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Abstract: A facile method for the preparation of ferrocene (FC) loaded porous polyelectrolyte nanoparticles (FC-PPN) using CaCO3 as template was reported. Polyelectrolyte, ferrocene and CaCO3 nanoparticles were dispersed in ethanol/water solution. After the evaporation of solution under stirring, the FC-PPN was prepared with the polyelectrolyte layer adsorbed onto CaCO3 surface during the solution evaporation process, and FC encapsulated within the polyelectrolyte framework. The resulted FC-PPN showed high FC loading and good stability. Sensitive electrochemical immunosensor for the detection of oral cancer biomarker interleukin-6 (IL-6) using this FC-PPN as label was prepared. Using the redox current of FC as signal, the immunosensor displays high sensitivity, wide linear range (0.002–20ng/mL), low detection limit (1pg/mL) and good reproducibility. In addition, this porous nanoparticle preparation method could be extended to the incorporation of different interesting materials onto nanoparticles and find wide applications in various areas, such as bioassay, drug delivery and catalysis. [Copyright &y& Elsevier]

Abstract: Ferrocene (Fc) functionalized self-assembled peptide nanowire (Fc-PNW) was synthesized, functionalized and used as label for the fabrication of electrochemical immunosensors to detect substance P (SP). To prepare the label, gold nanoparticles (AuNPs) were immobilized onto the Fc-PNW for the following adsorption of horseradish peroxidase (HRP) and secondary anti-SP antibody (Ab2, Fc-PNW-HRP-Ab2). The role of Fc-PNW in the electrochemical label was not only as supporting matrix for HRP and Ab2, but also as the mediator for HRP to enhance the sensitivity of HRP toward H2O2 detection. The immunosensor was fabricated based on the traditional sandwich protocol with primary anti-SP antibody (Ab1) immobilized onto graphene surface. The catalytic current of HRP toward H2O2 in the presence of mediator Fc was used as signal of the immunosensor. Different parameters, such as the weight ratio of HRP to Ab2 on the Fc-PNW and the antibody–antigen incubation time were optimized to improve the performance of the immunosensor. The resulting immunosensor has high sensitivity, wide linear range (0.01–50ng/mL) and low detection limit (5pg/mL). [Copyright &y& Elsevier]

Abstract: A simple and novel supramolecular hydrogel was prepared from ferrocene (Fc) modified amino acid phenylalanine (F) and utilized as electrochemical immunosensing platform for the detection of human IgG. Scanning electron microscopy (SEM) characterization indicated that the hydrogel is composed of fibrils with diameter around 50–100nm and length extend to 1mm. When the prepared hydrogel was reacted with H2O2, the Fc moieties on the amino acid was oxidized, leading to the disruption of the hydrogel structure and the decrease of its redox signal, which was characterized in detail by SEM and the electrochemical method. Regarding the redox current decrease upon the reaction of the hydrogel with H2O2, the hydrogel modified electrode was utilized as immunosensing interface. After the construction of the immunosensor based on the traditional sandwich protocol with glucose oxidase (GOx) functionalized carbon nanotube (CNT) as detection antibody label, the GOx attached onto electrode surface would catalyze glucose reaction to produce H2O2 and cause the decrease of redox current of the electrode. The current change is proportional to the concentration of IgG detected in the range from 0.1 to 100pg/mL. The high sensitivity, wide linear range and good reproducibility of the immunosensor indicate this immunosensing platform can be easily extended to the detection of other protein biomarkers. [Copyright &y& Elsevier]

A ferrocence (Fc)-tagged peptide comprising the phenylalanine–phenylalanine (Phe–Phe) sequence was synthesized and allowed to self-assemble into uniform nanowires with a diameter of ca. 100nm and lengths in the range of 5–10µm. The Fc-tagged peptide nanowire (Fc-PNW) become well dispersed in aqueous solution when coated with poly(diallyldimethylammonium chloride) (PDDA). Gold nanoparticles (AuNPs) and antibody molecules can then be adsorbed onto the Fc-PNW surface. The resultant antibody modified Fc-PNW was explored as a detection probe for sensitive electrochemical immunosensing in a sandwich assay wherein the capture antibody was attached onto a graphene/gold nanoparticle (AuNPs–GN) composite film. The as prepared electrochemical immunosensor possesses a low detection limit (5fg/mL) for human IgG and a wide linear range encompassing four orders of magnitude (from 10fg/mL to 100pg/mL). Such a low detection limit stems from the significant signal amplification by the large number of Fc moieties on the PNW (for a 5-µm-long Fc-PNW, the number of Fc moieties is 5×105). The electrochemical immunosensor is also highly selective and the sensor was demonstrated to be amenable to real sample analysis. [ABSTRACT FROM AUTHOR]

