Gel-like Carbon Dots: Characterization and their Potential Applications

A fast hemostatic and enhanced photodynamic 2-dimensional metal-organic framework loaded aerogel patch for wound management

Achieving rapid hemostasis and highly effective antibacterial holds significant importance in the early-stage treatment of wounds. In this study, a hybrid aerogel patch comprising carbon quantum dots (CQDs) modified 2-dimensional (2D) porphyrinic metal-organic framework (MOF) nanosheets was designed by incorporating gelatin methacrylate (GelMA) and polyacrylamide (PAM) based matrix. On one hand, CQDs were stably doped onto the surface of the 2D MOF nanosheets, thereby enhancing the photodynamic activity through fluorescence resonance energy transfer (FRET) process. After the preparation of hybrid aerogel patch, the patch loaded with CQDs-doped 2D MOF exhibited excellent photodynamic bactericidal activity against Gram-positive Staphylococcus aureus (>99.99 %) and Gram-negative Escherichia coli (>99.99 %). On the other hand, the hybrid patch with highly porous and absorbent structure can rapidly absorb blood to aggregate clotting components and form a hydration barrier covering the wound to enhance hemostasis. Besides, the hemolysis and cytotoxicity assays demonstrated a good biocompatibility of this designed patch. In summary, this 2D MOF-loaded aerogel patch holds a potential to achieve rapid hemostasis and effective anti-infection in the early-stage treatment of traumatic wounds.

High Quantum Yield Amino Acid Carbon Quantum Dots with Unparalleled Refractive Index

Carbon quantum dots (CQDs) are one of the most promising types of fluorescent nanomaterials due to their exceptional water solubility, excellent optical properties, biocompatibility, chemical inertness, excellent refractive index, and photostability. Nitrogen-containing CQDs, which include amino acid based CQDs, are especially attractive due to their high quantum yield, thermal stability, and potential biomedical applications. Recent studies have attempted to improve the preparation of amino acid based CQDs. However, the highest quantum yield obtained for these dots was only 44%. Furthermore, the refractive indices of amino acid derived CQDs were not determined. Here, we systematically explored the performance of CQDs prepared from all 20 coded amino acids using modified hydrothermal techniques allowing more passivation layers on the surface of the dots to optimize their performance. Intriguingly, we obtained the highest refractive indices ever reported for any CQDs. The values differed among the amino acids, with the highest refractive indices found for positively charged amino acids including arginine-CQDs (∼2.1), histidine-CQDs (∼2.0), and lysine-CQDs (∼1.8). Furthermore, the arginine-CQDs reported here showed a nearly 2-fold increase in the quantum yield (∼86%) and a longer decay time (∼8.0 ns) compared to previous reports. In addition, we also demonstrated that all amino acid based CQD materials displayed excitation-dependent emission profiles (from UV to visible) and were photostable, water-soluble, noncytotoxic, and excellent for high contrast live cell imaging or bioimaging. These results indicate that amino acid based CQD materials are high-refractive-index materials applicable for optoelectronic devices, bioimaging, biosensing, and studying cellular organelles in vivo. This extraordinary RI may be highly useful for exploring cellular elements with different densities.

Nano-carrier for gene delivery and bioimaging based on pentaetheylenehexamine modified carbon dots

Carbon dots (CDs) have attracted much attention due to their excellent properties and applications, especially the use for gene delivery. Considering the risks and concerns involved in the use of viral vectors for gene delivery in vivo, non-viral vectors such as CDs have gradually become an ideal alternative due to their biocompatibility and low toxicity. Therefore, in this study, the potential to apply CDs as a non-viral vector for gene delivery was investigated. The CDs were prepared using citric acid and pentaethylenehexamine (PEHA) as precursors via a one-step microwave-mediated approach. The optical, structural, and morphological properties of PEHA-derived CDs (PCDs) were characterized by ultra-violet spectroscopy (UV-vis), photoluminescence (PL), Fourier Transform Infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), zeta potential, circular dichroism spectrometry, atomic force (AFM) and transmission electron microscopies (TEM). The analysis demonstrated that the as-prepared PCDs were rich in amine groups and were positively charged. Subsequently, gel retardation assay showed that PCDs could non-covalently bind with DNA at a mass ratio of 2:1 (PCDs: DNA). Additionally, PCDs possessed a tremendously lower cytotoxicity compared with polyethylenimine (PEI), a popular precursor/dopant for many CDs preparations, and their plasmid composite showed a high transfection efficiency. Meanwhile, PCDs were also observed to cross the blood-brain barrier (BBB) by using a zebrafish model. In conclusion, these results significantly indicate that PCDs are a potential non-viral nucleic acid/gene vector to gene therapy. Also, PCDs can be utilized in drug delivery for treating brain diseases, such as Alzheimer's disease and brain tumors.

