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.