Abstract: A novel kind of hydrogel was prepared from ferrocene (Fc) functionalized amino acid phenylalanine (Phe) and applied for the fabrication of electrochemical immunosensor to detect tumor necrosis factor α (TNF-α). The prepared hydrogel displays high redox activity due to the incorporation of a significant number of Fc moieties into the hydrogel. When the hydrogel was reacted with ascorbic acid (AA), the redox activity of the hydrogel was decreased as the Fc moieties in the hydrogel were reduced by AA. Based on this phenomenon, the immunosensor was constructed utilizing the traditional sandwich format using the hydrogel modified electrode as sensing platform and alkaline phosphatase (ALP) modified polystyrene sphere (PS) as label. First, primary anti-TNF-α antibody was immobilized onto the electrode surface via gold nanoparticles (AuNPs), then TNF-α and ALP were sequentially captured onto electrode. The ALP captured onto the electrode will catalyzes the hydrolysis of ascorbic acid 2-phosphate (AA-p) to form AA. The latter, in return, will cause the decrease of the redox current of the electrode. The decrease of the redox current is proportional to the concentration of TNF-α detected in the range from 1pg/mL to 10ng/mL. The immunosensor testing results were validated through the detection of clinical serum sample with satisfactory results. [Copyright &y& Elsevier]

Abstract: Sensitive electrochemical immunosensor for the detection of protein biomarker tumor necrosis factor α (TNF-α) was reported that uses ferrocene carboxylic acid (Fc) functionalized self-assembled peptide nanowire (Fc-PNW) as sensor platform and glucose oxidase (GOx) modified gold nanorod (GNR) as label. Greatly enhanced sensitivity is achieved based on a dual signal amplification strategy: first, the synthesized Fc-PNW used as the sensor platform increased the loading of primary anti-TNF-α antibody (Ab1) onto electrode surface due to its large surface area. At the same time, the Fc moiety on the nanowire is used as a mediator for GOx to catalyze the glucose reaction. Second, multiple GOx and secondary anti-TNF-α antibody (Ab2) molecules are bounded onto each GNR to increase the sensitivity of the immunosensor. After the preparation of the immunosensor based on the traditional sandwich protocol, the response of the immunosensor towards glucose was used as a signal to differentiate various concentrations of TNF-α. The resulting immunosensor has high sensitivity, wide linear range (0.005–10ng/mL) and good selectivity. This immunosensor preparation strategy is a promising platform for clinical screening of protein biomarkers. [Copyright &y& Elsevier]

Abstract: Ultrasensitive sandwich type electrochemical immunosensors for the detection of cancer biomarker prostate specific antigen (PSA) is described which uses graphene sheet (GS) sensor platform and ferrocene functionalized iron oxide (Fe3O4) as label. To fabricate the labels, dopamine (DA) was first anchored onto Fe3O4 surface followed by conjugating ferrocene monocarboxylic acid (FC) and secondary-antibody (Ab2) onto Fe3O4 through the amino groups of DA (DA-Fe3O4-FC-Ab2). The great amount of DA molecules anchored onto Fe3O4 surface increased the immobilization of FC and Ab2 onto the Fe3O4 nanoparticle, which in turn increased the sensitivity of the immunosensor. GS used as biosensor platform increased the surface area to capture a great amount of primary antibodies (Ab1) and the good conductivity of GS enhanced the detection sensitivity to FC. Using the redox current of FC as signal, the immunosensor displays high sensitivity, wide linear range (0.01–40ng/mL), low detection limit (2pg/mL), good reproducibility and stability. In addition, this method could be extended to the immobilization of other interesting materials (fluorescence dyes) onto Fe3O4 for preparing various kinds of labels to meet the different requirements in immunoassays. [Copyright &y& Elsevier]