Interfacial Electron Transfer Reactions Research Articles

Supercapacitor based on the redox of quinone-carbon negative electrode with high cycle performance

A high specific surface area sucrose-derived porous carbon (SPC) using ZnCl2 as a salt template was successfully synthesized. Anthraquinone (AQ) molecules were then immobilized onto the SPC surface via the non-covalent functionalization approach to prepare the quinone-carbon (AQ/SPC) composites. The synthesized composites exhibited excellent self-synergy properties because of SPC's effective three-dimensional (3D) electron transmission network and the rapid-reversible interfacial proton-coupled electron transfer reaction of AQ molecules. Our experimental results indicated that the AQ/SPC-3 electrode in the three-electrode system with a 1 M H2SO4 electrolyte gave the highest specific capacitance (400.7 F g−1), more than twice that of SPC (155.1 F g−1) at a 1 A g−1 current density, exhibiting excellent rate capability and electrochemical reversibility. The cyclic voltammetry of AQ/SPC-3 also exhibited a symmetric and reversible redox peak at negative potential. Hence, we assembled an asymmetric supercapacitor (SPC@AQ/SPC-3) with a two-electrode system and tested it under the same conditions as the three-electrode system. The SPC@AQ/SPC system yielded 71.3 F g−1 and 11.8 Wh kg−1 at 50 W kg−1. At a 5 A g−1 current density, all the SPC@AQ/SPC-3, SPC@DCAQ/SPC-1, and SPC@DMAQ/SPC-1 systems could establish at least 96.94 % of high cycle stability after 10,000 cycles. Notably, by comparing the electron-withdrawing group (Cl) with the electron-donating group (NH2) at the same substitution position of AQ, we found that the electron-withdrawing group has a noticeable promotion effect on redox reversibility and long-term cycle stability.

Potential-Modulated Ion Distributions in the Back-to-Back Electrical Double Layers at a Polarised Liquid|Liquid Interface Regulate the Kinetics of Interfacial Electron Transfer.

Biphasic interfacial electron transfer (IET) reactions at polarisable liquid|liquid (L|L) interfaces underpin new approaches to electrosynthesis, redox electrocatalysis, bioelectrochemistry and artificial photosynthesis. Herein, using cyclic and alternating current voltammetry, we demonstrate that under certain experimental conditions, the biphasic 2-electron O2 reduction reaction can proceed by single-step IET between a reductant in the organic phase, decamethylferrocene, and interfacial protons in the presence of O2. Using this biphasic system, we demonstrate that the applied interfacial Galvani potential difference provides no direct driving force to realise a thermodynamically uphill biphasic IET reaction in the mixed solvent region. We show that the onset potential for a biphasic single-step IET reaction does not correlate with the thermodynamically predicted standard Galvani IET potential and is instead closely correlated with the potential of zero charge at a polarised L|L interface. We outline that the applied required to modulate the interfacial ion distributions, and thus kinetics of IET, must be optimised to ensure that the aqueous and organic redox species are present in substantial concentrations at the L|L interface simultaneously in order to react.

Impedance response of electrochemical interfaces. III. Fingerprints of couplings between interfacial electron transfer reaction and electrolyte-phase ion transport.

Electron transfer (ET), electric double layer (EDL) charging, and ion transport (IT) are three elementary physicochemical processes in electrochemistry. These processes are coupled with each other in the way that the local reaction environment for the ET is shaped by EDL charging, which is nothing but IT in a nanoscale nonelectroneutral region. Herein, we investigate fingerprints of the coupling between these processes in electrochemical impedance spectroscopy. EDL charging and IT are described uniformly using the Poisson-Nernst-Planck theory, and interfacial ET is described using the Frumkin-Butler-Volmer theory. Different diffusion coefficients for cations and anions (D+ ≠ D-) are considered. Exact analytical expressions are obtained when the potential of zero charge (Epzc), the equilibrium potential of the reaction (Eeq), and electrode potential (EM) are equal. The analytical solution shows that a decoupling treatment is valid only for the case of D+ = D-. Using a new scheme of calculating impedance response at any electrode potential, we observe an inductive loop in the low frequency range, which is a clear impedance fingerprint of the coupling effects.

