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.

Recent Advances in Synthesis, Modification, Characterization, and Applications of Carbon Dots

Although there is significant progress in the research of carbon dots (CDs), some challenges such as difficulty in large-scale synthesis, complicated purification, low quantum yield, ambiguity in structure-property correlation, electronic structures, and photophysics are still major obstacles that hinder the commercial use of CDs. Recent advances in synthesis, modification, characterization, and applications of CDs are summarized in this review. We illustrate some examples to correlate process parameters, structures, compositions, properties, and performances of CDs-based materials. The advances in the synthesis approach, purification methods, and modification/doping methods for the synthesis of CDs are also presented. Moreover, some examples of the kilogram-scale fabrication of CDs are given. The properties and performance of CDs can be tuned by some synthesis parameters, such as the incubation time and precursor ratio, the laser pulse width, and the average molar mass of the polymeric precursor. Surface passivation also has a significant influence on the particle sizes of CDs. Moreover, some factors affect the properties and performance of CDs, such as the polarity-sensitive fluorescence effect and concentration-dependent multicolor luminescence, together with the size and surface states of CDs. The synchrotron near-edge X-ray absorption fine structure (NEXAFS) test has been proved to be a useful tool to explore the correlation among structural features, photophysics, and emission performance of CDs. Recent advances of CDs in bioimaging, sensing, therapy, energy, fertilizer, separation, security authentication, food packing, flame retardant, and co-catalyst for environmental remediation applications were reviewed in this article. Furthermore, the roles of CDs, doped CDs, and their composites in these applications were also demonstrated.

DNA-Mediated Assembly of Carbon Nanomaterials

Carbon nanomaterials (CNMs) have attracted extensive attentions on account of their superior electrical, mechanical, optical, and biological properties. However, the dimensional limit and irregular arrangement have hampered their further application. It is necessary to find an easy, efficient and controllable way to assemble CNMs into well-ordered array. DNA nanotechnology, owning to the advantages of precise programmability, highly structural predictability and spatial addressability, has been widely applied in the assembly of CNMs. Summarizing the progress and achievements in this field will be of great value to related studies. Herein, based on the different dimensions of CNMs containing 0-dimensional (0D) carbon dots (CDs), fullerenes, 1-dimensional (1D) carbon nanotubes (CNTs) and 2-dimensional (2D) graphene, we introduced the conjugation strategies between DNA and CNMs, their different assembly methods and their applications. In addition, we also discuss the existing challenges and future opportunities in the field.

Carbon dots: synthesis, properties and biomedical applications

Carbon dots (CDs) are a new type of carbon nanomaterial that have unique physical and chemical properties, good biocompatibility, low toxicity, and easy surface functionalization, making them widely used in biological imaging, environmental monitoring, chemical analysis, targeted drug delivery, disease diagnosis, therapy, etc. In this review, our content is mainly divided into four parts. In the first part, we focused on the preparation methods of CDs, including arc discharge, laser ablation, electrochemical oxidation, chemical oxidation, combustion, hydrothermal/solvent thermal, microwave, template, method etc. Next, we summarized methods of CD modification, including heteroatom doping and surface functionalization. Then, we discussed the optical properties of CDs (ultraviolet absorption, photoluminescence, up-conversion fluorescence, etc.). Lastly, we reviewed the common applications of CDs in biomedicine from the aspects of in vivo and in vitro imaging, sensors, drug delivery, cancer theranostics, etc. Furthermore, we also discussed the existing problems and the future development direction of CDs.

Morphological analysis of chromium in carbon quantum dots pairs Co-doped with zirconium and nitrogen and their applications in imaging of living cells

As a new nanomaterial in the biochemistry field, carbon quantum dots (CDs) have been widely applied by scientists. In this study, CDs co-doped with zirconium and nitrogen (Zr-N-CDs) were synthesized quickly with lemon, ethylenediamine, and zirconium chloride through a hydrothermal method. The yield of Zr-N-CDs reached as high as 82.7%. The Zr-N-CDs showed outstanding water solubility in aqueous solution. The formation of Zr-N-CDs was verified by characterization technologies, such as high-resolution transmission electron microscopy (HRTEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Moreover, the optical properties of Zr-N-CDs were investigated through fluorophotometer and ultraviolet spectroscopy. The synthesized Zr-N-CDs were applied to test hexavalent chromium (Cr (VI)), which showed a good linear relationship with the fluorescence quenching of Zr-N-CDs. The limit of detection was 0.52 µM. An analytical method for Cr morphology in natural water areas was developed in this experiment. The sensor showed good stability. The results demonstrate that the sensor detected 98.35%-100.9% Cr (VI) recovery rate in water samples. Based on the cytotoxicity of Zr-N-CDs to human cervical cancer cells (HeLa cells), the Zr-N-CDs had no evident cytotoxicity. The applications of Zr-N-CDs in bioimaging of cells were determined through laser scanning confocal microscopy.

