Phosphorus and Nitrogen Dual-Doped Hollow Carbon Dot as a Nanocarrier for Doxorubicin Delivery and Biological Imaging

Carbon dots for ratiometric fluorescence detection of morin

The B,N dual-doped carbon dots (B,N-CDs) for ratiometric fluorescence detection the morin were prepared from sodium tetraborate and polyethyleneimine through the single-step hydrothermal method. The B,N-CDs exhibited the optimum excitation and emission wavelength at 340 nm and 467 nm, respectively. Interestingly, the intensities of emission peak at 467 nm of B,N-CDs reduced meanwhile a new peak emerged at 560 nm with the continuous addition of morin, which revealed the ratio fluorescence characteristic between F_560nm/F_467nm and morin concentration with the linearity range and detection limit of 14.5-32.5 μmol/L and 0.3 μmol/L (S/N = 3), respectively. The interference of common antibiotics and remedies could be ignored when the concentration of morin was detected by the B,N-CDs, which demonstrating the outstanding selectivity. Furthermore, the proposed fluorescence method is used to detect morin in urine with recoveries are 99.8-104.5%. The results of this research indicate the feasibility and practicality of B,N-CDs as an effective fluorescent probe for the determination of morin.

Multifunctional N-Doped Carbon Dots for Bimodal Detection of Bilirubin and Vitamin B12, Living Cell Imaging, and Fluorescent Ink

A N-doped carbon dot (NCD) has been synthesized via a simplistic one-step hydrothermal technique using l-aspartic acid and 3,6-diaminoacridine hydrochloride. The NCDs exhibit a high quantum yield (22.7%) and excellent optical stability in aqueous media. Additionally, NCDs display good solid-state yellowish-green emission and are suitable for security ink applications. The remarkable fluorescence (FL) properties of NCDs are further applied to develop a multifunctional sensor for bilirubin (BR) and vitamin B₁₂ (VB12) via fluorescence quenching. We have systematically studied the FL quenching mechanisms of the two analytes. The primary quenching mechanism of BR is via the Förster resonant energy transfer (FRET) pathway facilitated by the H-bonding network between the hydrophilic moieties existing at the surface of BR and NCDs. In contrast, the inner filter effect (IFE) is mainly responsible for the recognition of VB12. The practicability of the nanoprobe NCDs is further tested in real-sample analysis for BR (human serum and urine samples) and VB12 (VB12 tablets, human serum, and energy drink) with a satisfactory outcome. The in vitro competency is also verified in the human cervical cancer cell line (HeLa cell) with negligible cytotoxicity and significant biocompatibility. This result facilitates the application of NCDs for bioimaging and recognition of VB12 in a living organism.

Preparation of microfluidic-based pectin microparticles loaded carbon dots conjugated with BMP-2 embedded in gelatin-elastin-hyaluronic acid hydrogel scaffold for bone tissue engineering application

The controlled delivery of the bone morphogenetic protein-2 (BMP-2) with tracking ability would overcome most of the side effects linked to the burst release and uncontrolled delivery of this growth factor for bone regeneration. Herein, BMP-2-conjugated carbon dots (CDs) was used as noninvasive detection platforms to deliver BMP-2 for therapeutic applications where osteogenesis and bioimaging are both required. With this in mind, the present work aimed to develop a controlled BMP-2-CDs release system using composite scaffolds containing BMP-2-CDs loaded pectin microparticles, which had been optimized for bone regeneration. By using microfluidic approach, we encapsulated BMP-2-CDs in pectin microparticles with narrow size distribution and then incorporated into composite scaffolds composed of gelatin, elastin, and hyaluronic acid. The BMP-2-CDs was released from the composite scaffolds in a sustained fashion for up to 21 days exhibited a high controlled delivery capacity. When tested in vitro with MG-63 cells, these extraction mediums showed the intercellular uptake of BMP-2-CDs and enhanced biological properties and pro-osteogenic effect. By utilizing the pectin microparticles carrying BMP-2-CDs as promising bioimaging agents for growth factor delivery and by tuning the composition of the scaffolds, this platform has immense potential in the field of bone tissue regeneration.

Nitrogen-doped carbon dots for wash-free imaging of nucleolus orientation

Carbon dots (CDs) are a rising star in the field of cellular imaging, especially cytoplasmic imaging, attributing to the super-stable optical performance and ultra-low biological toxicity. Nucleolus can accurately reflect the expression state of a cell and is strongly linked to the occurrence and development of many diseases, so exploring bran-new CDs for nucleolus-orientation imaging with no-wash technology has important theoretical value and practical significance. Herein, nitrogen-doped carbon dots (N-CDs) with green fluorescence (the relative fluorescence quantum yield of 24.4%) was fabricated by the hydrothermal treatment of m-phenylenediamine and p-aminobenzoic acid. The N-CDs possess small size, bright green fluorescence, abundant surface functional groups, excellent fluorescence stability and good biocompatibility, facilitating that the N-CDs are an excellent imaging reagent for cellular imaging. N-CDs can particularly bind to RNA in nucleoli to enhance their fluorescence, which ensures that the N-CDs can be used in nucleolus-orientation imaging with high specificity and wash-free technique. This study demonstrates that the N-CDs have a significant feasibility to be used for nucleolus-orientation imaging in biomedical analysis and clinical diagnostic applications.

