Ferrocene Dimethanol Research Articles

A Propylpyridinyl Triazine Salt for Dual‐Band Electrochromic Devices with Accelerated Response by Sulfonyl Group

AbstractThe chromophore 2,4,6‐tri(pyridyl‐4‐(3‐sulphonatopropyl))‐1,3,5‐triazine (TPST) was used in hydrogel electrochromic devices (ECDs). The hydrogel consists of TPST, K3[Fe(CN)6]/K4[Fe(CN)6] (K3) or 1,1’‐ferrocenedimethanol (FM), and sodium carboxymethyl cellulose. The devices showed dual‐band properties, K3‐TPST exhibiting absorption in NIR region at low voltage, while absorption of ECDs blue‐shifting at −2.8 V. ECDs changed from transparent to olive green to black with a coloration efficiency of >126.74 cm2/C at 850 nm and high cycling stability. The optical contrast of FM‐TPST ECD remains 79.3 % of the first cycle contrast after 2100 cycles. TPST can change its color from transparent to black at a high voltage of −2.2 V, with relatively short switching times (FM‐TPST, 5.3 s, and K3[Fe(CN)6]/K4[Fe(CN)6]‐TPST, 3.8 s). The response was accelerated up to 5 times by introducing a sulfonyl group with comparison to our previous work. The devices using TPST with sulfonyl moiety provide a new way for the fast‐response energy‐saving smart windows.

Specific and ultrasensitive detection of Staphylococcus aureus with a catechol-chitosan redox capacitor based electrochemical aptasensor

• To construct an ultrasensitive electrochemical aptasensor for S. aureus analysis. • Preparation of a redox capacitor amplification system to improve sensitivity. • The aptasensor shows an LOD of 2 CFU/mL and a detection time of 25 mins. • The aptasensor shows good adaptability to real blood samples. The effective and accurate detection of Staphylococcus aureus ( S. aureus ) is of great importance for quickly treating infected patients, preventing the spread of infection and reducing the formation of resistant strains. This paper describes an electrochemical aptasensor for specific and ultrasensitive detection of S. aureus by combining a redox capacitor amplification system and a specific aptamer. The redox capacitor amplification system was constructed using catechol-chitosan film and 1,1′-ferrocene dimethanol (Fc)-hexaammineruthenium (III) chloride (Ru 3+ ) mediators. The aldehyde-modified aptamer was immobilized on the electrode surface by the Schiff base reaction with the amino groups of chitosan and served as a specific biological recognition element for S. aureus . The proposed electrochemical aptasensor presented great performance in terms of detection time (25 min), linear range (10 ∼ 10 8 cfu/mL) and detection limit (2 cfu/mL). The proposed biosensor also displayed good reproducibility and selectivity. The electrochemical apatsensor can quantitatively and directly detect S. aureus in whole blood samples (the spiked recovery rate was 90.5–100.1%), laying the foundation for its clinical application.

Nanoscale Visualization of Electrochemical Activity at Indium Tin Oxide Electrodes.

Indium tin oxide (ITO) is a popular electrode choice, with diverse applications in (photo)electrocatalysis, organic photovoltaics, spectroelectrochemistry and sensing, and as a support for cell biology studies. Although ITO surfaces exhibit heterogeneous local electrical conductivity, little is known as to how this translates to electrochemistry at the same scale. This work investigates nanoscale electrochemistry at ITO electrodes using high-resolution scanning electrochemical cell microscopy (SECCM). The nominally fast outer-sphere one-electron oxidation of 1,1′-ferrocenedimethanol (FcDM) is used as an electron transfer (ET) kinetic marker to reveal the charge transfer properties of the ITO/electrolyte interface. SECCM measures spatially resolved linear sweep voltammetry at an array of points across the ITO surface, with the topography measured synchronously. Presentation of SECCM data as current maps as a function of potential reveals that, while the entire surface of ITO is electroactive, the ET activity is highly spatially heterogeneous. Kinetic parameters (standard rate constant, k0, and transfer coefficient, α) for FcDM0/+ are assigned from 7200 measurements at sites across the ITO surface using finite element method modeling. Differences of 3 orders of magnitude in k0 are revealed, and the average k0 is about 20 times larger than that measured at the macroscale. This is attributed to macroscale ET being largely limited by lateral conductivity of the ITO electrode under electrochemical operation, rather than ET kinetics at the ITO/electrolyte interface, as measured by SECCM. This study further demonstrates the considerable power of SECCM for direct nanoscale characterization of electrochemical processes at complex electrode surfaces.

