Watermelon (Citrullus lanatus) urease immobilized on chitosan-unzipped multi-walled carbon nanotubes (UZMWCNTs) nanobiocomposite for enhanced blood urea sensing

Abstract

Urease, a hydrolytic enzyme, facilitates the conversion of urea into ammonia and carbon dioxide and serves as a critical biomarker for assessing renal function. Developing a sensor to monitor urea is essential, as elevated urea levels in the blood often indicate renal impairments. In contrast, low levels may reflect inadequate protein intake or diminished kidney performance. To address this need, a novel nanobiocomposite was synthesized by incorporating purified urease from watermelon into chitosan-modified chemically unzipped multi-walled carbon nanotubes (UZMWCNTs). High immobilization efficiency (92.5 %) validated predictive modeling. Immobilized urease exhibited a V<inf>max</inf> of 3225.8 µmol/min/mg and K<inf>m</inf> of 0.24 mM. At 277 K, 53 % activity was retained after 200 days. Operational stability showed 90 % activity after 13 cycles. The sensor exhibited a broad linear detection range from 10 mg/dL to 400 mg/dL. It demonstrated exceptional sensitivity, with a limit of detection (LOD) of 3.17 ± 0.158 mg/dL and a limit of quantification (LOQ) of 10.58 ± 0.52 mg/dL. Its high selectivity, highlighted by a selectivity coefficient below 0.1 (k<inf>sel</inf> < 0.1), ensured precise urea detection even within complex biological samples. Validation using artificial blood serum revealed recovery rates of 86.4–96.9 % (RSD < 5 %), underscoring the sensor's reliability and accuracy. The nanobiocomposite also showcased excellent stability and reproducibility, making it a promising tool for clinical applications. This sensor offers a robust solution for precise and efficient urea quantification, paving the way for enhanced diagnostics of renal health. © 2025 Elsevier B.V.