Bio-inspired nitrogen-doped carbon quantum dots: A green route for bioimaging and nano-biosensing

Carbon quantum dots (CQDs) have emerged as promising nanomaterials due to their tunable fluorescence, high biocompatibility, and diverse applications in bioimaging, diagnostics, and theranostics. Sustainable synthesis approaches utilizing plant biomass-derived carbon sources, such as cellulose, citric acid, and terephthalic acid derivatives, offer an eco-friendly alternative to conventional methods. Here, we report a facile one-pot solvothermal synthesis of novel nitrogen-doped CQDs (ATA100) using 2-aminoterephthalic acid (ATA) as an alternative to biomass-based carbon and nitrogen precursor, with 1,2-ethylenediamine (EDA) as a surface passivation agent. Nitrogen doping enhances fluorescence quantum yield to 38 %, outperforming citric acid-derived CQDs (CA100). Structural characterization via Fourier-transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (¹H NMR), high-resolution transmission electron microscopy (HR-TEM), dynamic light scattering (DLS) confirms the formation of uniform nanoparticles (<5 nm) with enriched amine functionalities. Biocompatibility assessments reveal low cytotoxicity and enhanced cellular uptake, with 2.6-fold higher fluorescence in A549 cancer cells compared to normal chondrocytes, demonstrating its potential as an efficient bioimaging agent. Moreover, ATA100 exhibits fluorescence quenching upon catalase interaction, while its fluorescence intensity increases in response to hydrogen peroxide, highlighting its application for reactive oxygen species (ROS) detection in oxidative stress-related diseases. This study underscores the industrial feasibility of nitrogen-doped CQDs for large-scale bioimaging, biosensing, and therapeutic monitoring. By leveraging renewable resources, ATA100 presents a sustainable, eco-friendly and scalable alternative to traditional semiconductor-based fluorescent probes, advancing bio-inspired nanomaterials for precision medicine and industrial diagnostics. • Bio-inspired terephthalic nitrogen-doped Carbon Quantum Dots (CQDs) was achieved using a one-pot solvothermal approach. • Nitrogen doping boosted quantum yield to 38 %, outperforming conventional citric acid-derived CQDs. • Nitrogen-doped CQDs demonstrated high biocompatibility, and their ROS-responsive fluorescence enabled nano biosensing. • Eco-friendly CQDs offer industrial scalability with potential applications in cancer theragnostics.