Metal-based Quantum Dots Research Articles

Bioinspired Carbon Dots-Based Fluorescent Sensor for the Selective Determination of a Potent Anti-Inflammatory Drug in the Presence of Its Photodegradation Products.

Herein, we synthesized biogenic carbon dots (CDs) with blue-shifted maximum excitation (λex/λem of 320/404 nm) from largely wasted tangerine seeds for the first time via a one-step hydrothermal method. The biogenic CDs exhibit a maximum excitation wavelength that overlaps with the absorption spectrum of ketorolac tromethamine (KETO) at 320 nm. The developed CDs serve as a turn-off fluorescent probe via an inner filter effect (IFE) quenching mechanism. The resulting CDs have high quantum yield (QY) (39% ± 2.89%, n = 5) and exhibited great performance toward KETO over a concentration range of 0.50-16.00 μg/mL with a limit of detection (LOD) = 0.17 μg/mL. The nanoprobe achieved a high % recovery in assaying KETO in tablet dosage form and had not been significantly affected by various interferents including co-formulated and co-administered drugs. The nanoprobe shows selectivity toward KETO, even in the presence of its photocatalytic degradation products. It can effectively investigate the elimination of KETO from aquatic systems and test its stability in pharmaceutical preparations. The developed nanoprobe underwent a comprehensive evaluation of its environmental impact using analytical eco-scale (AES), complex green analytical procedure index (Complex GAPI), and the Analytical GREEnness calculator (AGREE). The sustainability of the developed nano sensor was assessed and compared to the reported metal-based quantum dots probe for KETO using the innovative RGB 12 model, considering 12 white analytical chemistry (WAC) perspectives.

Fluorescent carbon dots for labeling of bacteria: mechanism and prospects-a review.

The search for bacteria-labeling agents that are more efficient and less toxic compared to existing staining dyes is ongoing. Fluorescent quantum dots and carbon dots (CDs) have been extensively researched for various bioimaging applications. Priority is given to CDs due to several advantages, including lower toxicity, versatility in tuning their properties, and better photostability compared to metal-based quantum dots. Although significant progress is still needed to replace existing dyes with CDs for bacteria labeling, they offer promising potential for further improvement in efficiency. Surface charges and functional groups have been reported as decisive factors for bacterial discrimination and live/dead assays; however, a complete guideline for preparing CDs with optimum properties for efficient staining and predicting their labeling performance is lacking. In this review, we discuss the application of fluorescent CDs for bacterial labeling and the underlying mechanisms and principles. We primarily focus on the application and mechanism of CDs for Gram differentiation, live imaging, live/dead bacteria differentiation, bacterial viability testing, biofilm imaging, and the challenges associated with application of CDs. Based on proposed mechanisms of bacterial labeling and ambiguous results reported, we provide our view and guidelines for the researchers in this field to overcome the challenges associated with bacteria labeling using fluorescent CDs.

Fabrication of highly luminescent and thermally stable composites of sulfur nanodots through surface modification and assembly.

Sulfur nanodots (S-dots) have emerged as a promising luminescent material to excel over traditional heavy metal-based quantum dots. However, their relatively low emission efficiency and poor thermal stability in the solid state have limited their wide applications in photoelectric devices. In this work, highly luminescent, with a photoluminescence quantum yield higher than 50%, and thermally stable composites of S-dots were produced through modulating their surface states and aggregation behaviors by introducing pyromellitic dianhydride (PMDA) and benzoyleneurea (BEU), respectively. PMDA eliminated the relatively short-lived surface states and defects on the surface of S-dots and BEU regulated the aggregation states and facilitated the energy transfer from BEU to S-dots. The as-obtained composites also showed significantly improved thermal stability compared to S-dots, aided by the hydrophobic chemical groups and dense matrix of PMDA and BEU, which extended their applications in fabricating light-emitting diodes. Our presented results provide a new approach to produce highly luminescent S-dots, which widen their applications in the fields of bioimaging, sensing, photoelectric devices, and environmental science.

Effect of Operating Parameters on the Properties of Carbon Dots from Spent Coffee Grounds

Carbon dots (nanosized materials) exhibit excellent properties such as strong fluorescence, low cytotoxicity, biocompatibility, and good biodegradability which can be synthesized from various carbon sources such as biomass and food waste etc. Due to their unique properties, they are considered as potential alternatives to replace conventional metal-based quantum dots in a number of applications from energy storage, biomedicine to water treatment. In this work, we demonstrate an intensified and green approach to synthesize carbon dots from waste coffee. The synthesized carbon dots have application in sensing e.g. detecting heavy metals, contaminants in water, drug delivery and bioimaging.

