Probe Ferrocene Research Articles

Síntese e caracterização de filmes de Polipirrol dopados com Tetraquis(4-carboxifenil) porfirina para aplicações fotoelectroquímicas

Photoelectrochemistry is emerging as a promising technology for harvesting and utilizing solar energy in a wide range of applications. However, electrode materials still need to be improved to achieve optimal performance. Conductive polymers emerge as particularly promising organic compounds for this purpose due to their highly versatile properties. In this study, the galvanostatic synthesis of polypyrrole films co-doped with tetrakis(4-carboxyphenyl) porphyrin (PPy/TCPP) on fluorine doped tin oxide (FTO)-coated glass substrates was performed for the first time. In addition, an evaluation of these films as photoelectrodes was performed, focusing on key properties. The incorporation of porphyrin into the polymer matrix was confirmed by UV-Vis and IR characterization. SEM micrographs showed the morphological changes induced by the codopant. Cyclovoltammetry was used to evaluate the conductivity of the film, its electroactivity, electroactive area and HOMO energy level. The chopped chronoamperometry confirmed the photoactivity of the material and its stability for 3000 s. The electrical and optical properties of the polymer were characterized by EIS and light absorption measurements to propose its energy level diagram. The PPy/TCPP coatings were obtained with high homogeneity on FTO, good conductivity, quasi-reversible electrochemical activity to ferrocene probe and stable photoactivity. Electrical characterization indicates high charge flow under illumination. An indirect bandgap of 2.51 eV and a HOMO level value of -4.59 eV were obtained for PPy/TCPP.

CRISPR-powered microfluidic biosensor for preamplification-free detection of ochratoxin A

The CRISPR technology, which does not require complex instruments, expensive reagents or professional operators, has attracted a lot of attention. When utilizing the CRISPR-Cas system for detection, the pre-amplification step is often necessary to enhance sensitivity. However, this approach tends to introduce complexity and prolong the time required. To address this issue, we employed Pd@PCN-222 nanozyme to label single-stranded DNA, referred to as Pd@PCN-222 CRISPR nanozyme, which serves as the reporter of the CRISPR system. Pd@PCN-222 nanozyme possess exceptional catalytic activity for the reduction of H2O2. Compared with traditional electrochemical probe ferrocene and methylene blue without catalytic activity, there is a significant amplification of the electrochemical signal. So the need for pre-amplification was eliminated. In this study, we constructed a CRISPR-Cas system for ochratoxin A, utilizing the Pd@PCN-222 CRISPR nanozyme to amplified signal avoiding pre-amplification with outstanding detection of 1.21 pg/mL. Furthermore, we developed a microfluidic electrochemical chip for the on-site detection of ochratoxin A. This achievement holds significant promise in establishing a practical on-site detection platform for identifying food safety hazards.

Boron Carbon Nitride Nanosheets-Ru Nanocomposite Self-Enhancement Electrochemiluminescence Emitter with a Three-Dimensional DNA Network Structure as a Signal Amplifier for Ultrasensitive Detection of TK1 mRNA.

In this study, a neoteric self-enhanced nanocomposite boron carbon nitride nanosheets (BCN NSs)-Ru obtained by chemical crosslinking between boron carbon nitride nanosheets (BCN NSs) and tris (4,4'-dicarboxylicacid-2,2'-bipyridyl) ruthenium(II) dichloride (Ru(dcbpy)3Cl2) was used as an emitter to build an electrochemiluminescence (ECL) biosensor for ultrasensitive detection of the cancer marker human thymidine kinase 1 (TK1) mRNA. Importantly, the self-enhanced BCN NSs-Ru could exhibit strong ECL emission because boron radicals and amine groups derived from BCN NSs could significantly enhance the ECL response of Ru(dcbpy)3Cl2, which avoided the defects of the long electron transfer path and large energy loss between the emitter and coreactant in the traditional coreaction ECL system. Impressively, in the presence of target TK1 mRNA, three-dimensional DNA network structure-labeled numerous ferrocene probes could be assembled to quickly quench the ECL signal of BCN NSs-Ru, resulting in improved biosensor sensitivity. The obtained "on-off" biosensor showed excellent stability and high sensitivity with a detection limit of 32.3 aM. In general, the developed strategy provided a new biosensing way for ultrasensitive detection of biomolecules in early disease diagnosis.

