Surface-Engineered Carbon Dots for Plant Photosynthesis and Carbon Assimilation

Carbon dots (CDs) are emerging as plant-interfacing nanomaterials whose optical, redox, and interfacial properties can be adjusted through composition and surface chemistry. This critical review links material descriptors and deposition to chloroplast exposure, photosynthesis, carbon allocation, and agronomic output. Spectral conversion and electron transfer have direct support in selected assays, but fluorescence localization and increased electron-transport rate alone do not establish intact-particle chloroplast entry or direct electron donation. Nutrient, water, antioxidant, and stress-recovery effects provide additional physiological routes. Reported gains depend on the formulation, plant state, and comparator and cannot be ranked across heterogeneous studies. Emerging wall-polymer responses do not yet establish a causal flux from CD-enhanced photosynthesis into structural carbon. We propose a tiered framework separating essential reporting, claim-dependent mechanistic validation, and longer-term agricultural and safety assessment. The framework connects surface engineering to reproducible exposure and avoids treating all advanced assays as requirements for every study.