Applications of Carbon Dots for the Treatment of Alzheimer's Disease

There are currently approximately 50 million victims of Alzheimer's disease (AD) worldwide. The exact cause of the disease is unknown at this time, but amyloid plaques and neurofibrillary tangles in the brain are hallmarks of the disease. Current drug treatments for AD may slow the progression of the disease and improve the quality of life of patients, but they are often only minimally effective and are not cures. A major obstacle to developing and delivering more effective drug therapies is the presence of the blood-brain barrier (BBB), which prevents many compounds with therapeutic potential from reaching the central nervous system. Nanotechnology may provide a solution to this problem. Among the medical nanomaterials currently being studied, carbon dots (CDs) have attracted widespread attention because of their ability to cross the BBB, non-toxicity, and potential for drug/gene delivery.

Photo- and Radiofrequency-Induced Heating of Photoluminescent Colloidal Carbon Dots

Nitrogen- and oxygen-containing carbon nanoparticles (O, N-CDs) were prepared by a facile one-step solvothermal method using urea and citric acid precursors. This method is cost-effective and easily scalable, and the resulting O, N-CDs can be used without additional functionalization and sample pretreatment. The structure of O, N-CDs was characterized by TEM, AFM, Raman, UV-vis, and FTIR spectroscopies. The obtained O, N-CDs with a mean diameter of 4.4 nm can be easily dispersed in aqueous solutions. The colloidal aqueous solutions of O, N-CDs show significant photothermal responses under red-IR and radiofrequency (RF) irradiations. The as-prepared O, N-CDs have a bright temperature-dependent photoluminescence (PL). PL/PLE spectral maps were shown to be used for temperature evaluation purposes in the range of 30–50 °C. In such a way, the O, N-CDs could be used for biomedicine-related applications such as hyperthermia with simultaneous temperature estimation with PL imaging.

Unconventional aliphatic fluorophores discovered as the luminescence origin in citric acid-urea carbon dots

Carbon dots (CDs) are emerging as the material of choice in a range of applications due to their excellent photoluminescence properties, ease of preparation from inexpensive precursors, and low toxicity. However, the precise nature of the mechanism for the fluorescence is still under debate, and several molecular fluorophores have been reported. In this work, a new blue fluorophore, 5-oxopyrrolidine-3-carboxylic acid, was discovered in carbon dots synthesized from the most commonly used precursors: citric acid and urea. The molecular product alone has demonstrated interesting aggregation-enhanced emission (AEE), making it unique compared to other fluorophores known to be generated in CDs. We propose that this molecular fluorophore is associated with a polymer backbone within the CDs, and its fluorescence behavior is largely dependent on intermolecular interactions with the polymers or other fluorophores. Thus, a new class of non-traditional fluorophores is now relevant to the consideration of the CD fluorescence mechanism, providing both an additional challenge to the community in resolving the mechanism and an opportunity for a greater range of CD design schemes and applications.

Carbon Nanotubes, Graphene, and Carbon Dots as Electrochemical Biosensing Composites

Carbon nanomaterials (CNMs) have been extensively used as electrochemical sensing composites due to their interesting chemical, electronic, and mechanical properties giving rise to increased performance. Due to these materials' unknown long-term ecological fate, care must be given to make their use tractable. In this review, the design and use of carbon nanotubes (CNTs), graphene, and carbon dots (CDs) as electrochemical sensing electrocatalysts applied to the working electrode surface are surveyed for various biosensing applications. Graphene and CDs are readily biodegradable as compared to CNTs. Design elements for CNTs that carry over to graphene and CDs include Coulombic attraction of components and using O or N atoms that serve as tethering points for attaching electrocatalytically active nanoparticles (NPs) and/or other additives.

