Chirality Inversion on the Carbon Dot Surface via Covalent Surface Conjugation of Cyclic α-Amino Acid Capping Agents

Colloidal Chiral Carbon Dots: An Emerging System for Chiroptical Applications

Chiral CDots (c-CDots) not only inherit those merits from CDots but also exhibit chiral effects in optical, electric, and bio-properties. Therefore, c-CDots have received significant interest from a wide range of research communities including chemistry, physics, biology, and device engineers. They have already made decent progress in terms of synthesis, together with the exploration of their optical properties and applications. In this review, the chiroptical properties and chirality origin in extinction circular dichroism (ECD) and circularly polarized luminescence (CPL) of c-CDots is briefly discussed. Then, the synthetic strategies of c-CDots is summarized, including one-pot synthesis, post-functionalization of CDots with chiral ligands, and assembly of CDots into chiral architectures with soft chiral templates. Afterward, the chiral effects on the applications of c-CDots are elaborated. Research domains such as drug delivery, bio- or chemical sensing, regulation of enzyme-like catalysis, and others are covered. Finally, the perspective on the challenges associated with the synthetic strategies, understanding the origin of chirality, and potential applications is provided. This review not only discusses the latest developments of c-CDots but also helps toward a better understanding of the structure-property relationship along with their respective applications.

Green and Red Emissive N,O-Doped Chiral Carbon Dots Functionalized with l-Cysteine

Although chirality plays an important role in the natural world, it has also attracted much scientific attention in nanotechnology, in particular, spintronics and bioapplications. Chiral carbon dots (CDs) are promising nanoparticles for sensing and bioimaging since they are biocompatible, ecofriendly, and free from toxic elements. Herein, green and red emissive chiral CDs are fabricated via surface modification treatment of achiral CDs at room temperature. After modification with l-cysteine molecules, the treated CDs demonstrate an intense chiral signal in the region of 200-300 nm with a dissymmetry factor up to 2.3 × 10-4 and high photoluminescence quantum yields of 19% and 15% for green and red emission bands, respectively. These CDs preserve their chiral signal in different ion systems, such as those with pH changes or in the presence of metal ions, along with remarkably low cytotoxicity, making them potential candidates for use as photoluminescent labels for biological objects.

Preparation of Chiral Carbon Quantum Dots and its Application

Chiral carbon quantum dots (cCQDs) , as a new type of carbon nano-functional material with tunable emission wavelength, superior photostability, low toxicity, biocompatibility and chirality, are playing an increasingly important role in the fields of chemistry, biology and medicine. This paper reviews the preparation methods (one-step and two-step), optical properties (UV, fluorescence, chirality) and applications in chiral catalysis, chiral recognition, targeted imaging as well as other fields, while lists some of the issues and challenges in the research of chiral carbon quantum dots. Finally, due to its good fluorescence and other properties, it is expected that chiral carbon quantum dots will have broad commercial prospects in future applications.

Recent Progress on Chiral Carbon Dots: Synthetic Strategies and Biomedical Applications

The discovery of chiral carbon dots (Ch-CDs) has opened up an exciting new research direction in the field of carbon dots. It not only retains the chirality of the precursor and exhibits highly symmetric chiral optical properties but also has properties such as chemical stability, antibacterial and antitumor properties, and good biocompatibility of carbon dots. Based on these advantages, the application of Ch-CDs in the biomedical field has attracted significant interest among researchers. However, a comprehensive review of the selection of precursors for Ch-CDs, preparation methods, and applications in biomedical fields is still lacking. Here, we summarize their precursor selection and preparation methods based on recent reports on Ch-CDs and provide the first comprehensive review for specific applications in biomedical engineering, such as biosensing, bioimaging, drug carriers, antibacterial and antibiofilm, and enzyme activity modulation. Finally, we discuss application prospects and challenges that need to be overcome. We hope this review will provide valuable guidance for researchers to prepare novel Ch-CDs and facilitate their application in biomedical engineering.