Stable and highly efficient Co–Bi nanoalloy decorated on reduced graphene oxide (Co–Bi@rGO) anode for formaldehyde and urea oxidation reactions

Extremely energetic and low-cost novel nanoelectrodes for fuel cell reactions are always important for examining more elaborative electrochemical studies at interfacial electron transfer reactions. Herein, this work demonstrated a bifunctional electrocatalyst with its oxophilic character and promoting the role of p-electrons of Bi to be supported with Co (nanoalloy) and further decoration on reduced graphene oxide i.e. Co–Bi@rGO presenting as an auspicious electrochemical activity towards formaldehyde and urea oxidation reactions. Synthesized Co–Bi@rGO composite have been well characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), BET surface area measurement, and X-ray photoelectron spectroscopy (XPS) studies, etc. Further, the electrochemical evaluation shows exceptionally higher activity towards formaldehyde and urea oxidation reactions having onset potential of 0.32 V, 0.35 V vs. SCE respectively. Interestingly, ultra-high enhancement factor for Co–Bi@rGO could be initiated from the cooperative role of Bi with Co centres, assisting for formaldehyde and urea oxidation reactions. Electrochemical impedance spectroscopy (EIS) and chronoamperometry (i-t) studies using Co–Bi@rGO nanocomposite shows excellent long-term current/potential stability with lower charge transfer resistance towards the formaldehyde and urea molecules. This work deals with practical information for the build of a stable and proficient electrocatalyst for direct formaldehyde and urea fuel cells and also will extendable towards the industrial waste water treatment.

Role of interfacial electron transfer reactions on sulfamethoxazole degradation by reduced nontronite activating H2O2

It has been documented that organic contaminants can be degraded by hydroxyl radicals (•OH) produced by the activation of H2O2 by Fe(II)-bearing clay. However, the interfacial electron transfer reactions between structural Fe(II) and H2O2 for •OH generation and its effects on contaminant remediation are unclear. In this study, we first investigated the relation between •OH generation sites and sulfamethoxazole (SMX) degradation by activating H2O2 using nontronite with different reduction extents. SMX (5.2–16.9 µmol/L) degradation first increased and then decreased with an increase in the reduction extent of nontronite from 22% to 62%, while the •OH production increased continually. Passivization treatment of edge sites and structural variation results revealed that interfacial electron transfer reactions between Fe(II) and H2O2 occur at both the edge and basal plane. The enhancement on basal plane interfacial electron transfer reactions in a high reduction extent rNAu-2 leads to the enhancement on utilization efficiencies of structural Fe(II) and H2O2 for •OH generation. However, the •OH produced at the basal planes is less efficient in oxidizing SMX than that of at edge sites. Oxidation of SMX could be sustainable in the H2O2/rNAu-2 system through chemically reduction. The results of this study show the importance role of •OH generation sites on antibiotic degradation and provide guidance and potential strategies for antibiotic degradation by Fe(II)-bearing clay minerals in H2O2-based treatments.

Free Energy Dependencies for Interfacial Electron Transfer from Tin-Doped Indium Oxide (ITO) to Molecular Photoredox Catalysts

