Scientists figured out how to replace enzymes in sensors for quantitative determination of glucose

Scientists at the Ural Federal University (UrFU Russia) have solved the problem of synthesizing enzymefree electrocatalytic sensors for quantitative determination of glucose. Researchers proposed to cover the electrode surface on the test strip with palladium and silver. Such electrodes will more accurately determine the concentration of glucose in the blood. Its shelf life will be longer with less whimsical to storage conditions. And, according to preliminary calculations by the developers, it’s cheaper than existing analogs with enzymes (one strip requires millionths of a gram of metals). An article describing the method of layer-by-layer electrochemical deposition was published in the Russian Chemical Bulletin. The article presents the first description of such a method in the scientific literature.

“For deposition, we used a printed electrode - a miniature carbon substrate coated with a suspension of multi-walled, that is, inserted into each other, carbon nanotubes,” said Andrey Okhokhonin, associate professor of the Department of Analytical Chemistry at UrFU, head of the research group. “Water from the suspension deposited on the electrode evaporates, while the nanotubes remain on the electrode, thus increasing its specific surface area. Then we alternately deposited silver and then palladium on the modified electrode surface several times.”

The essence of the layer-by-layer deposition method is as follows. The electrode is alternately lowered into solutions of silver salt and palladium salt in dilute sulfuric acid. In this form, silver and palladium are lack one and two electrons, respectively, before the transition to the insoluble metallic state. By placing an electrode in a solution, an electric current is applied to it. The current reduces metals, and this leads to the formation of solid particles on the surface of the electrode. The procedure is repeated four times. The new system, the developers say, can be used to create an enzyme-free electrocatalytic sensor for determining glucose in whole blood.

“This technique has not yet been applied, but it has proven to be effective,” said Andrey Okhokhonin. “The resulting new material has significant catalytic activity in the electrochemical oxidation of glucose. At the same time, in contrast to analogs, the oxidation reaction effectively proceeds in a neutral medium of a phosphate buffer solution, which corresponds to the acidity of human blood. Other similar systems are either noticeably less sensitive to glucose, or operate in an alkaline environment and provide for an additional stage of dilution of blood samples, in certain cases a thousand times. All this complicates the procedure and reduces the reliability of the analysis results.”

Note

Complex protein compounds are used in modern glucometers. These are enzymes glucose oxidase or glucose dehydrogenase, which are produced by microorganisms. Enzymes are fixed on the working sensitive part of the test strip (sensor), where a drop of blood is fed. Test systems based on the use of enzymes are widespread, but they have a number of disadvantages. Since enzymes are of a protein nature, they denaturate under heat or light exposure, and their shelf life is limited. Replacing enzymes with more stable and cheaper oxidation catalysts will reduce the cost of glucometers and extend their shelf life. Possible substitution options include palladium (it has stability and increased sensitivity to glucose). However, it shows activity only upon preliminary treatment in a saturated alkaline solution, where a blood sample is then fed. This complicates and slows down the analysis procedure.

To date, only one method has been developed for direct blood analysis using enzyme-free catalysts based on palladium nanoparticles. But it does not provide the necessary sensitivity of the system and, therefore, the accuracy of the analysis results.

The catalytic activity of palladium is enhanced in combination with silver: two elements, co-applied to the electrode portion of the test strip, improve each other's catalytic properties. This increases the sensitivity of the blood glucose test. However, the existing technologies for creating such compounds do not allow full control of the ongoing processes. Thus, scientists are faced with the task of synthesizing enzyme-free catalysts, which will make it possible to more accurately and with lower financial costs determine the concentration of glucose in the blood.