Chiral Polymer Dots Show Unexpected Versatility of Highly Ordered Self-Assembly into Chiroptical Liquid Crystals, Ultra-Thin Films, and Long-Ribbons

Compared to the organic counterparts, chiral self-assembly of nanomaterials shows persistency to kinetic factors such as solvent environments, and consequently, dynamic modulation of self-assembly and functions remains major challenge. Here, it is shown that alkylated, chiral polymer dots (c-PDs) give highly ordered self-assemblies with amplified chirality adaptive to solvent environments, and one-to-many hierarchical aggregation can be realized. The c-PDs tended to self-assemble into nanohelices with cubic packing in the solid state, which, thanks to the thermo-responsiveness, transformed into thermic liquid crystals upon heating. Cotton effects and circularly polarized luminescence evidenced the chirality transfer from central chirality to supramolecular chirality. At the air-water interface, the c-PDs are self-assembled into monolayers, which further stack into multiple layers with chirality transfer and highly ordered packing. In addition, undergoing a good/poor solvent exchange, the c-PDs afforded ultra-long microribbons up to a length scale of millimeters, which are constituted by the bilayer lamellar stacking. The versatile chiral self-assembly modalities with long-range ordered packing arrays of carbonized c-PDs via solvent strategy are realized. This feature is comparable to the organic species, although the c-PDs have no atomic precise structures. This work would surely expand the applications of quantum dot ordered self-assembly with adaptiveness to kinetic factors.

A narrative review on the role of carbon nanoparticles in oncology

The lymphatic system is the first site of metastasis for most tumors and is a common reason for the failure of cancer therapy. The lymphatic system's anatomical properties make it difficult to deliver chemotherapy agents at therapeutic concentrations while avoiding systemic toxicity. Carbon nanoparticles offer a promising alternative for identifying and transporting therapeutic molecules. The larger diameter of lymphatic vessels compared to the diameter of blood vessels, allows carbon nanoparticles to selectively enter the lymphatic system once administered subcutaneously. Carbon nanoparticles stain tumor-draining lymph nodes black following intratumoral injection, making them useful in sentinel lymph node mapping. Drug-loaded carbon nanoparticles allow higher concentrations of chemotherapeutics to accumulate in regional lymph nodes while decreasing plasma drug accumulation. The use of carbon nanoparticles for chemotherapy delivery has been associated with lower mortality, fewer histopathology changes in vital organs, and lower serum concentrations of hepatocellular enzymes. This review will focus on the ability of carbon nanoparticles to target the lymphatics as well as their current and potential applications in sentinel lymph node mapping and oncology treatment regimens. This article is categorized under: Implantable Materials and Surgical Technologies > Nanoscale Tools and Techniques in Surgery.

A Multifunctional, Highly Biocompatible, and Double-Triggering Caramelized Nanotheranostic System Loaded with Fe3O4 and DOX for Combined Chemo-Photothermal Therapy and Real-Time Magnetic Resonance Imaging Monitoring of Triple Negative Breast Cancer

Purpose

Owing to lack of specific molecular targets, the current clinical therapeutic strategy for triple negative breast cancer (TNBC) is still limited. In recent years, some nanosystems for malignancy treatment have received considerable attention. In this study, we prepared caramelized nanospheres (CNSs) loaded with doxorubicin (DOX) and Fe₃O₄ to achieve the synergistic effect of combined therapy and real-time magnetic resonance imaging (MRI) monitoring, so as to improve the diagnosis and therapeutic effect of TNBC.

Methods

CNSs with biocompatibility and unique optical properties were prepared by hydrothermal method, DOX and Fe₃O₄ were loaded on it to obtain Fe₃O₄/DOX@CNSs nanosystem. Characteristics including morphology, hydrodynamic size, zeta potentials and magnetic properties of Fe₃O₄/DOX@CNSs were evaluated. The DOX release was evaluated by different pH/near-infrared (NIR) light energy. Biosafety, pharmacokinetics, MRI and therapeutic treatment of Fe₃O₄@CNSs, DOX and Fe₃O₄/DOX@CNSs were examined in vitro or in vivo.

Results

Fe₃O₄/DOX@CNSs has an average particle size of 160 nm and a zeta potential of 27.5mV, it demonstrated that Fe₃O₄/DOX@CNSs is a stable and homogeneous dispersed system. The hemolysis experiment of Fe₃O₄/DOX@CNSs proved that it can be used in vivo. Fe₃O₄/DOX@CNSs displayed high photothermal conversion efficiency, extensive pH/heat-induced DOX release. 70.3% DOX release is observed under the 808 nm laser in the pH = 5 PBS solution, obviously higher than pH = 5 (50.9%) and pH = 7.4 (less than 10%). Pharmacokinetic experiments indicated the t1/2β, and AUC_0-t of Fe₃O₄/DOX@CNSs were 1.96 and 1.31 -fold higher than those of DOX solution, respectively. Additionally, Fe₃O₄/DOX@CNSs with NIR had the greatest tumor suppression in vitro and in vivo. Moreover, this nanosystem demonstrated distinct contrast enhancement on T2 MRI to achieve real-time imaging monitoring during treatment.