John B. Goodenough proposed that interfacial electron transfer kinetics from main group metal oxides should be fundamentally different from that of transition metal oxides, an expectation that has not been widely tested. Herein, the kinetics for interfacial electron transfer from mesoporous transparent conductive oxide Tin-doped Indium Oxide (ITO) to four photoredox catalysts (PCs) were characterized in acetonitrile electrolytes. The photocatalysts had the form: [Ru(4,4ʹ-R2-2,2′-bipyridine)2(4,4ʹ-(PO3H2)2-2,2′-bipyridine)]2+, where R was H, methoxy, tert-butyl, and Br. The impact of the surface binding group was characterized with [Ru(2,2′-bipyridine)2(4,4ʹ-(CO2H)2-bpy)]2+. The interfacial electron transfer reaction ITO(e−)∣PC+ → ITO∣PC was quantified by nanosecond absorption spectroscopy as a function of the applied potential (and hence ‒ΔG°). Specific conditions of applied potential were identified where the kinetics were sensitive to the incident irradiance. A layer-by-layer method was used to insert ionic methylene bridge(s) between the PC and the oxide surface. Marcus-Gerischer analysis of the kinetic data indicates non-adiabatic interfacial electron transfer with total reorganization energies that increase when bridges were placed between the photocatalyst and the ITO surface.

Interfacial Electron Transfer in Dye-Sensitized TiO2 Devices for Solar Energy Conversion

The development of cost-effective molecular devices that efficiently capture and convert sunlight into other useful forms of energy is a promising approach to meet the world’s increasing energy demands. These devices are designed through a successful combination of materials and molecules that work synergistically to promote light-driven chemical reactions. Light absorption by a surface-bound chromophore triggers a sequence of interfacial electron transfer processes. The efficiencies of the devices are governed by the dynamic balance between the electron transfer reactions that promote energy conversion and undesirable side reactions. Therefore, it is necessary to understand and control these processes to optimize the design of the components of the devices and to achieve higher energy conversion efficiencies. In this context, this review discusses general aspects of interfacial electron transfer reactions in dye-sensitized TiO2 molecular devices for solar energy conversion. A theoretical background on the Marcus-Gerischer theory for interfacial electron transfer and theoretical models for electron transport within TiO2 films are provided. An overview of dye-sensitized solar cells (DSSCs) and dye-sensitized photoelectrosynthesis cells (DSPECs) is presented, and the electron transfer and transport processes that occur in both classes of devices are emphasized and detailed. Finally, the main spectroscopic, electrochemical and photoelectrochemical experimental techniques that are employed to elucidate the kinetics of the electron transfer reactions discussed in this review are presented.

Interfacial Field-Driven Proton-Coupled Electron Transfer at Graphite-Conjugated Organic Acids.

Interfacial proton-coupled electron transfer (PCET) reactions are central to the operation of a wide array of energy conversion technologies, but molecular-level insights into interfacial PCET are limited. At carbon surfaces, designer sites for interfacial PCET can be incorporated by conjugating organic acid functional groups to graphite edges though aromatic phenazine linkages. At these graphite-conjugated catalysts (GCCs) bearing organic acid moieties, PCET is driven by complex interfacial electrostatic and field gradients that are difficult to probe experimentally. Herein, the spatially inhomogeneous interfacial electrostatic potentials and electric fields of GCC organic acids are computed as functions of applied potential. The calculated proton-coupled redox potentials for the PCET reactions at the GCC phenazine bridges and organic acid sites are in agreement with cyclic voltammetry measurements for a series of GCC acids. The trends in these redox potentials are explained in terms of the acidity of the molecular analogues and continuous conjugation between the acid and the graphite surface. The calculations illustrate that this conjugation is interrupted in a GCC acetic acid system, providing an explanation for the absence of a cyclic voltammetry peak corresponding to PCET at this acid site. This combined theoretical and experimental study demonstrates the critical role of continuous conjugation and strong electronic coupling between the GCC acid site and the graphite to enable interfacial field-driven PCET at the acid site. Understanding the connection between the atomic structure of the surface and the interfacial electrostatic potentials and fields that govern PCET thermochemistry may guide heterogeneous catalyst design.

