Chemically doped fluorescent carbon and graphene quantum dots for bioimaging, sensor, catalytic and photoelectronic applications.

ZnCl2 Enabled Synthesis of Highly Crystalline and Emissive Carbon Dots with Exceptional Capability to Generate O2⋅–

SummaryProtons are highly related to cell viability during physiological and pathological processes. Developing new probes to monitor the pH variation could be extremely helpful to understand the viability of cells and the cell death study. Carbonized polymer dots (CPDs) are superior biocompatible and have been widely applied in bioimaging field. Herein, a new type of extreme-pH suitable CPDs was prepared from citric acid and o-phenylenediamine (CA/oPD-CPDs). Due to the co-existence of hydrophilic and hydrophobic groups, CA/oPD-CPDs tend to aggregate in neutral condition with a dramatic decrease of fluorescence, but disperse well in both acidic and alkaline conditions with brighter emission. This specialty enables them to selectively illuminate lysosomes in cells. Moreover, CA/oPD-CPDs in the cytoplasm could serve as a sustained probe to record intracellular pH variation during apoptosis. Furthermore, CA/oPD-CPDs present a continuous fluorescence increase upon 2-h laser irradiation in living cells, underscoring this imaging system for long-term biological recording.

Chapter 15 - Future aspects of carbon and graphene quantum dots for biomedical applications

A review of coal-based carbon and graphene quantum dots: synthesis, properties, and applications

Structural features regulated photoluminescence intensity and cell internalization of carbon and graphene quantum dots for bioimaging

Diamine compounds are widely used as surface modifiers in the functionalization of carbon quantum dots, yet the effects of different diamines on the properties of carbon quantum dots remain unclear. In this study, carbon dots (P-CDs) were synthesized from peanut shell powder via a simple one-step microwave-assisted hydrothermal method. The surface of these carbon dots was modified through co-heating with ethylenediamine (EDA), o-phenylenediamine (OPD), m-phenylenediamine (MPD), and p-phenylenediamine (PPD). The effects of different diamines on the morphology and optical properties of P-CDs were systematically analyzed. The diamine-modified P-CDs exhibited varying sizes and similar crystal structures, with significantly enhanced fluorescence and quantum yields, reaching 35.2% for EDA-CDs. EDA-CDs and OPD-CDs demonstrated excitation-dependent emission behavior, while MPD-CDs and PPD-CDs did not. Based on EDA-CDs, a probe with high sensitivity for Fe3+ was developed, showing a good linear response within the Fe3+ concentration range of 20–100 μM and a detection limit of 2.768 μM. Additionally, the ion probe exhibited a recovery rate of 100.85% in both deionized and tap water, indicating good practical applicability. This study provides essential guidance for the nitrogen surface modification of biomass-derived carbon quantum dots and presents a promising Fe3+ probe with potential applications.

The rapid outbreak of the deadly and contagious SARS-CoV-2 virus in 2019 that caused COVID-19 disease has demanded the development of novel antiviral materials. Since medical treatment and drug evaluation and approval by health authorities takes a longer time, nanomaterials can play a significant role in combating deadly disease. Carbon-based materials, such as carbon nanotubes (CNTs), graphene, fullerene, and carbon quantum dots (CQDs), have been widely reported in the literature as contributing to fighting the viral disease. Among them, CQDs have received significant attention as bionanomaterials recently, particularly in the biomedical field to treat various viral infections. Therefore, this mini-review discusses the recent achievements of CQDs and graphene quantum dots (GQDs) as bionanomaterials in fighting viral disease, specifically COVID-19 and other COVID-19-related works such as sensing and treatment, as well as virus inhibition.

Background: Pathogen bacteria appear and survive on various surfaces made of steel or glass. The existence of these bacteria in different forms causes significant problems in healthcare facilities and society. Therefore, the surface engineering of highly potent antimicrobial coatings is highly important in the 21st century, a period that began with a series of epidemics. Methods: In this study, we prepared two types of photodynamic polyurethane-based composite films encapsulated by N-doped carbon quantum dots and graphene quantum dots irradiated by gamma rays at a dose of 50 kGy, respectively. Further, we investigated their structural, optical, antibacterial, antibiofouling and biocompatibility properties. Results: Nanoelectrical and nanomechanical microscopy measurements revealed deviations in the structure of these quantum dots and polyurethane films. The Young’s modulus of elasticity of the carbon and graphene quantum dots was several times lower than that for single-walled carbon nanotubes (SWCNTs) with chirality (6,5). The electrical properties of the carbon and graphene quantum dots were quite similar to those of the SWCNTs (6,5). The polyurethane films with carbon quantum dots were much more elastic and smoother than the films with graphene quantum dots. Antibacterial tests indicated excellent antibacterial activities of these films against a wide range of tested bacteria, whereas the antibiofouling activities of both composite films showed the best results against the Staphylococcus aureus and Escherichia coli biofilms. Biocompatibility studies showed that neither composite film exhibited any cytotoxicity or hemolysis. Conclusions: Obtained results indicate that these composite films could be used as antibacterial surfaces in the healthcare facilities.

