Ferrocenecarboxylic Acid Research Articles

Simultaneous electrochemical immunosensing of alpha-fetoprotein and prostate specific antigen using a glassy carbon electrode modified with gold nanoparticle-coated silica nanospheres and decorated with Azure A or ferrocenecarboxylic acid

We describe an electrochemical immunosensor for the simultaneous determination of alpha-fetoprotein (AFP) and prostate specific antigen (PSA) via a modified glassy carbon electrode. Silica nanoparticles (200–300 nm i.d.) with good monodispersity and uniform shape were synthesized, and the following species were then consecutively immobilized on their surface: gold nanoparticles (AuNPs; 5–15 nm i.d.), secondary antibody (Ab2) and the redox-probes Azure A or ferrocenecarboxy acid (Fc). In parallel, two types of primary antibodies (Ab1) were co-immobilized on the surface of the dissolved reduced graphene oxide sheets (rGO) that were also decorated with AuNPs. In the presence of antigens (AFP or PSA), the Ab2/Si@AuNPs carrying Azure A and Fc are attached to the AuNP/rGO conjugate via a sandwich type immunoreaction. Differential pulse voltammetry (DPV) was employed to measure the resulting changes in the signal of Fc or Azure A. Two well-resolved oxidation peaks, one at −0.48 V (corresponding to Azure A) and other at + 0.12 V (corresponding to Fc; both vs. SCE) can be observed in the DPV curves. Under optimal conditions, AFP and PSA can be simultaneously determined in the range from 0.01 to 25 ng mL‾1 for AFP, and from 0.012 to 25 ng mL‾1 for PSA. The detection limits are 3.3 pg mL‾1 for AFP and 4.0 pg mL‾1 for PSA (at a signal-to-noise ratio of 3). The method was applied to (spiked) real sample analysis, and the recoveries are within 96.0 and 107.2 % for PSA, and within 100.9 and 105.8 % for AFP, indicating that this dual immunosensor matches the requirements of clinical analysis.

Ultrasensitive immunoassay for CA125 detection using acid site compound as signal and enhancer

A novel sensitive electrochemical immunosensor was proposed for detection of CA125 based on ferrocenecarboxylic acid (FA), HCl-doped polyaniline (H-PANI) and chitosan hydrochloride (CS-HCl), which were used as substrate materials to generate signal and to enlarge specific surface area. The composite of these three materials (acid center compound, FA@H-PANI@CS-HCl) can be connected by hydrogen (H) in each molecule. Ag@Co3O4 nanosheets were used in the immunosensor to amplify the antibody capacity and to enhance the sensitivity of the immunoassay. This kind of sensor was novel, concise and it is the first time to be used in the detection of CA125. The biosensor exhibited low detection limit (0.25pg/mL) and wide linear range (0.001–25ng/mL). The stability, selectivity and reproducibility were acceptable. Serum sample analysis proved that the proposed sensor owned well precision and it might be used in potential clinic testing application in the future.

