pH controlled green luminescent carbon dots derived from benzoxazine monomers for the fluorescence turn-on and turn-off detection

Construction of a stable fluorescent sensor based on CsPbBr3/CdS core/shell quantum dots for selective and sensitive detection of tetracycline in ethanol

The weakly bound organic ligand shells around perovskite quantum dots (QDs) are easily decomposed and cannot provide sufficient stability in polar solvents, which greatly obstructs their applications in sensing. Herein, a fluorescent sensor based on CsPbBr3/CdS core/shell QDs was developed for the detection of tetracycline (TC) in the polar solvent-ethanol. Pristine CsPbBr3 QDs were treated with cadmium diethyldithiocarbamate (Cd(DDTC)2) to form a shell on the surface at 110 °C, while extra oleylammonium bromide (OAmBr) was added to inhibit the phase transformation of CsPbBr3 into a Cs4PbBr6 impurity phase during high-temperature processing. And finally CsPbBr3/CdS core/shell QDs were successfully synthesized. The capping with the CdS inorganic shell remediated surface defects and improved the stability in ethanol without affecting the emission properties of the parent CsPbBr3 QDs. The results showed that the fluorescent sensor detected TC in the range of 0.05-25 μM with a low detection limit of 22.6 nM, whereas it had high selectivity and anti-interference ability for TC. And the fluorescence quenching mechanism of the sensor was mainly photoinduced electron transfer between TC and CsPbBr3/CdS QDs. Our research provides a unique way to improve the stability of perovskite QDs in polar solvents and applications in fluorescence detection.

Synthesis of 2,4-Dicyanoalkylated Benzoxazines through the Radical-Mediated Cascade Cyclization of Isocyanides with AIBN under Metal- and Additive-Free Conditions

A general and novel method for the radical cascade cyclization of aryl isocyanides with AIBN has been described. This strategy provides straightforward access to various 2,4-dicyanoalkylated benzoxazines in moderate to good yields under metal- and additive-free conditions. The reaction can apply to a gram scale and tolerate diverse functional groups. 2,4-Dicyanoalkylated benzoxazine derivatives feature a large Stokes shift and intramolecular charge transfer properties.

Acid-assisted ultrasonic preparation of nitrogen-doped MXene quantum dots for the efficient fluorescence "off-on-off" detection of Zn(II) in water and oxalic acid in vegetables

A novel fluorescence "off-on-off" probe was presented to detect Zn(II) and oxalic acid (OA) based on nitrogen-doped MXene quantum dots (N-MQDs), which were synthesized by an ultrasound approach at room temperature with nitric acid and ethylenediamine. These N-MQDs displayed small size (<10 nm), water dispersibility, and good photoluminescence. Furthermore, the N-MQDs showed an selective response towards Zn(II) through fluorescence enhancement, with a limit of detection (LOD) calculated as 0.127 μM in the linear range of 0-20 μM. Then, the fluorescence of N-MQDs/Zn(II) system could be selectively quenched after adding OA, with an effective response in the range from 0 to 20 μM (LOD: 0.883 μM). The fluorescence "turn-on" and "turn-off" properties of N-MQDs were resulted from the intramolecular charge transfer (ICT) of Zn(II) and the coordination between OA and Zn(II), respectively. This sensing platform was successfully applied for Zn(II) and OA detection in actual environmental and vegetable samples.

Fluorescence Sensing Mechanisms of Versatile Graphene Quantum Dots toward Commonly Encountered Heavy Metal Ions

Graphene quantum dots (GQDs) have received tremendous attention as fluorescent probes for detection of diverse heavy metal ions (HMIs). Nevertheless, the fluorescence sensing mechanisms of versatile GQDs with respect to different HMIs remain elusive. Herein, the fluorescence sensing behaviors and mechanisms of GQDs with amino and carboxyl groups toward commonly encountered Cr6+, Fe3+, Cu2+, Cr3+, Mn2+, Co2+, Ni2+, Zn2+, Cd2+, and Hg2+ under different pH conditions are systemically explored. The results show that the fluorescence of GQDs can be enhanced by Zn2+/Cd2+ and quenched by other HMIs at pH 5.8, while it can be enhanced by HMIs except Cr6+/Fe3+/Cu2+ at pH 2.0. Systematic studies verify that the fluorescence quenching/enhancing is mediated by the synergistic effect of the inner filter effect (IFE) and the photoinduced electron transfer (PET) or metal orbital-controlled chelation-quenched/enhanced fluorescence (CHQF/CHEF) effect. The strong and weak IFEs of Cr6+/Fe3+ and Cr3+/Cu2+, respectively, are one of the reasons for the fluorescence quenching, while other HMIs have no IFE. Moreover, the PET effect caused by the interaction of GQDs with Hg2+ at pH 5.8 and the CHQF/CHEF effect caused by the interaction of GQDs with other HMIs are also crucial for fluorescence quenching/enhancing. The findings suggest that the pH condition, the existing forms of functional groups on GQDs, and the complexation states of HMIs in aqueous systems dominate the PET and CHQF/CHEF effects. The elucidating of the fluorescence sensing mechanisms of GQDs toward different HMIs paves the way for developing versatile sensing platforms for monitoring of HMI contamination.