Engineering Mitochondriotropic Carbon Dots for Targeting Cancer Cells

Aiming to understand and enhance the capacity of carbon dots (CDs) to transport through cell membranes and target subcellular organelles—in particular, mitochondria—a series of nitrogen-doped CDs were prepared by the one-step microwave-assisted pyrolysis of citric acid and ethylenediamine. Following optimization of the reaction conditions for maximum fluorescence, functionalization at various degrees with alkylated triphenylphosphonium functional groups of two different alkyl chain lengths afforded a series of functionalized CDs that exhibited either lysosome or mitochondria subcellular localization. Further functionalization with rhodamine B enabled enhanced fluorescence imaging capabilities in the visible spectrum and allowed the use of low quantities of CDs in relevant experiments. It was thus possible, by the appropriate selection of the alkyl chain length and degree of functionalization, to attain successful mitochondrial targeting, while preserving non-toxicity and biocompatibility. In vitro cell experiments performed on normal as well as cancer cell lines proved their non-cytotoxic character and imaging potential, even at very low concentrations, by fluorescence microscopy. Precise targeting of mitochondria is feasible with carefully designed CDs that, furthermore, are specifically internalized in cells and cell mitochondria of high transmembrane potential and thus exhibit selective uptake in malignant cells compared to normal cells.

Gel-like carbon dots: A high-performance future photocatalyst

To protect water resources, halt waterborne diseases, and prevent future water crises, photocatalytic degradation of water pollutants arouse worldwide interest. However, considering the low degradation efficiency and risk of secondary pollution displayed by most metal-based photocatalysts, highly efficient and environmentally friendly photocatalysts with appropriate band gap, such as carbon dots (CDs), are in urgent demand. In this study, the photocatalytic activity of gel-like CDs (G-CDs) was studied using diverse water pollution models for photocatalytic degradation. The degradation rate constants demonstrated a remarkably enhanced photocatalytic activity of G-CDs compared with most known CD species and comparability to graphitic carbon nitride (g-C₃N₄). In addition, the rate constant was further improved by 1.4 times through the embedment of g-C₃N₄ in G-CDs to obtain CD-C₃N₄. Significantly, the rate constant was also higher than that of g-C₃N₄ alone, revealing a synergistic effect. Moreover, the use of diverse radical scavengers suggested that the main contributors to the photocatalytic degradation with G-CDs alone were superoxide radicals (O₂^-) and holes that were, however, substituted by O₂^- and hydroxyl radicals (OH) due to the addition of g-C₃N₄. Furthermore, the photocatalytic stabilities of G-CDs and CD-C₃N₄ turned out to be excellent after four cycles of dye degradation were performed continuously. Eventually, the nontoxicity and environmental friendliness of G-CDs and CD-C₃N₄ were displayed with sea urchin cytotoxicity tests. Hence, through various characterizations, photocatalytic degradation and cytotoxicity tests, G-CDs proved to be an environmentally friendly and highly efficient future photocatalyst.

Facile Hydrothermal and Solvothermal Synthesis and Characterization of Nitrogen-Doped Carbon Dots from Palm Kernel Shell Precursor

Carbon dots (CDs), a nanomaterial synthesized from organic precursors rich in carbon content with excellent fluorescent property, are in high demand for many purposes, including sensing and biosensing applications. This research focused on preparing CDs from natural and abundant waste, palm kernel shells (PKS) obtained from palm oil biomass, aiming for sensing and biosensing applications. Ethylenediamine and L-phenylalanine doped CDs were produced via the hydrothermal and solvothermal methods using one-pot synthesis techniques in an autoclave batch reactor. The as-prepared N-CDs shows excellent photoluminescence (PL) property and a quantum yield (QY) of 13.7% for ethylenediamine (EDA) doped N-CDs (CDs-EDA) and 8.6% for L-phenylalanine (L-Ph) doped N-CDs (CDs-LPh) with an excitation/emission wavelength of 360 nm/450 nm. The transmission electron microscopy (TEM) images show the N-CDs have an average particle size of 2 nm for both CDs. UV-Visible spectrophotometric results showed C=C and C=O transition. FTIR results show and confirm the presence of functional groups, such as -OH, -C=O, -NH2 on the N-CDs, and the X-ray diffraction pattern showed that the N-CDs were crystalline, depicted with sharp peaks. This research work demonstrated that palm kernel shell biomass often thrown away as waste can produce CDs with excellent physicochemical properties.

