Fluorescent-Nitrogen-Doped Carbon Quantum Dots Derived from Citrus Lemon Juice: Green Synthesis, Mercury(II) Ion Sensing, and Live Cell Imaging

Abstract

In this study, we report a green and economical hydrothermal synthesis of fluorescent-nitrogen-doped carbon quantum dots (NCQDs) using citrus lemon as a carbon source. The prepared NCQDs possess high water solubility, high ionic stability, resistance to photobleaching, and bright blue color under ultraviolet radiation with a high quantum yield (∼31%). Highresolution transmission electron microscopy (HRTEM) results show that the prepared NCQDs have a narrow size distribution (1−6 nm) with an average particle size of 3 nm. The mercury ion (Hg 2+ ) sensing efficiency of the NCQDs was studied, and the result indicated that the material has high sensitivity, high precision, and good selectivity for Hg 2+ . The limit of detection (LOD) is 5.3 nM and the limit of quantification (LOQ) is 18.3 nM at a 99% confidence level. The cytotoxicity was evaluated using MCF7 cells, and the cell viabilities were determined to be greater than 88% upon the addition of NCQDs over a wide concentration range from 0 to 2 mg/mL. Based on the low cytotoxicity, good biocompatibility, and other revealed interesting merits, we also applied the prepared NCQDs as an effective fluorescent probe for multicolor live cell imaging.

Preparation of Multifunctional N-Doped Carbon Quantum Dots from Citrus clementina Peel: Investigating Targeted Pharmacological Activities and the Potential Application for Fe3+ Sensing

“…The broader interlayer spacing of (0.40 ± 0.01) nm compared to 0.34 nm of graphite also indicates the amorphous nature and low crystallinity of CQDs caused by the surface functionalization [31]. The low-density peak at 2θ = (43.30 ± 0.22) • corresponds to the (100) plane, also indicating the presence of graphitic carbon [8,32,33]. The average particle size and morphological characteristics of the CQD@Arg sample were determined by the transmission electron microscopy (TEM) and high-resolution TEM (HR-TEM) analysis.…”

“…The broader interlayer spacing of (0.40 ± 0.01) nm compared to 0.34 nm of graphite also indicates the amorphous nature and low crystallinity of CQDs caused by the surface functionalization [ 31 ]. The low-density peak at 2 θ = (43.30 ± 0.22)° corresponds to the (100) plane, also indicating the presence of graphitic carbon [ 8 , 32 , 33 ].…”

“…Moreover, several studies have used biomass waste for obtaining CQDs, including citrus [ 8 , 9 ], kitchen waste [ 10 ], mango peel [ 11 ], banana peel [ 12 ], expired milk [ 13 ], egg shell [ 14 ], and agarose waste [ 15 ], all exhibiting good chemical and optical properties, and obtained carbon dots were applicable for the bioimaging, biosensing, and environmental monitoring. A significant challenge in the fabrication of biomass-derived CQDs represents obtaining CQDs with a high quantum yield.…”

“…The synthesized N-CQDs were used as a fluorescent probe for Fe 3+ and tetracycline detection with good selectivity and sensitivity. Moreover, Gao et al [ 8 ] synthesized N-doped CQDs via the hydrothermal procedure in ammonia using orange and watermelon peel as carbon precursors, which were finally used for the oxytetracycline detection and analysis in water monitoring.…”

Doping and Surface Modification of Carbon Quantum Dots for Enhanced Functionalities and Related Applications

“…The unique photophysical properties, photostability leading to photobleaching resistance, and high water solubility due to functional groups on CQDs paved the way for developing applications ranging from sensors and catalysis to energy and medicine. [ 61,267 ] Photostability is attributed to the electrostatic stabilization achieved as a result of surface functionalization/passivation. [ 10,268 ] Several outstanding reviews are available, which concentrate on the medical applications of modified CQDs.…”