Conclusion

Fe₃O₄/DOX@CNSs is a highly biocompatible, double-triggering and improved DOX bioavailability nanosystem that combines chemo-PTT and real-time MRI monitoring to achieve integration of diagnosis and treatment of TNBC.

Antibacterial Carbon Dots-Based Composites

The emergence and global spread of bacterial resistance to conventionally used antibiotics have highlighted the urgent need for new antimicrobial agents that might replace antibiotics. Currently, nanomaterials hold considerable promise as antimicrobial agents in anti-inflammatory therapy. Due to their distinctive functional physicochemical characteristics and exceptional biocompatibility, carbon dots (CDs)-based composites have attracted a lot of attention in the context of these antimicrobial nanomaterials. Here, a thorough assessment of current developments in the field of antimicrobial CDs-based composites is provided, starting with a brief explanation of the general synthesis procedures, categorization, and physicochemical characteristics of CDs-based composites. The many processes driving the antibacterial action of these composites are then thoroughly described, including physical destruction, oxidative stress, and the incorporation of antimicrobial agents. Finally, the obstacles that CDs-based composites now suffer in combating infectious diseases are outlined and investigated, along with the potential applications of antimicrobial CDs-based composites.

Facile synthesis of nitrogen-doped carbon dots as sensitive fluorescence probes for selective recognition of cinnamaldehyde and l-Arginine/l-Lysine in living cells

The disorder of amino acid metabolism and the abuse of small molecule drugs pose serious threats to public health. However, due to the limitations of existing detection technologies in sensing cinnamaldehyde (CAL) and l-Arginine/l-Lysine (l-Arg/l-Lys), there is an urgent need to develop new sensing strategies to meet the severe challenges currently facing. Herein, nitrogen-doped carbon dots (N-CDs) were developed using a simple one-pot hydrothermal carbonization method. These N-CDs exhibited numerous distinctive characteristics such as excellent photoluminescence, high water dispersibility, favorable biocompatibility, and superior chemical inertness. Strikingly, the as-prepared CDs as a highly efficient fluorescent probe possessed significant sensitivity and selectivity toward CAL and l-Arg/l-Lys over other analytes with a low detection limit of 58 nM and 16 nM/18 nM, respectively. The fluorescence of N-CDs could be quenched by CAL through an electron transfer process. Then, the strong electrostatic interaction between l-Arg/l-Lys and N-CDs induced the efficient fluorescence recovery. More importantly, the outstanding biosafety and excellent analyte-responsive fluorescence characteristics of N-CDs have also been verified in living cells as well as in serum and urine. Overall, the N-CDs had a wide application prospect in the diagnosis of amino acid metabolic diseases and small molecule drug sensing.

Self-Assembly of Cholesteryl Carbon Dots with Circularly Polarized Luminescence in Solution and Solvent-Free Phases

Incorporating carbon dots (CDs) into chiral self-assemblies will endow the system with intriguing optoelectronic, catalytic, and chiroptical activities. Utilization of chiral substituents to rationally manipulate chiral self-assembly of the CDs, however, remains a major challenge. In this work, cholesteryl monoprotected ethylene diamine was used as a precursor to synthesize CDs with a cholesteryl periphery. The rigid, apolar, and chiral cholesteryl facilitates the polarity-sensitive self-assembly of CDs in organic solvents, showing circularly polarized luminescence (CPL) with dissymmetry g-factor at 10^-3 grade. Temperature-variable characterizations suggested the formation of thermotropic liquid crystals within a wide temperature range driven by the interdigitation of cholesteryl segments, which further anchor the graphitic CD cores into tetragonal and cubic arrays. Self-assembly in a solvent-free state arouses sufficient chirality transfer and boosted the g-factors to 10^-2 order of magnitude. This work unveils multiple and chiral self-assembly of CDs controlled by the cholesteryl substituents, exhibiting variable architectures and tunable CPL.