Size-focusing results in highly photoluminescent sulfur quantum dots with a stable emission wavelength

Sulfur quantum dots (SQDs) are a new kind of functional nanomaterial, but several challenges still exist in relation to their synthesis and application, such as low-yield and time-consuming synthetic methods, low photoluminescence quantum yields (PLQYs), and the non-selectivity of their detection mechanisms. Herein, we report the drastic enhancement of the fluorescence performance of water-soluble SQDs via the one-pot synthesis of size-focusing QDs using ultrasound microwave radiation. The synthetic period has been greatly shortened to 2 h via the present process. Notably, the proposed SQDs exhibit a highly stable emission wavelength with a record high PLQY of 58.6%. The mechanistic study indicates that size-focusing is a key factor relating to the proposed high-performance SQDs. As they also have robust stability, the proposed SQDs show a wide range of potential applications. Inspired by the characteristic properties of the SQDs and specific analytes, a simple SQD-based fluorescence sensing platform, via a redox-reaction-mediated mechanism, has been successfully developed for the rapid and selective detection of Ce(iv). In addition, this system has been effectively applied to some Ce(iv)-related biological assays, such as ascorbic acid (AA) analysis. This work is an important breakthrough in the SQD field, opening up avenues for solving the challenging problems relating to SQD-based probes, enriching the fundamental understanding of them, and greatly extending their applications, especially in biomedicine.

DNA thermotropic liquid crystals controlled by positively charged catanionic bilayer vesicles

We report DNA thermotropic liquid crystal (TLC) formation by positively charged catanionic surfactant bilayer vesicles. The properties of DNA TLCs were found to be manipulated by both the chemical structures of cationic and anionic surfactants and the DNA amount. Positively charged catanionic bilayer vesicles bond to negative DNA sites resulting in the transition from vesicles to long range ordered lamellar crystals of DNA-catanionic surfactants, as confirmed by cryo- and freeze-fracture (FF) TEM observations and small-angle X-ray scattering (SAXS) measurements.

Review of the Application of Nanovesicles and the Human Interstitial Fluid in Gastrointestinal Premalignant Lesion Detection, Diagnosis, Prognosis and Therapy

Premalignant lesions arise from cells that abnormally proliferate and have a tendency to become cancerous. Developing methods to specifically target and remove these premalignant lesions is imperative to the prevention of malignant progression into gastrointestinal (GI) tumors. However, accurate detection and diagnosis of GI precancerous lesions is challenging, as these lesions show little or no structural change. Thus, this prevents early intervention and reduces the success rate of therapy. In this review, we performed a systematic analysis of the technological advancements in the combined application of nanovesicles (NVs) and the human interstitial fluid (HIF) to specifically target GI premalignant lesions. NVs, which include quantum dots (QDs), are small membranous vehicles of a nanometer diameter that are widely used as drug delivery vectors, therapeutic effectors and diagnostic sensors. HIF is the fluid that is present in human interstitial tissues (HITs) in which signaling molecules and agents travel and can be found throughout the body. HIF is exploited by tumor cells for their invasion, migration and spread. Because the HITs span the entire submucosa of the gastrointestinal tract, they have been increasingly targeted in GI tumor therapy. The challenges involved in the combined application of NVs and HIF in the detection, diagnosis, prognosis and therapy of GI premalignant lesions are also discussed.

Fluorescent carbon dots functionalization

Carbon dots (CDs), as a new type of luminescent zero-dimensional carbon nanomaterial, have been applied in a variety of fields. Currently, functionalization of CDs is an extremely useful method for effectively tuning their intrinsic structure and surface state. Heteroatom doping and surface modification are two functionalization strategies for improving the photophysical performance and broadening the range of applications for fluorescent CDs. Heteroatom doping in CDs can be used to tune their intrinsic properties, which has received significant research interests because of its simplicity. Surface modification can be applied for varying active sites and the functional groups on the CDs surface, which can endow fluorescent CDs with the unique properties resulting from functional ligand. In this review, we summarize the structural and physicochemical properties of functional CDs. We focused our review on the latest developments in functionalization strategies for CDs and discuss the detailed characteristics of different functionalization methods. Ultimately, we hope to inform researchers on the latest progress in functionalization of CDs and provide perspectives on future developments for functionalization of CDs and their potential applications.