Azithromycin detection in cells and tablets by N,S co-doped carbon quantum dots

Azithromycin (AZM)¹ is one of the most widely used antibiotics. AZM abuse is easy to cause great harm to human body, so developing a rapid and sensitive method to detect AZM is of great importance. Herein, 3-aminothiophenol as only reaction precursor, nitrogen and sulfur co-doped carbon quantum dots (N,S-CQDs)² were fabricated by one-step hydrothermal carbonization method. All characteristics demonstrate that N,S-CQDs possess good water solubility, high fluorescence stability and low cytotoxicity. Without being disturbed by amino acids and drugs, the most interesting finding is that AZM can efficiently quench the fluorescence of N,S-CQDs by a synergistic effect of electrostatic interaction and static quenching. A fluorescent probe for the detection of AZM was constructed with high selectivity and good sensitivity, achieving two linear ranges of 2.5-32.3 μM and 37.2-110 μM and a limit of detection of 0.76 µM. The proposed fluorescent method was used for the detection of AZM in cells with fulfilling results. More importantly, the fluorescent probe was successfully used to the detection of AZM in tablets and human urine with recovery rate and relative standard deviations of 98.2-104.8% and 0.04-3.46%, respectively, which was confirmed by the standard method of HPLC-UV. This finding illustrates the usefulness and feasibility of N,S-CQDs as an effective fluorescent probe for the detection of AZM in tablets and human urine, which is helpful for supervising and guiding pharmacy.

An Improved Synthesis of Water-Soluble Dual Fluorescence Emission Carbon Dots from Holly Leaves for Accurate Detection of Mercury Ions in Living Cells

Background

Carbon dots (CDs) emitting near-infrared fluorescence were recently synthesized from green leaves. However, the Hg²⁺ detection of CDs was limited because of the insufficient water solubility, low fluorescence and poor stability.

Methods

Dual fluorescence emission water-soluble CD (Dual-CD) was prepared through a solvothermal method from holly leaves and low toxic PEI_1.8k. PEG was further grafted onto the surface to improve the water solubility and stability.

Results

The Dual-CD solution can emit 487 nm and 676 nm fluorescence under single excitation and exhibit high quantum yield of 16.8%. The fluorescence at 678 nm decreased remarkably while the emission at 470 nm was slightly affected by the addition of Hg²⁺. The ratiometric Hg²⁺ detection had a wide linear range of 0–100 μM and low detection limit of 14.0 nM. In A549 cells, there was a good linear relation between F₄₈₇/F₆₇₆ and the concentration of Hg²⁺ in the range of 0–60 μM; the detection limit was 477 nM. Furthermore, Dual-CD showed visual fluorescence change under Hg²⁺.

Conclusion

Dual-CD has ratiometric responsiveness to Hg²⁺ and can be applied for quantitative Hg²⁺ detection in living cells.

Ultrasound-enhanced fluorescence imaging and chemotherapy of multidrug-resistant tumors using multifunctional dendrimer/carbon dot nanohybrids

Development of innovative nanomedicine enabling enhanced theranostics of multidrug-resistant (MDR) tumors remains to be challenging. Herein, we report the development of a newly designed multifunctional yellow-fluorescent carbon dot (y-CD)/dendrimer nanohybrids as a platform for ultrasound (US)-enhanced fluorescence imaging and chemotherapy of MDR tumors. Generation 5 (G5) poly(amidoamine) dendrimers covalently modified with efflux inhibitor of d-α-tocopheryl polyethylene glycol 1000 succinate (G5-TPGS) were complexed with one-step hydrothermally synthesized y-CDs via electrostatic interaction. The formed G5-TPGS@y-CDs complexes were then physically loaded with anticancer drug doxorubicin (DOX) to generate (G5-TPGS@y-CDs)-DOX complexes. The developed nanohybrids display a high drug loading efficiency (40.7%), strong y-CD-induced fluorescence emission, and tumor microenvironment pH-preferred DOX release profile. Attributing to the DOX/TPGS dual drug design, the (G5-TPGS@y-CDs)-DOX complexes can overcome the multidrug resistance (MDR) of cancer cells and effectively inhibit the growth of cancer cells and tumors. Furthermore, the introduction of US-targeted microbubble destruction technology was proven to render the complexes with enhanced intracellular uptake and anticancer efficacy in vitro and improved chemotherapeutic efficacy and fluorescence imaging of tumors in vivo due to the produced sonoporation effect. The developed multifunctional dendrimer/CD nanohybrids may represent an advanced design of nanomedicine for US-enhanced theranostics of different types of MDR tumors.

Construction of Poly(amidoamine) Dendrimer/Carbon Dot Nanohybrids for Biomedical Applications

Design of intelligent hybrid nanoparticles that can integrate diagnosis and therapy components plays an important role in the field of nanomedicine. Poly(amidoamine) (PAMAM) dendrimers possessing a unique architecture and tunable functional groups have been widely developed for various biomedical applications. Carbon dots (CDs) are considered as a promising fluorescence probe or drug delivery system due to their stable fluorescence property and excellent biocompatibility. The distinctive merits of PAMAM dendrimers and CDs are amenable for them to be constructed as perfect nanohybrids for different biomedical applications, in particular for cancer nanomedicine. Here, the recent advances in the construction of PAMAM dendrimer/CD nanohybrids for diverse biomedical applications, in particular for sensing and cancer theranostics are summarized. Finally, the future perspectives of the PAMAM dendrimer/CD nanohybrids are also briefly discussed.

