Palladium catalyzed C(sp3)-H alkylation of 8-methylquinolines with aziridines: access to functionalized γ-quinolinylpropylamines

Palladium-catalyzed directed site-selective C(sp3)-H alkylation of 8-methylquinolines has been accomplished using aziridine as the alkylating source via a sequential C-H and C-N bond activation process. The site selectivity, functional group tolerance and possible late-stage modifications are important practical features of this reaction.

Gold catalysis in quinoline synthesis

Quinolines are biologically and pharmaceutically important N-heterocyclic aromatic compounds, which have broad applications in medicinal chemistry. Thus, their efficient synthesis has attracted extensive attention, and a broad range of synthetic strategies have been established. Of note, gold-catalyzed methodologies for the synthesis of quinolines have greatly advanced this field. Various gold-catalyzed intermolecular annulation reactions, such as annulations of aniline derivatives with carbonyl compounds or alkynes, annulations of anthranils with alkynes, and annulations based on A3-coupling reactions, as well as intramolecular cyclization reactions of azide-tethered alkynes, 1,2-diphenylethynes, and 2-ethynyl N-aryl indoles, have been developed. This review provides an overview of this exciting research area. Typical achievements in reaction methodologies and plausible reaction mechanisms are summarized.

Carbon dots as potential candidate for photocatalytic treatment of dye wastewater

Water is the utmost important element for the existence of life. In recent decades, water resources have become highly contaminated by a variety of pollutants, especially toxic dyes that are harmful to both living beings and environment. Hence, there is an urgent need to develop more effective methods than traditional wastewater treatment approaches for treatment of hazardous dyes. Herein, we have addressed the various aspects related to the effective and economically feasible method for photocatalytic degradation of these dyes employing carbon dots. The photocatalysts based on carbon dots including those mediated from biomass have many superiorities over conventional methods such as utilization of economically affordable, non-toxic, rapid reactions, and simple post-processing steps. The current study will also facilitate better insight into the understanding of photocatalytic treatment of dye-polluted wastewater for future wastewater treatment studies. Additionally, the possible mechanistic pathways of photocatalytic dye decontamination, several challenges, and future perspectives have also been summarized.

Red emitting carbon dots: surface modifications and bioapplications

Quantum dots (QDs), and carbon quantum dots (CDs) in particular, have received significant attention for their special characteristics. These particles, on the scale of several nanometers, are often produced using simple and green methods, with naturally occurring organic precursors. In addition to facile production methods, CDs present advantageous applications in the field of medicine, primarily for bioimaging, antibacterial and therapeutics. Also, CDs present great potential for surface modification through methods like doping or material mixing during synthesis. However, the bulk of current literature focuses on CDs emitting in the blue wavelengths which are not very suitable for biological applications. Red emitting CDs are therefore of additional interest due to their brightness, photostability, novelty and deeper tissue penetration. In this review article, red CDs, their methods of production, and their biological applications for translational research are explored in depth, with emphasis on the effects of surface modifications and doping.

Chemical Sensors using Single-Molecule Electrical Measurements

Driven by the digitization and informatization of contemporary society, electrical sensors are developing toward minimal structure, intelligent function, and high detection resolution. Single-molecule electrical measurement techniques have been proven to be capable of label-free molecular recognition and detection, which opens a new strategy for the design of efficient single-molecule detection sensors. In this review, we outline the main advances and potentials of single-molecule electronics for qualitative identification and recognition assays at the single-molecule level. Strategies for single-molecule electro-sensing and its main applications are reviewed, mainly in the detection of ions, small molecules, oligomers, genetic materials, and proteins. This review summarizes the remaining challenges in the current development of single-molecule electrical sensing and presents some potential perspectives for this field.

