Carbon quantum dots: Classification-structure-property-application relationship for biomedical and environment remediation

Abstract

Carbon quantum dots (CQDs) hold immense potential across diverse fields, yet a gap exists between their promise and practical applications. This review tackles this challenge by providing a critical analysis beyond standard approaches. To begin, we differentiate CQDs from semiconductor quantum dots (SQDs) and other nanomaterials, addressing the ambiguity surrounding fluorescent nanoparticles. We then introduce a novel section, “SQDs vs. CQDs: Unmasking the Nanoparticles Duo,” which dissects the critical differences between these closely related nanostructures. Shifting the focus to CQDs, we give an in-depth discussion of their properties and applications across various disciplines. However, a significant obstacle hindering progress is the lack of standardized terminology. Terms like “carbon nanodots,” “carbonized polymer dots,” and “graphene quantum dots,” are often used interchangeably with “CQDs,” creating ambiguity. This review critically examines the problems arising from this lack of uniformity: the absence of a universal definition, inconsistent size criteria, conflicting emission mechanisms, overlapping properties, and precursor misnomers. These inconsistencies impede communication, hinder comparisons, and obscure the link between CQD structure and properties. To address this, we propose a framework for a unified nomenclature system, paving the way for greater clarity and precision in CQD research. Furthermore, the review explores the exciting properties of CQDs, highlighting recent advancements in biomedical and environmental fields that demonstrate their real-world potential. We also critically evaluate the current state-of-the-art, highlighting essential obstacles that must be solved before CQD technology can be successfully applied in practical applications. Finally, a quick summary of the findings and some projections about the future direction of CQD research wrap the review, laying the groundwork for a more deliberate and significant endeavor to realize their full potential. © 2025 Elsevier B.V.