In the recent decade, Carbon Quantum Dots (CQDs) have attracted lots of attention due to their excellent properties such as tunable photoluminescence, high chemical stability, low toxicity, and biocompatibility. Among all synthesis methods, the hydrothermal/solvothermal rout has been considered as one of the most common and simplest method. The type of precursors can affect the size of CQDs and determine their surface functional groups, the essential properties that deeply influence the optical specifications. In this work, the effect of different precursors on the final properties of carbon quantum dots is investigated. The carbon quantum dots were synthesized by hydrothermal/solvothermal rout using citric acid, thiourea, ethylamine and monoethanolamine as precursors in almost the same conditions of time and temperature. Resultant CQDs were characterized by using FTIR, UV-Visible Spectroscopy and Photoluminescence (PL) analysis. The results of UV-Vis spectroscopy showed that quantum dots synthesized from monoethanolamine have wider absorption band rather than the CQDs from other precursors and the absorption edge shifted from about 270 nm for ethylamine to about 470 nm in monoethanolamine. Furthermore, the results demonstrate that using citric acid and monoethanolamine as precursor improved production efficiency and emission quantum yield of the carbon dots.

Fluorescence-filled photonic crystal multi-layer films are widely used in laser, sensing, display and other fields due to their photonic bandgap and fluorescence emission properties. In this paper, photonic crystals filled with carbon quantum dots from different precursors have been prepared. It is found that photonic crystals filled with fluorescent carbon quantum dots have optically variable properties excited by ultraviolet light. The optically variable properties of photonic crystals filled with carbon quantum dots at emission peaks of 616, 510 and 450 nm were studied. The fluorescent properties of carbon quantum dots at emission peaks of 616 nm were the best compared to 510 nm and 450 nm. The effects of hole radius R, hole gap d and hole depth h on optically variable properties of fluorescent filled photonic crystals were investigated using 510 nm carbon quantum dots. The results showed that the optically variable properties of fluorescent photonic crystals is strongest when R=400 nm, d=1.5 μm and h=200 nm.

The knowledge of the ways in which post-synthesis treatments may influence the properties of carbon quantum dots (CDs) is of paramount importance for their employment in biosensors. It enables the definition of the mechanism of sensing, which is essential for the application of the suited design strategy of the device. In the present work, we studied the ways in which post-synthesis thermal treatments influence the optical and electrochemical properties of Nitrogen-doped CDs (N-CDs). Blue-emitting, N-CDs for application in biosensors were synthesized through the hydrothermal route, starting from citric acid and urea as bio-synthesizable and low-cost precursors. The CDs samples were thermally post-treated and then characterized through a combination of spectroscopic, structural, and electrochemical techniques. We observed that the post-synthesis thermal treatments show an oxidative effect on CDs graphitic N-atoms. They cause their partially oxidation with the formation of mixed valence state systems, [CDs]0+, which could be further oxidized into the graphitic N-oxide forms. We also observed that thermal treatments cause the decomposition of the CDs external ammonium ions into ammonia and protons, which protonate their pyridinic N-atoms. Photoluminescence (PL) emission is quenched.

6 - Photodetector applications of carbon and graphene quantum dots

As a new zero-optic luminescent material, carbon quantum points are widely focused and sustained, and many researchers are trying to use simple and fast methods and stable, good carbon sources to be prepared with a good fluorescent properties of carbon quantum dots. In this paper, carbon quantum dots were synthesized by solvothermal method with vanillin as carbon source, and the effects of solvothermal temperature and time on the luminescence properties of carbon quantum dots were explored. Then, carbon quantum dots were characterized by X-ray diffraction analysis, transmission electron microscopy analysis, infrared spectrum analysis, fluorescence spectrum analysis. Research results showed that ethanol solvent with vanillin as a carbon source by solvothermal method could synthesize good water soluble carbon quantum dots with weak crystallization, and its size was about 10 nm. This carbon quantum dots had obvious excitation wavelength dependence and produce blue light, which had potential application value in ion fluorescence probe or cell labeling.

Tuning optical properties of printable carbon quantum dots using near-field environment

Chapter 28 - Physical properties of quantum dots