Supramolecular Chemistry of Carbon-Based Dots Offers Widespread Opportunities

Carbon dots are an emerging class of nanomaterials that has recently attracted considerable attention for applications that span from biomedicine to energy. These photoluminescent carbon nanoparticles are defined by characteristic sizes of <10 nm, a carbon-based core and various functional groups at their surface. Although the surface groups are widely used to establish non-covalent bonds (through electrostatic interactions, coordinative bonds, and hydrogen bonds) with various other (bio)molecules and polymers, the carbonaceous core could also establish non-covalent bonds (ππ stacking or hydrophobic interactions) with π-extended or apolar compounds. The surface functional groups, in addition, can be modified by various post-synthetic chemical procedures to fine-tune the supramolecular interactions. Our contribution categorizes and analyzes the interactions that are commonly used to engineer carbon dots-based materials and discusses how they have allowed preparation of functional assemblies and architectures used for sensing, (bio)imaging, therapeutic applications, catalysis, and devices. Using non-covalent interactions as a bottom-up approach to prepare carbon dots-based assemblies and composites can exploit the unique features of supramolecular chemistry, which include adaptability, tunability, and stimuli-responsiveness due to the dynamic nature of the non-covalent interactions. It is expected that focusing on the various supramolecular possibilities will influence the future development of this class of nanomaterials.

BSA-templated synthesis of Ir/Gd bimetallic oxide nanotheranostics for MR/CT imaging-guided photothermal and photodynamic synergistic therapy

Precision medicine urges the development of theranostics which can efficiently integrate precise diagnosis and effective therapy. In this study, a facile synthesis of Ir/Gd bimetallic oxide nanotheranostics (termed BSA@Gd₂O₃/IrO₂ NPs) with good biocompatibility was demonstrated using a biomineralization method where bovine serum albumin (BSA) served as a versatile template. BSA@Gd₂O₃/IrO₂ NPs exhibited high longitudinal relaxivity (5.2 mM^-1 s^-1) and X-ray absorption capability (14.5 Hu mM^-1), illustrating them to be a good contrast agent for magnetic resonance (MR) and computed tomography (CT) dual-modal imaging. Moreover, BSA@Gd₂O₃/IrO₂ NPs can act as not only a photothermal conversion agent with ultrahigh efficiency (66.7%) as well as a good photosensitizer, but also an effective catalase to decompose endogenous H₂O₂ to produce O₂, thus relieving hypoxia and enhancing the phototherapeutic effect. Both in vitro and in vivo experiments demonstrated the high effectiveness of BSA@Gd₂O₃/IrO₂ NPs in MR/CT dual-modal imaging and photothermal and photodynamic synergistic tumor treatments. This work sheds new light on the development of versatile nanotheranostic systems using mild and robust biomineralization methods.

Transition-metal-free approach to quinolines via direct oxidative cyclocondensation reaction of N,N-dimethyl enaminones with o-aminobenzyl alcohols

A transition-metal-free method for the construction of 3-substituted or 3,4-disubstituted quinolines from readily available N,N-dimethyl enaminones and o-aminobenzyl alcohols is reported. The direct oxidative cyclocondensation reaction tolerates broad functional groups, allowing the efficient synthesis of various quinolines in moderate to excellent yields. The reaction involves a C (sp3)-O bond cleavage and a C=N bind and a C=C bond formation during the oxidative cyclization process, and the mechanism was proposed.

Applications of Carbon Dots for the Photocatalytic and Electrocatalytic Reduction of CO2

The photocatalytic and electrocatalytic conversion of CO2 has the potential to provide valuable products, such as chemicals or fuels of interest, at low cost while maintaining a circular carbon cycle. In this context, carbon dots possess optical and electrochemical properties that make them suitable candidates to participate in the reaction, either as a single component or forming part of more elaborate catalytic systems. In this review, we describe several strategies where the carbon dots participate, both with amorphous and graphitic structures, in the photocatalysis or electrochemical catalysis of CO2 to provide different carbon-containing products of interest. The role of the carbon dots is analyzed as a function of their redox and light absorption characteristics and their complementarity with other known catalytic systems. Moreover, detailed information about synthetic procedures is also reviewed.