Chiral Carbon Dots: Synthesis and Applications in Circularly Polarized Luminescence, Biosensing and Biology

Chiral carbon dots (CDs) are a novel luminescent zero-dimensional carbon-based nanomaterial with chirality. They not only have the advantages of good biocompatibility, multi-color-emission, easy functionalization, but also exhibits highly symmetrical chiral optical characteristics, which broadens their applicability to enantioselectivity of some chiral amino acids like cysteine and lysine, asymmetric catalysis as well as biomedicine in gene expression and antibiosis. In addition, the exploration of the excited state chirality of CDs has developed its excellent circularly polarized luminescence (CPL) properties, opening up a new application scenario like recognition of chiral light sources and anti-counterfeit printing with information encryption. This review mainly focuses on the mature synthesis approaches of chiral CDs, including chiral ligand method and supramolecular self-assembly method, then we consider emerging applications of chiral CDs in CPL, biosensing and biological effect. Finally, we concluded with a perspective on the potential challenges and future opportunities of such fascinating chiral CDs.

Chiral chromatography and surface chirality of carbon nanoparticles

Chiral carbon nanoparticles (CNPs) represent a rapidly evolving area of research for optical and biomedical technologies. Similar to small molecules, applications of CNPs as well as fundamental relationships between their optical activity and structural asymmetry would greatly benefit from their enantioselective separations by chromatography. However, this technique remains in its infancy for chiral carbon and other nanoparticles. The possibility of effective separations using high performance liquid chromatography (HPLC) with chiral stationary phases remains an open question whose answer can also shed light on the components of multiscale chirality of the nanoparticles. Herein, we report a detailed methodology of HPLC for successful separation of chiral CNPs and establish a path for its future optimization. A mobile phase of water/acetonitrile was able to achieve chiral separation of CNPs derived from L- and D-cysteine denoted as L-CNPs and D-CNPs. Molecular dynamics simulations show that the teicoplanin-based stationary phase has a higher affinity for L-CNPs than for D-CNPs, in agreement with experiments. The experimental and computational findings jointly indicate that chiral centers of chiral CNPs are present at their surface, which is essential for the multiple applications of these chiral nanostructures and equally essential for interactions with biomolecules and circularly polarized photons.

Revealing the nature of optical activity in carbon dots produced from different chiral precursor molecules

Carbon dots (CDs) are light-emitting nanoparticles that show great promise for applications in biology and medicine due to the ease of fabrication, biocompatibility, and attractive optical properties. Optical chirality, on the other hand, is an intrinsic feature inherent in many objects in nature, and it can play an important role in the formation of artificial complexes based on CDs that are implemented for enantiomer recognition, site-specific bonding, etc. We employed a one-step hydrothermal synthesis to produce chiral CDs from the commonly used precursors citric acid and ethylenediamine together with a set of different chiral precursors, namely, L-isomers of cysteine, glutathione, phenylglycine, and tryptophan. The resulting CDs consisted of O,N-doped (and also S-doped, in some cases) carbonized cores with surfaces rich in amide and hydroxyl groups; they exhibited high photoluminescence quantum yields reaching 57%, chiral optical signals in the UV and visible spectral regions, and two-photon absorption. Chiral signals of CDs were rather complex and originated from a combination of the chiral precursors attached to the CD surface, hybridization of lower-energy levels of chiral chromophores formed within CDs, and intrinsic chirality of the CD cores. Using DFT analysis, we showed how incorporation of the chiral precursors at the optical centers induced a strong response in their circular dichroism spectra. The optical characteristics of these CDs, which can easily be dispersed in solvents of different polarities, remained stable during pH changes in the environment and after UV exposure for more than 400 min, which opens a wide range of bio-applications.

Chiral carbon dots: synthesis, optical properties, and emerging applications

Carbon dots are luminescent carbonaceous nanoparticles that can be endowed with chiral properties, making them particularly interesting for biomedical applications due to their low cytotoxicity and facile synthesis. In recent years, synthetic efforts leading to chiral carbon dots with other attractive optical properties such as two-photon absorption and circularly polarized light emission have flourished. We start this review by introducing examples of molecular chirality and its origins and providing a summary of chiroptical spectroscopy used for its characterization. Then approaches used to induce chirality in nanomaterials are reviewed. In the main part of this review we focus on chiral carbon dots, introducing their fabrication techniques such as bottom-up and top-down chemical syntheses, their morphology, and optical/chiroptical properties. We then consider emerging applications of chiral carbon dots in sensing, bioimaging, and catalysis, and conclude this review with a summary and future challenges.