Ratiometric Fluorescent Detection of Ultrasound-Regulated ATP Release: An Ultrasound-Resistant Cu,N-Doped Carbon Nanosphere

Focused ultrasound, as a protocol of cancer therapy, might induce extracellular adenosine triphosphate (ATP) release, which could enhance cancer immunotherapy and be monitored as a therapeutic marker. To achieve an ATP-detecting probe resistant to ultrasound irradiation, we constructed a Cu/N-doped carbon nanosphere (CNS), which has two fluorescence (FL) emissions at 438 and 578 nm to detect ultrasound-regulated ATP release. The addition of ATP to Cu/N-doped CNS was conducted to recover the FL intensity at 438 nm, where ATP enhanced the FL intensity probably via intramolecular charge transfer (ICT) primarily and hydrogen-bond-induced emission (HBIE) secondarily. The ratiometric probe was sensitive to detect micro ATP (0.2-0.6 μM) with the limit of detection (LOD) of 0.068 μM. The detection of ultrasound-regulated ATP release by Cu,N-CNS/RhB showed that ATP release was enhanced by the long-pulsed ultrasound irradiation at 1.1 MHz (+37%, p < 0.01) and reduced by the short-pulsed ultrasound irradiation at 5 MHz (-78%, p < 0.001). Moreover, no significant difference in ATP release was detected between the control group and the dual-frequency ultrasound irradiation group (+4%). It is consistent with the results of ATP detection by the ATP-kit. Besides, all-ATP detection was developed to prove that the CNS had ultrasound-resistant properties, which means it could bear the irradiation of focused ultrasound in different patterns and detect all-ATP in real time. In the study, the ultrasound-resistant probe has the advantages of simple preparation, high specificity, low limit of detection, good biocompatibility, and cell imaging ability. It has great potential to act as a multifunctional ultrasound theranostic agent for simultaneous ultrasound therapy, ATP detection, and monitoring.

Nanocomposites of nitrogen-doped carbon dots/hydrotalcite with enhanced solid-state fluorescence for the recognition of latent fingerprints

In this work, a green emissive nanocomposite was synthesized by embedding nitrogen-doped carbon dots into hydrotalcite (N-CD/hydrotalcite) via a hydrothermal process for the recognition of latent fingerprints (LFPs). Good dispersion of the nano-sized N-CD on the surface of hydrotalcite overcomes the fluorescence quenching of N-CD in the solid state and can enhance solid-state fluorescence. N-CD/hydrotalcite emits stable strong green fluorescence even at different excitation wavelengths and exhibits good selectivity and sensitivity for the visualization of LFPs on various substrates such as glass slides, tiles, leather, aluminum foil, printing paper, colored surfaces of plastic packing, copper foil, planks, leaves, currencies, and bar codes. The high-level details of the ridge patterns of both fresh and aged LFPs can be clearly identified with good clarity and high contrast without background interferences under the excitation of a 450 nm light source. There is no significant difference in the LFP image visualized by N-CD/hydrotalcite and commercial fluorescent powders, indicating that the effectiveness of N-CD/hydrotalcite for the visualization of LFPs is equivalent to that of commercial fluorescent powders. These observations illustrate that N-CD/hydrotalcite has great potential in the recognition of LFPs.