Synthesis and Applications of Asymmetric Catalysis Using Chiral Ligands Containing Quinoline Motifs

In the past decade, asymmetric synthesis of chiral ligands containing quinoline motifs, a family of natural products displaying a broad range of structural diversity and their metal complexes have become the most significant methodology for the generation of enantiomerically pure compounds of biological and pharmaceutical interest. This review provides comprehensive insight on the plethora of nitrogen-based chiral ligands containing quinoline motifs and organocatalysts used in asymmetric synthesis. However, it is circumscribed to the synthesis of quinoline-based chiral ligands and metal complexes, and their applications in asymmetric synthesis as a homogeneous and heterogeneous catalyst.

Gadolinium-porphyrin based polymer nanotheranostics for fluorescence/magnetic resonance imaging guided photodynamic therapy

Nanotheranostics for fluorescence/magnetic resonance (FL/MR) dual-modal imaging guided photodynamic therapy (PDT) are highly desirable in precision and personalized medicine. In this study, a facile non-covalent electrostatic interaction induced self-assembly strategy is developed to effectively encapsulate gadolinium porphyrin (Gd-TCPP) into homogeneous supramolecular nanoparticles (referred to as Gd-PNPs). Gd-PNPs exhibit the following advantages: (1) excellent FL imaging property, high longitudinal relaxivity (16.157 mM^-1 s^-1), and good singlet oxygen (¹O₂) production property; (2) excellent long-term colloidal stability, dispersity and biocompatibility; and (3) enhanced in vivo FL/MR imaging guided tumor growth inhibition efficiency for CT 26 tumor-bearing mice. This study provides a new strategy to design and synthesize metalloporphyrin-based nanotheranostics for imaging-guided cancer therapy with enhanced theranostic properties.

Carbon dots for cancer nanomedicine: a bright future

Cancer remains one of the main causes of death in the world. Early diagnosis and effective cancer therapies are required to treat this pathology. Traditional therapeutic approaches are limited by lack of specificity and systemic toxicity. In this scenario, nanomaterials could overcome many limitations of conventional approaches by reducing side effects, increasing tumor accumulation and improving the efficacy of drugs. In the past few decades, carbon nanomaterials (i.e., fullerenes, carbon nanotubes, and carbon dots) have attracted significant attention of researchers in various scientific fields including biomedicine due to their unique physical/chemical properties and biological compatibility and are among the most promising materials that have already changed and will keep changing human life. Recently, because of their functionalization and stability, carbon nanomaterials have been explored as a novel tool for the delivery of therapeutic cancer drugs. In this review, we present an overview of the development of carbon dot nanomaterials in the nanomedicine field by focusing on their synthesis, and structural and optical properties as well as their imaging, therapy and cargo delivery applications.

One-pot synthesis of fluorescent nitrogen and sulfur-carbon quantum dots as a sensitive nanosensor for trimetazidine determination

Water-soluble and highly stable N,S-doped CQDs (N,S-CQDs) were synthesized using a low-cost strategy with citric acid and thiosemicarbazide in one step for use as a fluorescent nanosensor. The achieved N,S-CQDs produced strong emission at 446 nm upon excitation at 370 nm and a high quantum yield of 58.5%. The quenching effect on the prepared N,S-CQDs was utilized for determination of trimetazidine (TMZ) spectrofluorimetrically over a wide linear range 0.04-0.5 μM (0.0106-0.133 μg ml^-1 ) and a low limit of detection of 0.01 μM (0.002 μg ml^-1 ). Furthermore, CDs were used as a simple and rapid fluorescent probe to determine TMZ in its pharmaceutical formulations as well as in human plasma. The method was tested in compliance with International Council for Harmonisation guidelines. The results obtained were compared statistically with those given for a reported method showing no significant variation regards accuracy and precision.

Photoluminescent Nanomaterials for Medical Biotechnology

Creation of various photoluminescent nanomaterials has significantly expanded the arsenal of approaches used in modern biomedicine. Their unique photophysical properties can significantly improve the sensitivity and specificity of diagnostic methods, increase therapy effectiveness, and make a theranostic approach to treatment possible through the application of nanoparticle conjugates with functional macromolecules. The most widely used nanomaterials to date are semiconductor quantum dots; gold nanoclusters; carbon dots; nanodiamonds; semiconductor porous silicon; and up-conversion nanoparticles. This paper considers the promising groups of photoluminescent nanomaterials that can be used in medical biotechnology: in particular, for devising agents for optical diagnostic methods, sensorics, and various types of therapy.