Controllable Synthesis of Biocompatible Fluorescent Carbon Dots From Cellulose Hydrogel for the Specific Detection of Hg2

Heavy metal ions overload can seriously harm human health. Simple and effective strategies for the specific detection of heavy metal ions are of great important. In this work, using different pretreatment methods, a series of carbon dots (CDs) with different particle sizes and doped with varying amounts of elements (O, N, S) were prepared based on the natural polymer, cellulose hydrogel. The CDs exhibit excellent fluorescence and biocompatibility. When the particle size decreased from 8.72 to 2.11 nm, the fluorescence quantum yield increased from 0.029 to 0.183. In addition, doping with elements (N) also effectively enhanced the fluorescent performance of the CDs. The fluorescence of the CDs, especially for the smallest, CD-4a, was significantly quenched in the presence of the heavy metal ion, Hg2+. Thus, CD-4a may be used as a fluorescence sensor for the detection of Hg2+. The fluorescence intensity of CD-4a exhibited a two-stage, concentration-dependent fluorescence response in the range 0.2-10 and 10-100 μmol/L Hg2+, with each stage having different slopes; the detection limit was 0.2 μM. More importantly, even in the presence of interfering metal ions, the detection of Hg2+ using the CDs-4a remained stable. Therefore, these biocompatible CDs may serve as a promising candidate for the specific detection of Hg2+.

Facile Synthesis of "Boron-Doped" Carbon Dots and Their Application in Visible-Light-Driven Photocatalytic Degradation of Organic Dyes

Carbon dots (C-dots) were facilely fabricated via a hydrothermal method and fully characterized. Our study shows that the as-synthesized C-dots are nontoxic, negatively charged spherical particles (average diameter 4.7 nm) with excellent water dispersion ability. Furthermore, the C-dots have a rich presence of surface functionalities such as hydroxyls and carboxyls as well as amines. The significance of the C-dots as highly efficient photocatalysts for rhodamine B (RhB) and methylene blue (MB) degradation was explored. The C-dots demonstrate excellent photocatalytic activity, achieving 100% of RhB and MB degradation within 170 min. The degradation rate constants for RhB and MB were 1.8 × 10⁻² and 2.4 × 10⁻² min⁻¹, respectively. The photocatalytic degradation performances of the C-dots are comparable to those metal-based photocatalysts and generally better than previously reported C-dots photocatalysts. Collectively considering the excellent photocatalytic activity toward organic dye degradation, as well as the fact that they are facilely synthesized with no need of further doping, compositing, and tedious purification and separation, the C-dots fabricated in this work are demonstrated to be a promising alternative for pollutant degradation and environment protection.

Direct conjugation of distinct carbon dots as Lego-like building blocks for the assembly of versatile drug nanocarriers

As a promising drug nanocarrier, carbon dots (CDs) have exhibited many excellent properties. However, some properties such as bone targeting and crossing the blood-brain barrier (BBB) only apply to a certain CD preparation with limited drug loading capacity. Therefore, it is significant to conjugate distinct CDs to centralize many unique properties on the novel drug nanocarrier. Considering that CDs have abundant and tunable surface functionalities, in this study, a direct conjugation was initiated between two distinct CD models, black CDs (B-CDs) and gel-like CDs (G-CDs) via an amidation reaction. As a result of conjugation at a mass ratio of 5:3 (B-CDs to G-CDs) and a two-step purification process, the conjugate, black-gel CDs (B-G CDs) (5:3) inherited functionalities from both CDs and obtained an enhanced thermostability, aqueous stability, red-shifted photoluminescence (PL) emission, and a figure-eight shape with a width and length of 3 and 6 nm, respectively. In addition, the necessity of high surface primary amine (NH₂) content in the CD conjugation was highlighted by replacing G-CDs with other CDs with lower surface NH₂ content. Meanwhile, the carboxyl groups (COOH) on G-CDs were not enough to trigger self-conjugation between G-CDs. Moreover, the drug loading capacity was enhanced by 54.5% from B-CDs to B-G CDs (5:3). Furthermore, when the mass ratio of B-CDs to G-CDs was decreased from 5:30, 5:100 to 5:300, the obtained nanostructures revealed a great potential of CDs as Lego-like building blocks. Also, bioimaging of zebrafish demonstrated that various B-G CDs exhibited properties of both bone targeting and crossing the BBB, which are specific properties of B-CDs and G-CDs, respectively.

