A supramolecular indicator system (cellulose - nanodiamond - urease) for biochemical determination of urea was constructed by layer-by-layer immobilization of the com- ponents. Modified nanodiamonds (MND) were covalently immobilized on polymeric carrier (DEAE-cellulose granules) using nucleophilic addition reaction. It was established that during the reaction carried out at a weight ratio of components 4:1 (DEAE-cellulose : MND) up to 110 µg of the nanoparticles can be immobilized on 1 mg of the polymer. Biomarker (ure- ase) was covalently immobilized on the surface of polymer- MND composite previously activated by benzoquinone. In comparative experiments the enzyme was immobilized on initial polymeric granules using nonspecific adsorption and covalent immobilization. The enzyme activity in obtained supramolecular complexes was assessed spectrophotometrically in the size of optical density of formed colored reaction product using urease salicylate-hypochlorite method. It was shown that urease molecules can be immobi- lized on DEAE-cellulose granules by adsorption and covalent immobilization, exhibiting their functional activity in both cas- es. However, it was shown that at reusable use of these indi-cator systems for testing of analyte testing noticeable inacti- vation of enzyme that is followed by the decrease in an exit of painted product was observed. At the same time, in compara- tive experiments it was established that enzyme covalently immobilized on the DEAE-cellulose - MND composite had higher functional efficiency and enabled more stable yield of the colored product at multiple urea testing. Comparative studies showed that the enzyme covalently immobilized on the DEAE-cellulose - MND composite had also had higher thermal stability and more slowly lost its functional activity during multiple use of indicator system for urea testing at a temperature of 37°C, in comparison with enzyme immobilized in the same way on the polymer. The results of the study open the prospects for creation of a new class of reusable indicator systems (polymeric carrier - nanodiamond - bi- omarker supramolecular complexes) for biomedical analytics.
nanodiamond, cellulose, urease, immobiliza- tion, supramolecular complex, indicator system
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