Nitrogen-Doped Carbon Quantum Dots: Green Synthesis, Drug Loading and Biomedical Applications

Abstract

Nanotechnology continues to redefine strategies in drug delivery, diagnostics, and therapeutic engineering, with carbon quantum dots (CQDs) emerging as a versatile class of nanomaterials. Owing to their ultrasmall size, high aqueous solubility, low inherent toxicity, and tunable photoluminescence, CQDs have attracted considerable interest for biomedical use. Recent advances indicate that nitrogen doping significantly alters their electronic structure and surface chemistry, leading to improved fluorescence efficiency, enhanced electron transfer, and superior drug loading capability. This review critically examines nitrogen-doped carbon quantum dots (N-CQDs) with a focus on green synthesis approaches employing renewable precursors such as plant-derived materials and biomolecules, offering sustainable and biocompatible alternatives to conventional methods. Key synthesis parameters, doping mechanisms, and their influence on physicochemical properties are systematically discussed. In addition, the review evaluates drug loading interactions, stimuli-responsive release behavior, and the performance of N-CQDs in targeted delivery systems. Emerging applications in bioimaging, cancer therapy, antimicrobial activity, and biosensing are analyzed with emphasis on functional advantages and current limitations. Despite promising laboratory-scale outcomes, challenges related to large-scale production, reproducibility, and long-term safety remain significant barriers to clinical translation. Overall, N-CQDs represent a promising multifunctional platform, although further quantitative validation and regulatory alignment are required to advance their role in precision nanomedicine.