Insights and Perspectives Regarding Nanostructured Fluorescent Materials toward Tackling COVID-19 and Future Pandemics

The COVID-19 outbreak has exposed the world's preparation to fight against unknown/unexplored infectious and life-threatening pathogens. The unavailability of vaccines, slow or sometimes unreliable real-time virus/bacteria detection techniques, insufficient personal protective equipment (PPE), and a shortage of ventilators and many other transportation equipments have further raised serious concerns. Material research has been playing a pivotal role in developing antimicrobial agents for water treatment and photodynamic therapy, fast and ultrasensitive biosensors for virus/biomarkers detection, as well as for relevant biomedical and environmental applications. It has been noticed that these research efforts nowadays primarily focus on the nanomaterials-based platforms owing to their simplicity, reliability, and feasibility. In particular, nanostructured fluorescent materials have shown key potential due to their fascinating optical and unique properties at the nanoscale to combat against a COVID-19 kind of pandemic. Keeping these points in mind, this review attempts to give a perspective on the four key fluorescent materials of different families, including carbon dots, metal nanoclusters, aggregation-induced-emission luminogens, and MXenes, which possess great potential for the development of ultrasensitive biosensors and infective antimicrobial agents to fight against various infections/diseases. Particular emphasis has been given to the biomedical and environmental applications that are linked directly or indirectly to the efforts in combating COVID-19 pandemics. This review also aims to raise the awareness of researchers and scientists across the world to utilize such powerful materials in tackling similar pandemics in future.

Thermally Stable Fluorogenic Zn(II) Sensor Based on a Bis(benzimidazole)pyridine-Linked Phenyl-Silsesquioxane Polymer

A 2,6-bis(2-benzimidazolyl) pyridine-linked silsesquioxane-based semi-branched polymer was synthesized, and its photophysical and metal-sensing properties have been investigated. The polymer is thermally stable up to 285 °C and emits blue in both solid and solution state. The emission of the polymer is sensitive to pH and is gradually decreased and quenched upon protonation of the linkers. The initial emission color is recoverable upon deprotonation with triethylamine. The polymer also shows unique spectroscopic properties in both absorption and emission upon long-term UV irradiation, with red-shifted absorption and emission not present in a simple blended system of phenylsilsesquioxane and linker, suggesting that a long-lived energy transfer or charge separated state is present. In addition, the polymer acts as a fluorescence shift sensor for Zn(II) ions, with red shifts observed from 464 to 528 nm, and reversible binding by the introduction of a competitive ligand such as tetrahydrofuran. The ion sensing mechanism can differentiate Zn(II) from Cd(II) by fluorescence color shifts, which is unique because they are in the same group of the periodic table and possess similar chemical properties. Finally, the polymer system embedded in a paper strip acts as a fluorescent chemosensor for Zn(II) ions in solution, showing its potential as a solid phase ion extractor.

Quantum dots as nanosensors for detection of toxics: a literature review

Great advances have been made in sensor-based methods for chemical analysis owing to their high sensitivity, selectivity, less testing time, and minimal usage of chemical reagents. Quantum Dots (QDs) having excellent optical properties have been thoroughly explored for variety of scientific applications wherein light plays an important role. In recent years, there have been an increasing number of publications on the applications of QDs as photoluminescent nanosensors for the detection of chemicals and biomolecules. However, there has been hardly any publication describing the use of QDs in the detection of various toxic chemicals at one place. Hence, a literature survey has been made on the applications of QDs as chemosensors for the detection of gaseous, anionic, phenolic, metallic, drug-overdose, and pesticide poison so as to open a new perspective towards the role of sensors in analytical toxicology. In this review, the QD-based analysis of biospecimens for poison detection in clinical and forensic toxicology laboratories is highlighted.