Saccharide-originated fluorescent carbon dots synthesized by in-liquid plasma with controlled orderliness of carbon core through precursor alteration for selective and rapid metal ion detection

Carbon dots (CDs) have grown interested in replacing metal-based quantum dots due to their fluorescent properties with low toxicity. The green synthesis, therefore, represents a contribution to this research field. Here, we demonstrate the synthesis of CDs from simple saccharides, including fructose, glucose, and sucrose, using an eco-friendly method—solution plasma (SP)—by applying plasma in the aqueous solution of the precursor. Variations and characterizations are conducted to understand the role or influence of each synthesis parameter, i.e. saccharide precursor's molecular structure, solution pH (2, 5, and 8), and post-treatment method (freeze-drying and heat-drying), in the materials' structure and fluorescent properties. Blue light-emitting CDs are prepared from all precursors of pH 5 and 8 through SP, followed by heat-drying. Results show that SP is responsible for the carbon core formation, and thus the precursor type affects the carbon core's orderliness. Heat-drying causes oxidation on the CDs' surface, whereby OH functional groups change to C=O. Among all samples, the CDs synthesized from fructose at pH 5 (Fru-CDs-5) perform the best photoluminescence property, having the highest quantum yield (QY) of 9.16% and exhibiting an outstanding ability to detect Fe 3+ ions. This is the first attempt to evince the potential use of SP to synthesize CDs from natural carbon sources and obtain CDs exhibiting superior fluorescence properties without any doping and complex synthesis steps. In addition to offering a new synthetic approach, this work specifies the role of the SP and the effect of the saccharide's molecular structure, which is the most relevant synthesis parameters mandatory to obtain tailored CDs with precise control. • Carbon dots (CDs) are synthesized from fructose, glucose, and sucrose using the ‘solution plasma (SP)’ process. • This is the first attempt to use SP to synthesize CDs from natural carbon sources. • The role of the SP and the post-treatment method and the effect of the precursor's molecular structure are explored. • The obtained CDs display outstanding sensitivity and selectivity toward Fe 3+ ion detection.

Carbon Dot - An Updated Review

These days, carbon dots (CDs) are the rising stars of nanomaterials. Carbon dots (CDs) are small carbon nanoparticles with the same type of surface passivation (less than 10 nm in size). Researchers found C-dots by accident while purifying single-walled carbon nanotubes (SWCNTs) manufactured using the arc-discharge process. Toxic metal-based quantum dots are being replaced with carbon dots (QDs). Carbon dots are currently being prepared from a variety of natural resources in order to obtain self-passivated products at a reasonable cost. Because of their superior photo physical characteristics, biocompatibility, and low toxicity, carbon dots have prospective applications in bio sensing, bio imaging, and drug administration. Different synthetic processes, precursors, salient properties, and applications were reviewed in this review, as well as some future prospects, obstacles, and possible solutions for future development. Because of their tunable optical characteristics and better biocompatibility, luminous carbon-based nanomaterials have sparked a lot of scientific interest. Different light emission properties of carbon are discussed in this review. Distinct synthesis procedures have resulted in different carbon dots (CDs). Summarized here. The optical properties of CDs that haven’t been synthesized yet surface doping and element doping can be used to further control it. CDs are being functionalized for an adjustable band gap. As a result of their luminescent with reduced cytotoxicity and tunable optical characteristics CDs have been thoroughly investigated in terms of their potential uses in biomedicine, such as analytical sensors, and instruments for bioimaging. Fluorescent carbon dots are a new type of nanomaterial from the carbon family. Green CDs, which have attracted a lot of attention from researchers because of their better water solubility, high biocompatibility, and eco-friendly nature when compared to chemically generated CDs, can be made from a variety of inexpensive and renewable resources. The presence of heteroatoms on the surface of green CDs in the form of amine, hydroxyl, carboxyl, or thiol functional groups, which can improve their physicochemical qualities, quantum yield, and likelihood of visible light absorption, eliminates the need for additional surface passivation.

Development of Highly Luminescent Water-Insoluble Carbon Dots by Using Calix[4]pyrrole as the Carbon Precursor and Their Potential Application in Organic Solar Cells.