Pd-Based Metal Aerogels with Promoted Bioelectrocatalytic Behavior

Aerogels derived from noble metal nanoparticles (NPs) are a new kind of metal materials, which combine the nano-sized scale with that of materials of macro dimensions.[1] These metal aerogels are expected to provide a matrix with high electrical conductivity and high surface area for electrochemical applications. They may also offer inherent catalytic activity and generally fast (reversible) electron-transfer kinetics. In that respect, enzyme-loaded metallic aerogels in combination with their meso/macroporous structure can facilitate electron and mass transfer processes, which are both important for bioelectronic applications, e.g., in electrochemical biosensors and in biofuel cells.[2] Here the controlled growth of Pd aerogels has been facilely realized by using calcium ions as the destabilizing agent. The involving Pd aerogels with different porosities and surface areas exhibited faster electrode kinetics and higher activities towards the bioelectrooxidation of glucose when co-immobilized with glucose oxidase (GOD), compared to the Pd NPs and glassy carbon.[3] Based on the Pd aerogels promoted bioelectrocatalysis, we have developed a newly designed metal aerogel-based biofuel cell system. In the text, a commonly used mediator, ferrocenecarboxylic acid (Fc), was integrated into the Pd hydrogel and thus produced a Pd-Fc composite aerogel mediator for GOD at the bioanode. Additionally, bilirubin oxidase (BOD) encapsulated into a Pd-Pt alloy aerogel played a synergetic role towards the reduction of O2, which promoted the direct electrocatalytic reduction of O2 at the biocathode with an onset potential of 0.56 V under neutral conditions. By employing these two bioelectrodes, the assembled membrane-less glucose/O2 biofuel cell showed a maximum power output of 20 μW cm-2 at 0.25 V.[4,5] References [1] N. Gaponik, A.-K. Herrmann, A. Eychmüller, J. Phys. Chem. Lett. 2012, 3, 8–17. [2] Gao, F.; Viry, L.; Maugey, M.; Poulin, P.; Mano, N. Nat. Commun. 2010, 1, 2. [3] D. Wen, A.-K. Herrmann, L. Borchardt, F. Simon, W. Liu, S. Kaskel, A. Eychmüller, J. Am. Chem. Soc. 2014, 136, 2727–2730. [4] W. Liu, P. Rodriguez, L. Borchardt, A. Foelske, J. Yuan, A.-K. Herrmann, D. Geiger, Z. Zheng, S. Kaskel, N. Gaponik, R. Kötz, T. Schmidt, A. Eychmüller, Angew. Chem., Int. Ed. 2013, 52, 9849–9852. [5] D. Wen, W. Liu, A.-K. Herrmann, A. Eychmüller, Chem. Eur. J. 2014, 20, 4380–4385. Figure 1

Electrochemistry and detection of dopamine at a poly(3,4-ethylenedioxythiophene) electrode modified with ferrocene and cobaltocene

Poly(3,4-ethylenedioxythiophene) (PEDOT) modified with ferrocene carboxylic acid (FC1), ferrocene (FC2), and cobaltocene (CC) is introduced as a sensor electrode. FC or CC was “sandwiched” between two layers of PEDOT in the presence of sodium dodecyl sulfate (PEDOT/mediator/PEDOT…SDS). The composite electrodes were evaluated for the electrocatalytic oxidation of dopamine (DA). The FC1 mediator showed the highest rate for electron transfer and enhanced electrocatalytic activity. This is due to the inclusion of the ferrocenium ion and the polar substituted –COOH group in the matrix which increases the electronic conduction of the film. SDS enhanced the preconcentration/accumulation of DA ions at the surface that resulted in enhanced detection. Detection limit in human urine was 0.069 μmol L−1 in the linear dynamic range of 6–300 μmol L−1, with satisfying recovery results. The PEDOT/FC1/PEDOT…SDS composite was used for simultaneous determination of dopamine in the presence of ascorbic acid (AA) and uric acid (UA).

Monomeric mixed cadmium-2,2′-dipyridylamine complex derived from ferrocenecarboxylic acid: Structural, electrochemical and biological studies

A mixed Cd(II) complex {[Cd(FcCOO)2(dpyam)(H2O)][Cd(dpyam)2 (H2O)2]·(ClO4)2·CH3OH} (1) (where FcCOO=ferrocenecarboxylic acid and dpyam=2,2′-dipyridylamine), has been synthesized and characterized by FT-IR, 1H & 13C NMR, UV–Vis spectroscopy and elemental analysis. The molecular structure of compound 1 has been determined by the single crystal X-ray diffraction technique, which consists of mixed two different cadmium(II) complexes and two uncoordinated perchlorate ions. The crystal packing shows that the compound 1 self-assembled by intermolecular hydrogen bonding via pyridyl N–H⋯O and coordinated water O⋯H–O–H⋯O, to afford the molecule 2D supramolecular network. Compound 1 exhibits high-energy intraligand (π–π∗) fluorescence emission. In electrochemical studies of compound 1 shows negative potential compared with ferrocenecarboxylic acid due to formation of coordination complex with Cd ions. The antibacterial study against the distinct bacterial strains show compound 1 has significant activity.