Red-emission carbon dots-quercetin systems as ratiometric fluorescent nanoprobes towards Zn2+ and adenosine triphosphate

Carbon dots (CDs) emitting red fluorescence (610 nm) were synthesized by solvent thermal treatment of p-phenylenediamine in toluene. Upon 440 nm excitation, quercetin (QCT) alone endowed slight effects on the red fluorescence of CDs. Once Zn²⁺ was further introduced, the QCT-Zn²⁺ complex was quickly formed. This complex absorbs excitation light and emits bright green fluorescence at 480 nm. The red fluorescence of CDs was greatly quenched owing to the inner-filter effect. The ratio of fluorescence intensity at 480 nm and 610 nm (I₄₈₀/I₆₁₀) gradually increases with increasing concentration (c) of Zn²⁺. Al³⁺ exhibits the same phenomen like Zn²⁺. Fluoride ions form a more stable complex with Al³⁺ than QCT-Al³⁺ complex but have a negligible effect on the QCT-Zn²⁺ complex. The possible interference of Al³⁺ on Zn²⁺ can thus be avoided by adding certain amount of F^-. The CD-QCT-F^- system was constructed as a ratio-metric fluorescent nanoprobe toward Zn²⁺ with determination range of 0.14-30 μM and limit of detection (LOD) of 0.14 μM. Due to the stronger affinity of adenosine triphosphate (ATP) to Zn²⁺ than QCT, the I₄₈₀/I₆₁₀ value of CD-QCT-F^--Zn²⁺ system gradually decreases with increasing c_ATP. The ratiometric fluorescent nanoprobe toward ATP was established with detection ranges of 0.55-10 and 10-35 μM and a LOD of 0.55 μM. The above two probes enable the quantitative determination of Zn²⁺ and ATP in tap and lake water samples with satisfactory recoveries. Graphical abstract Schematic representation of the ratiometric fluorescent nanoprobes based on the carbon dots (CDs)-quercetin (QCT) system towards Zn²⁺ and adenosine triphosphate (ATP) with high selectivity and sensitivity.

Coumarin-Modified Graphene Quantum Dots as a Sensing Platform for Multicomponent Detection and Its Applications in Fruits and Living Cells

In this work, coumarin derivatives (C) are used to enhance the fluorescence of graphene quantum dots (GQDs) by covalently linking the carboxyl groups on the edge of the GQD sheet. The as-synthesized coumarin-modified graphene quantum dots (C-GQDs) have a uniform particle size with an average diameter of 3.6 nm. Simultaneously, the C-GQDs have strong fluorescence emission, excellent photostability, and high fluorescence quantum yield. C-GQDs and CN- can form a C-GQDs+CN- system due to deprotonation and/or intermolecular interactions. The introduced hydroquinone (HQ) is oxidized to benzoquinone (BQ), and the interaction between BQ and the C-GQDs+CN- system could lead to fluorescence enhancement of C-GQDs. Meanwhile, the redox reaction between BQ and ascorbic acid (AA) can be used for quantitative detection of AA with CN- and HQ being used as substrates. Based on the above mechanism, C-GQDs are developed as a multicomponent detection and sensing platform, and the detection limits for CN-, HQ, and AA were 4.7, 2.2, and 2.2 nM, respectively. More importantly, satisfactory results were obtained when the platform was used to detect CN-, HQ, and AA in living cells and fresh fruits.

Carbon dot-based fluorometric optical sensors: an overview

Fluorescent carbon dots (CDs) are a new class of carbon nanomaterials and have demonstrated excellent optical properties, good biocompatibility, great aqueous solubility, low cost, and simple synthesis. Since their discovery, various synthesis methods using different precursors were developed, which were mainly classified as top-down and bottom-up approaches. CDs have presented many applications, and this review article mainly focuses on the development of CD-based fluorescent sensors. The sensing mechanisms, sensor design, and sensing properties to various targets are summarized. Broad ranges of detection, including temperature, pH, DNA, antibiotics, cations, cancer cells, and antibiotics, have been discussed. In addition, the challenges and future directions for CDs as sensing materials are also presented.

