Electrochemical and Enzymatic Studies of Electron Transfer Mediation by Ferrocene Derivatives with Nafion-Glucose Oxidase Electrodes

A Mediated Enzymatic Electrochemical Sensor Using Paper-Based Laser-Induced Graphene

Laser-induced graphene (LIG) has been applied in many different sensing devices, from mechanical sensors to biochemical sensors. In particular, LIG fabricated on paper (PaperLIG) shows great promise for preparing cheap, flexible, and disposable biosensors. Distinct from the fabrication of LIG on polyimide, a two-step process is used for the fabrication of PaperLIG. In this study, firstly, a highly conductive PaperLIG is fabricated. Further characterization of PaperLIG confirmed that it was suitable for developing biosensors. Subsequently, the PaperLIG was used to construct a biosensor by immobilizing glucose oxidase, aminoferrocene, and Nafion on the surface. The developed glucose biosensor could be operated at a low applied potential (-90 mV) for amperometric measurements. The as-prepared biosensor demonstrated a limit of detection of (50-75 µM) and a linear range from 100 µM to 3 mM. The influence of the concentration of the Nafion casting solution on the performance of the developed biosensor was also investigated. Potential interfering species in saliva did not have a noticeable effect on the detection of glucose. Based on the experimental results, the simple-to-prepare PaperLIG-based saliva glucose biosensor shows great promise for application in future diabetes management.

Next step in 2nd generation glucose biosensors: Ferrocene-loaded electrospun nanofibers

Glucose determination is one of the most common analyses in clinical chemistry. Employing biosensors for this purpose has become the method of choice for home use for diabetic patients. To limit the impact of dissolved O₂ concentration or possible interferences (known hindrances in the classical glucose detection approach), a variety of mediated pathways have been explored. Herein, an ingenious, facile and low-cost approach for immobilization of redox mediator within nanofibrous mats is presented. This '2^nd generation' biosensor is able to avoid common issues such as leaching or diffusion barriers whilst providing the necessary close contact between the enzyme and the redox shuttle, for enhancing the detection accuracy and accelerate the response. Polyacrylonitrile nanofibers loaded with carbon nanotubes and ferrocene (PAN/Fc/MWCNT-COOH NFs) have been successfully prepared and applied as biosensing matrices upon cross-linking of glucose oxidase (GOD). The morphology of the NFs was investigated by means of scanning electron microscopy (SEM-EDX) and correlated to the kinetics of mediated electron transfer and to the efficiency in glucose detection, which were evaluated through cyclic voltammetry (CV) and amperometric measurements. The content of Fc was varied from 0.5 to 5.0 wt%, with optimum biosensor performance at 1.0 wt% exhibiting a linear range up to 8.0 × 10^-3 M with sensitivity of ~27.1 mAM^-1 cm^-2 and 4.0 μM LOD. Excellent stability (RSD 2.68%) during 40 consecutive measurements along with insignificant interference and accurate recovery in real sample analysis (~100%) make for a very reliable sensor that can easily render itself to miniaturization and has the potential for a wide range of practical applications.

Mesoporous carbon amperometric glucose sensors using inexpensive, commercial methacrylate-based binders

Two ordered, soft-templated mesoporous carbon powders with cubic and hexagonal framework structure and four different commercial, low cost methacrylate-based polymer binders with widely varying physical properties are investigated as screen printed electrodes for glucose sensors using glucose oxidase and ferricyanide as the mediator. Both the chemistry and concentration of the binder in the electrode formulation can significantly impact the performance. Poly(hydroxybutyl methacrylate) as the binder provides hydrophilicity to enable transport of species in the aqueous phase to the carbon surface, but yet is sufficiently hydrophobic to provide mechanical robustness to the sensor. The current from the mesoporous carbon electrodes can be more than an order of magnitude greater than for a commercial printed carbon electrode (Zensor) with improved sensitivity for model glucose solutions. Even when applying these sensors to rabbit whole blood, the performance of these glucose sensors compares favorably to a standard commercial glucose meter with the lower detection limit of the mesoporous electrode being approximately 20mgdL(-1) despite the lack of a separation membrane to prevent non-specific events; these results suggest that the small pore sizes and high surface areas associated with ordered mesoporous carbons may effectively decrease some non-specific inferences for electrochemical sensing.

Electrochemical glucose sensors--developments using electrostatic assembly and carbon nanotubes for biosensor construction

In 1962, Clark and Lyons proposed incorporating the enzyme glucose oxidase in the construction of an electrochemical sensor for glucose in blood plasma. In their application, Clark and Lyons describe an electrode in which a membrane permeable to glucose traps a small volume of solution containing the enzyme adjacent to a pH electrode, and the presence of glucose is detected by the change in the electrode potential that occurs when glucose reacts with the enzyme in this volume of solution. Although described nearly 50 years ago, this seminal development provides the general structure for constructing electrochemical glucose sensors that is still used today. Despite the maturity of the field, new developments that explore solutions to the fundamental limitations of electrochemical glucose sensors continue to emerge. Here we discuss two developments of the last 15 years; confining the enzyme and a redox mediator to a very thin molecular films at electrode surfaces by electrostatic assembly, and the use of electrodes modified by carbon nanotubes (CNTs) to leverage the electrocatalytic effect of the CNTs to reduce the oxidation overpotential of the electrode reaction or for the direct electron transport to the enzyme.

Towards redox active liquid crystalline phases of lipids: a monoolein/water system with entrapped derivatives of ferrocene

The phase and electrochemical behavior of the aqueous mixtures of monoolein (MO) and synthetic ferrocene (Fc) derivatives containing long alkyl chains-(Z)-octadec-9-enoylferrocene (1), (Z)-octadecen-9-ylferrocene (2), and ferrocenylmethyl (Z)-octadec-9-enoate (3)-were studied. At low hydration, the reversed micelles (L(2) phase) and cubic Q(230) phase of MO can accommodate relatively high amounts (>6 wt.%) of the Fc-derivative 2, whereas at high hydration, the pseudoternary cubic phase Q(224) is destabilized even at about 2 wt.% of this Fc. Increasing the Fc-derivative content induces L(alpha)-->L(2) and L(alpha)-->reversed bicontinuous cubic phase (Q(II))-->H(II) transitions depending upon hydration. A rough study of the MO system containing compounds 1 and 3 indicates very similar phase behavior to that of the MO/2/H(2)O system. Compound 2 apparently has no effect on the lipid monolayer thickness in the pseudoternary L(alpha), H(II) and Q(II) liquid crystalline phases of MO. Within a 3D-structure of the Q(224) phase, derivatives 1-3 exhibit electrochemical activity on the gold electrode. The one-electron redox conversion processes are electrochemically quasi-reversible and controlled by diffusion. The values of apparent diffusion coefficient (D(app)) and heterogeneous electron-transfer rate constant (k(s)) of Fcs are significantly lower in the cubic phase matrix when compared to the acetonitrile solution. By contrast, the MO H(II) phase with entrapped Fc-derivatives does not exhibit electrochemical activity on the electrode surface. It is suggested that the diffusional anisotropy and/or localized aggregation of compounds 1-3 within a 2D-structure of the H(II) phase account(s) for the latter observation.