Construction and evaluation of an iron delivery system by ultra-small nanoparticles from roast sturgeon (Acipenser schrenckiid)

A new type of ultra-small food-borne nanoparticles with multiple functional groups from roast sturgeon were prepared, which had potential as efficient nanocarriers for Fe(ii) delivery.

A Novel Fluorescent Test Papers Based on Carbon Dots for Selective and Sensitive Detection of Cr (VI)

In recent years, carbon dots (CDs) are promising fluorescence probes for ions detection. In this paper, the CDs which are with an average diameter of 5.5 nm were synthesized through a simple one-step hydrothermal carbonization of ethylene diamine tetraacetic acid (EDTA) salt. The CDs have strong yellow photoluminescence (PL) with a maximum emission intensity at 550 nm under an excitation wavelength of 450 nm. As the electron transfer will occur between Cr (VI) and the CDs, yellow fluorescence was quenched after adding the Cr (VI) ions. The CDs probe allows the detection of Cr (VI) ions over a concentration range from 0 to 0.1 M (R² = 0.987) and the lower detection limit is 10⁻⁵ M. Simultaneously, the CDs show highly selectivity and stability toward the detection of Cr (VI) ions.

A sensitive spectrofluorimetry method based on S and N dual-doped carbon nanoparticles for ultra-trace detection of ferrocyanide ion in food salt samples

An ultra-sensitive spectrofluorimetry method was developed and validated for the rapid determination of ferrocyanide ions (hexacyanidoferrate(II), FeCN₆ ^4-, FCNs) by using sulphur (S) and nitrogen (N) dual-doped fluorescence carbon nanoparticles (S,N-FCNPs) as nanoprobe. The fluorescence of S,N-FCNPs was strongly reduced due to the dynamic interaction between S,N-FCNPs and FeCNs. The developed method proved to be highly sensitive and selective for FeCNs detection with linearity in three concentration ranges over four orders of magnitude, covering 0.01-200.0 μg/mL. A limit of detection (LOD) of 2.8 ng/mL was obtained. The method was successfully applied for the determination of FeCNs in a series of dietary food salt samples and gave satisfactory results; the spiked recoveries were 97.6‒104.6% with standard uncertainty less than 5.8%. The method proved to be applicable for ultra-trace detection of FeCNs in food salt samples, having advantages in great simplicity, rapid response, low cost, favourable selectivity, and high sensitivity.

Current trends in pyrrole and porphyrin-derived nanoscale materials for biomedical applications

This article is written to provide an up-to-date review of pyrrole-based biomedical materials. Porphyrins and other tetrapyrrolic molecules possess unique magnetic, optical and other photophysical properties that make them useful for bioimaging and therapy. This review touches briefly on some of the synthetic strategies to obtain porphyrin- and tetrapyrrole-based nanoparticles, as well as the variety of applications in which crosslinked, self-assembled, porphyrin-coated and other nanoparticles are utilized. We explore examples of these nanoparticles' applications in photothermal therapy, drug delivery, photodynamic therapy, stimuli response, fluorescence imaging, photoacoustic imaging, magnetic resonance imaging, computed tomography and positron emission tomography. We anticipate that this review will provide a comprehensive summary of pyrrole-derived nanoparticles and provide a guideline for their further development.

N, S, and P-Co-doped Carbon Quantum Dots: Intrinsic Peroxidase Activity in a Wide pH Range and Its Antibacterial Applications

Nanozymes have drawn significant scientific interest due to their high practical importance in terms of overcoming the instability, complicated synthesis, and high cost of protein enzymes. However, their activity is generally limited to particular pHs, especially acidic ones. Herein, we report that luminescent N, S, and P-co-doped carbon quantum dots (NSP-CQDs) act as attractive peroxidase mimetics in a wide pH range, even at neutral pH, for the peroxidase substrate 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) in the presence of H₂O₂. The synergistic effects of multiple heteroatoms doping in CQDs boost the catalytic activity in a wide pH range attributed to the presence of high density of active sites for enzymatic-like catalysis and accelerated electron transfer during the peroxidase-like reactions. A possible reaction mechanism for the peroxidase-like activity of CQDs is investigated based on the radical trapping experiments. Moreover, the multifunctional activity of NSP-CQDs was further utilized for antibacterial assays for both Gram-negative and Gram-positive model species, including Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), respectively. The growths of the employed E. coli and S. aureus were found to be significantly inhibited due to the peroxidase-mediated perturbation of cell walls. The present work signifies the current advance in the rational design of N, S, and P-co-doped CQDs as highly active peroxidase mimics for novel applications in diverse fields, including catalysis, medical diagnostics, environmental chemistry, and biotechnology.

An easy synthesis of nitrogen and phosphorus co-doped carbon dots as a probe for chloramphenicol

Heteroatom doping in carbon dots (CDs) was found to be an efficient way to regulate the structure of electronic energy levels and enhance the fluorescence characteristics of CDs. Nevertheless, most reported fabrication processes of heteroatom-doped CDs are rigorous and complex. Herein, a facile and novel strategy was developed to rapidly prepare nitrogen and phosphorus co-doped CDs (N,P-CDs) using acetic acid as the carbon source, and arginine, 1,2-ethylenediamine (EDA) and diphosphorus pentoxide as the dopants, respectively. The optical, morphological and structural characterizations of the synthesized N,P-CDs were investigated via UV and photoluminescence spectroscopy, X-ray photoelectron spectroscopy, TEM, and FT-IR spectroscopy. The N,P-CDs display outstanding fluorescence stability under high ionic strength (1.6 M KCl), and long time UV irradiation, indicating that they can be used as favorable candidates for fluorescent probes. The fluorescence of N,P-CDs was selectively quenched by chloramphenicol (CAP) with a short response time. The linear range of the response to CAP was from 0.8 to 70 μM with a limit of detection of 0.36 μM (S/N = 3). Notably, the fabricated N,P-CDs were employed for the highly selective and sensitive detection of CAP in milk samples, indicating their potential applications in biologically related areas.