Effect of some redox mediators on FAD fluorescence of glucose oxidase from Penicillium adametzii LF F-2044.1

Glucose oxidase (GOx) of Penicillium adametzii LF F-2044.1 recovered by ultrafiltration, was characterized by spectrophotometric and spectrofluorometric methods. It was shown that spectra of GOx from P. adametzii are typical for flavoproteins. Optimal buffer composition was chosen. It was determined that the GOx is the most efficiently interacting with substrate (glucose) in phosphate buffer at pH 7.0 with kkat/KM=15,217±550M−1s−1. P. adametzii GOx fluorescence in the presence of different redox mediators (9,10-phenanthroline-5,6-dione, 9,10-phenanthrenequinone, 1,4-benzoquinone, methylene blue, ferrocene, ferrocenecarboxylic acid, α-methylferrocenemethanol, ferrocenecarboxaldehyde) was evaluated. Maximal differences in fluorescence emission intensity were observed in the presence of ferrocene and 9,10-phenanthrenequinone.

Molecular recognition based on an electrochemical sensor of per(6-deoxy-6-thio)-β-cyclodextrin self-assembled monolayer modified gold electrode

This paper describes the preparation and characterization of a self-assembled monolayer of per(6-deoxy-6-thio)-β-cyclodextrin (β-CD-SH) on a gold electrode surface and the study of its inclusion interactions with d- and l-phenylalanine (Phe). The β-CD-SH was self-synthesized and characterized by Fourier-transform infrared (FTIR) and nuclear magnetic resonance (NMR). The modified electrode surface was carefully characterized by cyclic voltammetry (CV) using potassium ferricyanide ([Fe(CN)6]3−/4−) and ferrocenecarboxylic acid (Fc-COOH) as redox probes. Phe was labeled with gold nanoparticles (n-Au-Phe), and the chiral recognition between them and β-CD-SH on the surface of an electrode was carried out. The methods of gold labeling and silver staining was strengthened by SEM. Finally, silver enhancement was monitored by differential pulse voltammetry (DPV). The DPV signal was greatly amplified by the silver atoms coated on the n-Au. The proposed method distinguished d- from l-Phe with an enantioselectivity coefficient of 3.64. The association constants of o-, m- and p-ABA with β-CD-SH at pH 4.0 were calculated to be 2.84×104, 1.94×104, and 3.43×105mol−1L, respectively.

Characterisation of Nanoporous Gold for Use in a Dissolved Oxygen Sensing Application

A nanoporous gold (NPG) microdisc array in a three-electrode electrochemical cell arrangement has been fabricated and characterised for a dissolved oxygen sensing application. The device will be used for monitoring of drinking water quality in rural communities in India, where there is a need for a miniaturised, low-cost dissolved oxygen sensor. The NPG microdisc array exhibits improved electrochemical responses compared to a planar gold microdisc array, owing to its extended surface area. In 1 mM ferrocene carboxylic acid, the experimental limiting currents obtained are twice as large as the theoretical limiting current for a planar gold microarray. A 252-nm-thick NPG layer resulted in a limiting current of 627 nA (compared to the estimated current of 295 nA). The voltammetric behaviour in water samples from a pilot site in India was investigated for increasing oxygen content, and a comparison was made with a macrodisc gold electrode and an unmodified microdisc array. The NPG microdisc array demonstrated improved characteristics over both devices and exhibited a higher correlation (average value 0.925) compared with the unmodified array (0.819) and macrodisc (0.870). An improvement in signal-to-noise ratio was also observed to be 12.349 versus 5.259 (microelecrode array) and 5.604 (macroelectrode). The response time for the NPG microdisc array versus a commercial dissolved oxygen sensor showed a faster response time of 20 versus 40 s.

Binding Cellulose and Chitosan via Intermolecular Inclusion Interaction: Synthesis and Characterisation of Gel

