Biopermissible and Hydrophilic G-CNNPs for Noncooperative Binding with Picomolar of Cancer Drug Etoposide and Photodynamic Therapy

Etoposide (ETO), a chemotherapeutic agent for lung cancer, requires precise and prompt detection to optimize cancer management and mitigate toxicity. In this study, we present a scalable solid-state methodology for the synthesis of highly hydrophilic (average contact angle 10.73°) graphitic carbon nitride nanoparticles (g-CNNPs) employing urea and trisodium citrate. The synthesized g-CNNPs possess six surface active sites, enabling their function as effective fluorescence sensors for detecting the lung cancer drug ETO at physiological pH. The g-CNNPs demonstrate high selectivity and sensitivity for ETO detection (Φ_F 20.29 → 17.95%), with a detection limit (LoD) of 95 pM (<i>R</i>² = 0.99144), quantification limit (LoQ) of 310 pM, and an association constant (<i>K</i>_a) of 1.0162 M^-1. The fluorescence quenching of g-CNNPs by ETO is attributed to intermolecular hydrogen bonding, characterized by static quenching and a noncooperative binding mechanism within the g-CNNPs·ETO complex. Additionally, time-correlated single photon counting (TCSPC) analysis confirms the static quenching of g-CNNPs (lifetime 5.175 → 5.281 ns) upon ETO detection. The formation of the g-CNNPs·ETO complex is verified through DFT studies and a range of physicochemical characterization techniques, including XRD, FE-SEM, HR-TEM, XPS, Raman, FT-IR, and UV-vis. The developed detection method proved effective in identifying ETO in urine samples, achieving high recovery rates between 95.45% and 110.78%. To evaluate their biological efficacy, a series of experiments were conducted, including MTT cytotoxicity assays against mouse fibroblast cell lines L929, the anticancer activity of g-CNNPs toward HT29 cells (with and without light exposure), and ROS generation. Collectively, the results from these real samples and biological studies affirm that biopermissible g-CNNPs are promising candidates for clinical trials.