Absolutely "off-on" fluorescent CD-based nanotheranostics for tumor intracellular real-time imaging and pH-triggered DOX delivery

Carbon dots (CDs) have attracted intense attention in tumor nanotheranostics recently; however, those nanotheranostics exhibited similar fluorescence in both normal and tumor tissues, limiting their practical application. In the present work, absolutely "off-on" fluorescent CD-based nanotheranostics was designed for tumor intracellular real-time imaging and pH-triggered DOX delivery via both static quenching by the crosslinking of benzaldehyde-containing diblock copolymers and dynamic quenching because of the surrounding conjugated DOX molecules. The proposed PPEGMA₄₂-b-PFPMA₁₂₂-(CDs)-DOX nanotheranostics did not exhibit fluorescence in a normal physiological medium, while strong fluorescence recovery occurred in the tumor intracellular microenvironment due to pH-triggered disintegration, releasing the CDs and DOX. The pH-triggered DOX release and absolute "off-on" fluorescence make the proposed nanotheranostics promising for tumor-specific pH-triggered DOX delivery and imaging.

pH-responsive intramolecular FRET-based self-tracking polymer prodrug nanoparticles for real-time tumor intracellular drug release monitoring and imaging

An intramolecular fluorescence resonance energy transfer (FRET)-based macromolecular theranostic prodrug was designed by directly conjugating Doxorubicin (DOX) as the FRET acceptor onto the naphthalimide side groups in the fluorescent copolymer PPEGMA₂₀-PNAP₈ as the FRET energy donor via an acid-labile imine bond, without a fluorogenic linker. The proposed PPEGMA₂₀-PNAP₈-DOX theranostic prodrug showed a high DOX content of 24.3% owing to a conjugation efficiency of > 93% under mild conjugation conditions. It could easily self-assemble into unique theranostic nanoparticles with a D_h of 71 nm. The theranostic nanoparticles showed excellent pH-triggered DOX release performance with very low premature drug leakage of 6.3% in normal physiological medium over 129 h, while>91% of the conjugated DOX was released in the acidic tumor intracellular microenvironment. MTT assays indicated the enhanced antitumor efficacy of the proposed theranostic nanoparticles compared with free DOX. Furthermore, because drug release was triggered by pH, orange fluorescence was restored to the blue fluorescence of the backbone copolymer. Such self-tracking pH-responsive colorful fluorescence variations during intracellular drug delivery and release are expected to allow real-time tumor intracellular drug release monitoring and imaging diagnosis.

Synthesis of Novel Fluorescent Carbon Quantum Dots From Rosa roxburghii for Rapid and Highly Selective Detection of o-nitrophenol and Cellular Imaging

A novel carbon quantum dots (CQDs) were successfully synthesized by one-step hydrothermal reaction using Rosa roxburghii as a biomass-based precursor. The CQDs have an average size of 2.5 nm and a narrow size distribution. They display strong blue fluorescence with a quantum yield of 24.8% and good biocompatibility. Notably, these CQDs were capable of detecting trace o-nitrophenol in surface water and sewage with high sensitivity and specificity. The linear range is 0.08–40 μmol/L, and the limit of detection is 15.2 nmol/L. Furthermore, this CQDs was successfully applied for o-nitrophenol analysis in river water and sewage samples. Additionally, Hep3B cells, a human hepatocellular carcinoma cell line, can be easily imaged with high resolution using the as-prepared CQDs as nanoprobes. These results reveal that the as-prepared CQDs have potential applications for detecting o-nitrophenol and cell imaging.

Enhanced-fluorescent imaging and targeted therapy of liver cancer using highly luminescent carbon dots-conjugated foliate

Carbon dots (CDs) have shown great potential in drug delivery and biological imaging applications. In this work, a doxorubicin (DOX) delivery carrier and imaging probe for liver cancer-targeted therapy was designed based on CDs with high fluorescence quantum yield (97%), aiming to enhance the antitumor activity and imaging efficiency. Folic acid (FA), which showed high expression in hepatoma cells, was used as targeting components to modify CDs (FA-CDs), and then FA-CDs-DOX was obtained by loading DOX. Results show that CDs and FA-CDs have good biocompatibility, and the DOX release from FA-CDs-DOX is targeted and selective. Confocal microscope demonstrates that FA-CDs-DOX has excellent ability of fluorescence imaging in liver cancer cells. The imaging in vivo shows the fluorescence intensity of FA-CDs-DOX is strong enough to penetrate tumor tissue and skin, further verifying its enhanced-fluorescent imaging effects. Tumor inhibition in vivo indicates that the targeting ability of FA-CDs-DOX is significantly higher than that of free DOX, showing obvious better therapeutic effect. To sum up, the targeted and fluorescent drug delivery system based on CDs with high fluorescence quantum yield show an excellent imaging in vivo and tumor inhibition effect, which provide a novel strategy for promoting the potential clinical application of CDs in liver cancer treatment.

