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.

Enantioselective adsorption of ibuprofen enantiomers using chiral-active carbon nanoparticles induced S-α-methylbenzylamine

The chiral media is crucial to the chiral recognition and separation of enantiomers. In this study, we report the preparation of novel chiral carbon nanoparticles (CCNPs) via surface passivation using glucose as the carbon source and S-(-)-α-methylbenzylamine as the chiral ligand. The structures of the obtained CCNPs are characterized via FT-IR, Raman spectroscopy, DLS, XPS, XRD, TEM, and zeta potential analysis. These CCNPs could be employed as the chiral adsorbent and used for the enantioselective adsorption of the ibuprofen enantiomers. The results demonstrated that the CCNPs could selectively adsorb R-enantiomer from ibuprofen racemate solution and give an enantiomeric excess (e.e.) of about 50% under an optimal adsorption condition. Moreover, the regeneration efficiency of the CCNPs remained above e.e. of 43% after the fifth cycle. The present work confirmed that the prepared CCNPs show great potential in the enantioselective separation of ibuprofen racemate.

Chiral resolution of (±)-flurbiprofen using molecularly imprinted hydrazidine-modified cellulose microparticles

Flurbiprofen (FP) is one of the non-steroidal anti-inflammatory drugs (NSAIDs) commonly used to treat arthritic conditions. FP has two enantiomers: S-FP and R-FP. S-FP has potent anti-inflammatory effects, while R-FP has nearly no such effects. Herein, molecularly imprinted microparticles produced from hydrazidine-cellulose (CHD) biopolymer for the preferential uptake of S-FP and chiral resolution of (±)-FP were developed. First, cyanoethylcellulose (CECN) was synthesized, and the -CN units were transformed into hydrazidine groups. The developed CHD was subsequently shaped into microparticles and ionically interacted with the S-FP enantiomer. The particles were then imprinted after being cross-linked with glutaraldehyde, and then the S-FP was removed to provide the S-FP enantio-selective sorbent (S-FPCHD). After characterization, the optimal removal settings for the S- and R-FP enantiomers were determined. The results indicated a capacity of 125 mg/g under the optimum pH range of 5-7. Also, S-FPCHD displayed a noticeable affinity toward S-FP with a 12-fold increase compared to the R-FP enantiomer. The chiral resolution of the (±)-FP was successfully attempted using separation columns, and the outlet sample of the loading solution displayed an enantiomeric excess (ee) of 93 % related to the R-FP, while the eluent solution displayed an ee value of 95 % related to the S-FP.

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.

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.

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 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.

Amplifying inorganic chirality using liquid crystals

Chiral inorganic nanostructures have drawn extensive attention thanks to their unique physical properties as well as multidisciplinary applications. Amplifying inorganic chirality using liquid crystals (LCs) is an efficient way to enhance the parented inorganic asymmetry owing to chirality transfer. Herein, the universal synthetic methods and structural characterizations of chiral inorganic-doped LC hybrids are introduced. Additionally, the current progress and status of recent experiment and theory research about chiral interactions between inorganic nanomaterials (e.g. metal, semiconductor, perovskite, and magnetic oxide) and LCs are summarized in this review. We further present representative applications of these new hybrids in the area of encryption, sensing, optics, etc. Finally, we provide perspectives on this field in terms of material variety, new synthesis, and future practice. It is envisaged that LCs will act as a pivotal part in the amplification of inorganic chirality with versatile applications.

Rational Design of Surface-State Controlled Multicolor Cross-Linked Carbon Dots with Distinct Photoluminescence and Cellular Uptake Properties

We disclose for the first time a facile synthetic methodology for the preparation of multicolor carbon dots (CDs) from a single source barring any chromatographic separations. This was achieved via sequential intraparticle cross-linking of surface abundant carboxylic acid groups on the CDs synthesized from a precursor to control their photoluminescence (PL) spectra as well as affect their degree of cellular internalization in cancer cells. The change in PL spectra with sequential cross-linking was projected by theoretical density functional theory (DFT) studies and validated by multiple characterization tools such as X-ray photoelectron spectroscopy (XPS), PL spectroscopy, ninhydrin assay, etc. The variation in cellular internalization of these cross-linked CDs was demonstrated using inhibitor assays, confocal microscopy, and flow cytometry. We supplemented our findings with high-resolution dark-field imaging to visualize and confirm the colocalization of these CDs into distinct intracellular compartments. Finally, to prove the surface-state controlled PL mechanisms of these cross-linked CDs, we fabricated a triple-channel sensor array for the identification of different analytes including metal ions and biologically relevant proteins.

