Highly photoluminescent blue–green carbon quantum dots synthesized via plasma solution interaction for bioimaging applications

Blue (B-CQDs) and green (G-CQDs) Carbon Quantum Dots with exceptional photoluminescence were synthesized using a plasma solution interaction method, employing glucose as an environmentally friendly carbon source. The PSI process enabled rapid, catalyst-free synthesis with tunable optical properties by varying plasma exposure time. Both types of Carbon Quantum Dots consist of uniformly dispersed spherical nanoparticles (3–5 nm), with partially graphitic cores and a lattice spacing of 0.21 nm corresponding to the (100) plane of graphite. The B-CQDs emit intense blue light at 450 nm, with a quantum yield of 21%, while the G-CQDs display strong green emission at 515 nm, yielding a quantum yield of 19%. Structural and spectroscopic analyses indicate that blue emission results from intrinsic π–π* transitions within sp2-hybridized carbon domains, whereas green emission originates from surface or defect-state n–π* transitions linked to oxygen-containing groups formed during prolonged plasma treatment. Both types of CQDs exhibit excellent aqueous stability, photostability, and biocompatibility, with strong intracellular fluorescence observed in preliminary bioimaging tests. These findings underscore plasma solution interaction as an efficient, controllable method for producing color-tunable CQDs with potential for optical and biological applications.