Multifunctional N-P-doped carbon dots for regulation of apoptosis and autophagy in B16F10 melanoma cancer cells and in vitro imaging applications

Rationale: The present study reports the multifunctional anticancer activity against B16F10 melanoma cancer cells and the bioimaging ability of fluorescent nitrogen-phosphorous-doped carbon dots (NPCDs). Methods: The NPCDs were synthesized using a single-step, thermal treatment and were characterized by TEM, XPS, fluorescence and UV-Vis spectroscopy, and FTIR analysis. The anticancer efficacy of NPCDs was confirmed by using cell viability assay, morphological evaluation, fluorescent live-dead cell assay, mitochondrial potential assay, ROS production, RT-PCR, western-blot analysis, siRNA transfection, and cellular bioimaging ability. Results: The NPCDs inhibited the proliferation of B16F10 melanoma cancer cells after 24 h of treatment and induced apoptosis, as confirmed by the presence of fragmented nuclei, reduced mitochondrial membrane potential, and elevated levels of reactive oxygen species. The NPCDs treatment further elevated the levels of pro-apoptotic factors and down-regulated the level of Bcl2 (B-cell lymphoma 2) that weakened the mitochondrial membrane, and activated proteases such as caspases. Treatment with NPCDs also resulted in dose-dependent cell cycle arrest, as indicated by reduced cyclin-dependent kinase (CDK)-2, -4, and -6 protein levels and an enhanced level of p21. More importantly, the NPCDs induced the activation of autophagy by upregulating the protein expression levels of LC3-II and ATG-5 (autophagy-related-5) and by downregulating p62 level, validated by knockdown of ATG-5. Additionally, owing to their excellent luminescence property, these NPCDs were also applicable in cellular bioimaging, as evidenced by the microscopic fluorescence imaging of B16F10 melanoma cells. Conclusion: Based on these findings, we conclude that our newly synthesized NPCDs induced cell cycle arrest, autophagy, and apoptosis in B16F10 melanoma cells and presented good cellular bioimaging capability.

Sonochemical synthesis of carbon dots, mechanism, effect of parameters, and catalytic, energy, biomedical and tissue engineering applications

Carbon-based nanomaterials are gaining more and more interest because of their wide range of applications. Carbon dots (CDs) have shown exclusive interest due to unique and novel physicochemical, optical, electrical, and biological properties. Since their discovery, CDs became a promising material for wide range of research applications from energy to biomedical and tissue engineering applications. At same time several new methods have been developed for the synthesis of CDs. Compared to many of these methods, the sonochemical preparation is a green method with advantages such as facile, mild experimental conditions, green energy sources, and feasibility to formulate CDs and doped CDs with controlled physicochemical properties and lower toxicity. In the last five years, the sonochemically synthesized CDs were extensively studied in a wide range of applications. In this review, we discussed the sonochemical assisted synthesis of CDs, doped CDs and their nanocomposites. In addition to the synthetic route, we will discuss the effect of various experimental parameters on the physicochemical properties of CDs; and their applications in different research areas such as bioimaging, drug delivery, catalysis, antibacterial, polymerization, neural tissue engineering, dye absorption, ointments, electronic devices, lithium ion batteries, and supercapacitors. This review concludes with further research directions to be explored for the applications of sonochemical synthesized CDs.

Direct conjugation of distinct carbon dots as Lego-like building blocks for the assembly of versatile drug nanocarriers

As a promising drug nanocarrier, carbon dots (CDs) have exhibited many excellent properties. However, some properties such as bone targeting and crossing the blood-brain barrier (BBB) only apply to a certain CD preparation with limited drug loading capacity. Therefore, it is significant to conjugate distinct CDs to centralize many unique properties on the novel drug nanocarrier. Considering that CDs have abundant and tunable surface functionalities, in this study, a direct conjugation was initiated between two distinct CD models, black CDs (B-CDs) and gel-like CDs (G-CDs) via an amidation reaction. As a result of conjugation at a mass ratio of 5:3 (B-CDs to G-CDs) and a two-step purification process, the conjugate, black-gel CDs (B-G CDs) (5:3) inherited functionalities from both CDs and obtained an enhanced thermostability, aqueous stability, red-shifted photoluminescence (PL) emission, and a figure-eight shape with a width and length of 3 and 6 nm, respectively. In addition, the necessity of high surface primary amine (NH₂) content in the CD conjugation was highlighted by replacing G-CDs with other CDs with lower surface NH₂ content. Meanwhile, the carboxyl groups (COOH) on G-CDs were not enough to trigger self-conjugation between G-CDs. Moreover, the drug loading capacity was enhanced by 54.5% from B-CDs to B-G CDs (5:3). Furthermore, when the mass ratio of B-CDs to G-CDs was decreased from 5:30, 5:100 to 5:300, the obtained nanostructures revealed a great potential of CDs as Lego-like building blocks. Also, bioimaging of zebrafish demonstrated that various B-G CDs exhibited properties of both bone targeting and crossing the BBB, which are specific properties of B-CDs and G-CDs, respectively.

