Photoinduced absorption and linear/nonlinear emission of assembled carbon dot–silica nanocomposites for cellular imaging

Abstract

Carbon dot (CD)-based nanomaterials have become a popular candidate in biological fields due to their small size distribution, adjustable photoluminescence, high emission efficiency, quite low toxicity, etc. Herein, CDs were embedded into silica to construct CD–SiO₂ nanocomposites, which realized efficiency and long afterglow (including TADF and phosphorescence components) in both powdery and aqueous states. We also observed the conversion process from saturable absorption (SA) to anti-saturation absorption as the monitoring source was a 760 nm ultrafast femtosecond laser. The two-photon excited fluorescence (2PEF) property of CD–SiO₂ composites was also successfully confirmed and further applied in biological imaging, and it is more advantageous for cellular imaging than 1PEF. Besides, the phosphorescence signal from CD–SiO₂ composites was also successfully applied in cancer cellular imaging. Moreover, the photoinduced absorption (PIA) phenomenon was first observed by nanosecond transient absorption (ns-TA) spectroscopy among CD-based nanomaterials, and the detected PIA was peaked at 466 nm comprising of a “faster” component and a “slower” component. CD–SiO₂ composites can be a great candidate as the saturable absorber or the deeper-tissue imaging agent.