Shape-dependent performance of gold nanocrystals supported on TiO2 for photoelectrochemical water oxidation under different radiations

A number of studies are documented for enhanced solar energy conversion of titanium dioxide (TiO2) by surface modification with gold (Au) nanostructures. Herein, Au nanocrystals of different geometry (spherical, cubes, triangles and wires) are synthesized and immobilized on TiO2 (bare and nitrogen–doped) surface. The shape–dependent performance of the as-prepared photocatalysts is evaluated by studying water oxidation, both under UV–visible and visible illuminations. As expected, a strong dependency of PEC performance on the shape of Au nanocrystals is discerned. Also, the trend of performance under UV–visible is different than that of visible radiation, suggesting a distinct charge transport mechanism. In addition, the photocatalytic performance increases under visible light while decreases under UV–visible with increasing Au loading. A schematic is proposed showing a likely interfacial electron transfer reaction between Au nanostructures and TiO2, depending on illuminating wavelength. The performance variation in the as-prepared photoelectrodes is correlated to particle size, optical properties and electrical conductivity.

(Norman Hackerman Young Author Award) Multiphase Porous Electrode Theory

As batteries become increasingly common and important in products we use in our daily lives, it becomes similarly important to be able to model their behavior at full cell length and time scales. This capability facilitates both their design and use. The diverse applications in which batteries are applied each require careful design optimization in order to provide the most cost-effective solution satisfying the product needs, and experimentally exploring the full design space in order to find the optimum is impractical. Cell models help drastically narrow the space, enabling cost-effective product development. With existing cells, the models can help provide estimates of difficult-to-measurable internal variables, which may inform usage constraints. In order for the models to provide the most value and ability to extrapolate beyond their training data, their underlying physics must be as representative as possible of the real electrochemical system. Porous electrode theory has been developed, validated, and extended for many battery chemistries for decades and serves as the basis for most physical models at full cell length scales. In this work, we continue in that tradition by exploring the incorporation of new models for both the active particles and the interfacial electron transfer reaction kinetics. In the active particles, we employ non-equilibrium thermodynamics, enabling us to consistently describe particles with internal phase separation within a Cahn-Hilliard-type phase field framework. Many practically relevant electrode materials exhibit phase separation during lithium insertion, and various approaches have been used to model these systems, many of which either neglect the details of the resulting concentration profiles or describe the phase interfaces using numerically inconvenient phase boundaries with no interfacial tension. In the phase field approach, phase boundaries appear and disappear spontaneously according to the governing free energy functional without specialized numerical methods for interface tracking, and they naturally structure themselves in energy-minimizing configurations according to their interfacial tension, system stresses, etc. Rather than being a fit input, the equilibrium voltage emerges as a result of the free energy functional and the highly non-uniform concentration profiles as the average system concentration varies. The lithium in the active materials is consistently coupled to the electrolyte phase by variationally defined reaction kinetics, represented either by a generalized Butler-Volmer expression or quantum-mechanical electron transfer theories such as Marcus-Hush-Chidsey kinetics extended for concentrated solutions. This generalization of porous electrode models reduces directly to the more familiar “Newman” model with concentrated solution theory in the electrolyte in the case of solid solution active materials. Here, we will explore the theoretical developments in the model and present relevant examples, with a focus on comparisons with previous models and some experimental evidence in support of the approach.

Electron Transfer Reactions at Liquid-Liquid Interfaces

Liquid-liquid interfaces can be polarised to carry out charge transfer reactions, in particular electron transfer (ET) reactions between a hydrophilic and a lipophilic redox molecule. These reactions can be studied by classical electrochemical methods such as cyclic voltammetry. By combining spectroscopic time resolved techniques such Surface Second Harmonic Generation with electrochemical methods, we have studied photo-initiated electron transfer reactions between adsorbed porphyrins and redox quenchers located in one of the adjacent phases. By this approach, we can measure the ET kinetics of adsorbed species located mainly at the interface. We have shown that these interfacial ET reactions involving surface species are not sensitive to the interfacial polarisation. More generally, ET reactions at polarised liquid-liquid interfaces will be discussed to place the present results in perspective. In the second part of the talk, the concept of photo-ionic cells will be presented. Here, the photo-products of a photo-ET reactions occurring in the interfacial region are separated between the two adjacent immiscible phases, thereby resulting in energy storage. This electrochemical energy can then be recovered in a classical parallel plate flow cell. We shall discuss the pros and cons of this method of production of solar fuels.