Influence of the degree of oligomerization of surfactants on the DNA/surfactant interaction

The interaction between calf thymus DNA, ctDNA, and a series of oligomeric surfactants derived from N-benzyl-N,N-dimethyl-N-(1-dodecyl)ammonium chloride is investigated. The influence of the surfactants' degree of oligomerization (2, 3 and 4) on the ctDNA/surfactant interaction is studied, as well as the effect of the structure of the spacer group linking the individual surfactant fragments. In particular, the effect of the distance between the positive charges and the hydrophobic chains within the oligomers on these interactions was examined, by using the three positional isomers (i.e., ortho-, meta-, and para-) with the rigid xylidene moiety as spacer. Results show that the dimeric ("gemini") surfactants are much more efficient in the inversion of the nucleic acid charge than the single-chained (monomeric) surfactant. Whereas the ortho - isomer causes a partial condensation, the meta - and para - isomers can completely condense ctDNA. The meta - and para - isomers of the trimeric surfactants can also completely condense the polynucleotide. In contrast, the tetrameric surfactant investigated does not change the morphology of the nucleic acid from an elongated coil into a compacted form, in spite of effectively inverting the nucleic acid's charge in their complex. Accordingly, the capacity for ctDNA compaction of oligomeric surfactants is not simply correlated to their degree of oligomerization, but depends on a complex balance of the number and relative distance of cationic charges and/or hydrophobic tails in the surfactants for effectively interacting with the nucleic acid to form the appropriate complex. This information will help to design more effective cationic surfactants as non-viral vectors for gene therapy.

Vesicle formation by ultrashort alkyl-phosphonic acids and serine in aqueous solutions

Vesicles possess unique biofilm structures and offer biomimetic advantages for drug and gene delivery. Herein, we report the spontaneous vesicle formation from ultrashort alkyl-phosphonic acids in the presence of amino acids. The aggregation characteristics and self-assembly structures of vesicles in aqueous solution were investigated by using dynamic light scattering, zeta potential, and cryo-transmission electron microscopy. We combined low-field nuclear magnetic resonance and Fourier transform infrared spectroscopy to study the H-proton-induced multilamellar vesicle formation. When we increased the molar fraction of serine, stable and closed spherical vesicles were formed at relatively low critical micelle concentrations. This transition of the self-assembled structure indicates that vesicle formation occurs when the chain length and the magnitude of the surface charge cause a fluctuation in the volume of the vesicle. Density functional theory reveals the critical role of the mixed alkyl-phosphonic acid/amino acid-enhanced electrostatic attraction between the head groups and hydrogen bonds associated with the aggregated states.

Eu3+-Controlled Fluorescent Bilayer Vesicles

By appropriate substitution, polyoxometalates (POMs) can be modified to be organic-inorganic supramolecules (OISMs) that are nonaqueous or water soluble and form aggregates in solution. Here, we report a new OISM, (TBA)₃POM-PPCT, that can self-assemble to form bilayer vesicles controlled by Eu³⁺ in nonaqueous solution. Dynamic light scattering, transmission and scanning electron microscopy techniques, and atomic force microscopy clearly demonstrated the controllable formation of stable bilayer vesicles with an average hydrodynamic radius of about 510 nm. Because of the coordination between (TBA)₃POM-PPCT and Eu³⁺, the stable vesicles possess fluorescence, determined by studying fluorescence spectra, and show highly selective response to Cu²⁺, allowing them to function as an ion-detecting platform to Cu²⁺.

Fluorescent hybrid nanospheres induced by single-stranded DNA and magnetic carbon quantum dots

Assembled DNA nanospheres were preparedviaself-assembly with magnetic CQDGd as the building blocks and negatively charged ssDNA as the assembly units.

Magnetic networks of carbon quantum dots and Ag particles

Self-assembly exploits a facile non-covalent way to couple structurally different building blocks for creating soft materials with synergetic novel properties and functions. Taking advantage of magneto-properties from magnetic surfactants as well as versatile functional ligand formed by carbon quantum dots with cysteine (cys-CQDs), the magnetic network materials were firstly constructed by using magnetic surfactants and cys-CQDs as self-assembly building blocks. Counterions of Br^-, [GdCl₃Br]^-, [HoCl₃Br]^- in surfactants could control the morphology of magnetic network structures, and the concentration of magnetic surfactants manoeuvres a versatile scenario of self-assembly behavior. Self-assembly of cys-CQDs and CTAHo brought out a 10-fold increase in magnetic moment of CTAHo. The fluorescent property of carbon quantum dots firstly served as an effective indicator element to dissect the collective effect in self-assembly process. For the sake of capturing the target sequence-specific DNA molecules, in situ growth of Ag nanoparticles (AgNPs) upon the magnetic network structures was realized by synergetically electrostatic and coordinated interaction of carboxyl groups and Ag ions. The magnetic Ag self-assemblies anchored thiol-containing DNA, serving as a magnetic separation booster for the target sequence-specific DNA molecules under an applied magnetic field, which will bring light on designing magneto-functional self-assembly materials according to practical application requirements.

