Amperometric glucose sensors based on ferrocene containing polymeric electron transfer systems-a preliminary report

A nanometallic conductive composite-hydrogel core-shell microneedle skin patch for real-time monitoring of interstitial glucose levels

A microneedle-based skin patch system allows the minimally invasive extraction of skin interstitial fluid, which offers hope for the realization of quantitative and non-invasive diagnosis/monitoring of biological/physiological signals (biomarkers) in the human body. This work describes a nanometallic conductive composite-hydrogel core-shell microneedle skin patch that can realize minimally invasive real-time monitoring of physiological signals. The microneedle sensing system contains an inner conductive silver paste core and an outer bioactive hydrogel layer. The inner core is coated with biomarker-specific enzymes while the outer hydrogel layer extracts the biomarkers from the skin interstitial fluid. This patch can be integrated with the commercial signal processing and transmission modules and enable real-time monitoring. Taking glucose as a model biomarker, we confirm the function and potential application of this core-shell microneedle patch for transdermal diagnosis. It is proven that the core-shell microneedle patch can quickly extract skin interstitial fluid within 30 seconds and has a fast and linear response to glucose concentrations from 0 to 21 mM with a correlation coefficient of 0.9970, which may pave the way for the future development of smart wearable devices with minimally invasive transdermal biosensors.

Ferrocene-Modified Polyelectrolyte Film-Coated Electrode and Its Application in Glucose Detection

A polyelectrolyte film-coated electrode for the quantitative detection of glucose was reported. Carbon nanotubes, graphene oxide and polyelectrolyte with a ferrocenyl group were used to modify an enzyme electrode to facilitate the electron transfer between glucose oxidase and the electrode. Cyclic voltammetry and amperometric methods were adopted to investigate the effects of different polyelectrolytes and carbon nanomaterials on the electrochemical properties of enzyme electrodes. The results indicate that the ferrocenyl groups on a polyelectrolyte skeleton act as a mediator between the redox center of glucose oxidase and the electrode, which efficiently enhances the electron transfer between a glassy carbon electrode and glucose oxidase. The calibration curve of the sensor shows a linear range from 0.2 to 5 mM for glucose response. The sensor can achieve 95% of the steady-state current within 10 s. The electrodes also present high operational stability and long-term storage stability.

An amperometric biosensor for glucose detection from glucose oxidase immobilized in polyaniline-polyvinylsulfonate-potassium ferricyanide film

In this study, a novel amperometric glucose biosensor with immobilization of glucose oxidase on electrochemically polymerized polyaniline-polyvinylsulphonate-potassium ferricyanide (Pani-Pvs-Fc) films has been accomplished via the entrapment technique. Potassium ferricyanide was used as the mediator. Determination of glucose was carried out by the oxidation of potassium ferrocyanide at 0.3 V vs. Ag/AgCl. The effects of pH and temperature were investigated, and the optimum pH value was found to be 7.5. The storage stability and the operational stability of the enzyme electrode were also studied.

Patchy nanocapsules of poly(vinylferrocene)-based block copolymers for redox-responsive release

Nanocapsules composed of a poly(vinylferrocene)-block-poly(methyl methacrylate) shell and a hydrophobic liquid core are prepared in water. The nanocapsule shells display a patchy structure with poly(vinylferrocene) patches with sizes of 25 ± 3 nm surrounded by poly(methyl methacrylate). The functional nanopatches can be selectively oxidized, thereby influencing the colloidal morphology and introducing polar domains in the nanocapsule shell. The hydrophobic to hydrophilic transition in the redox-responsive nanopatches can be advantageously used to release a hydrophobic payload encapsulated in the core by an oxidation reaction.

Protein-carbon nanotube sensors: single platform integrated micro clinical lab for monitoring blood analytes

Design of a unique, single-platform, integrated, multichannel sensor based on carbon nanotube (CNT)-protein adducts specific to each one of the major analytes of blood, glucose, cholesterol, triglyceride, and Hb1AC is presented. The concept underlying the sensor, amperometric detection, is applicable to various disease-monitoring strategies. There is an urgent need to enhance the sensitivity of glucometers to <5% level instead of greater than the present 15% standard in these detectors. CNTs enhance the signals derived from the interaction of the enzymes with the different analytes in blood. Fabricated sensors using the new methodology is a point-of-care device that is targeted for home, clinical, and emergency use and can be redesigned for continuous monitoring for critical care patients.

Age-related muscle dysfunction

Aging is associated with a progressive decline of muscle mass, strength, and quality, a condition described as sarcopenia of aging. Despite the significance of skeletal muscle atrophy, the mechanisms responsible for the deterioration of muscle performance are only partially understood. The purpose of this review is to highlight cellular, molecular, and biochemical changes that contribute to age-related muscle dysfunction.