Evidence that ΔS‡ Controls Interfacial Electron Transfer Dynamics from Anatase TiO2 to Molecular Acceptors.

Recombination of electrons injected into TiO2 with molecular acceptors present at the interface represents an important loss mechanism in dye-sensitized water oxidation and electrical power generation. Herein, the kinetics for this interfacial electron transfer reaction to oxidized triphenylamine (TPA) acceptors was quantified over a 70° temperature range for para-methyl-TPA (Me-TPA) dissolved in acetonitrile solution, 4-[N,N-di(p-tolyl)amino]benzylphosphonic acid (a-TPA) anchored to the TiO2, and a TPA covalently bound to a ruthenium sensitizer, [Ru(tpy-C6H4-PO3H2)(tpy-TPA)]2+ "RuTPA", where tpy is 2,2':6',2''-terpyridine. Activation energies extracted from an Arrhenius analysis were found to be 11 ± 1 kJ mol-1 for Me-TPA and 22 ± 1 kJ mol-1 for a-TPA, values that were insensitive to the identity of different sensitizers. Recombination to RuTPA+ proceeded with Ea = 27 ± 1 kJ mol-1 that decreased to 19 ± 1 kJ mol-1 when recombination occurred to an oxidized para-methoxy TPA (MeO-TPA) dissolved in CH3CN. Eyring analysis revealed a smaller entropy of activation |ΔS‡| when the a-TPA was anchored to the surface or covalently linked to the sensitizer, compared to that when Me-TPA was dissolved in CH3CN. In all cases, Eyring analysis provided large and negative ΔS‡ values that point toward unfavorable entropic factors as the key contributor to the barrier that underlies the slow recombination kinetics that are generally observed at dye-sensitized TiO2 interfaces.

DFT and TD-DFT calculations of metallotetraphenylporphyrin and metallotetraphenylporphyrin fullerene complexes as potential dye sensitizers for solar cells

Density functional theory (DFT) and time-dependent DFT calculations have been employed to model metallotetraphenylporphyrin dyes and metallotetraphenylporphyrin –fullerene complexes in order to investigate the geometries, electronic structures, the density of states, non-linear optical properties (NLO), IR–vis spectra, molecular electrostatic potential contours, and electrophilicity. To calculate the excited states of the tetraphenyl porphyrin analogs, time-dependent density functional theory (TD-DFT) are used. Their UV–vis spectra were also obtained and a comparison with available experimental and theoretical results is included. The results reveal that the metal and the tertiary butyl groups of the dyes are electron donors, and the tetraphenylporphyrin rings are electron acceptors. The HOMOs of the dyes fall within the (TiO2)60 and Ti38O76 band gaps and support the issue of typical interfacial electron transfer reaction. The resulting potential drop of Mn-TPP-C60 increased by ca. 3.50% under the effect of the tertiary butyl groups. The increase in the potential drop indicates that the tertiary butyl complexes could be a better choice for the strong operation of the molecular rectifiers. The introduction of metal atom and tertiary butyl groups to the tetraphenyl porphyrin moiety leads to a stronger response to the external electric field and induces higher photo-to-current conversion efficiency. This also shifts the absorption in the dyes and makes them potential candidates for harvesting light in the entire visible and near IR region for photovoltaic applications.