Function-adaptive clustered nanoparticles reverse Streptococcus mutans dental biofilm and maintain microbiota balance

Dental plaques are biofilms that cause dental caries by demineralization with acidogenic bacteria. These bacteria reside inside a protective sheath which makes any curative treatment challenging. We propose an antibiotic-free strategy to disrupt the biofilm by engineered clustered carbon dot nanoparticles that function in the acidic environment of the biofilms. In vitro and ex vivo studies on the mature biofilms of Streptococcus mutans revealed >90% biofilm inhibition associated with the contact-mediated interaction of nanoparticles with the bacterial membrane, excessive reactive oxygen species generation, and DNA fragmentation. An in vivo examination showed that these nanoparticles could effectively suppress the growth of S. mutans. Importantly, 16S rRNA analysis of the dental microbiota showed that the diversity and richness of bacterial species did not substantially change with nanoparticle treatment. Overall, this study presents a safe and effective approach to decrease the dental biofilm formation without disrupting the ecological balance of the oral cavity.

Magnetic Molecularly Imprinted Polymers Based on Dehydroabietylamine as Chiral Monomers for the Enantioseparation of RS-Mandelic Acid

Stereoselective adsorption of the enantiomers shows potential in the resolution of a racemate. In this work, we synthesized novel magnetic surface molecularly imprinted polymers (MIPs) on the surface of the γ-methacryloxypropyltrimethoxysilane (MPS)-modified Fe₃O₄@SiO₂ particles to utilize chiral dehydroabietylamine (DHA) as a functional monomer and R-mandelic acid as a template molecule (DHA-MIPs). We performed the resolution of mandelic acid racemate (RS-MA) via adsorption on the as-prepared MIPs. The results revealed that the MIPs have good affinity and high adsorption capacity for R-MA and show better enantioselective adsorption ability for R-MA than that for S-MA. One-stage adsorption of RS-MA on the MIPs can achieve up to 53.7% enantiomeric excess (ee) for R-MA. These help us to improve the chiral separation ability of the traditional MIPs using a chiral rather than an achiral monomer in MIP preparation. The MIPs can be employed as an economic and efficient adsorbent for chiral separation of MA racemate.

Electrospinning chiral fluorescent nanofibers from helical polyacetylene: preparation and enantioselective recognition ability

Chirality is ubiquitous in nature and closely related to the pharmacological effects of chiral drugs. Therefore, chiral recognition of molecular enantiomers becomes an important research theme. Fluorescence detection is highly sensitive and fast but has achieved only limited success in enantiomeric detection due to the lack of powerful chiral fluorescence detection materials. In this paper, a novel chiral fluorescent probe material, i.e. a chiral fluorescent nanofiber membrane, is prepared from chiral helical substituted polyacetylene by the electrospinning technique. The SEM images demonstrate the success in fabricating continuous, uniform nanofibers with a diameter of about 100 nm. Circular dichroism spectra show that the nanofibers exhibit fascinating optical activity. One of the enantiomeric chiral fluorescent membranes has chiral fluorescence recognition effects towards alanine and chiral phenylethylamine, while the other enantiomeric membrane does not. The prepared chiral fluorescent nano-materials are expected to find various applications in chirality-related fields due to their advantages such as chirality, fluorescence, and a high specific surface area. The established preparation approach also promises a potent and versatile platform for developing advanced nanofiber materials from conjugated polymers.

