Application of carbon quantum dots in smart polymer films for biomedical diagnostics

In the era of personalized medicine and wearable technologies, there is a growing demand for flexible, biocompatible, and highly sensitive sensors capable of continuous biomarker monitoring directly on the skin surface. Carbon quantum dots (CQDs), due to their unique fluorescent properties, non-toxicity, and ease of functionalization, represent an attractive active component in the design of such devices. Depending on the polymer matrix and integration strategy, polymer-CQDs composites can operate via optical or electrochemical mechanisms, which significantly broadens their biomedical applications. This review article discusses the mechanisms of CQDs integration with polymer matrices, such as chemical and physical immobilization, crosslinking, and the formation of layered composites. Special attention is given to conductive polymers, hydrogels, and biodegradable polymers that serve structural, sensory, and protective functions. Current applications of such materials are presented, including smart wound dressings, microneedle devices, and wearable devices such as smartbands. The mechanisms of biomarker detection and electrical conduction in CQD-based systems are also characterized, and technological challenges such as selectivity, integration with electronics, and power supply are analyzed. The article also outlines future development directions for these technologies, considering energy autonomy, biodegradability, sensor personalization, and data management. The aim of the work is to provide a comprehensive analysis of the current state of knowledge in the design of functional polymer-CQDs composite materials for applications in modern skin-integrated bioelectronics for medical diagnostics.