In nanotechnology, the synthesis of carbon quantum dots (CQDs) by mixed doping with metals and non-metals has emerged as an appealing path of investigation. This review offers comprehensive insights into the synthesis, properties, and emerging applications of mixed-doped CQDs, underlining their potential for revolutionary advancements in chemical sensing, biosensing, bioimaging, and, thereby, contributing to advancements in diagnostics, therapeutics, and the under standing of complex biological processes. This synergistic combination enhances their sensitivity and selectivity towards specific chemical analytes. The resulting CQDs exhibit remarkable fluorescence properties that can be involved in precise chemical sensing applications. These metal-modified CQDs show their ability in the selective and sensitive detection from Hg to Fe and Mn ions. By influencing their exceptional fluorescence properties, they enable precise detection and monitoring of biomolecules, such as uric acid, cholesterol, and many antibiotics. Moreover, when it comes to bioimaging, these doped CQDs show unique behavior towards detecting cell lines. Their ability to emit light across a wide spectrum enables high-resolution imaging with minimal background noise. We uncover their potential in visualizing different cancer cell lines, offering valuable insights into cancer research and diagnostics. In conclusion, the synthesis of mixed-doped CQDs opens the way for revolutionary advancements in chemical sensing, biosensing, and bioimaging. As we investigate deeper into this field, we unlock new possibilities for diagnostics, therapeutics, and understanding complex biological processes.

The widespread presence of antibiotic residues, particularly norfloxacin (NFX), in food products and the environment has raised concern, underscoring the need for sensitive and selective detection methods. In this study, a novel broccoli-derived nitrogen-doped carbon quantum dots (N-CQDs) was synthesized via a green hydrothermal approach, 4-dimethylaminopyridine (DMAP) as both a nitrogen dopant and a functionalizing agent. The synthesized N-CQDs exhibit an average diameter of approximately ~4.2 nm and emit bright blue fluorescence, with a maximum emission at 445 nm upon excitation at 360 nm. A “Turn-ON” response toward NFX was achieved with a detection limit of 0.30 nM, attributed to hydrogen bonding and π–π stacking interactions that suppressed non-radiative decay. Moreover, the sensor demonstrates high selectivity for NFX, effectively distinguishing it from common interfering substances, including other antibiotics, organic acids, and biomolecules. The N-CQDs also exhibit excellent stability under diverse conditions, such as varying pH levels, high ionic strength, and prolonged irradiation. Finally, the practical applicability of the developed sensor was validated by detecting NFX in spiked broccoli extract and milk samples, with recovery rates ranging from 98.2% to 100.1% and relative standard deviations of less than 2.0%. This work presents a sustainable and efficient N-CQD-based fluorescent sensing platform, offering significant potential for rapid and reliable detection of NFX in food safety and environmental monitoring.

Glioblastoma multiforme (GBM) is an incurable primary brain malignancy characterized by prominent chemoresistance and poor prognosis. Herein, we report an in vitro proof-of-concept study of a green, ligand-functionalized carbon quantum dot (CQD) for combined drug delivery with pH-responsive release in glioblastoma cells. Nitrogen-doped red-emissive N-CQDs were synthesized via a hydrothermal method using locust biomass as a renewable carbon precursor, functionalized with glucuronic acid for active tumor targeting, and loaded with piperlongumine (PL) and silibinin (SIL) drugs at an optimized mass ratio. The nanosystem was characterized by XRD, FTIR, SEM, TEM, XPS, and optical spectroscopy, and evaluated in vitro for drug release, cellular uptake, apoptosis, ROS levels, and caspase-3 activity. The optimized nanoplatform exhibited uniform morphology (average size 2.76 nm), strong red fluorescence (Ex490nm/Em620nm), high dual-drug loading efficiency (46.0%), and pH-responsive release behavior with rapid drug liberation in the acidic tumor microenvironment (pH 5.5) and minimal leakage at physiological pH (pH 7.4). The nanosystem demonstrated efficient cellular internalization, dual mitochondrial/nuclear targeting, and enhanced combined antitumor effect via ROS overproduction and activation of the caspase-3 pathway. This work establishes a green and multifunctional nanotherapeutic platform with promising potential for future glioblastoma-directed drug delivery applications.