Amperometric needle-type glucose sensor based on a modified platinum electrode with diminished response to interfering materials

Flat-chip microanalytical enzyme sensor for salivary amylase activity

It is considered that measurement of salivary alpha-amylase activity is a useful tool for evaluating the sympathetic nervous system. The purpose of this research is to demonstrate a new design of a flat-chip microanalytical enzyme sensor (flat-chip sensor) for salivary amylase activity as a Micro-Electro-Mechanical Systems (MEMS), which may be used for wearable analytical systems. To meet this purpose, the biosensor needs to be miniaturized and to possess high-sensitivity. A pre-column and a flat-enzyme electrode were incorporated in a flow cell of volume 25.7 ml. In order to miniaturize the flow cell, two enzymatic membranes containing maltose phosphorylase obtained from Enterococcus hirae (MP membrane) and glucose oxidase and peroxidase (GOD-POD membrane) were immobilised on the same planar surface. As a result, a flat-chip sensor incorporating a flow cell as small as a C battery was produced. The optimum conditions of three parameters of the fabricated flat-chip sensor, the immobilising method of the enzymatic membrane, dropping volume of the mixed enzymatic solution and flow rate of the sample solution, were examined. An analytical system for 0-190 kU/l amylase activity with R(2) of 0.97 was fabricated with a sample volume of 50 microl. This research indicates the possibility of a wearable biosensor for continuous monitoring of salivary amylase activity.

Glucose monitoring: state of the art and future possibilities

This article reviews the development of glucose monitoring techniques and approaches during the last decade. The predominance of the electrochemical measuring principles reported in the literature makes them a focus of this work. Biosensors are still in the main stream of the research interest of most teams due to their high selectivity for glucose determination. Systematization and classification of the glucose monitoring principles and types of glucose sensors is shown. The review gives a brief description of the basic operational principles of the most popular types of glucose biosensors, providing an enhanced bibliography of the original works of the main groups in establishing or significantly contributing to the development of the particular type of glucose biosensor. Different design approaches are overviewed including needle-type sensors, sensors for chronical implantation and the combination of the glucose biosensors with microdialysis sampling technique. The authors approach for replacing of the spent enzyme and thus recharging the sensor in situ while implanted is widely discussed. This approach provides a way to increase the lifespan of the system and ultimately, it could lead to rare transcutaneous interventions for refilling of the implanted sensor.

Glucose biosensors based on oxygen electrode with sandwich-type membranes

A glucose biosensor based on an amperometric oxygen electrode has been developed. Polycarbonate and Silastic membranes were assembled (glued together) to form a multilayer sandwich glucose diffusion barrier. The effects of the glue layer composition and thickness of the Silastic membrane on sensor response parameters have been investigated in order to optimize the sensor. The parameters measured were the sensitivity, the concentration range of the linear dependence of the sensor response to glucose, and the long-term operation time. The sensors with the sandwich-type glucose diffusion membrane (Silastic membrane prepared from 20% Silastic suspension, glue layer prepared from polyurethane, 0.5 w/v % in ThF solution and standard polycarbonate membrane) demonstrated linearity of response up to 520 mg/dl glucose at 25 degrees C and up to 400 mg/dl at 37 degrees C. These sensor showed good reproducibility of response without significant interference effects (from 1 to 5% of the background current value). The long-term continuous operational time of the sensors was over 40 days at 37 degrees C, and over 60 days at 25 degrees C.

Effect of interference on the performance of glucose enzyme electrodes using Nafion coatings

The negatively charged perfluorinated ionomer Nafion was used as a coating on hydrogen peroxide detecting platinum electrode as well as on a polycarbonate diffusion membrane in the construction of a glucose amperometric enzyme electrode. The current response of these electrodes to hydrogen peroxide, ascorbic acid, acetaminophen, uric acid and glucose was studied and the coating procedure was optimized. It was confirmed that the Nafion coating prevents interference by anionic substances such as ascorbic acid and uric acid, and decreases acetaminophen interference. In this regard it was shown that coating the glucose diffusion membrane (polycarbonate) was more effective than coating the platinum wire itself, because of the prevention of the homogeneous redox reaction of the interference species with hydrogen peroxide, as well as the additional diffusional resistance to the glucose flux. The glucose levels in serum samples were estimated and the stability of the enzyme electrodes during continuous operation in serum was studied. An enzyme electrode with constant sensitivity of ca. 1 microA/mM and a linear range of up to 15 mM, unaffected by contact with serum, is reported.

A biocompatible needle-type glucose sensor based on platinum-electroplated carbon electrode

A biocompatible needle-type glucose sensor with a 3-electrode configuration was constructed. A platinum-electroplated carbon stick was used as the working electrode, Ag/AgCl as the reference electrode, and a disposable hypodermic needle made of stainless steel as the counter electrode. A Nafion membrane, an immobilized glucose oxidase (GOD) membrane, and a biocompatible membrane with diffusion-limiting effect were coated successively onto the working electrode. The sensor showed a rapid response (< 120 s in batch operation), good reproducibility (RE < 3%), good stability (over 36 h in control serum), a wide dynamic range (5-600 mg/dL glucose), and superior biocompatibility. It was used to determine glucose in serum. The data obtained from the sensor showed good agreement with that from a clinical autoanalyzer (R > 0.95).