3D-Printed electrochemical sensor-integrated transwell systems

This work presents a 3D-printed, modular, electrochemical sensor-integrated transwell system for monitoring cellular and molecular events in situ without sample extraction or microfluidics-assisted downstream omics. Simple additive manufacturing techniques such as 3D printing, shadow masking, and molding are used to fabricate this modular system, which is autoclavable, biocompatible, and designed to operate following standard operating protocols (SOPs) of cellular biology. Integral to the platform is a flexible porous membrane, which is used as a cell culture substrate similarly to a commercial transwell insert. Multimodal electrochemical sensors fabricated on the membrane allow direct access to cells and their products. A pair of gold electrodes on the top side of the membrane measures impedance over the course of cell attachment and growth, characterized by an exponential decrease (~160% at 10 Hz) due to an increase in the double layer capacitance from secreted extracellular matrix (ECM) proteins. Cyclic voltammetry (CV) sensor electrodes, fabricated on the bottom side of the membrane, enable sensing of molecular release at the site of cell culture without the need for downstream fluidics. Real-time detection of ferrocene dimethanol injection across the membrane showed a three order-of-magnitude higher signal at the membrane than in the bulk media after reaching equilibrium. This modular sensor-integrated transwell system allows unprecedented direct, real-time, and noninvasive access to physical and biochemical information, which cannot be obtained in a conventional transwell system.

Electrochemical Characterization of Redox Probes at Gold Screen‐Printed Electrodes: Efforts towards Signal Stability

AbstractIn this work, three universally used redox probes in amperometric biosensing devices, [Fe(CN)6]3−/[Fe(CN)6]4−, Ru[(NH3)6]3+, and ferrocenedimethanol (FDM), were selected to evaluate the stability of electrochemical signals provide by the reporting systems. Studies were carried out at disposable gold screen‐printed electrode (AuSPE) biosensing platforms, commonly used for screening chemical and biological relevant biomolecules. Firstly, electrochemical combined‐surface plasmon resonance (eSPR) studies were performed to evaluated adsorption reversibility and/or formation of redox probe complexes at the bare gold surface when routinely used electrochemical techniques, namely cyclic voltammetry (CV) and square‐wave voltammetry (SWV), are recorded. Then, the results obtained were compared with those obtained at the AuSPE under the same electrochemical conditions. Based on our findings, best experimental conditions, including the type of electrochemical technique used, are speculated for each reporting system in order to improve the analytical signal stability. Finally, a methodology based on SWV technique was applied to modified electrodes to provide a simple and easy tool to ensure diffusion controlled permeability of probes thorough the films to electrode surface.

Nanoconfinement Effects on Redox Probe Transport in Lipid Assemblies on and in Mesoporous Silica Thin Films

AbstractRedox probe transport through supported lipid bilayers and nanopore‐confined lipid assemblies on silica thin films is examined using electrochemical impedance spectroscopy (EIS). These supported lipid systems are emerging biomimetic separation and sensor platforms. The ability to quantify the accessibility of the pore structure of the mesoporous silica thin films is demonstrated, which is essential for the incorporation of carriers into the lipids for selective solute transport. Redox probe molecules with varying hydrophilicity are used to compare ion transport in supported lipid pore‐spanning bilayers (enveloped bilayers) and novel lipid filled pores of mesoporous silica thin films. The films feature orthogonally oriented 8–10 nm cylindrical nanopores formed by deposition of P123‐templated silica sols onto chemically modified fluorine‐doped tin oxide. Nanopore accessibility is confirmed by EIS with hydrophilic probe 1,1′‐ferrocenedimethanol (FDM). Filling the pores with lipid 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphocholine results in a superior barrier (with roughly 1/9 the permeability) to transport of FDM compared to fragile enveloped lipid bilayers deposited by vesicle fusion. The pore‐confined lipids not only provide a better barrier to FDM, but also a better pathway for the transport across the films of a hydrophobic redox probe 1,1′‐dioctadecyl‐4,4′‐bipyridinium dibromide, with an ideal transport selectivity of 11 compared to FDM.

