Carbon dot-copper nanocomposite-based fluorescent sensor for detection of creatinine in urine samples of CKD patients

Creatinine (CR) is accepted as a clinical biomarker of chronic kidney disease (CKD) such as renal injury and kidney failure. To help facilitate the prognosis of CKD, a highly luminescent carbon dot (CD)-based fluorescent (FL) sensor has been built and employed for CR detection in diverse media (e.g., artificial and human urine). CDs, synthesized from sucrose precursor by a rapid microwave-assisted method (average diameter 20 nm), exhibited highly luminescent green emission upon UV exposure (λ_excitation = 390 nm, λ_emission = 453 nm) with excellent temporal stability over three months. The nanocomposites are formed between CDs and metal ions (e.g., Cu²⁺) to realize the optimum biosensing of CR. Although Cu²⁺ ions showcases a maximum quenching (73 %) of the CDs, Cu²⁺/CDs system restores 77 % of the original FL intensity upon the addition of CR. The linear detection range and limit of detection for CR are estimated as 10^-5 to 0.1 mg·dL^-1 (R² = 0.936) and 5.1 × 10^-16 mg·dL^-1, respectively. Furthermore, our biosensor shows excellent reproducibility and selectivity for CR in urine samples of healthy subjects and CKD patients. The Bland-Altman analysis for urine samples (n = 30) showcased an excellent agreement (R² = 0.95) between our method and the gold standard 'Jaffe' method. These observations supported the practical utility of our method proposed for detection of CR in clinical samples.