Polycyclic Aromatic Hydrocarbon-Derived Hydrophilic Carbon Dots for NIR-Triggered Photothermal Antibacterial and Anticancer Therapy

다국어 초록 (Multilingual Abstract)

In this study, two types of polycyclic aromatic hydrocarbon (PAH)-derived carbon dots—nitroperylene-based (NP-CDs) and nitropyrene-based (NPy-CDs)—were synthesized via a hydrothermal strategy and systematically compared in terms of structural characteristics, photophysical behavior, photothermal performance, and biological functionality. Structural analyses using TEM, XRD, Raman, FT-IR, and XPS confirmed successful formation of partially graphitized, nitrogen-doped nanostructures with distinct differences in defect density and nitrogen configurations. NP-CDs exhibited a higher I_D/I_G ratio and more abundant defect-related nitrogen states compared with NPy-CDs. Optical analysis revealed that NP-CDs demonstrated stronger NIR absorption and suppressed photoluminescence, indicative of dominant non-radiative relaxation, while NPy-CDs showed higher PL intensity associated with radiative recombination pathways. Under 808 nm irradiation, NP-CDs achieved a photothermal conversion efficiency (PCE) of 56.6%, surpassing the 48.6% efficiency of NPy-CDs. Biological evaluations demonstrated the potent antibacterial efficacy of NP-CDs, reducing the viability of E. coli and B. subtilis by 71% and 69.3%, respectively, under 300 μg/mL and 10 min of 808 nm NIR irradiation. Morphological observations and ROS analyses further revealed membrane collapse, surface cracking, and elevated oxidative stress, confirming an irreversible thermal–oxidative bactericidal mechanism. In contrast, NPy-CDs exhibited excellent cytocompatibility in the absence of irradiation (0.1–400 μg/mL), but induced significant reductions in the viability of HeLa and SH-SY5Y cancer cells (47% and 45%, respectively) under 400 μg/mL and 10 min NIR exposure, demonstrating their effective photothermal anticancer capability. Overall, this study establishes a definitive structure–property–function correlation in PAH-derived CDs, demonstrating that differences in precursor ring structure (perylene vs. pyrene) critically determine defect density, electronic configuration, radiative/non-radiative energy relaxation pathways, and subsequent biological responses. These findings underscore the importance of molecular-level precursor engineering as an effective strategy for developing high-efficiency carbon-based photothermal platforms for antibacterial and anticancer therapies.

목차 (Table of Contents)

• CHAPTER 1. Introduction 1
• 1.1 Research Background 1
• 1.2 Polycyclic Aromatic Hydrocarbon-Derived Carbon Dots 4
• 1.2.1 Electronic Structure of PAHs 4
• 1.2.2 Structural Comparison Between Perylene and Pyrene 7
• 1.2.3 Effects of Nitration on Optical Properties 10
• 1.2.4 Suitability of PAH-Derived CDs for Photothermal Therapy 11
• 1.3 N-Doping and Hydrothermal Carbonization Mechanisms 13
• 1.3.1 Role of Urea as a Nitrogen Source 13
• 1.3.2 Reaction Pathways of Hydrothermal Carbonization 14
• 1.3.3 Transformation of Nitroperylene and Nitropyrene into CDs 15
• 1.3.4 Formation of Core Structures and Surface States 17
• 1.4 Photophysical and Photothermal Mechanisms 20
• 1.4.1 Near-Infrared (NIR) Absorption Characteristics 20
• 1.4.2 Non-Radiative Relaxation and Heat Generation 21
• 1.4.3 Photothermal Conversion Efficiency (PCE) 24
• 1.4.4 Photoluminescence and Excitation-Dependent PL 25
• 1.5 Photothermal Antibacterial and Anticancer Mechanisms 28
• 1.5.1 Photothermal Sensitivity of Bacterial Membranes 28
• 1.5.2 Photothermal-Induced Anticancer Mechanisms 29
• 1.5.3 Reactive Oxygen Species (ROS) Generation Pathways 30
• 1.6 Research Motivation 32
• CHAPTER 2. Nitroperylene–Urea Carbon Dots for Antibacterial Photothermal Therapy 34
• 2.1 Synthesis of Nitroperylene–Urea Carbon Dots 34
• 2.2 Structural and Optical Characterization 36
• 2.2.1 Morphology and Microstructure 36
• 2.2.2 Surface Chemistry and Elemental Composition 39
• 2.2.3 Optical and Photophysical Properties 42
• 2.3 Photothermal Performance 45
• 2.3.1 Concentration-Dependent Temperature Elevation 45
• 2.3.2 Thermal Imaging and Effect of Laser Power 46
• 2.3.3 Photothermal Conversion Efficiency (PCE) Measurement 46
• 2.4 Antibacterial Activity 49
• 2.4.1 Bacterial Viability Analysis 49
• 2.4.2 Plate Assay 50
• 2.4.3 Morphological Evaluation via SEM Analysis 52
• 2.4.4 Reactive Oxygen Species (ROS) Analysis 54
• 2.5 Photothermal Antibacterial Mechanism Discussion 56
• CHAPTER 3. Nitropyrene–Urea Carbon Dots for Anticancer Photothermal Therapy 59
• 3.1 Synthesis of Nitropyrene–Urea Carbon Dots 59
• 3.2 Structural and Optical Characterization 61
• 3.2.1 Morphology and Microstructure 61
• 3.2.2 Surface Chemistry and Elemental Composition 64
• 3.2.3 Optical and Photophysical Properties 67
• 3.3 Photothermal Performance 69
• 3.3.1 Concentration-Dependent Temperature Elevation 69
• 3.3.2 Thermal Imaging and Effect of Laser Power 70
• 3.3.3 Photothermal Conversion Efficiency (PCE) Measurement 70
• 3.4 Anticancer Activity 73
• 3.4.1 Cell Viability Analysis via MTT Assay 73
• 3.4.2 Morphological Evaluation via Microscopy 76
• 3.4.3 Reactive Oxygen Species (ROS) Analysis 78
• 3.5 Photothermal Anticancer Mechanism Discussion 80
• CHAPTER 4. Comparison and Conclusion 82
• 4.1 Comparison of NP-CDs and NPy-CDs 82
• 4.1.1 Structural and Surface Chemistry Comparison 82
• 4.1.2 Optical Properties Comparison 83
• 4.1.3 Photothermal Performance Comparison 84
• 4.1.4 Biological Application Comparison 85
• 4.2 Discussion of Structure–Property Relationships 88
• 4.3 Conclusion 90
• References 91
• Appendix A. Supplementary Experimental Methods 100
• Appendix A.1 Cell Culture 100
• Appendix A.2 MTT Assay 100
• Appendix A.3 DCFDA Assay 101
• 국문초록 102