Calibrant-Free Analyte Quantitation via a Variable Velocity Flow Cell.

In this paper, we describe a novel method for analyte quantitation that does not rely on calibrants, internal standards, or calibration curves but, rather, leverages the relationship between disparate and predictable surface-directed analyte flux to an array of sensing addresses and a measured resultant signal. To reduce this concept to practice, we fabricated two flow cells such that the mean linear fluid velocity, U, was varied systematically over an array of electrodes positioned along the flow axis. This resulted in a predictable variation of the address-directed flux of a redox analyte, ferrocenedimethanol (FDM). The resultant limiting currents measured at a series of these electrodes, and accurately described by a convective-diffusive transport model, provided a means to calculate an "unknown" concentration without the use of calibrants, internal standards, or a calibration curve. Furthermore, the experiment and concentration calculation only takes minutes to perform. Deviation in calculated FDM concentrations from true values was minimized to less than 0.5% when empirically derived values of U were employed.

Study of the Molecular Recognition Mechanism of an Ultrathin MIP Film-Based Chiral Electrochemical Sensor

This study is focused on the molecular recognition mechanism of a methacrylate-based R(+)-atenolol molecularly imprinted polymer (MIP), employed as a chiral sensing interface in the construction of a novel electrochemical sensor. The MIP was electrogenerated as an ultrathin-film onto the surface of a carbon paste working electrode under potentiodynamic conditions in a non-aqueous media. Differential pulse voltammetry served as signal transduction method for the direct and indirect (by means of two redox probes, [Fe(CN)6]3−/4− and 1,1′-ferrocene dimethanol, respectively) detection of the underlying molecular recognition process. The rebinding of the template enantiomer led to changes in solute permeability of the MIP-layer, indicating the presence of a “gate effect” as part of the molecular recognition process.

Amplified Charge Transfer for Anionic Redox Probes through Oriented Mesoporous Silica Thin Films

AbstractDiffusion of anionic species through ordered mesoporous silica films is considerably restricted due to electrostatic repulsion by the negatively charged silica surface and this effect is even worse in low ionic strength media (owing to Donnan exclusion effects). This is at the origin of the poor electrochemical response of anionic redox probes at electrodes modified with such mesoporous thin films. Here, by using indium–tin oxide (ITO) electrodes covered with vertically aligned mesoporous silica films generated by electrochemically assisted self‐assembly (EASA), we show that charge transfer for anionic redox probes [i.e. Fe(CN)63−/4−] can be dramatically amplified by using a neutral [ferrocene dimethanol, Fc(MeOH)2] or cationic [(Ru(NH3)63+] redox mediator. This has been observed by cyclic voltammetry, showing current enhancement in the presence of the mediator, which acts as a mobile electron shuttle between the charge‐excluded Fe(CN)63−/4− species from the mesoporous silica film and the underlying ITO surface owing to the ability of the mediator species to diffuse freely through the oriented mesopore channels. This behavior was significantly affected by the relative contents of Fe(CN)63−/4− probe to Fc(MeOH)2 mediator, the potential scan rate, and the supporting electrolyte concentration. The most effective improvements were reached at low Fe(CN)63−/4− concentration, high mediator content, low potential scan rate, and low ionic strength.

Paraquat-Melanin Redox-Cycling: Evidence from Electrochemical Reverse Engineering.

