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Chemists develop enzyme-free cholesterol testing system

Scientists at the Ural Federal University (UrFU) have developed a new sensor device for determining cholesterol levels in blood. The system does not use protein compounds such as enzymes. Chemists replaced them with an inorganic analog—copper chloride. This allowed them to make the process of creating cholesterol meters cheaper, to make blood testing easier, faster and more accessible. The results of the study are presented in the Journal of Electroanalytical Chemistry.

"Cholesterol determination is currently performed using colorimetry, chromatography, and enzymes. However, these methods use either extremely aggressive reagents or complex and expensive equipment, or—as recognizing and sensitive elements that determine cholesterol levels—enzymes—biological molecules that are extracted from living organisms," explains Andrei Okhokhonin, Associate Professor at the UrFU Department of Analytical Chemistry.

"For example, the enzyme cholesterol oxidase is produced by some species of bacteria. Also enzymes are natural polymers, proteins, therefore, they are prone to denaturation and require certain storage conditions, temperature and acidity regimes. We decided to select a non-biological analog of this enzyme to make the process of cholesterol analysis cheaper, easier and faster. One of the most affordable options is copper chloride, which we first discovered to be highly sensitive to cholesterol,"

To measure cholesterol levels with the new device, a small amount of blood is enough. The blood is placed in an analyzing chip containing a solution of copper chloride in acetonitrile. An electrode is integrated into this chip, which is connected to a voltammetry analyzer that gives the results of the analysis. The advantage of the new chip analyzing cholesterol levels is also that it contains magnetic nanoparticles with polymers with molecular imprints that selectively sorb cholesterol, screening out any other substances characteristic of blood composition.

"Molecular imprinted polymers are needed to effectively separate cholesterol from other substances in the blood. After trying several options, we chose ethylene glycol dimethacrylate as the crosslinking agent and vinylpyridine as the functional monomer. The polymer synthesized on the surface of magnetic nanoparticles effectively sorbs cholesterol, so we can talk about high selectivity of analysis, as no other substances interfere," says Andrei Okhokhonin.

The microfluidic chip, in which all elements of the system are integrated, is printed on a 3D printer, which also facilitates the production process of the device. Scientists note that the first test they conducted was not done on biological samples, but on model solutions that mimic blood serum. The next stage of the researchers' work is to test the system on real blood samples.