UV-Vis-NIR Full-Range Responsive Carbon Dots with Large Multiphoton Absorption Cross Sections and Deep-Red Fluorescence at Nucleoli and In Vivo

Carbon dots (CDs), with excellent optical property and cytocompatibility, are an ideal class of nanomaterials applied in the field of biomedicine. However, the weak response of CDs in the near-infrared (NIR) region impedes their practical applications. Here, UV-vis-NIR full-range responsive fluorine and nitrogen doped CDs (N-CDs-F) are designed and synthesized that own a favorable donor-π-acceptor (D-π-A) configuration and exhibit excellent two-photon (λ_ex = 1060 nm), three-photon (λ_ex = 1600 nm), and four-photon (λ_ex = 2000 nm) excitation upconversion fluorescence. D-π-A-conjugated CDs prepared by solvothermal synthesis under the assistance of ammonia fluoride are reported and are endowed with larger multiphoton absorption (MPA) cross sections (3PA: 9.55 × 10^-80 cm⁶ s² photon^-2 , 4PA: 6.32 × 10^-80 cm⁸ s³ photon^-3 ) than conventional organic compounds. Furthermore, the N-CDs-F show bright deep-red to NIR fluorescence both in vitro and in vivo, and can even stain the nucleoli of tumor cells. A plausible mechanism is proposed on the basis of the strong inter-dot and intra-dot hydrogen bonds through NH···F that can facilitate the expanding of conjugated sp² domains, and thus not only result in lower highest occupied molecular orbital-lowest unoccupied molecular orbital energy level but also larger MPA cross sections than those of undoped CDs.

High photoluminescence nitrogen, phosphorus co-doped carbon nanodots for assessment of microbial viability

Assessment of microbial viability plays a key role in human health protection. Optical imaging based on fluorescent dyes is a simple and convenient way to assess microbial viability. However, it is still a challenge to obtain stable, nontoxic and low-cost dyes. Herein, we prepared a nitrogen and phosphorus co-doped carbon nanodots (N, P-CDs) via a one-step solvothermal method. The prepared CDs possess plenty of functional groups and exhibit high stability, good biocompatibility, excellent photoluminescent and low toxicity. Especially, the properties of high quantum yield (89.9%) and highly negative surface charge (-41.9 mV) make the prepared N, P-CDs ideal materials for microbial differentiation. Compared with commercial dyes, our CDs are more stable, cost less, which can rapidly distinguish dead microorganisms from living ones with higher specificity.

Nitrogen and Phosphorus Co-Doped Carbon Dots for Selective Detection of Nitro Explosives

In this work, a highly selective and sensitive method has been developed for the detection of trinitrophenol (TNP), which is a dangerous explosive. For this purpose, N and P co-doped carbon dots (NP-Cdots) have been used. Synthesis of N and P co-doped carbon dots has been carried out by a simple and quick method. X-ray photoelectron spectroscopy analysis was carried out to detect the doping of N and P. These carbon dots are insoluble in water (inNP-Cdots). These carbon dots were functionalized by treating them with conc. HNO3 so that they become water-soluble (wsNP-Cdots). These dots were characterized by different analytical techniques such as IR, UV-vis, and fluorescence spectroscopy. The as-prepared wsNP-Cdots have good fluorescence properties. The average diameter of wsNP-Cdots is found to be 5.7 nm with an interlayer spacing (d-spacing) of 0.16 nm. The as-prepared wsNP-Cdots are highly sensitive and selective toward TNP, as observed using a fluorescence quenching technique. The quenching constant for TNP is found to be very high (8.06 × 104 M-1), which indicates its high quenching ability. The limit of detection is found to be 23 μM.

Selenium-doped two-photon fluorescent carbon nanodots for in-situ free radical scavenging in mitochondria

Mitochondrial oxidative stress is associated with the occurrence and development of a wide range of human diseases. The development of methodologies to alleviate oxidative stress-mediated injury may have therapeutic potential. Herein, we report the design and preparation of triphenylphosphonium-functionalized selenium-doped carbon nanodots (TPP-Se-CDs) that can efficiently scavenging hydroxyl radicals (OH) and superoxide anions (O₂^-) in mitochondria region. Se-CDs with two-photon blue fluorescence were initially prepared by facile hydrothermal treatment of selenomethionine, followed by the covalent conjugation with TPP. The as-obtained TPP-Se-CDs showed high colloidal stability, strong scavenging abilities towards OH and O₂^-. Moreover, TPP-Se-CDs exhibited low cytotoxicity and mitochondria targeting ability. Taking advantages of these prominent features, TPP-Se-CDs have been successfully applied to combat H₂O₂ and phorbol 12-myristate 13-acetate (PMA) induced oxidative stress in mitochondria.

Tumor-specific fluorescent Cdots-based nanotheranostics by acid-labile conjugation of doxorubicin onto reduction-cleavable Cdots-based nanoclusters

Carbon quantum dots (Cdots) have attracted more and more interests in bioimaging and tumor theranostics. However, their practical application has been limited due to the small particle size and non-tumor-specific fluorescence. Here, reduction-cleavable disulfide-linked Cdots-based nanoclusters were fabricated to conjugate doxorubicin (DOX) via an acid-labile hydrazone bond. Owing to the pH and reduction dual-stimuli responsiveness, the proposed Cdots-based nanotheranostics possessed unique tumor-specific fluorescent property and tumor-specific controlled drug release performance, indicating their promising potential for the in-situ real-time fluorescent monitoring of therapeutic response in future tumor therapy.