Parkinson's disease is a neurodegenerative disorder associated with oxidative stress and the death of melanin-containing neurons of the substantia nigra. Epidemiological evidence links exposure to the pesticide paraquat (PQ) to Parkinson's disease, and this link has been explained by a redox cycling mechanism that induces oxidative stress. Here, we used a novel electrochemistry-based reverse engineering methodology to test the hypothesis that PQ can undergo reductive redox cycling with melanin. In this method, (i) an insoluble natural melanin (from Sepia melanin) and a synthetic model melanin (having a cysteinyldopamine-melanin core and dopamine-melanin shell) were entrapped in a nonconducting hydrogel film adjacent to an electrode, (ii) the film-coated electrode was immersed in solutions containing PQ (putative redox cycling reductant) and a redox cycling oxidant (ferrocene dimethanol), (iii) sequences of input potentials (i.e., voltages) were imposed to the underlying electrode to systematically engage reductive and oxidative redox cycling, and (iv) output response currents were analyzed for signatures of redox cycling. The response characteristics of the PQ-melanin systems to various input potential sequences support the hypothesis that PQ can directly donate electrons to melanin. This observation of PQ-melanin redox interactions demonstrates an association between two components that have been individually linked to oxidative stress and Parkinson's disease. Potentially, melanin's redox activity could be an important component in understanding the etiology of neurological disorders such as Parkinson's disease.

Hydrodynamic Microgap Voltammetry under Couette Flow Conditions: Electrochemistry at a Rotating Drum in Viscous Poly(ethylene glycol).

Electrochemical processes in highly viscous media such as poly(ethylene glycol) (herein PEG200) are interesting for energy-conversion applications, but problematic due to slow diffusion causing low current densities. Here, a hydrodynamic microgap experiment based on Couette flow is introduced for an inlaid disc electrode approaching a rotating drum. Steady-state voltammetric currents are independent of viscosity and readily increased by two orders of magnitude with further potential to go to higher rotation rates and nanogaps. A quantitative theory is derived for the prediction of currents under high-shear Couette flow conditions and generalised for different electrode shapes. The 1,1'-ferrocene dimethanol redox probe in PEG200 (D=1.4×10-11 m2 s-1 ) is employed and data are compared with 1) a Levich-type equation expressing the diffusion-convection-limited current and 2) a COMSOL simulation model providing a potential-dependent current trace.

Interfacial electron-shuttling processes across KolliphorEL monolayer grafted electrodes.

Covalently grafted KolliphorEL (a poly(ethylene glycol)-based transporter molecule for hydrophobic water-insoluble drugs; MW, ca. 2486; diameter, ca. 3 nm) at the surface of a glassy-carbon electrode strongly affects the rate of electron transfer for aqueous redox systems such as Fe(CN)6(3-/4-). XPS data confirm monolayer grafting after electrochemical anodization in pure KolliphorEL. On the basis of voltammetry and impedance measurements, the charge transfer process for the Fe(CN)6(3-/4-) probe molecule is completely blocked after KolliphorEL grafting and in the absence of a "guest". However, in the presence of low concentrations of suitable ferrocene derivatives as guests, mediated electron transfer across the monolayer via a shuttle mechanism is observed. The resulting amplification of the ferrocene electroanalytical signal is investigated systematically and compared for five ferrocene derivatives. The low-concentration electron shuttle efficiency decreases in the following sequence: (dimethylaminomethyl)ferrocene > n-butyl ferrocene > ferrocene dimethanol > ferroceneacetonitrile > ferroceneacetic acid.

Information processing through a bio-based redox capacitor: Signatures for redox-cycling

Redox-cycling compounds can significantly impact biological systems and can be responsible for activities that range from pathogen virulence and contaminant toxicities, to therapeutic drug mechanisms. Current methods to identify redox-cycling activities rely on the generation of reactive oxygen species (ROS), and employ enzymatic or chemical methods to detect ROS. Here, we couple the speed and sensitivity of electrochemistry with the molecular-electronic properties of a bio-based redox-capacitor to generate signatures of redox-cycling. The redox capacitor film is electrochemically-fabricated at the electrode surface and is composed of a polysaccharide hydrogel with grafted catechol moieties. This capacitor film is redox-active but non-conducting and can engage diffusible compounds in either oxidative or reductive redox-cycling. Using standard electrochemical mediators ferrocene dimethanol (Fc) and Ru(NH3)6Cl3 (Ru3+) as model redox-cyclers, we observed signal amplifications and rectifications that serve as signatures of redox-cycling. Three bio-relevant compounds were then probed for these signatures: (i) ascorbate, a redox-active compound that does not redox-cycle; (ii) pyocyanin, a virulence factor well-known for its reductive redox-cycling; and (iii) acetaminophen, an analgesic that oxidatively redox-cycles but also undergoes conjugation reactions. These studies demonstrate that the redox-capacitor can enlist the capabilities of electrochemistry to generate rapid and sensitive signatures of biologically-relevant chemical activities (i.e., redox-cycling).