Nonfouling and ratiometric electrochemical detection of prostate specific antigen in whole serum

An efficient strategy for the establishment of ratiometric antifouling electrochemical biosensors was proposed based on the designed functional peptides and synthesized graphene oxide-nile blue A (GO-NB) nanocomposites. The peptide was designed to be of antifouling and recognizing functions, and the two branches of the peptide were labelled with the electrochemical probe ferrocene (Fc). The electrode was modified with synthesized GO-NB nanocomposites, and then followed by the electrodeposition of gold nanoparticles and the immobilization of Fc labelled peptides. NB was used as an internal probe to generate reference electrochemical signal, while the electrochemical sensing signal was generated by the Fc, and thus the ratiometric electrochemical sensing system was constructed. In this sensing system, the variances associated with electrochemical signal drift and the electrode-to-electrode difference, etc., can be calibrated with the reference signal of NB to generate stable ratiometric signal (Fc/NB). The electrochemical biosensor displayed a linear range from 5.0 pg mL−1 to 100 ng mL−1, with the limit of detection of 1.26 pg mL−1. The integration of the ratiometric signal with the antifouling strategy can be readily expanded to the development of highly stable and accurate electrochemical sensing systems to be performed in complex biological systems.

Ferrocene-Based Porous Organic Polymer (FPOP): Synthesis, Characterization and an Electrochemical Study

Ferrocene-based porous organic polymers (FPOPs) were prepared from phenol-formaldehyde polymer (Bakelite) and phenol as starting materials; and two possible mechanisms for polymerization were discussed. Solid-state 13C CP-MAS NMR, FTIR, powder XRD, elemental analysis and ICP (Fe, Na, B) were performed to characterize the prepared materials. The two synthetic approaches produced polymers with different pore sizes: the FPOP synthesized through Bakelite presented a higher surface area (52 m2 g−1) when compared to the one obtained by the bottom-up polymerization from phenol (only 5 m2 g−1). Thermogravimetric analysis confirmed the thermal stability of the material, which decomposed at 350 °C. Furthermore, cyclic voltammetry (CV) of the new FPOP on modified electrodes, in ACN and 0.1 M TBAP as an electrolyte, showed fully reversible electron transfer, which is similar to that observed for the ferrocene probe dissolved in the same electrolyte. As a proof-of-concept for an electrochromic device, this novel material was also tested, with a color change detected between yellow/brownish coloration (reduced form) and green/blue coloration (oxidized form). The new hybrid FPOP seems very promising for material science, energy storage and electrochromic applications, as well as for plastic degradation.

Electrochemical detection of chlorpyrifos in fruits with gold-histidine functionalized graphene quantum dot-graphene hybrid and target-induced DNA cycle amplification

Hybrid of gold and graphene may improve the electrochemical performances due to their unique structure and properties, but synthesis of gold-graphene hybrid with ideal dispersion and catalytic activity still faces great challenges. The paper describes synthesis of gold-graphene hybrid using histidine-functionalized graphene quantum dot (His-GQD) as the linker between gold and graphene and semiconductor. Firstly, His-GQDs were immobilized on graphene sheets via π-π stacking. Then, it coordinated with Au3+ and thermally reduced in N2. The resulting Au-His-GQD-G offers small gold nanoparticles, good dispersion and Schottky heterojunction. The Au-His-GQD-G was used for construction of electrochemical sensor for detection of chlorpyrifos coupled with DNA cycling signal amplification. Chlorpyrifos was hybridized with aptamer DNA in duplex DNA to release auxiliary strand DNA, triggering the DNA cycle. By the DNA cycle, one target molecule can bring many ferrocene probes to the electrode surface. This produces a significant signal amplification. Differential pulse voltammetric current increases linearly with the increase of chlorpyrifos in the range of 1 × 10−16-1.0 × 10−11 M with the detection limit is 3.8 × 10−17 Μ (S/N = 3). The proposed method exhibits ultrahigh sensitivity and selectivity and was successfully applied in electrochemical detection of chlorpyrifos in fruits.

