Photoluminescent Carbon Quantum Dots: Synthetic Approaches and Photophysical Properties

Ratio fluorescence and smartphone-assisted colorimetry dual-mode detection of creatinine based on F, B, N-doped of red fluorescent carbon dots

BACKGROUND

Creatinine is a small molecule disease biomarker that reflects kidney function, accurate and effective detection of creatinine will play an important role in the prevention and treatment of diseases. Currently, commonly used creatinine detection methods are limited by expensive instruments, complex sample preparation, many interference factors from biological samples, and environmental factors that can affect the accuracy of the measurement. Therefore, developing a fast, simple, inexpensive, sensitive analysis method that can eliminate background interference and provide multi-detection modes has strong attraction and value.

RESULTS

Here, we prepared ratio fluorescence and smartphone-assisted colorimetry dual-mode platform for the detection of creatinine based on F, B, N-doped of red fluorescent carbon dots (HAc-CDs). HAc-CDs were synthesized via hydrothermal method using o-phenylenediamine and tetrafluoroboric acid. Under an excitation wavelength of 360 nm, HAc-CDs exhibit two emission peaks at 599 nm and 652 nm with full width at half-maximums of 43.8 nm and 43.3 nm, respectively. In the presence of creatinine, the fluorescence peak at 599 nm with orange light increases, while the peak at 652 nm with red light decreases. This phenomenon of creatinine-HAc-CDs is inferred to be aggregation-induced emission. The ratio of fluorescence intensity (F652/F599) is linearly related to the concentration of creatinine range from 3.0 × 10-10 to 1.0 × 10-3 M with a detection limit of 0.084 nM. Additionally, a smartphone-assisted recognition creatinine intelligent detection system based on the color change of paper strips was constructed.

SIGNIFICANCE

Creatinine in urine can be dual-mode detected with ratio fluorescence and smartphone-assisted colorimetry based on the prepared F, B, N-doped of red fluorescent carbon dots. Dual-mode detection system enables convenient, reliable and visual detection for on-site applications, and it has reference significance for the development of other disease biomarker detection methods.

l-Cysteine-Modified Carbon Dots Derived from Hibiscus rosa-sinensis for Thiram Pesticides Identification on Edible Perilla Leaves

In this work, environmentally friendly fluorescent carbon dots (C-dots) were developed for the purpose of thiram identification in the leaves of perilla plants. Powdered plant petals from Hibiscus rosa-sinensis were hydrothermally combined to create C-dots. Analytical techniques, such as scanning electron microscopy, energy dispersive X-ray spectroscopy, high resolution transmission electron microscopy, Raman spectroscopy, ultraviolet spectroscopy, Fourier transmission infrared spectroscopy, and photoluminescence were employed to examine the properties of C-dots. To enhance their functionality, an l-cysteine dopant was added to the C-dots. Since this process produces highly soluble C-dots in water, it is simple, inexpensive, and safe. The excitation process and the size of the blue luminescent C-dots both affect their photoluminescent activity. Furthermore, thiram in aqueous solutions was effectively identified by using the generated C-dots. Additionally, the ImageJ program was used to measure the colors red, green, and blue. High-resolution TEM (HR-TEM) revealed that the l-cysteine-doped carbon dots had an average particle size of 2.208 nm. Additionally, the lattice fringes observed in the HRTEM image showed a d-spacing of around 0.285 nm, which nearly corresponds to the (100) lattice plane of graphitic carbon. A Raman spectrum study was also performed to investigate the relationship between carbon dots and pesticides in the actual samples. In the end, thiram levels in perilla leaves with nondoped and doped C-dots could be distinguished with 100% accuracy using the constructed partial least-squares discriminant analysis machine learning model. The information gathered therefore demonstrated that the synthetic C-dots successfully and efficiently provide rapid and sensitive detection of hazardous pesticides in edible plant products.

Neurological effects of carbon quantum dots on zebrafish: A review

Fluorescent carbon dots have emerged as promising nanomaterials for various applications, including bioimaging, food safety detection and drug delivery. However, their potential impact on neurological systems, especially in-vivo models, remains a critical area of investigation. This review focuses on the neurological effects of carbon dots and carbon quantum dots on zebrafish, an established vertebrate model with a conserved central nervous system. Recent studies have demonstrated the efficient uptake and distribution of carbon dots in zebrafish tissues, with a particular affinity for neural tissues. The intricate neural architecture of zebrafish allows for the precise examination of behavioral changes and neurodevelopmental alterations induced by fluorescent carbon dots. Neurotoxicity assessments reveal both short-term and long-term effects, ranging from immediate behavioral alterations to subtle changes in neuronal morphology. The review discusses potential mechanisms underlying these effects highlights the need for standardized methodologies in assessing neurological outcomes and emphasizes the importance of ethical considerations in nanomaterial research. As the field of nanotechnology continues to advance, a comprehensive understanding of the impact of fluorescent carbon dots on neurological function in zebrafish is crucial for informing safe and sustainable applications in medicine and beyond.