Ultraporous Polyquaternium-Carboxylated Chitosan Composite Hydrogel Spheres with Anticoagulant, Antibacterial, and Rapid Endotoxin Removal Profiles for Sepsis Treatment

Hemoperfusion is an important method to remove endotoxins and save the lives of patients with sepsis. However, the current adsorbents for hemoperfusion have disadvantages of insufficient endotoxin adsorption capacity, poor blood compatibility, and so on. Herein, we proposed a novel emulsion templating (ET) method to prepare ultraporous and double-network carboxylated chitosan (CCS)-poly(diallyl dimethylammonium chloride) (PDDA) hydrogel spheres (ET-CCSPD), bearing both negative and positive charges. CCS was introduced to balance the strong positive charges of PDDA to improve hemocompatibility, and emulsion templates endowed the adsorbent with an ultraporous structure for enhanced adsorption efficacy. The ET-CCSPDs neither damaged blood cells nor activated complement responses. In addition, the activated partial thromboplastin time (APTT) was prolonged to 8.5 times, which was beneficial for reducing the injection of anticoagulant in patients. The ET-CCSPDs had excellent scavenging performance against bacteria and endotoxin, with removal ratios of 96.7% for E. coli and 99.8% for S. aureus, respectively, and the static removal ratio of endotoxin in plasma was as high as 99.1% (C₀ = 5.50 EU/mL, critical illness level). An adsorption cartridge filled with the ET-CCSPDs could remove 84.7% of endotoxin within 1 h (C₀ = 100 EU/mL in PBS). Interestingly, the ET-CCSPDs had a good inhibitory effect on the cytokines produced by endotoxin-mediated septic blood. By developing the ET method to prepare ultraporous and double-network adsorbents, the problems of low adsorption efficiency and poor blood compatibility of traditional endotoxin adsorbents have been solved, thus opening a new route to fabricate absorbents for blood purification.

Carbon Dots: An Excellent Fluorescent Probe for Contaminant Sensing and Remediation

Pollution-induced degradation of the environment is a serious problem for both developing and developed countries. Existing remediation methods are restricted, necessitating the development of novel remediation technologies. Nanomaterials with unique characteristics have recently been developed for remediation. Quantum dots (QDs) are semiconductor nanoparticles (1-10 nm) with optical and electrical characteristics that differ from bigger particles owing to quantum mechanics, making them intriguing for sensing and remediation applications. Carbon dots (CDs) offer better characteristics than typical QDs, such as, CdSe QDs in terms of contaminant sensing and remediation. Non-toxicity, chemical inertness, photo-induced electron transfer, good biocompatibility, and adjustable photoluminescence behavior are all characteristics of CDs. CDs are frequently made from sustainable raw materials as they are cost-effective, environmentally compactable, and excellent in reducing waste generation. The goal of this review article is to briefly describe CDs fabrication methods, to deeply investigate the criteria and properties of CDs that make them suitable for sensing and remediation of contaminants, and also to highlight recent advances in their use in sensing and remediation of contaminants.

Nitrogen-Doped Carbon Dots as a Fluorescent Probe for the Highly Sensitive Detection of Bilirubin and Cell Imaging

Nitrogen-doped carbon dots (NCDs) with bright blue fluorescence were constructed by a hydrothermal method using sucrose and L-proline as raw materials. The NCDs were characterized by transmitted electron microscopy, X-ray diffractometry, Fourier transform infrared spectrometry, X-ray photoelectron spectroscopy, and ultraviolet-visible absorption (UV-vis) and fluorescence spectroscopy to investigate the morphology, elemental composition, and optical properties. The NCDs had good water solubility, high dispersibility with an average diameter of only 1.7 nm, and satisfactory optical properties with a fluorescence quantum yield of 23.4%. The NCDs were employed for the detection of bilirubin. A good linear response of the NCDs in the range 0.35-9.78 μM was obtained for bilirubin with a detection limit of 33 nM. The NCDs were also applied to the analysis of real samples, serum and urine, with a recovery of 95.34%-104.66%. The low cytotoxicity and good biocompatibility of the NCDs were indicated by an MTT assay and cell imaging of HeLa cells. Compared with other detection systems, using NCDs for bilirubin detection was a facile and efficient method with good selectivity and sensitivity.

A Label-Free Fluorescent Sensor Based on Si,N-Codoped Carbon Quantum Dots with Enhanced Sensitivity for the Determination of Cr(VI)

A signal shut-off probe of Si, N-codoped carbon quantum dots (Si, N-CQDs) was exploited to detect Cr(VI) by fluorescence quenching without the aid of any biomolecules or labeling materials. The sensing system prepared the precursor of diacetone acrylamide and the silane coupling agent 3-aminopropyltriethoxysilane (KH-550) by a simple hydrothermal method, and the quantum yield is as high as 75% Si, N-CQDs. The fluorescence stability and microstructure of the Si, N-CQDs were studied. The Si, N-CQDs has a high sensitivity for detecting Cr(VI) with the linear range of 0–200 μM and the detection limit of 0.995 μM. The quenching mechanism of Si, N-CQDs is attributed to FRET.

