Nanoporous and morphology-transforming g-CNNPs for trace-level detection of mefenamic acid in urine samples and in vitro protein denaturation inhibition

Abstract

Water-soluble graphitic carbon nitride nanoparticles (g-CNNPs) were synthesized via a solid-state method, resulting in quasi-spherical particles with an average size of approximately 3.1 nm. Comprehensive characterization was conducted using standard physicochemical techniques. To delve deeper into the structural, chemical and thermal stability, and surface properties of g-CNNPs, NMR (¹H and ¹³C), thermal gravimetric analysis (TGA and DTA), and BET adsorption–desorption isotherm analyses were employed. These analyses revealed the thermally stable (485 °C) nature and H3 hysteresis loop type of g-CNNPs, with a surface area of 10.687 m² g⁻¹, pore volume of 0.015 cc g⁻¹, and pore diameter of 2.143 nm. These g-CNNPs were successfully utilized for the nanomolar detection of the analgesic drug, mefenamic acid (MEF), at pH 7.0. The g-CNNPs exhibited excellent selectivity and sensitivity for MEF detection, as evidenced by their fluorescence quenching (640 → 376 a.u. at 465 nm) (λ_ex 420 nm) upon the addition of MEF. A linear concentration range of 10–100 nM was observed, with a detection limit (LoD) of 3.4 nM, limit of quantification (LoQ) of 11.4 nM, and an association constant (K_a) of 1.332 × 10³ M⁻¹ (R² = 0.99699). Time-correlated single photon counting (TCSPC) experiments confirmed the static quenching of g-CNNPs (lifetime 5.241 → 5.368 ns) in the presence of MEF. Furthermore, the interference study, time effect, zeta potential values, and pH responses of the g-CNNPs·MEF complex were investigated. Following MEF sensing, changes in the optical properties, crystalline nature, structural quality, elemental composition, surface morphology, and topography of g-CNNPs were examined. Additionally, the formation of intermolecular hydrogen bonding between g-CNNPs and MEF was explored. This work highlights the potential practical applications of g-CNNPs for (i) the detection of MEF in urine samples and (ii) protein denaturation inhibition, demonstrating their promising role in anti-inflammatory therapy.