Biocompatible PEGylated Carbon Quantum Dots Synthesized From Citrus Peel: Evaluation of Cell-Tracer Activity and In Vivo Imaging Potential

Dhasarathdev Srinivasan ¹, Ranjith Balakrishnan ¹, Rajasekaran Subbarayan ^1,2*, Rupendra Shrestha ^3*, Ankush Chauhan ², Premkumar Balasekar ⁴

1. Centre for Advanced Biotherapeutics and Regenerative Medicine, Faculty of Research, Chettinad Hospital and Research Institute, Chettinad Academy of Research and Education, Kelambakkam, Tamil Nadu, India

2. Centre for Herbal Pharmacology and Environmental Sustainability, Chettinad Hospital and Research Institute, Chettinad Academy of Research and Education, Kelambakkam, Tamil Nadu, India

3. Department of Natural and Applied Sciences, Nexus Institute of Research and Innovation (NIRI), Lalitpur, Nepal.

4. Department of Pharmacology, K.K. College of Pharmacy-Affiliated, Dr MGR Medical University, Chennai, Tamil Nadu, India

Publications: Journal of Nanotechnology. 2026;2026(1):5516948. doi: 10.1155/jnt/5516948

Abstract – Carbon quantum dots (CqDs) are a novel class of nanomaterials with excellent photoluminescence, biocompatibility, and sustainable synthesis potential. In this study, we explored the green synthesis of AqBlue-CqD from citrus peels using a microwave-assisted method, which incorporates citric acid and polyethylene glycol (PEG) to enhance solubility and overall biocompatibility. UV–vis spectroscopy confirmed the successful formation of CqDs, which exhibited a distinct absorption peak at 336 nm. Dynamic light scattering (DLS) and TEM analyses revealed a uniform spherical morphology with an average particle size of approximately 100–220 nm and zeta potential values of −18.1 mV, indicating adequate colloidal stability, while FTIR spectroscopy confirmed the presence of oxygenated functional groups that support surface passivation and aqueous dispersibility. AqBlue-CqD exhibited strong blue fluorescence under UV illumination, characterized by a high quantum yield and substantial photostability, as further validated by IVIS imaging. Spectrofluorometric evaluation revealed an emission onset at 360 nm, with a strong peak at 448 nm. Antimicrobial analyses confirmed effective antibacterial and antifungal activities against Escherichia coli and Candida tropicalis. To enhance their biomedical applicability, liposome-encapsulated AqBlue-CqD (AqBlue-CqD-Lip) formulations were developed, demonstrating improved stability, excellent biocompatibility, and negligible cytotoxicity in human mammary epithelial cells (HMECs). In vivo bioimaging studies using zebrafish and BALB/c mouse models revealed strong fluorescence distribution and enabled a comprehensive assessment of systemic distribution. Collectively, these findings demonstrate that citrus-derived AqBlue-CqD exhibits low toxicity, excellent photostability, and high biocompatibility, making it highly suitable for bioimaging and drug delivery applications. In summary, this study highlights a sustainable and economical approach for producing high-quality quantum dots from organic waste, offering a green alternative to conventional CqD nanomaterials in advanced biomedical and nanotechnology fields.

Cite: Srinivasan, D., Balakrishnan, R., Subbarayan, R., Shrestha, R., Chauhan, A., Balasekar, P. Biocompatible PEGylated Carbon Quantum Dots Synthesized From Citrus Peel: Evaluation of Cell-Tracer Activity and In Vivo Imaging Potential. Journal of Nanotechnology. 2026; 2026(1):5516948.