Development of biocompatible carbon dots derived from natural and chemical sources for high-performance multifunctional cosmetic applications and nanofluorescence sensing

Currently, excessive exposure to UV radiation (UVA, UVB, and UVC) poses a significant issue, as it can penetrate deep into the skin layers and lead to severe skin health risks such as skin cancer and premature aging. As a result, the development of biocompatible sunscreens with multifunctional properties has become crucial for protecting the skin against UV radiation. Simultaneously, concerns regarding exposure to harmful chemicals like fungicides and heavy metals from food and the environment pose a significant impact on human health and ecosystems. Therefore, the development of highly sensitive and selective chemical sensors has become crucial for monitoring contaminants in food and environmental systems to ensure food security. Carbon dots (CDs), as fluorescent carbon-based nanomaterials, have gained significant attention due to their versatile properties. Besides, their properties can be modified through synthese using chemical and natural precursors, which are crucial for controlling their morphology and surface functional groups. This, in turn, enhances various characteristics and enables desired performance for targeted applications. In this work, we demonstrate the synthesis of four distinct types of carbon dots, including green tea leaves-derived carbon dots (GTCDs) and blue pea flowers-derived carbon dots (BPCDs) for cosmetic applications, as well as hybrid iron oxide/carbon dots (HICs) nanocomposites and nitrogen-doped carbon dots (NCDs) for sensing applications. Firstly, the GTCDs were synthesized from green tea leaves as the main precursor, along with alpha-hydroxy acids (AHAs) such as gluconic acid (GA), citric acid (CA), and tartaric acid (TA). Among these, carbon dots derived from green tea leaves with gluconic acid (G-CDs) exhibited the strongest UVB and UVC absorption and an antioxidant activity of 100%, which is higher than that of commercial antioxidant agents. The G-CDs also demonstrated excellent photostability, and cell viability exceeded 60%. These features position G-CDs as strong candidates for safe and multifunctional cosmetic UV protection. Secondly, the BPCDs were developed by integrating blue pea flowers with and without AHAs as co-precursors to enhance UV protection, antioxidant activity, moisturizing effects, and eco-friendly properties. The carbon dots derived from blue pea flowers with gluconic acid (BGCDs) exhibited enhanced antioxidant activity of 96.9%, and the assessed cell viability exceeded 80%, indicating low cytotoxicity. Moreover, the UV protection ability of BGCDs, indicated by sun protection factor (SPF) values of 1.34 and 1.86 in the UVB and UVC regions, respectively, was higher than that of other BPCDs. Additionally, all BPCDs showed high moisture retention and absorption levels, closely resembling commercial humectant agents. The significant finding emerging from this study is that the BGCDs can be strong candidates for using as effective UVB and UVC absorbers, antioxidants, moisturizing agents, and biocompatible cosmetic ingredients. Thirdly, we developed a novel fluorescence nanosensor of HICs with high sensitivity, selectivity, and rapidity, which is critical for detecting ferric ion (Fe3+) in beverages and food products. HICs were synthesized from blue pea flowers and iron oxide nanoparticles through a solvothermal treatment. More importantly, the HICs demonstrated a linear detection range (0.06 - 100 µM) and an impressively low limit of detection (LOD) of 13.61 nM. Additionally, the detection of Fe3+ in milk and herbal drinks was achieved using HICs, yielding satisfactory recovery rates ranging from 94.4% to 103.7%. Therefore, the HICs exhibited remarkable selectivity toward Fe3+, remaining unaffected by various interferences. It occurs through a combination of static quenching and dynamic quenching mechanisms and the inner filter effect. These qualities make them promising candidates for advanced detection applications in food products to ensure food safety. Fourthly, we developed a novel fluorescence sensor utilizing label-free nitrogen self-doped carbon dots (NCDs) for the sensitive, selective, and rapid determination of dichloran fungicide. The NCDs were prepared from maleic anhydride and diethylenetriamine via a one-step pyrolysis process. Moreover, NCDs demonstrated a linear detection range (1–50 µM) and a remarkably low detection limit of 7.6 nM, the best reported to date. Additionally, the NCDs exhibited selectivity towards dichloran amidst interferences within 30 seconds, indicating rapid detection of dichloran. With the addition of dichloran, the fluorescence emission of NCDs was quenched, attributed to the inner filter effect and dynamic quenching. The sensor demonstrated excellent selectivity and was successfully applied to real samples (carrots, grapes, and water) with recovery rates ranging from 95.1% to 108.7%. Moreover, a paper-based sensor utilizing NCDs as sensing probes was demonstrated to observe fluorescence quenching towards dichloran, with a detection limit of 4.24 µM. It also showed high efficacy in distinguishing and selectively detecting dichloran against interferences. Therefore, this work contributes to the development of efficient and portable detection platforms with applications in environmental monitoring and agricultural fields.