Nontoxic amphiphilic carbon dots as promising drug nanocarriers across the blood-brain barrier and inhibitors of β-amyloid

The blood-brain barrier (BBB) is a main obstacle for drug delivery targeting the central nervous system (CNS) and treating Alzheimer's disease (AD). In order to enhance the efficiency of drug delivery without harming the BBB integrity, nanoparticle-mediated drug delivery has become a popular therapeutic strategy. Carbon dots (CDs) are one of the most promising and novel nanocarriers. In this study, amphiphilic yellow-emissive CDs (Y-CDs) were synthesized with an ultrasonication-mediated methodology using citric acid and o-phenylenediamine with a size of 3 nm that emit an excitation-independent yellow photoluminescence (PL). The content of primary amine and carboxyl groups on CDs was measured as 6.12 × 10-5 and 8.13 × 10-3 mmol mg-1, respectively, indicating the potential for small-molecule drug loading through bioconjugation. Confocal image analyses revealed that Y-CDs crossed the BBB of 5-day old wild-type zebrafish, most probably by passive diffusion due to the amphiphilicity of Y-CDs. And the amphiphilicity and BBB penetration ability didn't change when Y-CDs were coated with different hydrophilic molecules. Furthermore, Y-CDs were observed to enter cells to inhibit the overexpression of human amyloid precursor protein (APP) and β-amyloid (Aβ) which is a major factor responsible for AD pathology. Therefore, data suggest that Y-CDs have a great potential as nontoxic nanocarriers for drug delivery towards the CNS as well as a promising inhibiting agent of Aβ-related pathology of the AD.

Sustainable Synthesis of Bright Green Fluorescent Nitrogen-Doped Carbon Quantum Dots from Alkali Lignin

Sustainable, inexpensive, and environmentally friendly biomass waste can be exploited for large-scale production of carbon nanomaterials. Here, alkali lignin was employed as a precursor to synthesize carbon quantum dots (CQDs) with bright green fluorescence through a simple one-pot route. The prepared CQDs had a size of 1.5-3.5 nm, were water-dispersible, and showed wonderful biocompatibility, in addition to their excellent photoluminescence and electrocatalysis properties. These high-quality CQDs could be used in a wide range of applications such as metal-ion detection, cell imaging, and electrocatalysis. The wide range of biomass lignin feedstocks provide a green, low-cost, and viable strategy for producing high-quality fluorescent CQDs and enable the conversion of biomass waste into high-value products that promote sustainable development of the economy and human society.

Conjugation of Carbon Dots with β-Galactosidase Enzyme: Surface Chemistry and Use in Biosensing

Nanoparticles have been conjugated to biological systems for numerous applications such as self-assembly, sensing, imaging, and therapy. Development of more reliable and robust biosensors that exhibit high response rate, increased detection limit, and enhanced useful lifetime is in high demand. We have developed a sensing platform by the conjugation of β-galactosidase, a crucial enzyme, with lab-synthesized gel-like carbon dots (CDs) which have high luminescence, photostability, and easy surface functionalization. We found that the conjugated enzyme exhibited higher stability towards temperature and pH changes in comparison to the native enzyme. This enriched property of the enzyme was distinctly used to develop a stable, reliable, robust biosensor. The detection limit of the biosensor was found to be 2.9 × 10⁻⁴ M, whereas its sensitivity was 0.81 µA·mmol⁻¹·cm⁻². Further, we used the Langmuir monolayer technique to understand the surface properties of the conjugated enzyme. It was found that the conjugate was highly stable at the air/subphase interface which additionally reinforces the suitability of the use of the conjugated enzyme for the biosensing applications.

Carbon Dots: Diverse Preparation, Application, and Perspective in Surface Chemistry

Carbon dots (CDs) are a novel class of nanoparticles with excellent properties. The development of CDs involves versatile synthesis, characterization, and various applications. However, the importance of surface chemistry of CDs, especially in applications, is often underestimated. In fact, the study of the surface chemistry of CDs is of great significance in the explanation of the unique properties of CDs as well as the pursuit of potential applications. In this feature article, we do not only introduce the development of CDs in our group but also highlight their applications where surface chemistry plays a critical role.

Size-Dependent Photocatalytic Activity of Carbon Dots with Surface-State Determined Photoluminescence

Carbon dots (CDs) were synthesized by a microwave-mediated method and separated by size exclusion chromatography into three different size fractions. There was no correlation of the size with photoluminescence (PL) emission wavelength, which shows that the PL mechanism is not quantum-size dependent. UV/vis absorption and diffuse reflectance spectroscopies showed that the light absorption properties as well as the band gap of the CDs changed with the size of the particle. The combination of FTIR and XPS measurements revealed the composition on the surface of each fraction. The three CDs fractions were separately used in the photocatalytic degradation of organic dyes under simulated sunlight irradiation. The catalytic activity of the as-prepared CDs was found to increase as the size of the particles decreased. Complete degradation of both rhodamine B (RhB) and methylene blue (MB) was achieved in 150 min by the 2-nm CDs. The scavenger studies showed that the holes and superoxide radicals are the main species involved in the photocatalytic degradation of the dye by the 2-nm CDs. These CDs displayed high stability in the degradation of organic dyes for multiple cycles. The 2-nm CDs displayed promising photocatalytic degradation of p-nitrophenol (PNP) . These results demonstrate for the first time the application of bare carbon dots in the degradation of environmental contaminants.

