Harnessing Maillard reaction byproducts for dual emissive carbon quantum dots: a tunable optical platform

Quantum dots (QDs) have diverse applications, ranging from optics and energy to biomedical. In this study, carbon quantum dots (CQDs) were synthesized using glucose and tryptophan as precursors using one-step microwave (MW) and sand bath (SB) thermal methods, and the CQDs exhibit distinct photoluminescence behaviors. CQD-SB shows enhanced and stable fluorescence despite its amorphous structure, likely due to prolonged thermal treatment, facilitating the formation of robust surface states and stable reaction products. Notably, CQD-SB generates a dual emissive bands activated at both shorter and longer excitation wavelengths (330-390 nm) reveals both core-localized and surface bound group emission. This stable dual emission suggests a hybrid fluorescence mechanism involving excitation, concentration and size-dependent effects. However, CQD-MW possesses a partially crystalline structure and exhibits excitation-dependent dual emission even at higher excitation energies, showing less stability. This behavior of CQD-MW is due to rapid carbonization and limited passivation owing to instant microwave heating. Fluorescence staining reveals that CQD-SB offers stronger and more stable blue and green emission in human buccal and onion epidermal cells, supporting its potential as an efficient bioimaging probe and alternative to synthetic dyes.