Noise Phenomena Caused by Reversible Adsorption in Nanoscale Electrochemical Devices

We theoretically investigate reversible adsorption in electrochemical devices on a molecular level. To this end, a computational framework is introduced, which is based on 3D random walks including probabilities for adsorption and desorption events at surfaces. We demonstrate that this approach can be used to investigate adsorption phenomena in electrochemical sensors by analyzing experimental noise spectra of a nanofluidic redox cycling device. The evaluation of simulated and experimental results reveals an upper limit for the average adsorption time of ferrocene dimethanol of ∼200 μs. We apply our model to predict current noise spectra of further electrochemical experiments based on interdigitated arrays and scanning electrochemical microscopy. Since the spectra strongly depend on the molecular adsorption characteristics of the detected analyte, we can suggest key indicators of adsorption phenomena in noise spectroscopy depending on the geometric aspect of the experimental setup.

Redox cycling in nanoporous electrochemical devices

Nanoscale redox cycling is a powerful technique for detecting electrochemically active molecules, based on fast repetitive oxidation and reduction reactions. An ideal implementation of redox cycling sensors can be realized by nanoporous dual-electrode systems in easily accessible and scalable geometries. Here, we introduce a multi-electrode array device with highly efficient nanoporous redox cycling sensors. Each of the sensors holds up to 209,000 well defined nanopores with minimal pore radii of less than 40 nm and an electrode separation of ~100 nm. We demonstrate the efficiency of the nanopore array by screening a large concentration range over three orders of magnitude with area-specific sensitivities of up to 81.0 mA (cm(-2) mM(-1)) for the redox-active probe ferrocene dimethanol. Furthermore, due to the specific geometry of the material, reaction kinetics has a unique potential-dependent impact on the signal characteristics. As a result, redox cycling experiments in the nanoporous structure allow studies on heterogeneous electron transfer reactions revealing a surprisingly asymmetric transfer coefficient.

Electrochemistry using single multiwalled carbon nanotubes – A step further

Abstract We have characterized the electrochemical behavior of single CCVD-grown multiwalled carbon nanotubes (MWCNTs) directly connected to and protruding from the tip of tapered gold wires. Single MWCNTs were connected to gold by electrical breakdown, in absence of binder, under an optical microscope. This procedure minimizes surface contamination in comparison to micromanipulations performed in an electron microscope. The MWCNT-gold adhesive contact was found stable enough to allow immersion of the freely suspended portion of the MWCNT in aqueous electrolytes containing 1 mM 1,1′-ferrocene dimethanol (FeDM) or hexaammine ruthenium ion Ru NH 3 6 3 + . Cyclic voltammograms were recorded at various immersion depths, and analyzed using Butler–Volmer (BV) kinetic model to extract transfer coefficient (α) and standard heterogeneous rate constant (k0). The latter was found Ru NH 3 6 3 + , with a large scattering of data suggesting MWCNTs react via inhomogeneous active sites. We also show that complete electrodes terminated by a single MWCNT can be isolated by use of an electrophoretic polymer. Electrochemical activity of the MWCNT can then be partially regenerated over a few microns by electrical breakdown of the polymer layer. Such electrodes could be useful to investigate electrochemical reactions inside micron-sized vesicles.

Study on the Photo-Degradation and Photo-Stabilization of Poly(p-Phenylene Benzobisoxazole)

As a kind of rig-rod-like polymer, poly(p-phenylene benzobisoxazole) (PBO) has received great interest because of its excellent mechanical properties and good thermal stability. The use of PBO materials, however, is limited due to its low sunlight stability. In this study, photolysis of PBO films was studied by infrared spectroscopy and molecular mass determination. It found that at the beginning of photolysis, the I.V. values of PBO almost did not changed. Then, it underwent fast decrease stage. Moreover, PBO degrade slowly in N2 atmosphere than in air atmosphere. The most likely photo-degradation mechanism was put forward. Attempts to stabilize PBO from photolysis were also investigated. It found that heat treatment could alleviate photo-degradation speed of PBO. Traditional light stabilizers showed a marginal effect on photolysis of PBO, whereas ferrocene dimethanol behaved better effect on the photo-stabilization of PBO.

