Microwave-assisted N,S doped carbon quantum dots as fluorescent nanoprobes for vibegron determination: face-centered design optimization, validation, and green chemistry assessment

Abstract

A novel, sensitive, and environmentally sustainable spectrofluorimetric method was developed for vibegron quantification in pharmaceutical formulations and biological matrices using nitrogen and sulfur co-doped carbon quantum dots (N,S CQDs) as fluorescent nanoprobes. The N,S-CQDs were synthesized via rapid microwave-assisted green chemistry and comprehensively characterized through transmission electron microscopy, dynamic light scattering, Fourier-transform infrared spectroscopy, ultraviolet-visible absorption spectroscopy, and fluorescence spectroscopy, revealing optimal excitation and emission wavelengths at 344 nm and 418 nm, respectively. Mechanistic investigation demonstrated that vibegron induced concentration-dependent fluorescence quenching through static complex formation, as evidenced by decreasing Stern–Volmer constants with increasing temperature (9.68 × 10⁵ to 6.86 × 10⁵ M⁻¹). Thermodynamic analysis revealed spontaneous binding (ΔG° = −34.70 kJ mol⁻¹) driven by electrostatic interactions and hydrogen bonding, with negative enthalpy and positive entropy. Critical experimental parameters were systematically optimized using face-centered central composite design, revealing a significant reduced quadratic model (R² = 0.9866) with optimal values identified and further employed for method validation. The method was rigorously validated according to ICH Q2 (R2) guidelines, demonstrating excellent linearity (30–1500 ng mL⁻¹, r² = 0.9998), high sensitivity (LOD 9.85 ng mL⁻¹, LOQ 29.54 ng mL⁻¹), superior accuracy (100.88 ± 1.34%) and precision (repeatability 1.33%, intermediate precision 1.74%). Successful application to commercial tablets yielded 100.07 ± 0.81% content with statistical equivalence to established HPLC methods confirmed through t-test, F-test, and interval hypothesis testing. Furthermore, spiked human plasma analysis demonstrated recoveries ranging from 96.44% to 104.28% with RSD values below 4%, confirming applicability to biological matrices for therapeutic drug monitoring. Comprehensive green chemistry assessment using AGREE (0.65), CaFRI (80/100), and BAGI (70.0/100) metrics demonstrated favorable environmental sustainability characterized by minimal hazardous reagent consumption, low carbon footprint, reduced waste generation, and excellent practical applicability, providing an environmentally benign analytical tool for routine pharmaceutical quality control and therapeutic drug monitoring applications.