Characterization of Photoactivity of Nanostructured BiVO4 at Polarized Liquid–Liquid Interfaces by Scanning Electrochemical Microscopy

Scanning electrochemical microscopy (SECM) has been used for recording the photoinduced charge-transfer reactions at bismuth vanadate (BiVO4) photocatalyst nanostructures arranged at chemically polarized liquid/liquid (L/L) interfaces between an organic butyronitrile electrolyte and an aqueous electrolyte containing perchlorate as common anion. In addition, [Co(bpy)3](PF6)3 soluble in the organic phase was used as a probe of SECM analysis but also as a sacrificial agent, which effectively improves the separation efficiency of photogenerated charge carriers at the BiVO4 modified L/L interface. The nanoassembled layer did not require contact to a current collector. Interfacial polarization effects on the photoinduced charge-transfer reactions have been investigated by recording the regeneration of the reduced form [Co(bpy)3](PF6)2 at the BiVO4 particle layer in organic phase in SECM feedback approach curves. The kinetic parameters of the interfacial photoinduced electron transfer (ET) reaction have been ana...

Kinetics analysis of interfacial electron-transfer processes in goethite suspensions systems

The photochemical behavior of goethite has been one of the most important topics in the field of environmental science due to it plays a significant role in the removal and transformation process of numerous pollutants. However, the interfacial electron transfer process of goethite is not clear. Using a nanosecond laser flash photolysis spectrometer, we report the transient spectroscopic observations of interfacial electron-transfer reactions in goethite dispersion under UV irradiation. Excitation of goethite generated conduction-band electron (ecb−) and hole (h+). The conduction band electron (ecb−) reacted with an electron acceptor, methylviologen dichloride hydrate (MV2+), forming reduced methylviologen (MV+) with a second-order rate constant of (2.6 ± 0.3) × 109 L mol−1 s−1. The concentration of MV+ was strongly influenced by MV2+ initial concentration and pH values. The flat band potential of goethite was calculated to be Efb (goethite, pH = 7) = 0.24 V (vs NHE). Oxygen did not react with conduction band electron of goethite. The present study provides a reliable method to investigate the photo-induced interfacial charge transfer of goethite.

A novel impedimetric aptasensor, based on functionalized carbon nanotubes and prussian blue as labels

A simple and feasible electrochemical sensing protocol was developed for the detection of bisphenol A (BPA) by employing the gold nanoparticles (AuNPs), prussian blue (PB) and functionalized carbon nanotubes (AuNPs/PB/CNTs-COOH). An aminated complementary DNA as a capture probe and specific aptamer against BPA as a detection probe was immobilized on the surface of a modified glassy carbon (GC) electrode via the formation of covalent amide bond and hybridization, respectively. The proposed nanoaptasensor combined the advantages of the in situ formation of PB as a label, the deposition of neatly arranged AuNPs, and the covalent attachment of the capture probe to the surface of the modified electrode. Upon addition of target BPA, the analyte reacted with the aptamer and caused the steric/conformational restrictions on the sensing interface. The formation of BPA–aptamer complex at the electrode surface retarded the interfacial electron transfer reaction of the PB as a probe. Sensitive quantitative detection of BPA was carried out based on the variation of electron transfer resistance which relevant to the formation of BPA– aptamer complex at the modified electrode surface. Under the optimized conditions, the proposed aptasensor exhibited a high sensitivity, wide linearity to BPA and low detection limit. This aptasensor also displayed a satisfying electrochemical performance with good stability, selectivity and reproducibility.

A simple and label-free aptasensor based on amino group-functionalized gold nanocomposites-Prussian blue/carbon nanotubes as labels for signal amplification

Herein, a novel label-free electrochemical aptasensor based on gold nanoparticles/Prussian blue/carbon nanotubes (AuNPs/PB/CNTs) for dopamine (DA) determination was reported. A special AuNPs/PB/CNTs nanocomposite which integrated the individual properties of each nanomaterial was utilized to improve the conductivity and performance characteristics of the biosensor as well as to increase the loading amount of aptamer. Chitosan was coated onto nanocomposite and provided a biocompatible interface with abundant-NH2 groups for the immobilization of DA-specific aptamer. Abundant-NH2 groups in nanocomposite made this platform as significant transduction by allowing phosphoramidate bonds formed between the amino group of chitosan and phosphate group of the aptamer at 5′end. To translate the binding events between aptamer and DA into the measurable electrochemical signal, the PB as signal probe was in situ introduced on the electrode surface, exhibiting well-defined peaks with good stability and reproducibility. The designed immobilized DA–aptamer resulted in the formation of long tunnels on modified electrode surface, while aptamer acted as gate of the tunnels. The aptamer gates were closed due to change in conformation of aptamer upon target (DA) binding, retarding the interfacial electron transfer reaction of the probe, resulting in the decrease of the electrochemical signal. Under optimized conditions, the proposed aptasensor showed good detection range from 0.5 to 50nM with unprecedented detection limit of 200pM. This aptasensor also exhibited good stability and high selectivity for DA detection without an interfering effect of some other compounds.