Dual "Turn-On" Fluorescent and Colorimetric Sensing of Permanganate Based on Yellow Carbon Dots

Existing permanganates (MnO4 -) sensing methods suffered from the poor selectivity, restricted solubility, and/or less desirable signaling mechanisms (e.g., "turn-off" processes), resulting in the false positive result. In this work, an effective "turn-on" fluorescence method for MnO4 - detection in aqueous media was proposed via yellow fluorescence carbon dots (Y-CDs) with the maximum emission peak of 553 nm. Upon the introduction of MnO4 -, the fluorescence of Y-CDs increased significantly due to the enhanced surface passivation degree and intramolecular charge transfer. In the range of 0.1-10 μM, the fluorescence ratio (F/F0) is proportional to the MnO4 - ions concentration, realizing the "turn-on" fluorescence sensing of MnO4 -. On the other hand, utilizing the significant color change of Y-CDs by MnO4 - ions, the colorimetric analysis can also be established for MnO4 - assay. Compared with other probes, the analysis results obtained by bimodal sensing tactics of fluorescent and colorimetric can be mutually verified to improve the reliability and meet the sensing needs of targets in complex environments.

Regulation of Brightness Attributes of High-Stability Carbon Quantum Dots Applicable in LED Digital Color Display

Fluorescent carbon dots (CDs) attract much attention due to high stability and low toxicity. For high brightness, multi-color emission and fluorescence stability, polystyrene (PS)/CDs composite films were prepared. First, three types of CDs and three PS/CDs films were prepared. Then, three light-emitting-diode (LED) devices were achieved. Compared to CDs solutions, CDs filled films show almost unchanged photoluminescence (PL) spectra. PL peaks of blue, green and red films appear at 462 nm, 544 nm and 603 nm, separately. Blue CDs lead to highest photoluminescence quantum yields (PLQYs) of 76% (solution) and 49% (film). A certain level of thermal stability and fluorescent reversibility of blue film were verified. After 60 days of air exposure, PL intensities of blue and green films reach 97% and 93% of original values, separately. Improving work time cannot vary PL wavelengths of devices. For blue-emitted device, PL intensity reaches 55% of original value after working for 600 min. For green-emitted device, PL intensity reaches 80% after working for 300 min. The novelty is effective PS encapsulation and uniform dispersion of CDs to yield favorable fluorescence properties of devices. This work inspires ideas for large-scale preparation of fluorescent films for LED digital color display.

Photoluminescence quantum yield of carbon dots: emission due to multiple centers versus excitonic emission

Carbon dots (CDs) are recognized as promising fluorescent nanomaterials with bright emission and large variations of photoluminescence quantum yield (PLQY). However, there is still no unique approach for explanation of mechanisms and recipes for synthetic procedures/chemical composition of CDs responsible for the enhancement of PLQY. Here, we compare photophysical behavior and PLQY of two types of CDs synthesized by different routes, leading to the different extent of oxidation and composition. The first type of CDs represents a conjugated carbon system oxidized by F, N and O heteroatoms, whereas the second type represents a non-conjugated carbon system oxidized by oxygen. Photophysical data, photoemission spectroscopy and microscopy data yield the suggestion that in the first case, a structure with a distinct carbon core and highly oxidized electron-accepting shell is formed. This leads to the excitonic type non-tunable emission with single-exponent decay and high PLQY with a strong dependence on the solvent polarity, being as high as 93% in dioxane and as low as 30% in aqueous medium, but which is vulnerable to photobleaching. In the second case, the oxidized CDs do not indicate a clear core-shell structure and show poor solvatochromism, negligible photobleaching, low PLQY varying in the range of 0.7-2.3% depending on the solvent used, and tunable emission with multi-exponent decay, which can be described by the model of multiple emission centers acting through a clustering-triggered emission mechanism. The obtained results lead to a strategy that allows one to design carbon nanomaterials with principally different PLQYs that differ by orders of magnitude.

