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

Chong Qi,Jie Xu,Huaidong Wang,Xiaoxu Wang,Ailing Yang

doi:10.1021/acsomega.1c04903

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.

Highlights

Quantum dots (QDs), a kind of semiconductor nanomaterial with a size smaller than the exciton Bohr radius, have attracted much attention in the last 30 years due to their unique surface effect, small size effect, and excellent electronic, optical, and electrochemical properties.[1]
Environment-friendly carbon-based fluorescent nanomaterials have aroused great research interests, especially carbon dots (CDs),[10−14] a kind of zero-dimensional nanomaterials with a size less than 10 nm, which were first discovered in 2004.15−17 According to different carbon cores, CDs are usually divided into graphene quantum dots (GQDs), carbon nanodots (CNDs), and polymer dots.[18]
The high-resolution transmission electron microscopy (HRTEM) results indicate that N-carbon quantum dots (CQDs)-1 (Figure 1A) and N-CQDs-2 (Figure 1B) are spherical nanoparticles and nanosheets, respectively, exhibiting a clear lattice, and a lattice spacing of 0.21 nm (Figure 1C,D)

Summary

Introduction

Quantum dots (QDs), a kind of semiconductor nanomaterial with a size smaller than the exciton Bohr radius, have attracted much attention in the last 30 years due to their unique surface effect, small size effect, and excellent electronic, optical, and electrochemical properties.[1] QDs can be used in many fields such as light-emitting diodes (LEDs), artificial photosynthesis, biomedical imaging, and biosensing because of their high fluorescent quantum yield (QY), good photostability, and excellent photobleaching resistance.[2−4] most of the high-performance QDs are composed of heavy-metal elements (i.e., Cd, Pb, and Hg),[5−9] whose toxicities and potential environmental hazards limit their applications. Because of their merits in terms of low toxicity, strong photoluminescence (PL), good photostability, excellent biocompatibility, and low cost, CDs have great potential for application in optoelectronics, metal ion detection, and biomedicine.[20−25]

Methods

Results

Conclusion