Close-Packed Langmuir Monolayers of Saccharide-Based Carbon Dots at the Air-Subphase Interface

Carbon dots (CDs) are zero-dimensional carbon-based spherical nanoparticles with diameters less than 10 nm. Here, we report for the first time CDs forming stable Langmuir monolayers at the air-subphase interface. Langmuir monolayers are of great interest both fundamentally to study the interactions at the interfaces and for many applications such as the development of sensors. However, CDs usually do not form Langmuir monolayers because of their highly hydrophilic nature. In this study, amphiphilic CDs were prepared through hydrothermal carbonization using saccharides as the precursors. The surface chemistry behavior and optical properties of CDs at the air-subphase interface were studied. CDs derived from saccharides consistently formed stable Langmuir monolayers which show all essential phases, namely, gas, liquid-expanded, liquid-condensed, and solid phases. The compression-decompression cycle method showed minimum hysteresis (4.3%), confirming the retaining capacity of the CDs as a monolayer. Limiting CD areas from surface pressure-area isotherm at the air-subphase interface were used to calculate the average diameter of the CDs at the air-subphase interface. UV/vis absorption spectra of CDs dispersed in water and in Langmuir monolayers had the same bands in the UV region. The intensity of the UV/vis absorption increases with increasing surface pressure at the air-subphase interface. Interestingly, photoluminescence (PL) of the Langmuir monolayer of CDs was excitation-independent, whereas the same CDs had excitation-dependent PL when dispersed in water.

Tryptophan carbon dots and their ability to cross the blood-brain barrier

Drug traversal across the blood-brain barrier has come under increasing scrutiny recently, particularly concerning the treatment of sicknesses, such as brain cancer and Alzheimer's disease. Most therapies and medicines are limited due to their inability to cross this barrier, reducing treatment options for maladies affecting the brain. Carbon dots show promise as drug carriers, but they experience the same limitations regarding crossing the blood-brain barrier as many small molecules do. If carbon dots can be prepared from a precursor that can cross the blood-brain barrier, there is a chance that the remaining original precursor molecule can attach to the carbon dot surface and lead the system into the brain. Herein, tryptophan carbon dots were synthesized with the strategy of using tryptophan as an amino acid for crossing the blood-brain barrier via LAT1 transporter-mediated endocytosis. Two types of carbon dots were synthesized using tryptophan and two different nitrogen dopants: urea and 1,2-ethylenediamine. Carbon dots made using these precursors show excitation wavelength-dependent emission, low toxicity, and have been observed inside the central nervous system of zebrafish (Danio rerio). The proposed mechanism for these carbon dots abilities to cross the blood-brain barrier concerns residual tryptophan molecules which attach to the carbon dots surface, enabling them to be recognized by the LAT1 transporter. The role of carbon dots for transport open promising avenues for drug delivery and imaging in the brain.

Nanoparticle-mediated targeted drug delivery for breast cancer treatment

Breast cancer (BC) is the most common malignancy in women worldwide, and one of the deadliest after lung cancer. Currently, standard methods for cancer therapy including BC are surgery followed by chemotherapy or radiotherapy. However, both chemotherapy and radiotherapy often fail to treat BC due to the side effects that these therapies incur in normal tissues and organs. In recent years, various nanoparticles (NPs) have been discovered and synthesized to be able to selectively target tumor cells without causing any harm to the healthy cells or organs. Therefore, NPs-mediated targeted drug delivery systems (DDS) have become a promising technique to treat BC. In addition to their selectivity to target tumor cells and reduce side effects, NPs have other unique properties which make them desirable for cancer treatment such as low toxicity, good compatibility, ease of preparation, high photoluminescence (PL) for bioimaging in vivo, and high loadability of drugs due to their tunable surface functionalities. In this study, we summarize with a critical analysis of the most recent therapeutic studies involving various NPs-mediated DDS as alternatives for the traditional treatment approaches for BC. It will shed light on the significance of NPs-mediated DDS and serve as a guide to seeking for the ideal methodology for future targeted drug delivery for an efficient BC treatment.