A new approach for the treatment of Alzheimer's disease: insulin-quantum dots

The potential use of insulin supplementation for Alzheimer's Disease (AD) was aimed to investigate and explore CQDs as an alternative delivery system. CQDs were produced by microwave and characterised. Insulin-loaded Ins-CQDs and in-situ Gel-Ins-CQDs were developed. The in vitro release kinetics, penetrations of insulin through excised sheep nasal mucosa were determined. Toxicity of CQDs were calculated on SH-SY5Y cells. The stability and usability of the prepared formulations were assessed. The insulin release from the solution was 70.75% after 3 hours, while it was 37.51% for in-situ Gel-Ins-CQDs. IC50 value was 52 µM. The mean particle diameters of Ins-CQDs and in-situ Gel-Ins-CQDs varied between 8.35 ± 0.19 to 8.75 ± 0.03 nm during a 6-month period. Zeta potentials ranged from -31.51 ± 1.39 to -24.43 ± 0.26 mV, and PDI values were between 9.8 ± 0.01 to 5.3 ± 3.2%(SD, n = 3) for Ins-CQDs and in-situ Gel-Ins-CQDs, respectively.Our results show that Gel-Ins-CQDs represented a controlled release over time and can be used for AD through the nasal route.

Solid-State Phosphors from Coal-Derived Carbon Quantum Dots

With unique optical and chemical properties, carbon quantum dots (CQDs) find tremendous applications in chemistry, biology, and materials science to medicine. To expand the applicability of coal-derived CQDs from the liquid to solid state, we herein report the sustainable synthesis of solid phosphors from coal-derived CQDs using poly(vinyl alcohol) (PVA) and silica (SiO₂) as an organic and inorganic matrix. Two coal-derived CQDs were obtained using an eco-friendly ultrasonic-assisted wet oxidation method. The structural and chemical properties of the CQDs were extensively investigated and compared with commercial CQDs. The coal-derived CQDs exhibited blue fluorescence with 8.9 and 14.9% quantum yields. The CQDs were found to be self-co-doped with nitrogen and sulfur heteroatoms through surface and edge functional groups. Solid-state fluorescence of PVA/CQD composite films confirmed that the CQDs retained their excellent blue emission in a dry solid matrix. A facile one-pot sol-gel method was employed to fabricate SiO₂/CQD phosphors with the unique fluorescence emission. Due to their special structural features, coal-derived CQDs favored the heterogeneous nucleation and rapid formation of SiO₂/CQD phosphors. Further, coal-derived CQDs caused high-intensity white light emission with CIE coordinates of (0.312, 0.339) by endowing a suitable band gap structure in a SiO₂/CQD solid phosphor for potential optical applications.

Carbon Quantum Dots from Roasted Coffee Beans: Their Degree and Mechanism of Cytotoxicity and Their Rapid Removal Using a Pulsed Electric Field

Carbon quantum dots (CQDs) from heat-treated foods show toxicity, but the mechanisms of toxicity and removal of CQDs have not been elucidated. In this study, CQDs were purified from roasted coffee beans through a process of concentration, dialysis and lyophilization. The physical properties of CQDs, the degree and mechanism of toxicity and the removal method were studied. Our results showed that the size of CQDs roasted for 5 min, 10 min and 20 min were about 5.69 ± 1.10 nm, 2.44 ± 1.08 nm and 1.58 ± 0.48 nm, respectively. The rate of apoptosis increased with increasing roasting time and concentration of CQDs. The longer the roasting time of coffee beans, the greater the toxicity of CQDs. However, the caspase inhibitor Z-VAD-FMK was not able to inhibit CQDs-induced apoptosis. Moreover, CQDs affected the pH value of lysosomes, causing the accumulation of RIPK1 and RIPK3 in lysosomes. Treatment of coffee beans with a pulsed electric field (PEF) significantly reduced the yield of CQDs. This indicates that CQDs induced lysosomal-dependent cell death and increased the rate of cell death through necroptosis. PEF is an effective way to remove CQDs from roasted coffee beans.