Electrochemical Sensing of Adenosin Triphosphate by Specific Binding to Dipicolylamine Group in Cyclodextrin Supramolecular Complex.

Electrochemical detection based on cyclodextrin supramolecular complexes is founded on the competitive binding between electroactive probes and target molecules. This limits their versatility to be used for sensing a broad range of metabolites. In this work, we demonstrate the significant role of zinc ions as well as of β-cyclodextrins modified with dipicolylamine and of a phenylboronic acid-modified ferrocene probe to address a selective electrochemical detection of adenosin triphosphate (ATP). Our findings will definitively have an impact in oncological point-of-care systems, since a high level of extracellular ATP reveals the inflammatory response due to chemotherapeutic treatments.

An electrochemical and fluorescence dual-signal assay based on Fe3O4@MnO2 and N-doped carbon dots for determination of hydrogen peroxide.

A novel electrochemical and fluorescence dual-signal assay was developed for the determination of hydrogen peroxide (H2O2) based on Fe3O4@MnO2 and N-doped carbon dots (NCDs). Fe3O4@MnO2 was not only applied as the recognizer for H2O2 but also served as the fluorescence quencher and electrochemical enhancer. This permits the dual-signal readout of the analytical system. In the absence of H2O2, the NCDs were quenched by Fe3O4@MnO2, and the oxidation of the electrochemical probe ferrocene (Fc) was catalyzed by Fe3O4@MnO2. In the presence of H2O2, MnO2 was reduced to Mn2+, leading to the fluorescence recovery of NCDs and the reduction in the oxidation signal of Fc. By combining the electrochemical method and the fluorescence assay, more comprehensive and valuable information for H2O2 determination was provided to meet different analytical demands. The method exhibits good repeatability and selectivity with a detection limit of 1.0μM for the fluorescence assay and 0.6μM for the electrochemical method. The proposed approach holds great potential for probing released targets from living cells. Graphical abstract.

Voltammetric determination of organophosphorus pesticides using a hairpin aptamer immobilized in a graphene oxide-chitosan composite.

An aptasensor is described for electrochemical determination of organophosphorus pesticides (OPPs), specifically of profenofos, phorate, isocarbophos, and omethoate. The method uses a hairpin aptamer as signalling donor. Its 5' and 3' ends were modified with amino groups and the redox probe ferrocene (Fc), respectively. A nanocomposite consisting of graphene oxide and chitosan (GO-chit) was used to immobilize the aptamer via formation of an amide link. Its good conductivity facilitates monitoring of the electrochemical responses. Upon addition of an OPP, it will be bound by the aptamer. This results in an opening of the hairpin structure. Thus, Fc is shifted away from the surface of the electrode. As a result, the impedance increases and the redox signal of Fc decreases. The electrochemical performance, binding capacity and response of the aptasensor for profenofos, phorate, isocarbophos and omethoate were studied. The limits of detection are as low as 0.01, 0.1, 0.01 and 0.1nM, respectively. Graphical abstract Schematic representation of anelectrochemical aptasensor prepared by immobilizing ferrocene (Fc) labeled hairpin aptamer (HP) on the surface of graphene oxide-chitosan (GO-chit) modified electrode, and its application to the determination of organophosphorus pesticides (OPPs) by voltammetry.

