determine the thermodynamic formation constant of Fc@CB[7] at FcC11S-/C8S-Au (7.3 ± 1.8 × 104 M–1). With time-dependent redox responses, we were able to, for the first time, deduce both the binding and dissociation rate constants, 2.8 ± 0.3 × 103 M−1s−1 and 0.08 ± 0.01 s–1, respectively. These results showed substantial differences both thermodynamically and kinetically for the formation of host–guest inclusion complex at molecular interfaces with respect to solution-diffused, homogeneous environments.

•The mercaptosuccinic acid works like “glue” to stick partially oxidized graphene on the electrodes.•The electrodes show the tunable electron-transfer mediation ability which is controlled by the oxidation degree of the graphene.•The electrodes show the ability of in-situ electrochemical disassembly.In this research a class of graphene modified electrodes based on self-assembled monolayer assisted binding of partially oxidized graphene on gold was achieved. The electrodes show two features: (1) the tunable electron-transfer mediation ability which is controlled by the oxidation degree of the graphene, and (2) the ability of in-situ electrochemical disassembly. The tunable electron-transfer mediation ability was investigated by interpreting the cyclic voltammogram recorded with the classic redox couple, potassium ferricyanide/ferrocyanide. The ability of in-situ electrochemical disassembly was investigated by cyclic voltammetry and electrochemical impedance spectroscopy in the case of enzyme adsorption. It was found that the “on” and “off” conditions of the partially oxidized graphene correspond to the assembly and disassembly of the mercaptosuccinic acid self-assembled monolayer respectively, endowing the electrodes with the ability of in-situ electrochemical disassembly. In addition, the experimental results on glucose sensing illustrate the potential applications of the graphene modified electrodes.

•The enhanced positive feedback current of SECM is observed at a large tip-substrate separation in the case of a 3-MPA SAM.•The long-range effect is resulting from concentration increment of redox species by untying the hydrogen bonds beforehand formed between the tip redox species and the 3-MPA SAM.•The long-range effect is applied to the single cell test using SECM which is beneficial for cell tests without affecting the natural metabolic pathway and cell morphology.The enhanced positive feedback current of scanning electrochemical microscopy (SECM) is observed at a large separation between the tip and the substrate surface in the case of a 3-mercaptopropionic acid (3-MPA) self-assembled monolayer (SAM). The effect that induces the large separation (named the long-range effect) is confirmed by SECM and quantitatively studied by electrochemical quartz crystal microbalance (EQCM). A key finding is that the long-range effect results from untying hydrogen bonds beforehand formed between the hydroxyl group of tip redox species and the carboxyl group of 3-MPA SAM. It is found that the long-range effect is increased with the packing density of the 3-MPA SAM. On the basis of these findings, the long-range effect is applied to the nondestructive test of living cells using SECM.

A facile one-step approach has been developed to fabricate partially reduced graphene oxide–polypyrrole (prGO-PPy) film via self-oxidation–reduction strategy, in which graphene oxide acts as the oxidant to polymerize pyrrole into PPy leading to the spontaneous partial reduction of GO and cross-linking between prGO and PPy via π–π interaction. With the convenient preparation method, a well controlled designed asymmetric actuator based on GO (or G)/prGO-PPy film with excellent humidity and electrochemical responses has been achieved for versatile stimulated actuations that will also play essential roles in advanced actuators for many important intelligent applications.Keywords: actuator; film; graphene oxide; nanocomposites; polypyrrole

•Electrochemistry at immiscible liquid–liquid interfaces is fundamentally important.•Methods for studying redox processes at liquid–liquid interfaces are reviewed.•Thin-film voltammetry is simple in experimental operation and kinetic data analysis.•Thin-film voltammetry’s analytical applications are prevailing and comprehensive.Electrochemical reactions at the interfaces of immiscible electrolyte solutions (ITIES) are of fundamental importance in the fields of chemical, biological and pharmaceutical sciences. Four-electrode cell setup, scanning electrochemical microscopy (SECM) and thin-film voltammetry are the three most frequently used methods for studying the electrochemical processes at these interfaces. The principle, experimental design, advantages and challenges of the three methods are described and compared. The thin-film voltammetry is highlighted for its simplicity in experimental operation and kinetic data analysis. Its versatile analytical applications are discussed in detail, including the study of redox properties of hydrophobic compounds, evaluation of interfacial electron transfer kinetics, synthesis of nanoparticles/nanostructures, and illustration of cross-membrane ion transport phenomena.