Carbon dots (CDs) are carbon-based fluorescent nanomaterials that are of interest in different research areas due to their low cost production and low toxicity. Considering their unique photophysical properties, hydrophobic/amphiphilic CDs are powerful alternatives to metal-based quantum dots in LED and photovoltaic cell designs. On the other hand, CDs possess a considerably high amount of surface defects that give rise to two significant drawbacks: (1) causing decrease in quantum yield (QY), a crucial drawback that limits their utilization in LEDs, and (2) affecting the efficiency of charge transfer, a significant factor that limits the use of CDs in photovoltaic cells. In this study, we synthesized highly luminescent, water-insoluble, slightly amphiphilic CDs by using a macrocyclic compound, calix[4]pyrrole, for the first time in the literature. Calix[4]pyrrole-derived CDs (CP-DOTs) were highly luminescent with a QY of over 60% and size of around 4–10 nm with graphitic structure. The high quantum yield of CP-DOTs indicated that they had less amount of surface defects. Furthermore, CP-DOTs were used as an additive in the active layer of organic solar cells (OSC). The photovoltaic parameters of OSCs improved upon addition of CDs. Our results indicated that calix[4]pyrrole is an excellent carbon precursor to synthesize highly luminescent and water-insoluble carbon dots, and CDs derived from calix[4]pyrrole are excellent candidates to improve optoelectronic devices.

Silicon Quantum Dot-Polymer Fabry-Pérot Resonators with Narrowed and Tunable Emissions.

Luminescent silicon nanoparticles have been widely recognized as an alternative for metal-based quantum dots (QDs) for optoelectronics partly because of the high abundance and biocompatibility of silicon. To date, the broad photoluminescence line width (often >100 nm) of silicon QDs has been a hurdle to achieving competitive spectral purity and incorporating them into light-emitting devices. Herein we report fabrication and testing of straightforward configuration of Fabry-Pérot resonators that incorporates a thin layer of SiQD-polymer hybrid/blend between two reflective silver mirrors; remarkably these devices exhibit up-to-14-fold narrowing of SiQD emission and achieve a spectral bandwidth as narrow as ca. 9 nm. Our polymer-based, SiQD-containing Fabry-Pérot resonators also provide convenient spectral tunability, can be prepared using a variety of polymer hosts and substrates, and enable rigid as well as flexible devices.

Perspective on recent developments of nanomaterial based fluorescent sensors: Applications in safety and quality control of food and beverages.

As the highly toxic pollutants will seriously harm human health, it is particularly important to establish the analysis and detection technology of food pollutants. Compared with the traditional detection methods, fluorescent detection techniques based on nanomaterials trigger wide interesting because of reduced detection time, simple operation, high sensitivity and selectivity, and economic. In this review, the application of fluorescent sensors in food pollutants detection is presented. Firstly, conventional fluorescent nanomaterials including metal-based quantum dots, carbon dots, graphene quantum dots and metal nanoclusters were summarized, with emphasis on the photoluminescence mechanism. Then, the fluorescence sensors based on these nanomaterials for food pollutants detection were discussed, involving in the established methods, sensor mechanisms, sensitivity, selectivity, and practicability of fluorescence sensors. The selected analytes focus on five types of higher toxic food pollutants, including mycotoxins, foodborne pathogens, pesticide residues, antibiotic residues, and heavy metal ions. Finally, outlook on the future and potential development of fluorescence detection technology in the field of food science were proposed, including green synthesis and reusability of fluorescence probes, large-scale industrialization of sensors, nondestructive testing of samples and degradation of harmful substances.

Microfluidic synthesis of robust carbon dots-functionalized photonic crystals

Robust hybrid microbeads with multiple optical signals have garnered widespread interests for various applications. However, the inefficient physical combination and the potential toxicity of raw materials (heavy metal-based quantum dots) have limited their sustainable development. Herein, we report a microfluidic strategy to achieve the continuous production of environmentally friendly carbon dots (CDs)-functionalized photonic crystal (PC) microbeads. The efficient mass and heat transfer on microscales and the covalent bonding crosslink between CDs and poly (methyl methacrylate-butyl acrylate-methacrylic acid) (P(MMA-BA-MAA)) colloid particles ensure effective assembly of CDs-P(MMA-BA-MAA) PC microbeads in the microchannel. Benefiting from this, the CDs-P(MMA-BA-MAA) hybrid microbeads behave stable fluorescence properties, together with highly saturated and angle-independent structural color, which can overcome the optical information confusion and distortion. Meanwhile, the obtained CDs-P(MMA-BA-MAA) hybrid microbeads show dual optical signal responsiveness through the variation of fluorescence and structural color under different ionic environment. Based on this, we realize the dual ionic sensing by constructing CDs-P(MMA-BA-MAA) hybrid microbeads arrays, which broadens the application of optical hybrid microbeads. In addition, we also prepare robust hybrid film and flexible lamp belt. The obtained robust CDs-functionalized PC hybrid microbeads with various attractive optical properties have a broad prospect in optical display, sensors, biological coding and antireflection coatings.