Evaluation of graphite sheets for production of high-quality disposable sensors

Flexible graphite sheets or graphite paper are conductive substrates produced in large scale for use in a wide range of applications, such as in telecommunications, lighting, computer and peripherals, power conversion, and heat generating semiconductors (low-cost material). In this paper we show, for the first time, that commercially available graphite sheets can be used in the as-received condition for the construction of disposable electrodes with excellent performance for electroanalysis (comparable to glassy carbon). Nine different graphite sheets were evaluated by different techniques, such as scanning electron microscopy (SEM), Raman spectroscopy, cyclic voltammetry, square wave voltammetry, and amperometry. The obtained results revealed the existence of large variations between different commercially available materials (not all the sheets work well as sensors in the as-received condition). Our studies have shown that there are commercial flexible graphite sheets with higher electrical conductivity and superior homogeneous composition, which are ideal for use as disposable unmodified or modified sensors. The quality of the results obtained with graphite sheets are dependent on the type of material selected as substrate. However, repetitive results are obtained if the same material is always used. The graphite sheets were coupled to low cost 3D-printed cells forming easy to use disposable devices. The performance of the disposable devices was evaluated using ferri-ferrocyanide and ferrocene probes, dopamine (LOD=0.7μmolL−1), catechol (LOD=0.8μmolL−1), ciprofloxacin (LOD=5.9μmolL−1), cadmium (LOD=0.013μmolL−1), and lead (LOD=0.07μmolL−1) as model analytes. According to our knowledge, the electroanalytical performance of graphite sheets demonstrated here surpasses previously reported results.

Voltammetric immunoassay for α-fetoprotein by using a gold nanoparticle/dendrimer conjugate and a ferrocene derived ionic liquid.

An immunosensor is described for the voltammetric determination of α-fetoprotein. It is making use of an AuNP-dendrimer conjugate and an ionic liquid. A gold electrode was first modified with chitosan. Then, the AuNP-dendrimer conjugate was covalently immobilized on the electrode. Following this, an ionic liquid was placed on the electrode via formation of a covalent bond between the amino groups of PAMAM and the aldehyde groups of an ionic liquid containing ferrocene. Thus, the redox probe ferrocene becomes immobilized on the electrode surface. PAMAM increases the amount of ferrocene immobilized on the electrode due to its globular shape and rich amino groups. The use of AuNPs improves the conductivity of the electrode. The modified electrode was applied to the determination of α-fetoprotein in human serum and has a linear response that covers the 0.05 to 30ngmL-1 α-fetoprotein concentration range, with a detection limit of 0.02ngmL-1. This assay is stable, selective and reproducible. It is perceived to provide a powerful tool for the early detection of cancer markers. Graphical abstract Schematic of a voltammetric immunoassay for α-fetoprotein based on a gold nanoparticle/dendrimer conjugate and ionic liquids anchored with both aldehyde and ferrocene. Chit: chitosan; GA: glutaraldehyde ; PAMAM: G4 polyamidoaminic dendrimers; AuNP: Au nanoparticle; Fc: ferrocene; IL: ionic liquid. PB: phosphate buffer solution.

Ultrafast Tailoring of Carbon Surfaces via Electrochemically Attached Triazolinediones.

The straightforward coupling between a triazolinedione (TAD) unit and citronellyl derivatives via an Alder-ene reaction has been exploited to tailor the physicochemical surface properties of glassy carbon (GC) surfaces in an ultrafast and additive-free manner. For this purpose, we first covalently grafted a TAD precursor onto GC via electrochemical reduction of an in situ generated diazonium salt, which was then electrochemically oxidized into the desired GC-bonded TAD unit. A kinetic study of the modification of this reactive layer with an electroactive ferrocene probe proved that a complete functionalization was obtained in merely 1 minute. Further modification experiments with a fluorinated probe demonstrated that the surface properties can be swiftly tailored on demand. The different modification steps, as well as the efficiency of this strategy, were investigated by electrochemistry, contact angle goniometry, and X-ray photoelectron spectroscopy analysis.

Polyazulenes Based Materials for Heavy Metal Ions Detection

Azulene is a special monomer used to functionalize electrodes due to its high polarizability, because it makes possible spontaneous electron drift from the five-membered ring to the seven-membered ring. Our study concerns the electrochemical characterization by cyclic voltammetry, differential pulse-voltammetry and rotating disk electrode voltammetry of a new azulene monomer, 4-(5-isopropyl-3,8-dimethylazulen-1-yl)-2,6-bis((E)-2-(thiophen-2-yl)vinyl) pyridine (L). It has been used to obtain complexing modified electrodes by electrochemical polymerization. PolyL films modified electrodes have been characterized by cyclic voltammetry in ferrocene probe solution. The complexing properties of polyL based functional materials have been investigated towards heavy metals (Pb, Cd Hg, Cu) by preconcentration � anodic stripping technique.