Recent development of carbon quantum dots regarding their optical properties, photoluminescence mechanism, and core structure

Carbon quantum dots (CDs) are a relatively new class of carbon nanomaterials which have been studied very much in the last fifteen years to improve their already favorable properties. The optical properties of CDs have drawn particular interest as they display the unusual trait of excitation-dependent emission, as well as high fluorescence quantum yields (QY), long photoluminescence (PL) decay lifetimes, and photostability. These qualities naturally lead researchers to apply CDs in the field of imaging (particularly bio-imaging) and sensing. Since the amount of publications regarding CDs has been growing nearly exponentially in the last ten years, many improvements have been made in the optical properties of CDs such as QY and PL lifetime. However, a great deal of confusion remains regarding the PL mechanism of CDs as well as their structural properties. Therefore, presented in this review is a summary and discussion of the QYs and PL lifetimes reported in recent years. The effect of method as well as precursor has been evaluated and discussed appropriately. The current theories regarding the PL mechanism of CDs are discussed, with special attention to the concept of surface state-controlled PL. With this knowledge, the improvement of preparation and applications of CDs related to their optical properties will be easily accomplished. Further improvements can be made to CDs through the understanding of their structural and optical properties.

Carbon Nitride Dots: A Selective Bioimaging Nanomaterial

In contrast to the recent immense attention in carbon nitride quantum dots (CNQDs) as a heteroatom-doped carbon quantum dot (CQD), their biomedical applications have not been thoroughly investigated. Targeted cancer therapy is a prominently researched area in the biomedical field. Here, the ability of CNQDs as a selective bioimaging nanomaterial was investigated to assist targeted cancer therapy. CNQDs were first synthesized using four different precursor sets involving urea derivatives, and the characteristics were compared to select the best candidate material for bioapplications. Characterization techniques such as UV-vis, luminescence, X-ray photoelectron spectroscopy, nuclear magnetic resonance spectroscopy, and transmission electron microscopy were used. These CNQDs were analyzed in in vitro studies of bioimaging and labeling using pediatric glioma cells (SJGBM2) for possible selective biolabeling and nanodistribution inside the cell membrane. The in vitro cellular studies were conducted under long-wavelength emission without the interference of blue autofluorescence. Thus, excitation-dependent emission of CNQDs was proved to be advantageous. Importantly, CNQDs selectively entered SJGBM2 tumor cells, while it did not disperse into normal human embryonic kidney cells (HEK293). The distribution studies in the cell cytoplasm indicated that CNQDs dispersed into lysosomes within approximately 6 h after the incubation. The CNQDs exhibited great potential as a possible nanomaterial in selective bioimaging and drug delivery for targeted cancer therapy.

Highly Photoluminescent and Stable N-Doped Carbon Dots as Nanoprobes for Hg2+ Detection

We developed a microreactor with porous copper fibers for synthesizing nitrogen-doped carbon dots (N-CDs) with a high stability and photoluminescence (PL) quantum yield (QY). By optimizing synthesis conditions, including the reaction temperature, flow rate, ethylenediamine dosage, and porosity of copper fibers, the N-CDs with a high PL QY of 73% were achieved. The PL QY of N-CDs was two times higher with copper fibers than without. The interrelations between the copper fibers with different porosities and the N-CDs were investigated using X-ray photoelectron spectroscopy (XPS) and Fourier Transform infrared spectroscopy (FTIR). The results demonstrate that the elemental contents and surface functional groups of N-CDs are significantly influenced by the porosity of copper fibers. The N-CDs can be used to effectively and selectively detect Hg²⁺ ions with a good linear response in the 0~50 μM Hg²⁺ ions concentration range, and the lowest limit of detection (LOD) is 2.54 nM, suggesting that the N-CDs have great potential for applications in the fields of environmental and hazard detection. Further studies reveal that the different d orbital energy levels of Hg²⁺ compared to those of other metal ions can affect the efficiency of electron transfer and thereby result in their different response in fluorescence quenching towards N-CDs.

Embedding Carbon Dots in Superabsorbent Polymers for Additive Manufacturing

A type of orange carbon dots (O-CDs) synthesized via an ultrasonication route with citric acid and 1,2-phenylenediamine as precursors was embedded into sodium polyacrylate (SPA) as the ink for 3D printing. Characterizations of these spherical O-CDs revealed an ultra-small size (~2 nm) and excitation-independent, but solvent dependent, emission. The O-CDs were evenly distributed with low degree of aggregation in sodium polyacrylate (SPA), which was achieved due to the property that SPA can absorb water together with O-CDs. The 3D printed photoluminescent objective with the ink revealed a great potential for high yield application of these materials for additive manufacturing. This also represents the first time, bare CDs have been reported as a photoluminescent material in 3D printing, as well as the first time SPA has been reported as a material for 3D printing.