Silicon Quantum Dots: Synthesis, Encapsulation, and Application in Light-Emitting Diodes.

Silicon quantum dots (SiQDs) are semiconductor Si nanoparticles ranging from 1 to 10 nm that hold great applicative potential as optoelectronic devices and fluorescent bio-marking agents due to their ability to fluoresce blue and red light. Their biocompatibility compared to conventional toxic Group II-VI and III-V metal-based quantum dots makes their practical utilization even more attractive to prevent environmental pollution and harm to living organisms. This work focuses on their possible use for light-emitting diode (LED) manufacturing. Summarizing the main achievements over the past few years concerning different Si quantum dot synthetic methods, LED formation and characteristics, and strategies for their stabilization by microencapsulation and modification of their surface by specific ligands, this work aims to provide guidance en route to the development of the first stable Si-based light-emitting diodes.

The effect of hydrothermal conditions on photoluminescence properties of rice husk-derived silica-carbon quantum dots for methylene blue degradation

Carbon quantum dots (CQDs) have potential to replace metal-based quantum dots due to its low-toxicity. However, studies on CQDs preparation were dominated by synthetic carbon precursors. Switching the precursors into natural ingredient is preferred since they are highly abundant and low-cost. In this study, composite of silica-carbon quantum dots (Si-CQDs) were fabricated from rice husk through a hydrothermal process. Si-CQDs with diverse properties are beneficial for its application in the future; therefore, the variation of hydrothermal conditions (i.e., temperature and pH) was performed to investigate their influence on its properties. Investigation using HRTEM, XPS, Raman spectroscopy, and UV-Vis spectroscopy suggested that hydrothermal conditions affect carbonization reaction. Hydrothermal temperature controls carbonization rate of rice husk ash, while acid addition accelerates polymerization and base addition tends to cut more carbons into small particles. The photoluminescence (PL) analysis showed that the obtained Si-CQD samples have emission in the range of 469–552 nm with various intensities. The application of sole Si-CQDs was evaluated in methylene blue (MB) degradation under visible light irradiation.

N-doped carbon dots triggered the induction of ROS-mediated cytoprotective autophagy in Hepa1-6 cells

Carbon dots (CDs) are an emerging fluorescent nano-imaging probe due to their unique characteristics, such as good conductivity, carbon-based chemical composition, and photochemical stability, which sets up the potential of outperforming the classic metal-based quantum dots (QDs). It is a timely effort to proactively investigate the biocompatibility feature of CDs with a view to safely utilize this emerging nanomaterial in biological systems. In this study, we assessed the safety profile of an in-house synthesized CDs in hepatocyte-like Hepa 1–6 cells, which represents an important target organ for CDs exposure through either particle uptake and/or accumulation and elimination from primary exposure sites post particle administration. We not only demonstrated a dose- and time-dependent compromised cell viability, but also observed the induction of autophagy at high concentration (i.e. 400 μg mL-1), authenticated by the conversion of microtubule-associated protein light chain 3 (LC3)-I to LC3-II. We attributed these changes as the protective mechanism by which the cells used to compensate for CDs-induced apoptosis and cytotoxicity. The involvement of autophagy was further confirmed because the cytotoxicity profile can be increased or reduced by the use of 3-MA (autophagy inhibitor) and NAC (ROS inhibitor), respectively. Collectively, our findings revealed dose-dependent moderate cytotoxicity in Hepa 1–6 cells. Mechanistic understanding of autophagy during the cellular process revealed the homeostasis when liver cells deal with CDs as an external insult.

Comparative life cycle assessment of bottom-up synthesis routes for carbon dots derived from citric acid and urea

Carbon dots (CDs) are carbon-based nanoparticles with remarkable luminescent properties, which have made them exciting and suitable alternatives to more traditional fluorophores and even to more recent luminescent nanomaterials (such as metal-based quantum dots). However, despite this high interest on CDs, there has been no focus on their sustainable development and fabrication, and so, there is lacking concrete data on their environmental impacts. A life cycle assessment (LCA) approach was used here to compare and understand the environmental impacts of carbon dots (CDs) obtained via six representative bottom-up synthetic strategies (cradle-to-gate). These routes consist on hydrothermal and microwave-assisted synthesis of CDs derived of citric acid (with the occasional addition of urea), which represent current trends in the synthesis of CDs. Results show that for hydrothermal synthesis the use of electricity is dominant for almost all environmental categories, while citric acid produces most impacts for microwave-assisted synthesis. A performance-based comparison was also made by rescaling results with the fluorescence quantum yield of the CDs. This approach changed the rank order of preference in all categories by a significant margin. While previous analysis indicated microwave-assisted synthesis of citric acid-derived CDs to be the most benign in environmental terms, now the option is the synthesis (either by hydrothermal or microwave-assisted treatment) of urea and citric acid-derived CDs.