Rational Design of Multicolor-Emitting Chiral Carbonized Polymer Dots for Full-Color and White Circularly Polarized Luminescence

Light-emitting chiral carbonized polymer dots (Ch-CPDs) are attracting great interest because of their extraordinary photonic properties, but modulating their band-gap emission, especially at long wavelength, and maintaining their chiral structure to achieve multicolor, high-emission Ch-CPDs remains challenging. Reported here for the first time is the synthesis of red- and multicolor-emitting Ch-CPDs using the common precursors L-/D-tryptophan and o-phenylenediamine, and a solvothermal approach at one temperature. The quantum yield of the Ch-CPDs was between 31 % and 54 %. Supramolecular self-assembly provided multicolor-emitting Ch-CPDs showing novel circularly polarized luminescence, with the highest dissymmetric factor (g_lum ) of 1×10^-2 . Importantly, circularly polarized white-emitting CPDs were fabricated for the first time by tuning the mixing ratio of the three colored Ch-CPDs in a gel. This strategy affords exciting opportunities for designing functional chiroptical materials.

Chiral carbon dots based on L/D-cysteine produced via room temperature surface modification and one-pot carbonization

Since chirality is one of the phenomena often occurring in nature, optically active chiral compounds are important for applications in the fields of biology, pharmacology, and medicine. With this in mind, chiral carbon dots (CDs), which are eco-friendly and easy-to-obtain light-emissive nanoparticles, offer great potential for sensing, bioimaging, enantioselective synthesis, and development of emitters of circularly polarized light. Herein, chiral CDs have been produced via two synthetic approaches using a chiral amino acid precursor l/d-cysteine: (i) surface modification treatment of achiral CDs at room temperature and (ii) one-pot carbonization in the presence of chiral precursor. The chiral signal in the absorption spectra of synthesized CDs originates not only from the chiral precursor but from the optical transitions attributed to the core and surface states of CDs. The use of chiral amino acid molecules in the CD synthesis through carbonization results in a substantial (up to 8 times) increase in their emission quantum yield. Moreover, the synthesized CDs show two-photon absorption which is an attractive feature for their potential bioimaging and sensing applications.

You Don't Learn That in School: An Updated Practical Guide to Carbon Quantum Dots

Carbon quantum dots (CQDs) have started to emerge as candidates for application in cell imaging, biosensing, and targeted drug delivery, amongst other research fields, due to their unique properties. Those applications are possible as the CQDs exhibit tunable fluorescence, biocompatibility, and a versatile surface. This review aims to summarize the recent development in the field of CQDs research, namely the latest synthesis progress concerning materials/methods, surface modifications, characterization methods, and purification techniques. Furthermore, this work will systematically explore the several applications CQDs have been subjected to, such as bioimaging, fluorescence sensing, and cancer/gene therapy. Finally, we will briefly discuss in the concluding section the present and future challenges, as well as future perspectives and views regarding the emerging paradigm that is the CQDs research field.

Noncovalent Fluorescent Biodot-Protein Conjugates with Well-Preserved Native Functions for Improved Sweat Glucose Detection

To overcome the traditional issues of protein labeling, we report herein an effective approach for noncovalent conjugation of the biomolecule-derived fluorescent nanodots (biodot) to functional proteins without the addition of chemical linkers for biosensor development. The as-prepared fluorescent biodot-protein conjugates are very stable near physiological pH, exhibiting excellent photostability and thermal stability. More importantly, the native functions of proteins, including drug binding and enzymatic activities, are well-preserved after conjugating with biodots. The optimized protein conjugation strategy is then applied to prepare biodot-glucose oxidase (GOx) fluorescent sensing probes for sweat glucose detection. Results show that the as-prepared sensing probes could achieve better assay performance than those covalent conjugates as demonstrated herein. Specifically, GOx in the noncovalently bound conjugates are able to catalyze the oxidation of glucose effectively, which generates hydrogen peroxide as a byproduct. In the presence of Fe²⁺, Fenton reaction takes place to produce hydroxyl radicals and Fe³⁺, leading to significant fluorescence quenching of biodots on the conjugates. This simple one-step enzymatic assay in a single probe achieves a wide linear range of 25-1000 μM (R² = 0.99) with a low detection limit of 25 μM. Furthermore, negligible interference is observed in the complex artificial sweat sample for accurate glucose quantification, achieving an excellent recovery rate of 100.5 ± 2.2%. This work provides a facile conjugation method that is generally applicable to a wide range of proteins, which will help to accelerate future development of multifunctional fluorescent probes to provide optical signals with unique protein functions (e.g., enzymatic, recognition, etc.) for biomedical sensing and imaging.

Optical nanoprobes for chiral discrimination

Chiral recognition can be achieved by exploiting chiral properties of nanoparticles within various colorimetric and luminescent sensing systems.