A complicated biocomputing system based on multi-responsive P(NIPAM-co-APBA) copolymer film electrodes and electrocatalysis of NADH.

In this paper, poly(N-isopropylacrylamide-co-3-aminophenylboronic acid) (P(NIPAM-co-APBA)) copolymer films were successfully electropolymerized on the Au electrode surface. The electroactive probe ferrocene carboxylic acid (FCA) in solution showed reversible thermal-, glucose- and pH-responsive on-off cyclic voltammetric (CV) behaviors at the film electrodes. The comparative experiments demonstrated that the thermo-responsive property of the film electrode was ascribed to the PNIPAM component of the films, whereas the glucose- and pH-sensitive behaviors came from the PAPBA constituent. The reduced form of nicotinamide adenine dinucleotide (NADH) could be electrocatalytically oxidized by FCA at the film electrodes, which would greatly amplify the multi-responsive CV signal difference between the on and off states. On the basis of these results, a binary 4-input/4-output logic circuit was fabricated with temperature, glucose, pH and NADH as inputs and the CV responses at 4 different levels as outputs. Moreover, a ternary CONSENSUS logic circuit was established on the same platform, which was the first report on the combination of ternary logic gate and bioelectrocatalysis without using enzymes. This work provided a novel idea for constructing complicated biocomputing systems by increasing the number of inputs/outputs with multi-sensitive interfaces and by designing new types of multi-valued logic gates on the basis of bioelectrocatalysis.

Cyclodextrin functionalized graphene–gold nanoparticle hybrids with strong supramolecular capability for electrochemical thrombin aptasensor

We demonstrate a facile one-pot synthetic strategy for controlled synthesis of thio-β-cyclodextrin functionalized graphene/gold nanoparticles (SH-β-CD-Gr/AuNPs) composites using SH-β-CD as both the dispersant and linker. The obtained SH-β-CD-Gr/AuNPs integrate the excellent electrical properties and large surface area of graphene and AuNPs with supramolecular recognition ability of CD, which show more effective electron transfer and higher enriched ability for the ferrocene probe via the host–guest interaction between CD and ferrocene than SH-β-CD-Gr. In the presence of target, the stronger interaction between aptamer and target makes the ferrocene move closer to the electrode surface, thus facilitating the electron transfer. Based on this sensing mechanism, a new and highly sensitive biosensing concept by the use of SH-β-CD-Gr/AuNPs as enhancing materials is demonstrated for “signal-on” detection of targets (thrombin as a model target). This biosensor exhibits a wide linear range for thrombin from 1.6×10−17M to 8.0×10−15M and a very low limit of detection 5.2×10−18M, which is two-order magnitude better than those of SH-β-CD-Gr (the detection linear range from 1.6×10−15M to 8.0×10−13M and detection limit of 1.0×10−15M). Our proposed electrochemical aptasensor based on SH-β-CD-Gr/AuNPs shows good selectivity against other proteins such as human serum albumin, lysozyme and insulin. To the best of our knowledge, the present SH-β-CD-Gr/AuNPs hybrids are the most efficient graphene-based electrochemical active probes ever reported for biosensors.

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.

Evaluation of Surface Active Properties and Voltammetric Characterizations of Some New Anionic Copolymer Surfactants