Green synthesis of CQDs for determination of iron and isoniazid in pharmaceutical formulations

Camphor leaves were used as the precursor for the hydrothermal synthesis of carbon quantum dots. The preparation method is simple and rapid, and the raw material is environmentally friendly and easy to obtain. Without additional modification, the carbon quantum dots were used as fluorescent probes for the sensitive and selective detection of Fe³⁺ and isoniazid at different excitation wavelengths. For Fe³⁺, at the excitation wavelength of 320 nm, the ratio of fluorescence intensity of CQD solution after adding Fe³⁺ to CQD solution without Fe³⁺ addition, F/F₀, and Fe³⁺ concentration showed a good linear relationship in the range of 2.72 × 10^-5 to 1.00 × 10^-4 mol L^-1 (R² = 0.9912), and the limit of detection was 8.16 μmol L^-1. For isoniazid, at the excitation wavelength of 270 nm, the ratio of fluorescence intensity of CQDs solution with isoniazid to CQDs solution without isoniazid, F/F₀, and isoniazid concentration showed good linear relationships in the range of 3.81 × 10^-6 to 1.00 × 10^-5 mol L^-1 (R² = 0.9941) and 1.00 × 10^-5 to 2.10 × 10^-4 mol L^-1 (R² = 0.9910) respectively, and the limit of detection was 1.14 μmol L^-1. A fluorescence method for the determination of Fe and isoniazid content was proposed. The method has been used to detect iron in iron supplement tablets and isoniazid in isoniazid tablets with satisfactory results.

Recent progress of biocompatible carbon dots in hypoxia-related fields

Almost all eukaryotes need oxygen to maintain regular physiological activities. When the organism is under hypoxic situation for a persistent or periodic, it will induce irreversible physiological disorders and even pathological results. Hypoxia is closely related to the pathogenesis of metabolic diseases, cancer, chronic heart disease and kidney disease, myocardial ischemia, as well as reproductive diseases like preeclampsia and endometriosis. Therefore, monitoring and treatment of hypoxia have important implications for the pathophysiology of human-related diseases. Carbon dots (CDs) are emerging nanomaterials developed after 2004 with excellent performance, and have broad application potential in variousdomains likeoptical, biomedicine, energy. Advanced hypoxia therapeutics should be integrated with monitoring and treatment, and CDs with excellent performance are good potential options when sensing is combined with various therapeutic methods. Some researchers have also begun to carry out research in related fields and achieved some results. This article aims to clarify the various applications of CDs in hypoxia-related fields in recent years, including hypoxia sensing and hypoxia tumor theranostics. Finally, the possible challenges and prospects for the application of CDs in hypoxia-related fields are discussed.

Development of a Quantum Dot-Based Fluorescence-Linked Immunosorbent Assay for Puerarin

In this study, a rapid and highly sensitive fluorescence-linked immunosorbent assay for puerarin determination was developed by the conjugation of quantum dots with an antibody against puerarin. The linear range and detection limit of the fluorescence-linked immunosorbent assay were validated. The detection curve (y = -1041ln(x)+5366, R² = 0.999) was linear in the range of 7.8-125 ng/mL. The 50% inhibitory concentration determined by fluorescence-linked immunosorbent assay was 33.8 ng/mL puerarin in water. The limit of detection for PUE was 6.1 ng/mL. To our knowledge, this is the first report on the quantitative detection of a natural product using quantum dots as fluorescent markers. Furthermore, the newly developed fluorescence-linked immunosorbent assay was successfully applied to determine puerarin in several commercial Gegen Qinlian tablets, with a higher sensitivity than that of conventional enzyme-linked immunosorbent assays.

Synthetic chiral molecular nanographenes: the key figure of the racemization barrier

Chirality is one of the most intriguing concepts of chemistry, involving living systems and, more recently, materials science. In particular, the bottom-up synthesis of molecular nanographenes endowed with one or several chiral elements is a current challenge for the chemical community. The wilful introduction of defects in the sp² honeycomb lattice of molecular nanographenes allows the preparation of chiral molecules with tuned band-gaps and chiroptical properties. There are two requirements that a system must fulfill to be chiral: (i) lack of inversion elements (planes or inversion centres) and (ii) to be configurationally stable. The first condition is inherently established by the symmetry group of the structure, however, the limit between conformational and configurational isomers is not totally clear. In this feature article, the chirality and dynamics of synthetic molecular nanographenes, with special emphasis on their racemization barriers and, therefore, the stability of their chiroptical properties are discussed. The general features of nanographenes and their bottom-up synthesis, including the main defects inducing chirality in molecular nanographenes are firstly discussed. In this regard, the most common topological defects of molecular NGs as well as the main techniques used for determining their energy barriers are presented. Then, the manuscript is structured according to the dynamics of molecular nanographenes, classifying them in four main groups, depending on their respective isomerization barriers, as flexible, detectable, isolable and rigid nanographenes. In these sections, the different strategies used to increase the isomerization barrier of chiral molecular nanographenes that lead to configurationally stable nanographenes with defined chiroptical properties are discussed.