•Unique intramolecular electronic communications (electron withdrawing and π-bond delocalization effects) exist in the mono-ferrocenylpyrimidine derivatives.•The redox potential shift correlates the pyrimidine ring torsion angle with the extent of electron delocalization.•The correlation between redox properties and structural nature in mono-ferrocenylpyrimidine derivatives is evident.The correlation between redox properties and structural nature in a complete set of mono-ferrocenylpyrimidine derivatives (2-ferrocenylpyrimidine, 2-FcPy; 4-ferrocenylpyrimidine, 4-FcPy; 5-ferrocenylpyrimidine, 5-FcPy) was evaluated by investigating the intramolecular electronic communications. Both conventional electrochemical measurements in organic solvents and thin-film voltammetric studies of these compounds were carried out. It was discovered that their formal potentials are significantly different from each other, and shift negatively in the order of 4-FcPy > 5-FcPy > 2-FcPy. This result suggests that the intramolecular electronic communication is dictated by the delocalization effect of the π-bonding systems in 2-FcPy, and that the electron-withdrawing effect of the nitrogen atoms in the pyrimidine ring plays the key role in 4-FcPy and 5-FcPy. The single crystal X-ray structure analyis and Density Functional Theory (DFT) calculation provided additional evidence (e.g., different torsion angles between the cyclopentadienyl and pyrimidine rings) to support the observed correlation between the redox properties and structural nature.

Pore-rich graphene networks hold great promise as advanced supporting materials of metals and metal oxides for high electrochemical performance. In this work, a dual substrate-assisted reduction and assembly (DSARA) process has been devised and demonstrated as a general approach for the spontaneous reduction of graphene oxide, well-organized assembly of reduced graphene oxide into three-dimensional porous networks, and simultaneous functionalization of graphenes with metal-based nanocomponents on demand, including metals, metal oxides, metal/metal oxide hybrids or alloys. The newly designed process avoids the use of toxic reducing agents, multiple steps, and long reaction times, and offers a facile but powerful pathway to greatly enhance the merits of using pristine graphenes in energy-related applications such as lithium ion batteries, fuel cells, photoelectric conversion devices, and so on. Specifically, as an anode material in a lithium ion battery (LIB), the DSARA-produced RGO decorated with NiO/Ni nanohybrids presents a record capacity with a high charge–discharge rate compared to those reported so far for Ni based materials. PdPt alloy nanoparticles on 3D RGO generated by DSARA exhibits a highly efficient catalytic performance for the oxygen reduction reaction (ORR) in fuel cells.

The intramolecular electronic communication and multilevel ion-pairing effect of triferrocenylmethane (TriFcM) in organic phase was studied with the “thin-layer electrochemistry” approach. Three pairs of symmetric peaks in cyclic voltammetry of TriFcM correspond to three one-electron electrochemical reaction processes and indicate strong intramolecular electronic communication, which could be used to study the multilevel ion-pairing effect. Three different formation constants of ion-pairs between the three ferroceniums of TriFcM and perchlorate in thin organic film were obtained and compared.The multilevel ion-pairing effect was first investigated using triferrocenylmethane through “thin-layer electrochemistry” approach and the influence of intramolecular electronic communication on multilevel ion-pairing effect was also studied.

Ferrocenylalkanethiols are excellent probes to study the structure and properties of mixed self-assembled monolayers (SAMs) on gold; in this paper, the molecular heterogeneity in binary redox-active SAMs on gold prepared via postassembly exchange and coadsorption processes is revealed electrochemically. The exchange process of single-component 11-ferrocenyl-1-undecanethiolate SAMs on gold (FcC11S–Au) with 1-undecanethiol (C11SH) is first investigated; it is shown that a single pair of redox peaks can be obtained upon prolonged immersion in C11SH/ethanol solution. For the coadsorption of FcC11SH and C11SH on gold, the splitting of the redox peak diminishes when the molar ratio FcC11SH decreases to <10%. The binary FcC11S-/C11S–Au SAMs with low surface density of ferrocene moieties prepared by these two methods are compared by fitting the cyclic voltammograms (CVs) in considering their intermolecular interactions. The essentially different distributions of the redox centers in these diluted binary SAMs, as indicated by the varied formal potentials and intermolecular repulsion forces, provide further insights in understanding molecular self-assembly processes on the surface.