Vinylferrocene homopolymer and copolymers: an electrochemical comparison

Poly(vinylferrocene) (pVFc) homopolymer was synthesized by free radical polymerization, along with a series of pVFc-based copolymers containing either styrene, vinylanthracene or methylmethacrylate. This report details the electrochemical experiments conducted to examine the stability of the various pVFc based polymers, which is shown to be critically dependent on the extent of copolymerization. A trend was found that when the concentration of co-monomer was decreased, electrochemical stability was enhanced. Furthermore incorporation of a second monomer into the polymer chain produced a profound effect on the scan rate behaviour of the vinylferrocene moiety. As the concentration of co-monomer was decreased, the behaviour tended towards that of a diffusion controlled process. These results are of vital significance for the development of pVFc-based electrochemical sensors.

Protein nitration with aging in the rat semimembranosus and soleus muscles

On the basis of the accelerated age-related effects in type II muscle, we hypothesized that with aging the semimembranosus (type II) muscle would accumulate a greater amount of oxidized proteins compared to proteins in the soleus (type I) muscle. In this study, 3-nitrotyrosine (3-NT) was used as a stable marker of protein oxidative damage. The presence of 3-NT was evaluated in muscles from young adult, old, and very old Fischer 344 rats to provide an indication of the time course of muscle protein oxidative damage. A significant age-associated increase in nitrotyrosine-modified proteins was observed. The modified proteins identified by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry include the sarcoplasmic reticulum Ca(+2)-ATPase, aconitase, beta-enolase, triosephosphate isomerase, and carbonic anhydrase III. These proteins, involved in metabolism and calcium homeostasis, exhibited an age-dependent increase in 3-NT content in both muscles. However, significant levels of 3-NT modification were present at an earlier age in the semimembranosus muscle.

Polyvinylferrocenium modified Pt electrode for anaerobic glucose monitoring

An amperometric enzyme electrode for the determination of glucose under anaerobic solution conditions was developed by immobilizing glucose oxidase and then by adsorbing ferrocene in polyvinylferrocenium matrix coated on a Pt electrode surface. The amperometric response due to the electrooxidation of ferrocene that the reduced flavin adenine dinucleotide centers of glucose oxidase was measured at a constant potential. The response characteristics of the enzyme electrode were investigated. The effects of the thickness of the polymeric film, the amount of the enzyme immobilized, the amount of the mediator, the glucose concentration, the applied potential, operating pH and temperature on the response of the enzyme electrode were studied. The response time and the optimum pH were found to be 30-40 s and pH 7.4 at 25 degrees C, respectively. The linear response was observed up to 5.0 mM glucose concentration that the produced detectable current was 0.0075 mM glucose concentration. The activation energy (E(a)) of immobilized enzyme reaction was calculated to be 41.3 kJ mol(-1) from the Arrhenius plot. The apparent Michaelis-Menten constant (K(Mapp)) was found to be 6.05 mM glucose according to the Lineweaver-Burk graph of the Michaelis-Menten equation under the optimum conditions. The interference signal due to the most common electrochemical interfering species was also evaluated.

Mixed 1D−2D Inorganic Polymeric Zinc Ferrocenylphosphonate: Crystal Structure and Electrochemical Study

Needs for ferrocene immobilization on robust host structures are considerable since derivative materials may find applications in medical areas, optical devices, or catalysis. Synthesis of phosphonate functionalized ferrocene allowed its subsequent inorganic polymerization with a zinc salt. The crystallographic structure of the compound obtained, Zn(HO(3)PFc)(2).2H(2)O, shows a unique two-dimensional ferrocene arrangement anchored on a one-dimensional Zn-O-P-O-Zn backbone. The ferrocene packing in the title compound is very similar to the packing found in molecular ferrocene. The electroactivity of Zn(HO(3)PFc)(2).2H(2)O is thoroughly studied. It shows a reversible surface oxidation of ferrocene. Mössbauer spectroscopy for the oxidized compound shows an isomer shift of IS(2b) = 0.432 mm x s(-1) and a quadrupolar splitting of QS(2b) = 0.205 mm x s(-1), which is consistent with a stable S = 1/2 ferrocenium state. The magnetic susceptibility study, Mössbauer spectroscopy, and galvanostatic titration show that only the ferrocene moieties present at the surface of the crystallites are reversibly oxidized. This observation is reinforced by a complex impedance study showing mainly resistive behavior and conductivity measurements indicating weak, thermally assisted, conductivity. The general properties of this compound demonstrate that phosphonato functionalization may be a useful approach for all fields concerned by immobilization of ferrocene.