Biomimetic Approach to Confer Redox Activity to Thin Chitosan Films

AbstractElectron transfer in biology occurs with individual or pairs of electrons, and is often mediated by catechol/o‐quinone redox couples. Here, a biomimetic polysaccharide‐catecholic film is fabricated in two steps. First, the stimuli‐responsive polysaccharide chitosan is electrodeposited as a permeable film. Next, the chitosan‐coated electrode is immersed in a solution containing catechol and the electrode is biased to anodically‐oxidize the catechol. The oxidation products covalently graft to the chitosan films as evidenced by electrochemical quartz crystal microbalance (EQCM) studies. Cyclic voltammetry (CV) measurements demonstrate that the catechol‐modified chitosan films are redox‐active although they are non‐conducting and cannot directly transfer electrons to the underlying electrode. The catechol‐modified chitosan films serve as a localized source or sink of electrons that can be transferred to soluble mediators (e.g., ferrocene dimethanol and Ru(NH3) 6Cl3). This electron source/sink is finite, can be depleted, but can be repeatedly regenerated by brief (30 s) electrochemical treatments. Further, the catechol‐modified chitosan films can i) amplify currents associated with the soluble mediators, ii) partially‐rectify these currents in either oxidative or reductive directions (depending on the mediator), and iii) switch between regenerated‐ON and depleted‐OFF states. Physical models are proposed to explain these novel redox properties and possible precedents from nature are discussed.

Molecular transport in thiacalix[4]arene-modified nanoporous colloidal films

The surface of nanopores in colloidal films assembled from 200 nm silica spheres was modified with thiacalix[4]arene moieties and transport of two redox-active species, ferrocene dimethanol and iron tris(bipyridyl) hexafluorophosphate, through the films has been studied using cyclic voltammetry. Evidence for two different molecular transport mechanisms was observed. Ferrocene dimethanol is transported via a simple diffusive mechanism while iron tris(bipyridyl) is transported via a surface-hopping mechanism. The difference in transport mechanisms is believed to result from different interaction strength between the diffusing species and the surface-bound organic moieties, and sheds light on transport mechanisms in nanoporous systems.

Heterogeneous Electron Transfer at Polyoxometalate-modified Electrode Surfaces

The heterogeneous electron transfer at <TEX>$SiMo_{12}O_{40}^{4-}$</TEX> monolayers on GC, HOPG, and Au electrode surfaces are investigated using cyclic voltammetric and electrochemical impedance spectroscopic (EIS) methods. The electron transfer of negatively charged <TEX>$Fe(CN)_6^{3-}$</TEX> species is retarded at <TEX>$SiMo_{12}O_{40}^{4-}$</TEX>-modified electrode surfaces, while that of positively charged <TEX>$Ru(NH_3)_6^{3+}$</TEX>species is accelerated at the modified surfaces. This is due to the electrostatic interactions between <TEX>$SiMo_{12}O_{40}^{4-}$</TEX> layers on surfaces and charged redox species. The electron transfer kinetics of a neutral redox species, 1,1‘-ferrocenedimethanol (FDM), is not affected by the modification of electrode surfaces with <TEX>$SiMo_{12}O_{40}^{4-}$</TEX>, indicating the <TEX>$SiMo_{12}O_{40}^{4-}$</TEX> monolayers do not impart barriers to electron transfer of neutral redox species. This is different from the case of thiolate SAMs which always add barriers to electron transfer. The effect of <TEX>$SiMo_{12}O_{40}^{4-}$</TEX> layers on the electron transfer of charged redox species is dependent on the kind of electrodes, where HOPG surfaces exhibit marked effects. Possible mechanisms responsible for different electron transfer behaviors at <TEX>$SiMo_{12}O_{40}^{4-}$</TEX> layers are proposed.