A novel cellulose-chitosan gel was successfully prepared in three steps: (1) ferrocene- (Fc-) cellulose with degrees of substitution (DS) of 0.5 wt% was synthesised by ferrocenecarboxylic acid and cellulose within dimethylacetamide/lithium chloride (DMAc/LiCl); (2) theβ-cyclodextrin (β-CD) groups were introduced onto the chitosan chains by reacting chitosan with epichlorohydrin in dimethyl sulphoxide and a DS of 0.35 wt%; (3) thus, the cellulose-chitosan gel was obtained via an intermolecular inclusion interaction of Fc-cellulose andβ-CD-chitosan in DMA/LiCl, that is, by an intermolecular inclusion interaction, between the Fc groups of cellulose and theβ-CD groups on the chitosan backbone at room temperature. The successful synthesis of Fc-cellulose andβ-CD-chitosan was characterised by13C-NMR spectroscopy. The gel based onβ-CD-chitosan and Fc-cellulose was formed under mild conditions which can engender autonomous healing between cut surfaces after 24 hours: the gel cannot self-heal while the cut surfaces were coated with a solution of a competitive guest (adamantane acid). The cellulose-chitosan complex made by this method underwent self-healing. Therefore, this study provided a novel method of expanding the application of chitosan by binding it with another polymer.

Selective recognition and sensing for adenosine triphosphate by label-free electrochemistry based on its inclusion with per-6-ammonium-β-cyclodextrin

A method for sensing adenosine triphosphate by its competitive inclusion to displace ferrocenecarboxylic acid from its inclusion complex with per-6-ammonium-β-cyclodextrin and the DPV curves.

Multi-walled carbon nanotubes–chitosan with a branched structure modified with ferrocenecarboxylic acid for carcinoembryonic antigen detection

A novel electrochemical immunosensor for the detection of CEA was proposed based on Fc-COOH connected to the branched structure of a MWCNT–CS complex modified electrode.

Comparison of Glucose Oxidases from Penicillium Adametzii, Penicillium Funiculosum and Aspergillus Niger in the Design of Amperometric Glucose Biosensors

The properties of amperometric glucose biosensors based on three different glucose oxidases and various redox mediators were evaluated. Glucose oxidases (GOx) from Penicillium adametzii, Penicillium funiculosum and Aspergillus niger and artificial redox mediators, such as ferrocene, ferrocenecarboxaldehyde, α-methylferrocene methanol and ferrocenecarboxylic acid, were used for modifying the graphite rod electrode and amperometrical reagent-less glucose detection. The obtained results were compared using N-methylphenazonium methyl sulphate in the solution. Taking into account the experimental kinetic parameters and the stability of the tested enzymatic electrodes, GOx from Penicillium funiculosum proved to be more suitable for glucose biosensor design in comparison with other evaluated enzymes.

Synthesis, Characterization and Electrical Conductance of Ferrocenylazobenzene

Ferrocenylazobenzene was synthesized by condensing an aminoazobenzene dye with ferrocenecarboxylic acid previously treated with oxalyl chloride. The compound displayed an anticipated chemically reversible one-electron oxidation process and gave a formal potential, E° = 0.65 V. In the UV-Vis region, the azo π-π* and n-π* transitions appeared at 355 and 460 nm respectively. On oxidation of the ferrocenyl moiety, the azo π-π* band was blue-shifted to 348 nm with an increase in intensity, while a new broad, lower energy absorption band assigned to the ligand-to-metal charge transfer appeared at 622 nm. The growth of this new band was concurrent with the bleaching of the metal-to-ligand charge transfer band which was largely obscured by the azo n-π* band at 460 nm. The compound in the form of thin film gave an average electrical conductivity of 0.239 ± 0.001 Scm−1 and a non-linear I-V curve with knee voltage at 2.3 V in dark condition.

Fabrication of Dual-Path Electron Transfer Electrode for Electrochemical Glucose Sensing

A novel type of glucose biosensor was designed based on dual-path electron transfer mechanism. Ferrocenecarboxylic acid (FcCA), the indirect mediator, transfers the electrons of enzymatic reaction from embedded redox active center via redox process. Reduced graphene oxide (rGO) and silver nanoparticles (AgNPs) both are conductive materials, providing fast direct electron transfer path. In this system, β-cyclodextrin (β-CD) is of key importance for not only reducing rGO and AgNPs, but providing biocompatible microenvironment for the enzyme as well. At the same time, carboxymethyl-β-cyclodextrin (CM-β-CD) formed inclusion complex with FcCA and then covalently bound with the enzyme to immobilize FcCA and GOD. The structure and morphology of modified film were characterized by FTIR, TEM, AFM, XRD, Raman and UV-vis. The rate constant (ks) of modified electrode is calculated to be 4.648 s−1, indicating the fast electron transfer rate on electrode. The glucose biosensor exhibited a wide linear response range from 0.105 to 11.805 mM with a low detection limit of 0.035 mM.

