Bioderived in situ Nitrogen-Doping Carbon Dots as an Effective Fluorescent Probe for Turn-on Ultrasensitive and Selective Detection of Nonenzymatic Bilirubin in Human Urine

Herein, we harnessed the transformative power of waste sugarcane-derived in situ nitrogen-doped carbon dots (N-CDs) to develop a fluorescent probe, poised to revolutionize the sensitive and selective detection of Bilirubin (BIL) in human urine. By utilizing waste sugarcane bagasse as the source of carbon and nitrogen, we embraced a combination of greener, solvent-free, and chemical-free thermal carbonization and the Sonochemical process to create N-CDs. The electronic, crystallographic, photochemical, and morphological behaviors of the synthesized N-CDs have been meticulously analyzed using various spectroscopic and microscopic techniques. When excited at 360 nm, these N-CDs emit a captivating blue fluorescence at 440 nm with an impressive color purity of 75.1%. Remarkably, the addition of BIL, without the need for labels on the N-CDs, results in a striking selective enhancement of this fluorescence with a striking color purity of 81%. This enhancement is driven by the formation of a ground-state interaction between BIL and the N-CDs, which is confirmed through a particle size analyzer and atomic force microscopy. The turn-on mechanism, which could be due to the formation of pi-pi stacking, is validated through FT-IR, and ¹H-NMR reveals the powerful interactions at play. This exceptional probe exemplifies unparalleled sensitivity, ultrastability, rapid response times, and unmatched accuracy for BIL concentrations ranging from 6.6 to 1876 nM, culminating in a limit of detection (LOD) of 3 nM, showcasing its efficacy in both synthetic urine samples and real human urine sample analysis with impressive recovery results. This study ignites inspiring insights into trailblazing approaches for quantifying BIL levels in urine, paving the way for significant advancements in noninvasive, stable, and accessible alternative medical diagnostics.