Hg2+ detection, pH sensing and cell imaging based on bright blue-fluorescent N-doped carbon dots

A multifunctional sensing platform based on bright blue-fluorescent nitrogen-doped carbon dots (N-CDs) has been ingeniously designed for the sensitive determination of Hg²⁺ and pH.

Amphiphilic fluorescent carbon nanodots as a selective nanoprobe for nitrite and tetracycline both in aqueous and organic solutions

The dispersibility of carbon dots in organic and/or aqueous solvents plays a critical role in various application fields.

Theranostic applications of stimulus-responsive systems based on carbon dots

Over recent years, many different nanoparticle-based drug delivery systems (NDDSs) have been developed. Recently the development of stimulus-responsive NDDSs has come into sharper focus. Carbon dots (CDs) possess outstanding features such as useful optical properties, good biocompatibility, and the ability for easy surface modification. Appropriate surface modification can allow these NDDSs to respond to various chemical or physical stimuli that are characteristic of their target cells or tissue (frequently malignant cells or tumors). The present review covers recent developments of CDs in NDDSs with a particular focus on internal stimulus response capability that allows simultaneous imaging and therapeutic delivery (theranostics). Relevant stimuli associated with tumor cells and tumors include pH levels, redox potential, and different enzymatic activities can be used to activate the CDs at the desired sites.

Nitrogen, phosphorus and sulfur tri-doped carbon dots are specific and sensitive fluorescent probes for determination of chromium(VI) in water samples and in living cells

A rapid, sensitive, and selective fluorometric assay is described for the determination of chromium(VI) in real waters and living cells. The method is making use of nitrogen, phosphorus, and sulfur tri-doped carbon dots (NPS-CDs) which have absorption/emission maxima at 360/505 nm/nm. Cr(VI) has an absorption maximum at 350 nm and causes an inner filter effect (IFE) on the blue fluorescence of the NPS-CDs. The NPS-CDs were hydrothermally synthesized using p-aminobenzenesulfonic acid and tetrakis(hydroxymethyl)phosphonium chloride as precursors. The NPS-CDs were characterized by transmission electron microscopy, X-ray diffraction, and several spectroscopic methods. They are biocompatible and negligibly cytotoxic when tested with HeLa cells and MCF-7 cells even after 48 h of incubation. The NPS-CDs were used as fluorescent probes for Cr(VI). The detection limit is 0.23 μM (three times standard deviation versus slope), and the linear response covers the 1 to 500 μM chromate concentration range. The NPS-CDs were applied to the determination of Cr(VI) in real waters and living cells (HeLa and MCF-7) and gave satisfying results. Graphical abstractSchematic representation of hydrothermal synthesis of nitrogen, phosphorus, and sulfur tri-doped carbon dots (NPS-CDs) for Cr(VI) detection via inner filter effect (IFE). NPS-CDs were applied to the determination of Cr(VI) in living cells (HeLa and MCF-7) with satisfying results.

N,S co-doped carbon dots as a dual-functional fluorescent sensor for sensitive detection of baicalein and temperature

In this work, nitrogen and sulfur dual-doped CDs (N,S-CDs) were prepared via a facile one-pot hydrothermal method from citric acid and N-acetyl-L-cysteine with a high quantum yield (QY) of 49%. As-fabricated N,S-CDs had a size around 2.5 nm and exhibited excitation-independent emission and excellent luminescent properties. The fluorescent sensor based on the N,S-CDs showed a highly sensitive detection of baicalein with a detection limit (LOD) of 0.21 μmol L^-1 in the linear range from 0.69 to 70.0 μmol L^-1. The fluorescence of the N,S-CDs could be effectively quenched by baicalein based on static quenching. In addition, the temperature sensor based on the synthesized N,S-CDs showed a good linear relationship between temperature and fluorescence (FL) intensity with a temperature range from 5 °C to 75 °C. Furthermore, the synthesized N,S-CDs were successfully applied to the measurement of baicalein in real samples. In a word, the N,S-CDs had great potential to be worked as fluorescence sensors to monitor the concentration of baicalein and temperature.

From in vitro to ex vivo: subcellular localization and uptake of graphene quantum dots into solid tumors

Among various nanoparticles tested for pharmacological applications over the recent years, graphene quantum dots (GQDs) seem to be promising candidates for the construction of drug delivery systems due to their superior biophysical and biochemical properties. The subcellular fate of incorporated nanomaterial is decisive for transporting pharmaceuticals into target cells. Therefore a detailed characterization of the uptake of GQDs into different breast cancer models was performed. The demonstrated accumulation inside the endolysosomal system might be the reason for the particles' low toxicity, but has to be overcome for cytosolic or nuclear drug delivery. Furthermore, the penetration of GQDs into precision-cut mammary tumor slices was studied. These constitute a far closer to reality model system than monoclonal cell lines. The constant uptake into the depth of the tissue slices underlines the systems' potential for drug delivery into solid tumors.