Direct electrochemistry of glucose oxidase (GOD) on three-dimensional (3D) interpenetrating porous graphene electrodes has been reported, which have been fabricated by one-step electrochemical reduction of graphene oxide (GO) from its aqueous suspension. The electrochemically reduced GO (ERGO) modified electrodes exhibited excellent electron transfer properties for GOD and enhanced the enzyme activity and stability by the assistance of chitosan. The immobilized GOD shows a fast electron transfer with the rate constant (ks) of 6.05 s−1. It is worth mentioning that in the air-saturated phosphate buffer solution without any mediator, the resultant modified electrodes exhibited low detection limit of 1.7 μM with wide linear range of 0.02–3.2 mM and high sensitivity and high selectivity for measuring glucose. It would also be extended to various enzymes and bioactive molecules to develop the biosensor or other bio-electrochemical devices.

Redox-labeled self-assembled monolayers (SAMs) on gold are excellent model systems for the study of long-range electron transfer processes at electrolyte–electrode interfaces, particularly the distance and reorganization energy dependences. In this work, we have shown that the intermolecular interaction among redox centers is in fact a crucial factor in the overall, nonideal electrochemical response of ferrocenylalkanethiolate SAMs on gold. In both single-component and high-ratio binary monolayers of 11-ferrocenyl-1-undecanethiol (FcC11SH), the two distinct pairs of redox peaks are corresponding to rather moderate differences in the packing densities of the two structural domains. We have discovered that the redox peak at lower potential becomes narrower and higher when organic solvents (nitrobenzene or octanol) are added to the aqueous electrolyte, while the peak at the higher potentials is barely influenced. On the basis of the Frumkin isotherm, we have obtained the intermolecular interaction parameters in the different structural domains of the monolayers by fitting the experimental data. The results showed that the intermolecular interaction in the FcC11S–Au SAMs can change from repulsion to attraction upon adding organic solvent in the aqueous electrolyte. It is suggested that the solvent perturbation to the SAM structure at monolayer/electrolyte interface induces remarkable change in the intermolecular interactions and therefore modulates the observed electrochemical responses from nonideal to nearly ideal.

A highly selective nitric oxide (NO) sensor is fabricated and applied to devise an enhanced flow injection analysis (FIA) system for S-nitrosothiols (RSNOs) measurement in biological samples. The NO sensor is prepared using a polytetrafluoroethylene (PTFE) gas-permeable membrane loaded with Teflon AF® solution, a copolymer of tetrafluoroethylene and 2,2-bis(trifluoroethylene)-4,5-difluoro-1,3-dioxole, to improve selectivity. This method is much simpler and possesses good performance over a wide range of RSNOs concentrations. Standard deviation for three parallel measurements of blood plasma is 4.0%. The use of the gas sensing configuration as the detector enhances selectivity of the FIA measurement vs. using less selective electrochemical detectors that do not use PTFE/Teflon type outer membranes.

We report a new method for detection and oxidation of adsorbed carbon monoxide (CO(ads)) generated from serine on a polycrystalline platinum ultramicroelectrode (UME) by bromine (Br2) using in situ surface interrogation (SI) mode of scanning electrochemical microscopy (SECM). In the SI mode, tip and substrate are both Pt UMEs, and CO(ads) on Pt substrate, generated from serine, can be oxidized by the tip-generated Br2 giving a positive response. Dosing CO(ads) from serine instead of purging CO gas expands the newly introduced reaction of Br2 with CO(ads) and further enhances the hope to get rid of CO(ads) on Pt for fuel cells.

•A graphene fiber hydroelectric power generator (GF-Pg) is produced.•A 1 mm GF-Pg with a diameter of 80 µm can supply an output of ca. 0.4 V.•The flexible fiber device can be easily integrated into fabric for electronical label.With the fast development of wearable electronics, portable energy generation devices are attracting our considerable attention. Among them, the wearable self-powered system spontaneously harvesting energy from the environment will be much needed. Herein, a high-performance graphene fiber power generator (GF-Pg) is produced based on graphene oxide (GO) fiber. The GF-Pg has highly oriented GO sheets assembled within the fiber, which provide favorable channels for efficient ion transport and thus harvests energy from the moisture. A single fiber generator unit with a length of less than 1 mm and a diameter of 80 µm was able to supply a voltage output of 355 mV in response to the humidity variation, which could be enhanced to 1.3 V by simply increasing the number of device units. Impressively, this moisture-enabled self-powered fiber could be integrated into flexible textiles to realize an information storage/expression based on the breath activated electronic labels of GF-Pg, demonstrating the promising applications in wearable electronics.