A review on nanostructured carbon quantum dots and their applications in biotechnology, sensors, and chemiluminescence

Carbon quantum dots (CQDs) are a member of carbon nanostructures family which have received increasing attention for their photoluminescence (PL), physical and chemical stability and low toxicity. The classical semiconductor quantum dots (QDs) are semiconductor particles that are able to emit fluorescence by excitation. The CQDs is mainly referred to photoluminescent carbon nanoparticles less than 10 nm, with surface modification or functionalization. Contrary to other carbon nanostructures, CQDs can be synthesized and functionalized fast and easily. The fluorescence origin of the CQDs is a controversial issue which depends on carbon source, experimental conditions, and functional groups. However, PL emissions originated from conjugated π-domains and surface defects have been proposed for the PL emission mechanisms of the CQDs. These nanostructures have been used as nontoxic alternatives to the classical heavy metals containing semiconductor QDs in some applications such as in-vivo and in-vitro bio-imaging, drug delivery, photosensors, chemiluminescence (CL), and etc. This paper will introduce CQDs, their structure, and PL characteristics. Recent advances of the application of CQDs in biotechnology, sensors, and CL is comprehensively discussed.

Carbon quantum dot-based fluorescent vesicles and chiral hydrogels with biosurfactant and biocompatible small molecule

In recent years, it is heartening to witness that carbon quantum dots (CQDs), a rising star in the family of carbon nanomaterials, have displayed tremendous applications in bioimaging, biosensing, drug delivery, optoelectronics, photovoltaics and photocatalysis. However, the investigations toward self-assembly of CQDs are still in their infancy. The participation of CQDs can bring additional functions to supramolecular self-assemblies, with photoluminescent property as the most exciting aspect. Here, we introduce CQDs into two types of classic colloidal systems containing low molecular weight surfactant and gelator to construct fluorescent vesicles and chiral hydrogels. The CQD-based vesicles were constructed through electrostatic interaction between the positively charged CQDs with peripherally substituted imidazolium cations and a negatively-charged biosurfactant, i.e., sodium deoxycholate (NaDC). The chiral hydrogels were prepared by increasing the concentration of NaDC and addition of a tripeptide (glutathione, GSH). It was found that both the hydrogels and corresponding xerogels are highly photoluminescent. A solid sensing system was prepared by coating a uniform layer of the hydrogel onto the silica gel plates by doctor blade technique followed by air-drying, which was then utilized to semiquantitatively detect Cu2+ in aqueous solutions.

Nanocapsules of Magnetic Au Self-Assembly for DNA Migration and Secondary Self-Assembly

To endow valuable responsiveness to self-assemblies of Au nanoparticles (Au NPs), the magnetic Au nanoparticles (Au NPs)/C₁₆H₃₃(CH₃)₃N⁺[CeCl₃Br]^- (CTACe) mixtures were first prepared by using an emulsion self-assembly of a magnetic surfactant, C₁₆H₃₃(CH₃)₃N⁺[CeCl₃Br]^-. A versatile morphology of self-assemblies of Au NPs could be controlled by the counterions in surfactants including [CeCl₃Br]^-, [FeCl₃Br]^-, and Br^- as well as solvent. In particular, the magnetic counterion, [CeCl₃Br]^-, can induce self-growth of Au NPs in an emulsion self-assembly process due to the oxidability of [CeCl₃Br]^-. It enhances the rigidity of Au NPs/CTACe scaffolds template compared with Au NPs/hexadecyltrimethylammonium bromide. [CeCl₃Br]^- engaged Au NPs/CTACe with fascinating capability of conglutination and targeted migration of DNA (150 μmol/L) under a magnet field. The conglutination capability of the DNA molecules can increase to 39.8% by adopting the magnetic strategy when using Au NPs/CTACe as a magnetic booster. Au NPs/CTACe mixtures can ideally self-assemble to be scaffolds, providing abundant conjugation sites of surface charges. Magnetic Au NPs/CTACe can serve as a template scaffold to secondary self-assemble with DNA (40 mmol/L) outside, producing smooth-faced and hollow DNA nanocapsules. We believe that the creative Au NPs/CTACe/DNA nanocapsules will extend the biological application field of Au NPs assemblies.