Near-infrared emissive carbon dots with 33.96% emission in aqueous solution for cellular sensing and light-emitting diodes

Near-infrared emissive carbon dots (CDs) were synthesized by hydrothermal method. The as-prepared CDs exhibited a relatively high quantum yield (QY) of 33.96% in an aqueous solution, and the peak toward the near-infrared fluorescence reached 685 nm. The CDs exhibited pH-sensitive characteristics under strong acidic conditions. Even at pH = 0, the as-prepared CDs retained a high fluorescence intensity, which proved that they possessed good acid resistance. More importantly, the CDs were sensitive to the Fe³⁺ changes in living cells. In addition, they could also be used for white and red emissive LEDs. This discovery will expand the use of aqueous-phase high QY CDs in the field of living cell sensing and imaging.

Review of Carbon and Graphene Quantum Dots for Sensing

Carbon and graphene quantum dots (CQDs and GQDs), known as zero-dimensional (0D) nanomaterials, have been attracting increasing attention in sensing and bioimaging. Their unique electronic, fluorescent, photoluminescent, chemiluminescent, and electrochemiluminescent properties are what gives them potential in sensing. In this Review, we summarize the basic knowledge on CQDs and GQDs before focusing on their application to sensing thus far followed by a discussion of future directions for research into CQDs- and GQD-based nanomaterials in sensing. With regard to the latter, the authors suggest that with the potential of these nanomaterials in sensing more research is needed on understanding their optical properties and why the synthetic methods influence their properties so much, into methods of surface functionalization that provide greater selectivity in sensing and into new sensing concepts that utilize the virtues of these nanomaterials to give us new or better sensors that could not be achieved in other ways.

N-doped carbon dots covalently functionalized with pillar[5]arenes for Fe3+ sensing

Fluorescent N-doped carbon dots (CN-dots) covalently functionalized with carboxylatopillar[5]arene (CP[5]), namely CCDs, have been prepared the first time. Compared with CN-dots without pillarene units, the newly constructed fluorescent CCDs could recognize Fe³⁺ with high selectivity. Therefore, such CCDs can potentially serve as a promising chemical sensor for Fe³⁺ ions.

A critical comparison of lanthanide based upconversion nanoparticles to fluorescent proteins, semiconductor quantum dots, and carbon dots for use in optical sensing and imaging

The right choice of a fluorescent probe is essential for successful luminescence imaging and sensing and especially concerning in vivo and in vitro applications, the development of new classes have gained more and more attention in the last years. One of the most promising class are upconversion nanoparticles (UCNPs)-inorganic nanocrystals capable to convert near-infrared light in high energy radiation. In this review we will compare UCNPs with other fluorescent probes in terms of (a) the optical properties of the probes, such as their brightness, photostability and excitation wavelength; (b) their chemical properties such as the dispersibility, stability under experimental or physiological conditions, availability of chemical modification strategies for labelling; and (c) the potential toxicity and biocompatibility of the probe. Thereby we want to provide a better understanding of the advantages and drawbacks of UCNPs and address future challenges in the design of the nanocrystals.

Electrical detection of trace zinc ions with an extended gate-AlGaN/GaN high electron mobility sensor

In this report, we have developed a high sensitivity zinc ion (Zn2+) detection method based on a Schiff base functionalized extended gate (EG)-AlGaN/GaN high electron mobility (HEMT) sensor. The complexation reaction between the Schiff base and the zinc ions would cause surface potential change on the extended gate, and achieve the purpose of zinc ion detection. Compared with conventional methods, the Schiff base functionalized EG-AlGaN/GaN high electron mobility sensor showed a rapid response (less than 10 seconds) and the limit of detection (LOD) was 1 fM. At the same time, the real-time detection of zinc ion concentration ranging from 1 fM to 1 μM showed good linearity (R2 = 0.9962). These results indicated that it provides a promising real-time detection method for trace-free zinc ion trace detection.

Recent advances in carbon quantum dot (CQD)-based two dimensional materials for photocatalytic applications

This review presents up-to-date research findings and critical insights on trending topics of pristine CQDs and CQDs-based 2D nanomaterial composites.