The onset of micelles formations critical micelle concentration, diffusion coefficients as well as particle sizes for some new synthesized anionic copolymer surfactants PSA4a, PSA4b, and PSA4c, were determined and discussed. Three different electrochemical techniques such as cyclic voltammetry (CV), rotating disk voltammetry (RDV), and chronocoulometry (CC) were used in this investigation. The voltammetry of electroactive hydrophobic probe ferrocene solubilized surfactants was investigated in aqueous buffer carbonate solutions of pH 10. The CMC for each PSA4a, PSA4b, and PSA4c, was found to be 3.20 × 10−4, 4.60 × 10−4 and 6.30 × 10−4 M, respectively, using both CV and RDV techniques. The amount of adsorption contribution of ferrocene solubilized surfactants at the glassy carbon electrode was determined from chronocoulometric measurements and it was found in the range from (1.4 to 2.7) × 10−15 M. The apparent diffusion coefficients were estimated from RDV measurements and the real micelles diffusion coefficients were obtained. Re-quilibrium considerations of ferrocene probe kinetics at the electrode surface were treated according to two different modes of slow- and fast-kinetics. The corrected diffusion coefficient values showed constancy at (5.3 ± 0.1) × 10−7, (4.8 ± 0.1) × 10−7, and (3.6 ± 0.4) × 10−7 cm2/sec for PSA4a, PSA4b, and PSA4c, respectively in the concentration range from 20 to 200 mM. The morphological features of anionic copolymeric surfactants PSA4a, PSA4b, and PSA4c, micelles showed globular self-assembled structure.

Design and Synthesis of Ferrocene Probe Molecules for Detection by Electrochemical Methods

Design and Synthesis of Ferrocene Probe Molecules for Detection by Electrochemical Methods

Design and Synthesis Of Ferrocene Probe Molecules for Detection by Electrochemical Methods

A series of ferrocenyl conjugates to fatty acids have been designed and synthesized to establish the key properties required for use in biomolecular binding studies. Amperometric detection of the ferrocene conjugates was sought in the region of 0.3 V (vs Ag/AgCl) for use in protein/blood solutions. Different linkers and solubilizing moieties were incorporated to produce a conjugate with optimal electrochemical properties. In electrochemical studies, the linker directly attached to the ferrocene was found to affect significantly the E(1/2) value and the stability of the ferrocenium cation. Ester-linked ferrocene conjugates had E(1/2) ranging from +400 to +410 mV, while amide-linked compounds ranged from +350 to +370 mV and the amines +260 to +270 mV. Folding of long-chain substituents around the ferrocene, also significantly affected by the choice of linker, was inferred as a secondary effect that increased E(1/2). The stability of the ferrocenium cation decreased systematically as E(1/2) increased. Disubstituted ferrocene ester and amide conjugates, with oxidation potentials of +640 and +570 mV, respectively, showed only a barely discernible reduction wave in cyclic voltammetry at 50 mV/s. Electrochemical measurements identified two lead compounds with the common structural characteristics of an amide and carbamate linker (compounds 17 and 21) with a C(11) fatty acid chain attached. It is envisaged that such molecules can be used to mimic and study the biomolecular binding interaction between fatty acids and molecules such as human serum albumin.

Characterization of Micropatterned Lipid Membranes on a Gold Surface by Surface Plasmon Resonance Imaging and Electrochemical Signaling of a Pore-Forming Protein

We report the fabrication and characterization of a micropatterned membrane electrode for electrochemical signaling of a bacterial pore-forming toxin, Streptolysin O (SLO) from S. pyogenes. Microcontact printing of an alkylthiol monolayer was used to fabricate an array template, onto which cholesterol-containing DMPC vesicles were fused to form lipid layer structures. The construction of the supported membranes, including pattern transfer and vesicle fusion, was characterized by in-situ surface plasmon resonance (SPR) imaging and electrochemistry. Quantitative analysis of the resulting membrane by using SPR angular shift measurements indicates that the membranes in the hydrophilic pockets have an average thickness of 8.2 +/- 0.4 nm. Together with fluorescence microscopy studies, the results suggest that this could be a mixed lipid assembly that may consist of a bilayer, vesicle fragments, and lipid junctions. The voltammetric response of the redox probe ferrocene carboxylic acid (FCA) was measured to quantify the toxin action on the supported membrane. The electrochemical measurements indicate that fusion of vesicles on the template blocked the access of FCA, whereas the injection of SLO toxin restored the redox response. The anodic peak current of FCA was found to increase with toxin concentration until a plateau was reached at 40 HU/mL. The method is highly sensitive such that 0.1 HU/mL of SLO (1.25 pM) can yield a well-defined response. In addition, it eliminates the need for a highly insulating layer in membrane sensing, which opens up new avenues in developing novel sensing interfaces for membrane-targeting proteins and peptides.