Comparative study of Cl,N-Cdots and N-Cdots and application for trinitrophenol and ClO- sensor and cell-imaging

To understand the effect of Cl doping in carbon dots, nitrogen-doped carbon dots (N-Cdots) and nitrogen and chlorine dual-doped carbon dots (Cl,N-Cdots) were fabricated by high-temperature carbonization and low-temperature concentrated acid (HCl) acidification of dried shaddock peel, respectively. The quantum yield of Cl,N-Cdots is about four times of that of N-Cdots and the size of Cl,N-Cdots is smaller than that of N-Cdots. Furthermore, since trinitrophenol (PA) and ClO^- could effectively quench the fluorescence of Cl,N-Cdots, the fluorescence sensors for determining PA and ClO^- was constructed, respectively. The linear range of PA and ClO^- are 0.9-90 μM and 3.24-216 μM with the limit of detection of 37.1 nM and 2.88 μM, respectively. The proposed sensor was used to detect PA in Taiyuan tap water, Wutai tap water, Wutai rain water and Wutai river water samples with encouraging results. The as-constructed sensor was also used to detect ClO^- in Taiyuan tap water and commercial disinfectants. Last but not least, Cl,N-Cdots was employed as an agent for A549 and HeLa cell-imaging, possessing optimal imaging effect and ultra-low cytotoxicity. Our results suggested that Cl,N-Cdots has promising applications in sensing, water monitoring, commodity supervision and cell-imaging.

Controllable Fabrication, Photoluminescence Mechanism, and Novel Application of Green-Yellow-Orange Fluorescent Carbon-Based Nanodots

Carbon-based nanodots (CBNs), as spick-and-span carbon nanomaterials, have been widely studied and applied in numerous fields. However, the controlled fabrication and photoluminescence (PL) mechanism remains an incompletely understood and widely debated topic. Herein, green, yellow, and orange light-emitting CBNs were fabricated by a one-step hydrothermal process with 4-aminobenzoic acid and 1,3-diaminobenzene, 1,2-diaminobenzene, and 1,4-diaminobenzene as precursors, respectively; the resulting CBNs were named gCBNs, yCBNs, and oCBNs, respectively. By adjusting the reaction conditions, including precursor, solvent, atmosphere, and dissolved solvent, the controllable fabrication of CBNs can be realized. We speculate that the PL of CBNs is dominated by the degrees of oxidation and amidation, which, together, cause the differences in the density of N-states and quantum size, ultimately manifesting as changes in three CBNs' fluorescence behaviors. Finally, the CBNs were used as agents to image four model cells, demonstrating that CBNs are potentially useful in biological labeling and multicolor bioimaging. More importantly, CBNs can be conjugated to the targeted micromolecule, DNA, RNA, and/or anticarcinogen groups to construct nanocomposite materials, which could be applied to identify target materials and/or execute the sustained release of drugs. We want to offer a guide for controllable fabrication of CBNs and further expanding the application depth and breadth in the biomedical field.

The Low Toxicity of Graphene Quantum Dots is Reflected by Marginal Gene Expression Changes of Primary Human Hematopoietic Stem Cells

Graphene quantum dots (GQDs) are a promising next generation nanomaterial with manifold biomedical applications. For real world applications, comprehensive studies on their influence on the functionality of primary human cells are mandatory. Here, we report the effects of GQDs on the transcriptome of CD34+ hematopoietic stem cells after an incubation time of 36 hours. Of the 20 800 recorded gene expressions, only one, namely the selenoprotein W, 1, is changed by the GQDs in direct comparison to CD34+ hematopoietic stem cells cultivated without GQDs. Only a meta analysis reveals that the expression of 1171 genes is weakly affected, taking into account the more prominent changes just by the cell culture. Eight corresponding, weakly affected signaling pathways are identified, which include, but are not limited to, the triggering of apoptosis. These results suggest that GQDs with sizes in the range of a few nanometers hardly influence the CD34+ cells on the transcriptome level after 36 h of incubation, thereby demonstrating their high usability for in vivo studies, such as fluorescence labeling or delivery protocols, without strong effects on the functional status of the cells.

Carbon Dots for In Vivo Bioimaging and Theranostics

Carbon dots (CDs), a kind of carbon material discovered accidentally, exhibit unexpected advantages in fluorescence imaging/sensing such as photostability, biocompatibility, and low toxicity. For emerging theranostics, an interdiscipline created by integrating therapy and diagnostics, CDs are good candidates when they are combined with targeted chemo/gene/photodynamic/photothermal therapeutic moieties. Here, the development of CDs in nanomedicine is reviewed from their use as original imaging agents and/or drug carriers to multifunctional theranostic systems. Finally, the challenges and prospects of the next-generation of CD-based theranostics for clinical applications are also discussed.

Self-assembling of graphene oxide on carbon quantum dot loaded liposomes

This paper describes the design of stimuli-sensitive theranostic nanoparticles, composed of reduced graphene oxide (rGO) self-assembled on thermosensitive liposomes encapsulated doxorubicin (DOX) and carbon quantum dot (CQD) (CQD-DOX-rGO-Tlip). The rGO-Tlip particles have been observed to be flower-shaped objects. The thermoresponsive and theranostic potential of CQD-DOX-rGO-Tlips have been studied using differential scanning calorimetry (DSC), ultraviolet visible spectroscopy (UV-Vis), Raman spectroscopy and photoluminescent assays. The chemo-photothermal potential of rGO-Tlip on MD-MB-231 cells during NIR laser irradiation has been examined using MTT assay. Also, the ability of rGO-Tlip to be taken up by MD-MB-231 cells has been studied using confocal microscopy and flowcytometry. The results indicate that CQD-DOX-rGO-Tlips achieve a synergistic effect between photothermal therapy and chemotherapy for cancer treatment. Furthermore, online monitoring drug release is accomplished by studying the emission intensity of CQD while DOX released.