Uric acid (UA) is a crucial biomarker for various metabolic and renal disorders, making its accurate determination essential for clinical diagnostics and disease management. This study presents a novel fluorometric method for UA detection using a glutathione@cadmium/carbon dots/uricase system (GSH@Cd/CDs/uricase system), which offers enhanced sensitivity and selectivity compared to existing techniques. The method employs a cascade reaction mechanism initiated by uricase-catalyzed oxidation of UA to produce H₂O₂. This H₂O₂ subsequently oxidizes GSH to oxidized glutathione (GSSG), releasing cadmium ions from GSH complexes. The liberated Cd²⁺ ions interact with two types of carbon dots (CDs) in the system: blue-emitting CDs (BCDs) and red-emitting CDs (RCDs). This interaction triggers a dual fluorescence response, characterized by a decrease in fluorescence intensity at 400 nm (BCDs) and an increase at 610 nm (RCDs), enabling ratiometric detection of UA levels. Comprehensive characterization and mechanistic investigations were conducted using various optical and morphological techniques, including transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and fluorescence spectroscopy. The method exhibits outstanding analytical performance, characterized by strong linearity (R² = 0.9932), a broad detection range (0.05–7.0 μM), and a low detection limit of 0.015 μM. The method demonstrated excellent selectivity against common interfering substances and was successfully applied to human serum and urine samples with high recovery values (97.65 % to 99.20 %), highlighting its potential for clinical applications. This innovative approach combines the specificity of enzymatic recognition with the sensitivity of dual-emission fluorescence, offering a promising tool for accurate UA quantification in complex biological matrices.

A new ratiometric fluorescence strategy for sensitive and selective detection of cobalt ions (Co²⁺) and topotecan (TOP) is proposed. The dual-probe system consists of red-emissive nitrogen and sulphur doped carbon dots (R-NS@CDs) and TOP. For Co²⁺ detection, the fluorescence of R-NS@CDs at 680 nm is enhanced upon addition of Co²⁺, while complexed TOP emission peak at 545 nm remains constant. This enables ratiometric detection of Co²⁺ over a range of 5.0–160.0 ng mL⁻¹. The mechanism of R-NS@CDs fluorescence enhancement by Co²⁺ is elucidated using FTIR, fluorescence spectroscopy, zeta potential measurements, and TEM imaging. For the detection of TOP, a ratiometric probe system comprising R-NS@CDs and Co²⁺ was utilized. TOP forms a complex with Co²⁺ bounded to R-NS@CDs, quenching the R-NS@CDs-Co²⁺ fluorescence and simultaneously the native TOP fluorescence is enhanced. This allows ratiometric quantification of TOP from 1.0-90.0 ng mL⁻¹. The method provides high selectivity and low detection limits of 1.51 ng mL⁻¹ for Co²⁺ and 0.37 ng mL⁻¹ for TOP. Practical applicability is demonstrated through selective detection of Co²⁺ in environmental water samples and TOP in real plasma samples. The built-in self-calibration enabled by dual analyte modulation of R-NS@CDs makes this a simple and powerful analytical approach.

Fluoride is an essential ion for dental health that is optimally supplemented through drinking water, toothpastes, and other oral hygiene products. This work reports a selective, simple, and inexpensive fluorescent sesnor for fluoride quantification. The sensor exploits the red fluorescence of carbon dots coupled with the colorimetric response of a zirconium-alizarin complex. The zirconium-alizarin exhibits an absorption band at 530 nm that overlaps the carbon dot excitation peak, resulting in inner filter effect-based quenching of the 612 nm red emission. However, in the presence of fluoride, binding disrupts the zirconium complex, releasing free alizarin with an absorption blue shifted to 420 nm. This reduces spectral overlap and restores carbon dot fluorescence. The carbon dots were synthesized by a hydrothermal method and exhibited excellent fluorescence quantum yield (16.3 %). Structural and optical characterizations were performed using TEM, XRD, XPS, FTIR, UV–vis, and fluorescence techniques. Under optimized conditions, the probe provided selective turn-on fluorescence detection of fluoride with a linear response from 1.0 to 130.0 μM and limit of detection (S/N = 3) of 0.32 μM. Practical utility was demonstrated by accurate quantification of fluoride in Nile River water and human saliva samples. This dual nanoprobe strategy offers a rapid and cost-effective platform for fluoride analysis in support of healthcare and environmental monitoring applications.