The Renewable and Sustainable Conversion of Chitin into a Chiral Nitrogen-Doped Carbon-Sheath Nanofiber for Enantioselective Adsorption

Well-known hard-template methods for nitrogen (N)-doped chiral carbon nanomaterials require complicated construction and removal of the template, high-temperature pyrolysis, harsh chemical treatments, and additional N-doping processes. If naturally occurring chiral nematic chitin nanostructures [(C₈ H₁₃ NO₅ )_n ] in exoskeletons were wholly transformed into an N-doped carbon, this would be an efficient and sustainable method to obtain a useful chiral nanomaterial. Here, a simple, sacrificial-template-free, and environmentally mild method was developed to produce an N-doped chiral nematic carbon-sheath nanofibril hydrogel with a surface area >300 m²  g^-1 and enantioselective properties from renewable chitin biomass. Calcium-saturated methanol physically exfoliated bulk chitin and produced a chiral nematic nanofibril hydrogel. Hydrothermal treatment of the chiral chitin hydrogel at 190 °C produced an N-doped chiral carbon-sheath nanofibril hydrogel without N-doping. This material preferentially adsorbed d-lactic acid over l-lactic acid and produced 16.3 % enantiomeric excess of l-lactic acid from a racemic mixture.

Distinct Excitonic Circular Dichroism between Wurtzite and Zincblende CdSe Nanoplatelets

Nanocrystals (NCs) with identical components and sizes but different crystal structures could not be distinguished by conventional absorption and emission spectra. Herein, we find that circular dichroism (CD) spectroscopy can easily distinguish the CdSe nanoplatelets (NPLs) with different crystal structures of wurtzite (WZ) and zincblende (ZB) with the help of chiral l- or d-cysteine ligands. In particular, the CD signs of the first excitonic transitions in WZ and ZB NPLs capped by the same chiral cysteine are opposite. Theoretic calculation supports the viewpoint of different crystal structures and surfaces arrangements between WZ and ZB NPLs contributing to this significant phenomenon. The CD peaks appearing at the first excitonic transition band of WZ or ZB CdSe NPLs are clearly assigned to the different transition polarizations along 4p_{( x,y,z),Se} → 5s_Cd or 4p_{( x,y),Se} → 5s_Cd. This work not only provides a deep insight into the origin of the optical activity inside chiral semiconductor nanomaterials but also proposes the design principle of chiral semiconductor nanocrystals with high optic activity.

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

Manipulating the chiroptical properties at the nanoscale is of great importance in stereoselective reactions, enantioseparation, self-assembly, and biological phenomena. In recent years, carbon dots have garnered great attention because of their favorable properties such as tunable fluorescence, high biocompatibility, and facile, scalable synthetic procedures. Herein, we report for the first time the unusual behavior of cyclic amino acids on the surface of carbon dots prepared via microwave-based carbonization. Various amino acids were introduced on the surface of carbon dots via EDC/NHS conjugation at room temperature. Circular dichroism results revealed that although most of the surface conjugated amino acids can preserve their chirality on negatively charged, "bare" carbon dots, the "handedness" of cyclic α-amino acids can be flipped when covalently attached on carbon dots. Moreover, these chiroptical carbon dots were found to interact with the cellular membrane or its mimic in a highly selective manner due to their acquired asymmetric selectivity. A comprehensive inhibitor study was conducted to investigate the pathway of cellular trafficking of these carbon dots. Overall, it was concluded that the chirality of the amino acid on the surface of carbon dots could regulate many of the cellular processes.

Facile Chemical Strategy to Hydrophobically Modify Solid Nanoparticles Using Inverted Micelle-Based Multicapsule for Efficient Intracellular Delivery

Theranostic nanoparticles have incredible potential for biomedical applications by enabling visual confirmation of therapeutic efficacy. Numerous issues challenge their clinical translation and are primarily related to the complex chemistry and scalability of synthesizing Nanoparticles. We report a 2-step chemical strategy for high-throughput intracellular delivery of organic and inorganic solid nanoparticles. This process takes an additional step beyond hydrophobic surface modification facilitated by inverted micelle transfer, toward the packing of multiple solid nanoparticles into a soft-shelled lipid capsule, termed the Nano-multicapsule (NMC). This technique is high yielding and does not require the complex purification steps in anaerobic/hydrophobic reactions for hydrophobic modification. To demonstrate the efficacy across different material compositions, we separately entrapped ∼10 nm gold and carbon nanoparticles (AuNP and CNP) within inverted micelles, and subsequently NMCs, then quantified their internalization in a human breast cancer cell line. For encapsulated AuNPs (NMC-AuNP), we confirmed greater cellular internalization of gold through ICP-OES and TEM analyses. Raman spectroscopic analysis of cells treated with encapsulated CNPs (NMC-CNP) also exhibited high degrees of uptake with apparent intracellular localization as opposed to free CNP treatment.