Molecular Dynamics Study of Fe(II) Adsorption, Electron Exchange, and Mobility at Goethite (α-FeOOH) Surfaces

We present classical molecular simulations of the adsorption free energy profiles for the aqueous Fe(II) ion approaching key low index crystal faces of goethite at neutral surface charge conditions. Calculated profiles show minima corresponding to stable outer- and inner-sphere adsorbed structures. We analyzed the energetics and kinetics of most possible interfacial electron transfer reactions, as well as analyzing the same for subsurface migration pathways of injected electrons through calculating the Marcus free energy surfaces. We conclude that inner-sphere Fe(II)-complex formation is required for the interfacial electron transfer to occur, but the energetic cost of moving from the outer-sphere to inner-sphere geometry may prevent electron injection at some faces. We also show that some surfaces, especially (101), (100) and (001), are more energetically prone toward reduction than others. We demonstrate that subsurface charge migration in directions parallel to the surface, which run along the iron chains, is more energetically plausible than conduction through the resistive crystal bulk phase. Collectively this leads to the conclusion that Fe(II)-catalyzed recrystallization of goethite most likely proceeds by short path length electron migration through specific goethite surfaces along specific directions, until capture at Fe sites structurally susceptible to reduction and release.

A simple and label-free aptasensor based on nickel hexacyanoferrate nanoparticles as signal probe for highly sensitive detection of 17β-estradiol

A simple and label-free electrochemical aptasensor was developed for detecting 17β-estradiol (E2). To translate the binding events between aptamer and E2 into the measurable electrochemical signal, the nickel hexacyanoferrate nanoparticles (NiHCF NPs) as signal probe was in situ introduced on the electrode by a simple two-step deposition method, exhibiting well-defined peaks with good stability and reproducibility. Subsequently, Au nanoparticles (Au NPs) was covered on the NiHCF NPs, which not only provided a platform for immobilizing the aptamer by S–Au interaction, but further enhanced the conductivity and stability of the signal probe. With the addition of E2, the formation of E2–aptamer complexes on the sensing interface retarded the interfacial electron transfer reaction of the probe, resulting in the decrease of the electrochemical signal. E2 could be readily examined by measuring the signal change. A linear range of 1×10−12–6×10−10M was obtained with a low detection limit of 0.8×10−12M. The aptasensor also exhibited high specificity to E2 in control experiments employing seven endocrine disrupting compounds as the interferents that had similar structure or coexisted with E2 in the environment. Besides, the applicability of the aptasensor was successfully evaluated by determining E2 in the real samples.

Optical signal demultiplexing and conversion in the fullerene–oligothiophene–CdS system

We report the photoelectrochemical photocurrent switching (PEPS) effect in the system based on a C60 derivatives and nanostructured cadmium sulfide. Rapid and efficient photocurrent switching upon changes of the electrode potential was observed. This process relies on the photocurrent generation by semiconducting particles and interfacial electron transfer reactions governed by the redox chemistry of fullerene derivatives (fullerene–oligothiophene dyads) with molecular oxygen as a final electron acceptor. Surprisingly, fullerene derivatives without thiophene moieties were much less efficient as CdS modifiers. These peculiar photoelectrochemical properties were applied for construction of an optoelectronic logic device.