Quenched electrochemiluminescence of Ag nanoparticles functionalized g-C3N4 by ferrocene for highly sensitive immunosensing

In this paper, a novel sandwich electrochemiluminescence (ECL) immunosensor was constructed by ferrocene for quenching Ag nanoparticles functionalized g-C3N4 (Ag@g-C3N4) emission. The prepared Ag@g-C3N4 had strong and stable ECL signals compared to pure g-C3N4 and primary antibody (Ab1) can be immobilized on Ag@g-C3N4 by adsorption of Ag nanoparticles. Ferrocene carboxylic acid (Fc-COOH) labeled secondary antibody was immobilized on Au doped mesoporous Al2O3 nanorods (Au@Al2O3–Fc-COOH@Ab2) as labels through adsorption ability of Au toward proteins. After a sandwich-type immunoreaction, a remarkable decrease of ECL signal was observed due to the ECL quenching of Ag@g-C3N4 by Au@Al2O3–Fc-COOH@Ab2. As a result, the change of ECL intensity has a direct relationship with the logarithm of CEA concentrations in the range of 1pgmL−1–100ngmL−1 with a detection limit of 0.35pgmL−1 (S/N=3). Additionally, the proposed immunosensor shows high specificity, good reproducibility, and long-term stability.

Functionalized gold nanorod-based labels for amplified electrochemical immunoassay of E. coli as indicator bacteria relevant to the quality of dairy product

In this paper, we report an amplified electrochemical immunoassay for Escherichia coli as indicator bacteria relevant to the quality of dairy product using the functionalized gold nanorod-based labels ({dAb–AuNR–FCA}). The {dAb–AuNR–FCA} labels were designed by exploiting silica-functionalized gold nanorods (AuNR@SiO2) as the carriers for immobilization of detection antibody (dAb) and ferrocenecarboxylic acid (FCA), in which dAb was used for recognition of E. coli and FCA tags served as signal-generating molecule. Greatly amplified signal was achieved in the sandwich-type immunoassay when enormous FCA linked to AuNR@SiO2. Compared with the commercially available {dAb–FCA}, the {dAb–AuNR–FCA} labels exhibited a better performance for E. coli assay due to the advantages of AuNR@SiO2 as carriers. Under optimal experimental conditions, it showed a linear relationship between the peak current of FCA and the logarithmic value of E. coli concentration ranging from 1.0×102 to 5.0×104cfumL−1 with a detection limit of 60cfumL−1 (S/N=3), and the electrochemical detection of E. coli could be achieved in 3h. Moreover, the proposed strategy was used to determine E. coli in dairy product (pure fresh milk, yogurt in shelf-life, and expired yogurt), and the recoveries of standard additions were in the range of 95.1–106%. This proposed strategy exhibited rapid response, high sensitivity and specificity for E. coli assay in dairy product, and could become a promising technique to estimate the quality of dairy product.

C60 carboxyfullerene-based functionalised nanohybrids as signal-amplifying tags for the ultrasensitive electrochemical detection of procalcitonin

Electrochemical immunosensors have attracted much interest recently. Some researches on electrochemical PCT measurement have been reported but improvements are still needed to enhance detection performance for the clinical determination of PCT. In this work, a novel signal amplification strategy was developed by fabricating an electrochemical immunosensor for the sensitive detection of procalcitonin (PCT). Amino group-functionalised C(60) nanoparticles were used as a matrix to immobilise a redox probe, ferrocene carboxylic acid (Fc), and were subsequently coated with platinum nanoparticles (PtNPs) to form PtNP-Fc-C(60) nanocomposites. The experimental results demonstrated that the multi-labelled PtNP-Fc-C(60) nanocomposites displayed satisfactory electrochemical redox activity and high electrocatalytic activity from the PtNPs and glucose oxidase, consequently resulting in high sensitivity for the detection of PCT. The linear range of PCT was 0.01-10 ng/mL, with a detection limit of 6p g/mL (S/N = 3). Although the proposed immunosensor was only to determine PCT in this study, we expect that this immunosensor should be suitable for the determination of other targets in similar signal-enhanced immunoassays.