Multi-Shell Nano-CarboScavengers for Petroleum Spill Remediation

Increasingly frequent petroleum contamination in water bodies continues to threaten our ecosystem, which lacks efficient and safe remediation tactics both on macro and nanoscales. Current nanomaterial and dispersant remediation methods neglect to investigate their adverse environmental and biological impact, which can lead to a synergistic chemical imbalance. In response to this rising threat, a highly efficient, environmentally friendly and biocompatible nano-dispersant has been developed comprising a multi-shelled nanoparticle termed 'Nano-CarboScavengers' (NCS) with native properties for facile recovery via booms and mesh tools. NCS treated different forms of petroleum oil (raw and distillate form) with considerable efficiency (80% and 91%, respectively) utilizing sequestration and dispersion abilities in tandem with a ~10:1 (oil: NCS; w/w) loading capacity. In extreme contrast with chemical dispersants, the NCS was found to be remarkably benign in in vitro and in vivo assays. Additionally, the carbonaceous nature of NCS broke down by human myeloperoxidase and horseradish peroxidase enzymes, revealing that incidental biological uptake can enzymatically digest the sugar based core.

Facile synthesis and chiral recognition of block and star copolymers containing stereoregular helical poly(phenyl isocyanide) and polyethylene glycol blocks

A new Pd(ii) initiator bearing an alkyne headgroup was designed and synthesized.

Defined Host-Guest Chemistry on Nanocarbon for Sustained Inhibition of Cancer

Signal transducer and activator of transcription factor 3 (STAT-3) is known to be overexpressed in cancer stem cells. Poor solubility and variable drug absorption are linked to low bioavailability and decreased efficacy. Many of the drugs regulating STAT-3 expression lack aqueous solubility; hence hindering efficient bioavailability. A theranostics nanoplatform based on luminescent carbon particles decorated with cucurbit[6]uril is introduced for enhancing the solubility of niclosamide, a STAT-3 inhibitor. The host-guest chemistry between cucurbit[6]uril and niclosamide makes the delivery of the hydrophobic drug feasible while carbon nanoparticles enhance cellular internalization. Extensive physicochemical characterizations confirm successful synthesis. Subsequently, the host-guest chemistry of niclosamide and cucurbit[6]uril is studied experimentally and computationally. In vitro assessments in human breast cancer cells indicate approximately twofold enhancement in IC50 of drug. Fourier transform infrared and fluorescence imaging demonstrate efficient cellular internalization. Furthermore, the catalytic biodegradation of the nanoplatforms occur upon exposure to human myeloperoxidase in short time. In vivo studies on athymic mice with MCF-7 xenograft indicate the size of tumor in the treatment group is half of the controls after 40 d. Immunohistochemistry corroborates the downregulation of STAT-3 phosphorylation. Overall, the host-guest chemistry on nanocarbon acts as a novel arsenal for STAT-3 inhibition.

Functional carbon nanodots for multiscale imaging and therapy

As an emerging class of carbon nanomaterials, carbon dots (CDs) have garnered many researchers' interests in the past decade due to their excellent biocompatibility, replete surface functional groups, water dispersibility, and unique photoluminescence. These extraordinary properties have opened new avenues for their advanced application in cell labeling, bioimaging, drug delivery, sensors, and energy-related devices. In this paper, we critically review recent advances in the synthetic strategies and the application of CDs for biological purposes, specifically, imaging and therapy. Finally, a perspective has been given on the potential challenges facing the translation of these materials from the bench to the market. WIREs Nanomed Nanobiotechnol 2017, 9:e1436. doi: 10.1002/wnan.1436 For further resources related to this article, please visit the WIREs website.