Moscow Polytech to Develop Reusable Biosensor for Creatinine Determination
Existing enzymatic test systems for creatinine analysis are single-use and require stationary equipment. Scientists at Moscow Polytechnic University will develop a reusable biosensor to determine creatinine, a key indicator of kidney function. The project is supported by a grant from the Russian Science Foundation under a competition for research groups led by young scientists. The project leader is Alexander Kim, Associate Professor and PhD in Biological Sciences, and the co-investigator is Associate Professor Egor Musin; both work at the University.
Creatinine is a substance whose concentration in the blood allows doctors to assess the glomerular filtration rate and detect kidney dysfunction. Regular monitoring of this indicator is extremely important for patients with chronic kidney diseases, of which there are more than 14 million people in Russia, as well as for pregnant women and newborns. The Jaffe method, used in most laboratories, gives overestimated results due to foreign substances in the blood, such as glucose, bilirubin and other compounds. The more accurate enzymatic method uses free enzymes, but they work only once: after analysis they are disposed of, and the analysis itself is possible only with stationary laboratory equipment. As a result, patients have to go to a laboratory and wait hours for the result, although the indicator needs to be monitored regularly.
Scientists propose to solve this problem by placing enzymes inside polyelectrolyte microcapsules –microscopic shells several micrometers in size, which are assembled from alternating layers of oppositely charged polymers, like a layer cake. The shell allows molecules of the analyzed substance to reach the enzyme, but prevents the enzyme itself from being washed out and destroyed through contact with the external environment.
"A free enzyme applied directly to the surface of an electrode quickly loses activity and is suitable literally for a single measurement. The microcapsule works as a protective packaging: it allows the same enzyme to be used dozens of times, because it is physically isolated from destructive factors while remaining available for reaction with the analyzed substance," said Alexander Kim.
The biosensor is based on a cascade of three enzymes: creatininase, creatinase and sarcosine oxidase. They work sequentially: the first breaks down creatinine into creatine, the second converts creatine into sarcosine, and the third oxidizes sarcosine to form hydrogen peroxide. It is the hydrogen peroxide that is detected by the electrode; its quantity is used to calculate the initial concentration of creatinine in the sample. The enzyme capsules are planned to be fixed on a printed electrode coated with Prussian blue, a substance already used in disposable test strips for glucometers and which responds well to hydrogen peroxide.
Alexander Kim previously studied the encapsulation of individual enzymes, but this is the first time that three enzymes working in a chain have been placed in a single microcapsule. The task is complicated by the fact that when packed together, the enzymes may interfere with one another or lose activity because of the limited space inside the capsule.
The project is designed for three years. In 2026, the scientists will work out the encapsulation of the first enzyme in the cascade, sarcosine oxidase, and its fixation on the electrode. In 2027, similar work will be carried out with the two remaining enzymes, while the development of a device prototype using additive and printing technologies will begin in parallel. In 2028, all three enzymes will be combined in one microcapsule, the optimal method to attach it to the electrode will be determined, and the completed system will be tested on patient blood serum samples.
The developers expect the biosensor to remain operational for at least six months when stored in a refrigerator and withstand at least 50 measurement cycles without losing accuracy. According to the authors, such a device could eventually be used at home, without a visit to a laboratory. For people who need frequent monitoring of kidney function, this would eliminate regular trips to a clinic for a single test.
