Impedimetric and amperometric bifunctional glucose biosensor based on hybrid organic-inorganic thin films.

A novel glucose biosensor with an immobilized mediator was studied using electrochemical impedance spectroscopy (EIS) and amperometry measurements. The biosensor has a characteristic ultrathin form and is composed of a self-assembled monolayer anchoring glucose oxidase (GOx) covered with Langmuir-Blodgett (LB) films of Prussian blue (PB). The immobilized PB in the LB films acts as a mediator and enables the biosensor to work under a low potential (0.0V vs. Ag/AgCl). In the EIS measurements, a dramatic decrease in charge transfer resistance (Rct) was observed with sequential addition of glucose, which can be attributed to enzymatic activity. The linearity of the biosensor response was observed by the variation of the sensor response (1/Rct) as a function of glucose concentration in the range 0 to 25mM. The sensor also showed linear amperometric response below 130mM glucose. The organic-inorganic system of GOx and PB nanoclusters demonstrated bifunctional sensing action, both amperometry and EIS modes, as well as long sensing stability for 4 days.

Electrochemical impedance spectroscopy biosensor with interdigitated electrode for detection of human immunoglobulin A.

Interdigitated electrodes (IDEs) that have a series of parallel microband electrodes with alternating microbands connected together were utilized in electrochemical impedance spectroscopy (EIS) to build a label-free human immunoglobulin A (IgA) immunosensor. Anti-human IgA (anti-IgA) was employed as an IgA receptor and was covalently immobilized on the IDE surface through a self-assembled monolayer, as confirmed by atomic force microscopy. EIS measurements revealed that the specific adsorption of IgA onto the immobilized anti-IgA gave rise to a clear increase in the value of interfacial charge transfer resistance (R(ct)). A linear relationship between ΔR(ct) and the logarithm of IgA concentration was found for the concentration range of 0.01-100 ng/mL. No modulation of R(ct) was detected by immersing the sensor in solutions of other proteins such as human immunoglobulin G or bovine serum albumin, which confirmed a high selectivity of this immunosensor for IgA. These results demonstrated that the anti-IgA receptor simply immobilized on the IDE surface can provide a sensitive biosensor.

Incorporation of glucose oxidase into Langmuir-Blodgett films based on Prussian blue applied to amperometric glucose biosensor.

Glucose oxidase (GOx) was immobilized in the organic-inorganic Langmuir-Bldogett (LB) films consisting of octadecyltrimethylammonium (ODTA) and nanosized Prussian blue (PB) clusters. The amperometric glucose biosensors based on the LB films were fabricated and tested. It was found that the sensors exhibited a clear response current under an applied voltage of 0.0 V (vs Ag/AgCl). The linearity of current density versus glucose concentration was confirmed below 15 mmol/L concentration. This is the first observation of biosensor function of the hybrid organic-inorganic LB films. The successful preparation of glucose sensors operating at the very low potential indicates that the adsorbed PB clusters in the LB films act as an electrocatalyst for the electrochemical reduction of hydrogen peroxide, which is the final product of the enzymatic reaction sequence. The observed low potential applicability is estimated to inhibit the responses of interferants such as ascorbic acid, uric acid, and acetominophen. It was also found that an electrostatic interaction between positively charged ODTA+ and the adsorbed species of both GOx and PB provided a stabilized adsorption state in the LB films. Such stable immobilization contributes to the steady amperometric response current observed in the present ODTA/PB/GOx LB films.