Crossing the blood-brain barrier with nanoparticles

The blood-brain barrier (BBB) is one of the most essential protection mechanisms in the central nervous system (CNS). It selectively allows individual molecules such as small lipid-soluble molecules to pass through the capillary endothelial membrane while limiting the passage of pathogens or toxins. However, this protection mechanism is also a major obstacle during disease state since it dramatically hinders the drug delivery. In recent years, various tactics have been applied to assist drugs to cross the BBB including osmotic disruption of the BBB and chemical modification of prodrugs. Additionally, nanoparticles (NPs)-mediated drug delivery is emerging as an effective and non-invasive system to treat cerebral diseases. In this review, we will summarize and analyze the advances in the drug delivery across the BBB using various NPs in the last decade. The NPs will cover both traditional and novel nanocarriers. The traditional nanocarriers consist of poly(butylcyanoacrylate), poly(lactic-co-glycolic acid), poly(lactic acid) NPs, liposomes and inorganic systems. In the meanwhile, novel nanocarriers such as carbon quantum dots with their recent applications in drug delivery will also be introduced. In terms of significance, this review clearly depicts the BBB structure and comprehensively describes various NPs-mediated drug delivery systems according to different NPs species. Also, the BBB penetration mechanisms are concluded in general, emphasized and investigated in each drug delivery system.

Highly crystalline carbon dots from fresh tomato: UV emission and quantum confinement

In this article, fresh tomatoes are explored as a low-cost source to prepare high-performance carbon dots by using microwave-assisted pyrolysis. Given that amino groups might act as nucleophiles for cleaving covalent bridging ester or ether in the crosslinked macromolecules in the biomass bulk, ethylenediamine (EDA) and urea with amino groups were applied as nucleophiles to modulate the chemical composites of the carbon nanoparticles in order to tune their fluorescence emission and enhance their quantum yields. Very interestingly, the carbon dots synthesized in the presence of urea had a highly crystalline nature, a low-degree amorphous surface and were smaller than 5 nm. Moreover, the doped N contributed to the formation of a cyclic form of core that resulted in a strong electron-withdrawing ability within the conjugated C plane. Therefore, this type of carbon dot exhibited marked quantum confinement, with the maximum fluorescence peak located in the UV region. Carbon nanoparticles greater than 20 nm in size, prepared using pristine fresh tomato and in the presence of EDA, emitted surface state controlled fluorescence. Additionally, carbon nanoparticles synthesized using fresh tomato pulp in the presence of EDA and urea were explored for bioimaging of plant pathogenic fungi and the detection of vanillin.

Carbon dots: promising biomaterials for bone-specific imaging and drug delivery

Bone-related diseases and dysfunctions are heavy burdens on our increasingly aged society. One important strategy to relieve this problem is through early detection and treatment of bone-related diseases. Towards this goal, there has been constant interest in developing novel bone-specific materials for imaging and drug delivery. Currently, however, materials that have high affinity and specificity towards bone are very limited. Carbon dots (C-dots) synthesized from carbon nanopowder bind to calcified bones in vivo with high affinity and specificity. In this study we show that bone binding is highly unique to a specific type of C-dot, and that this binding is non-toxic. Significantly, C-dots derived from other raw materials did not show any bone binding properties. These differences are attributed to the differences in surface chemistry of C-dot preparations, highlighting the heterogeneous nature of C-dots. Importantly, bone-binding by carbon nanopowder derived C-dots is not significantly altered by chemical functionalization of their surface. These unique properties indicate the potential applications of carbon nanopowder-derived C-dots as highly bone-specific bioimaging agents and drug carriers.

Polymers in Carbon Dots: A Review

Carbon dots (CDs) have been widely studied since their discovery in 2004 as a green substitute of the traditional quantum dots due to their excellent photoluminescence (PL) and high biocompatibility. Meanwhile, polymers have increasingly become an important component for both synthesis and modification of CDs to provide polymeric matrix and enhance their PL property. Furthermore, critical analysis of composites of CDs and polymers has not been available. Herein, in this review, we summarized the use of polymers in the synthesis and functionalization of CDs, and the applications of these CDs in various fields.