Synthesis and Application of a Novel Intumescent Flame Retardant Containing Ferrocenyl

A novel intumescent flame retardant (IFR) containing ferrocene and caged bicyclic phosphate groups, 1-oxo-4-[4'-(ferrocene carboxylic acid phenyl ester)] amide-2, 6, 7-trioxa-1-phosphabicyclo- [2.2.2] octane (PFAM), was successfully synthesized. The synthesized PFAM were added to flammable polyurethane (PU) as flame retardants and smoke suppressants. The structure of PFAM was characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (1H NMR) and elemental analysis. Thermal stability of PFAM was tested by themogravimetric analysis (TGA). The results revealed that PFAM had good thermal stability and high char weight, the char weight up to 54% at 600 °C. Flammability properties of PU/PFAM composites were investigated by limiting oxygen index (LOI) test and UL-94 test, respectively. The results of LOI tests showed that the addition of PFAM enhanced flame retardancy of PU. When the content of PFAM reaches to 3%, the LOI value is 22.2. The morphologies of the char for PU and PU/3% PFAM composite can be obtained after LOI testing were examined by SEM. The results demonstrated that PFAM could promote to form the compact and dense intumescent char layer. Experiments showed that, the PFAM application of polyurethane showed positive effect.

Ascorbic acid-triggered electrochemical–chemical–chemical redox cycling for design of enzyme-amplified electrochemical biosensors on self-assembled monolayer-covered gold electrodes

l-Ascorbic acid 2-phosphate (AAP) is an optimal substrate for alkaline phosphatase (ALP) in electrochemical bioassays because of its low cost, good water solubility, less electrode passivation and high signal-to-background ratio. However, developing of electrochemical sensors with AAP as the enzyme substrate on self-assembled monolayer (SAM)-covered electrode is limited because the insulating SAM hinders the electron transfer between the electrode and ascorbic acid (AA, the enzymatic product of AAP). In this work, we first reported a strategy for developing AAP-based electrochemical biosensors on SAM-covered gold electrode. The method is based on AA-triggered “outer-sphere to inner-sphere” electrochemical–chemical–chemical (ECC) redox cycling with ferrocenecarboxylic acid (FcA) as the redox mediator. Specifically, AA produced from AAP facilitated the regeneration of FcA from its electrochemical-oxidation product (referred to as FcA+ in the text), leading to an increase in the anodic current of FcA. Electrochemically inert tris(2-carboxyethyl)phosphine (TCEP) was used as a chemical reducing reagent to regenerate AA from its oxidation product, thus amplifying the electrochemical signal. The applications and performances of the proposed method were demonstrated in the competitive assays of β-amyloid (Aβ) peptides. The theoretical simplicity and high sensitivity indicated that our work would be valuable for developing simple and sensitive electrochemical biosensors.

Three dimensional porous graphene–chitosan composites from ice-induced assembly for direct electron transfer and electrocatalysis of glucose oxidase

Three dimensional porous graphene–chitosan (GR–CS) composites via ice-induced assembly for glucose oxidase (GOD) immobilization were reported for the first time. By adjusting the GR amount, the porous GR–CS composites containing different GR content could be produced. It was found that the GR amount played an important role in their morphologies. Higher GR amount resulted in more pores appearing in the GR–CS composites. When the GR amount was 70 wt%, the GR–CS composites (GR70–CS) had good flexibility and interpenetrating porous structures. The GR70–CS composite showed good stability, and still kept a porous structure even after dispersing and coating on the substrates. Current response from the GR70–CS composite modified glassy carbon electrode (GR70–CS/GCE) was about two times that from the bare GCE with Fe(CN)63−/4− as a probe. The direct electrochemical behavior was observed when GOD was immobilized onto the GR70–CS/GCE. The GOD modified GCE also showed good electrocatalytic activity for glucose. Using ferrocenecarboxylic acid as a mediator, a linear relationship from 0.14 to 7.0 mM (R = 0.995) between currents and the glucose concentration with a detection limit of 17.5 μM was obtained.