Functionalized Carbon-based Quantum Dots: Optical Characterization and Potential Application as Bio-fluorophore

Carbon quantum dots (CQDs), in comparison to heavy metal-based quantum dots offer renewable, non-toxic, low cost and easy synthesis production route while having excellent physicochemical properties for biomedical or environmental use. This paper discusses development and application of functionalized carbon quantum dots from glycerol as primary carbon source and tetraethylene pentamine as functionalizing agent. As-synthesized CQDs were characterized by Fourier Transform Infrared Spectrometer (FTIR), UV-Vis Spectrophotometer and Spectrofluorometer. FTIR spectra confirmed functionalization of resulting CQDs with emission wavelength peaks at 314.18 nm and 381.15 nm and observed strong blue luminescence under UV lamp. The performance of produced CQDs as bio-fluorophore for Gram-stained bacterial models was validated. Results indicated that CQDs can effect fluoresced images but a more distinct image can be observed on S. aureus compared to E. coli. An attachment mechanism of carbon quantum dots to the bacteria surfaces was also proposed here.

The depuration fate of the mixtures of CdS/ZnS quantum dots (QDs) with different surface coatings on mangrove and wheat root epidermis: results from a novel method

BackgroundThe depuration fate of mixtures of metal-based quantum dots (QDs) in root epidermis is an important factor that determined their follow-up transportation and transformation processes in plant. However, the related mechanisms are poorly understood due to the lack of appropriate quantitative methods.ResultsIn our study, a novel method for in situ determination of mixtures of CdS/ZnS QDs with different surface coatings located on root epidermis was developed using an excitation–emission matrix combined with multi-way parallel factor analysis (PARAFAC) and n-way partial least squares (n-PLS). Then, the fates of CdS/ZnS QDs on mangrove and wheat root epidermis were investigated using the established method. During the rapid dissipation stage, intracellular and intercellular degradation of metal ions instead of transportation and rhizophytic bacteria degradation was the predominant reasons for the reduction in the CdS/ZnS QDs mixtures. However, due to vertical migration of CdS/ZnS QDs in the slow depuration stage, negative linear relationships were observed between the Ks values of oleic acid-CdS/ZnS QDs and the polarity index of the root epidermis (p < 0.05), which further indicated a difference between the single and mixture QDs.ConclusionsTo our knowledge, this study provided a new approach to investigate the fate of QDs located on root epidermis and revealed the related mechanisms.

Metal-based quantum dots: synthesis, surface modification, transport and fate in aquatic environments and toxicity to microorganisms

The intense interest in metal-based QDs is diluted by the fact that they cause risks to aquatic environments.

Quantum dot-sensitized solar cells based on directly adsorbed zinc copper indium sulfide colloids

Heavy metal-based quantum dots (QDs) have been demonstrated to behave as efficient sensitizers in QD-sensitized solar cells (QDSSCs), as attested by the countless studies and encouraging efficiencies reported so far. However, their intrinsic toxicity has arisen as a major issue for the prospects of commercialization. Here, we examine the potential of environmentally friendly zinc copper indium sulfide (ZCIS) QDs for the fabrication of liquid-junction QDSSCs by means of photoelectrochemical measurements. A straightforward approach to directly adsorb ZCIS QDs on TiO2 from a colloidal dispersion is presented. Incident photon-to-current efficiency (IPCE) spectra of sensitized photoanodes show a marked dependence on adsorption time, with longer times leading to poorer performances. Cyclic voltammograms point to a blockage of the channels of the mesoporous TiO2 film by the agglomeration of QDs as the main reason for the decrease in efficiency. Photoanodes were also subjected to the ZnS treatment. Its effects on electron recombination with the electrolyte are analyzed through electrochemical impedance spectroscopy and photopotential measurements. The corresponding results bring out the role of the ZnS coating as a barrier layer in preventing electron leakage toward the electrolyte, as argued in other QD-sensitized systems. The beneficial effect of the ZnS coating is ultimately reflected in the power conversion efficiency of complete devices, reaching values of 2%. In a more general vein, through these findings, we aim to call the attention to the potentiality of this quaternary alloy, virtually unexplored as a light harvester for sensitized devices.