Green Synthesis of Biocompatible Epigallocatechin Gallate-Derived Carbon Dots for Dual Fluorescent Detection of pH and Fe ³⁺

Sensitive and biocompatible fluorescent probes capable of simultaneously detecting pH and Fe³⁺ are crucial for applications in environmental monitoring, biomedical diagnostics, and food safety. In this study, we present an environmentally friendly, one-step hydrothermal synthesis of multifunctional carbon dots (ECDs) utilizing epigallocatechin gallate (EGCG) as a natural carbon precursor. The synthesized ECDs exhibit pronounced pH-dependent fluorescence quenching over a broad pH spectrum (1.3-13.5), characterized by a sigmoidal response (<i>R</i> ² = 0.9918) and remarkable sensitivity within the physiological range (pH 6-8). The mechanism of pH-induced quenching of ECDs has been verified to be the aggregation of ECDs and surface deprotonation under high-pH conditions. Furthermore, the ECDs facilitate highly selective detection of Fe³⁺ through fluorescence quenching, a process attributed to electron transfer from EGCG-derived phenolic groups. Its fluorescence response shows a linear relationship within the Fe³⁺ concentration range of 1-125 μM with <i>R</i> ² = 0.995. Additionally, the ECDs demonstrate excellent biocompatibility (cell viability >90%, hemolysis <5%) and exhibit significant antibacterial activity against <i>Escherichia coli</i> and <i>Staphylococcus aureus</i>. This research illustrates a straightforward approach to developing eco-friendly, cost-effective, and multifunctional probes for integrated sensing and antimicrobial applications.