Facile Fabrication of Highly Fluorescent N-Doped Carbon Quantum Dots Using an Ultrasonic-Assisted Hydrothermal Method: Optical Properties and Cell Imaging

Abstract

Fluorescent N-doped carbon nanodots (CNDs) are a type of environmentally friendly nanomaterial that is promising for application in cell imaging and optoelectronics. In this paper, a natural amino acid (L-glutamic acid) was used as a precursor, and two different morphological and structured N-doped carbon quantum dots (CQDs) were synthesized via a one-step ultrasonic-assisted hydrothermal method at 230 and 250 °C. Various microscopy and spectroscopy techniques were employed to characterize the morphology, structure, optical properties, and stability of the CQDs. The results showed that N-CQDs-1 are new CNDs composed of amorphous carbon with a large amount of pyroglutamic acid, and N-CQDs-2 are composed of pure amorphous carbon. The CQDs exhibit excellent optical properties, such as 40.5% quantum yield, strong photobleaching resistance, and superior photostability. Combining the fluorescence lifetimes and radiative and non-radiative decay constants, the photoluminescence mechanism of the CQDs was qualitatively explained. The two CQDs were used for BV2 cell imaging and showed good results, implying the ultrasonic-assisted hydrothermal approach as a facile method to obtain structure-and morphology-controllable N-doped CQDs with prospect for application in cell imaging.

Recent Progress on Carbon Quantum Dots Based Photocatalysis

“…The ultrasonic generator remained at 50% power during the reaction. The solution was heated to a particular temperature and then cooled to room temperature when it became yellow and no visible precipitation occurred, indicating the CQDs were formed ( Qi et al, 2021 ).…”

Sonochemistry of molten metals

“…49 Ultrasonic synthesis of C-dots was reported by several groups. [50][51][52][53][54][55] Li et al 52 irradiated acidic or basic aqueous solutions of glucose for 4 hours and obtained monodisperse C-dots of 5 nm size. Wei et al 55 prepared N-doped C-dots by sonicating a solution of citric acid as a carbon source and ethylene diamine as both the N-dopant source and a surface passivation agent.…”

“…Ultrasonic-assisted doping of C-dots with other metals (Zn, Ag, Au) was also performed, where the sources of silver and gold were the salts AgNO 3 and AuCl 3 . 50 An example of non-metallic doping of ultrasonically formed carbon dots was reported by Xu et al 64 N-doped multicolor C-dots (M-CDs) were synthesized by prolonged sonication of kiwifruit juice with one of the three organic additives (ethanol, ethylenediamine or acetone), each endowing C-dots with different colors (green, yellow and pink, respectively). The N source for doping was amino acids that are present in the kiwifruit.…”

Fabrication of “electroactive cells” using bio-inspired polydopamine-derived carbon nanoparticles for manipulation of cells with electrical stimulation

“…N-doping and N source introduction are the most-used strategies to enhance the emission of CNPs by inducing an upward shift in the Fermi level and electrons in the conduction band ( Ayala et al, 2010 ). The amine groups (especially primary amine) in the N source (PDA in our study) can supply doping precursors and surface-passivating agents for the CNPs, which enhanced the fluorescent performance ( Park et al, 2016 ; Qi et al, 2021 ).…”