A fluorometric and colorimetric dual-readout nanoprobe based on Cl and N co-doped carbon quantum dots with large stokes shift for sequential detection of morin and zinc ion

A novel visual nanoprobe was developed for the sequential detection of morin and zinc ion (Zn²⁺) based on Cl and N co-doped carbon quantum dots (ClNCQDs) via a fluorometric and colorimetric dual-readout mode. The yellow fluorescence ClNCQDs was synthesized by the one-step hydrothermal treatment of o-chlorobenzoic acid and p-phenylenediamine. The most distinctive property of the ClNCQDs is the large stokes shift (177 nm), which is significantly higher than other reported CQDs. The fluorescence of the ClNCQDs can be effectively quenched by morin based on the synergistic effect of IFE, electrostatic interaction, and dynamic quenching process, and recovered upon the addition of Zn²⁺ due to strong interaction between morin and Zn²⁺. The nanoprobe exhibited favorable selectivity and sensitivity toward morin and Zn²⁺ with detection limits of 0.09 µM and 0.17 µM, respectively. Simultaneously, the color of the ClNCQDs solution was changed (light-pink → faint-yellow → dark-yellow) along with the variation of the fluorescence signal of the ClNCQDs. This proposed nanoprobe was successfully applied for morin and Zn²⁺ analyses in actual samples and live cells with high accuracy. The results of this study demonstrate the great application prospects of the ClNCQDs for morin and Zn²⁺ detection in complex actual samples and biosystems.

Advanced Carbon Materials Derived from Polybenzoxazines: A Review

This comprehensive review article summarizes the key properties and applications of advanced carbonaceous materials obtained from polybenzoxazines. Identification of several thermal degradation products that arose during carbonization allowed for several different mechanisms (both competitive ones and independent ones) of carbonization, while also confirming the thermal stability of benzoxazines. Electrochemical properties of polybenzoxazine-derived carbon materials were also examined, noting particularly high pseudocapacitance and charge stability that would make benzoxazines suitable as electrodes. Carbon materials from benzoxazines are also highly versatile and can be synthesized and prepared in a number of ways including as films, foams, nanofibers, nanospheres, and aerogels/xerogels, some of which provide unique properties. One example of the special properties is that materials can be porous not only as aerogels and xerogels, but as nanofibers with highly tailorable porosity, controlled through various preparation techniques including, but not limited to, the use of surfactants and silica nanoparticles. In addition to the high and tailorable porosity, benzoxazines have several properties that make them good for numerous applications of the carbonized forms, including electrodes, batteries, gas adsorbents, catalysts, shielding materials, and intumescent coatings, among others. Extreme thermal and electrical stability also allows benzoxazines to be used in harsher conditions, such as in aerospace applications.

Multi-functionalized carbon aerogels derived from chitosan

Carbon aerogels are prepared by a thermal treating-freeze drying approach from chitosan, with glycine hydrochloride ionic liquid (IL) acting as solvent and nitrogen source. Different post-treatments such as ball milling and high temperature carbonization are employed to functionalize the obtained carbon aerogels with tuned properties, making it promising candidates as fluorescence material (NACs-Q), electrode material (FDC-800) and catalyst support (NAC_Pd-C). NACs-Q is water-soluble quantum dot with average particle sizes of 3.8 nm, presenting excitation-/emission-independent and pH-sensitive properties, which could be used as sensor for testing acetone vapor or an "on-off-on" sensor for detections of Fe³⁺ and vitamin C in fruits. FDC-800 exhibits fluffy lamellar structure with developed micro-mesopores and nitrogen-containing groups on their surfaces, which is beneficial for building flexible solid-state supercapacitor with excellent performance, delivering a capacitance of 208F/g at 0.5 A/g, and achieving an energy density of 7.2 W h/kg at a power density of 50 W/kg. Moreover, NAC_Pd-C can be used as catalyst for phenol hydrogenation, and phenol conversion of 100% with cyclohexanone selectivity of 98.3% is achieved, due to the synergetic effects of the Pd active-site, the N-containing groups, and the Lewis acid sites on the support.

Tribological properties of bismaleimide reinforced with Si-containing benzoxazine monomer

To improve the mechanical and tribological properties of bismaleimide (BMI) resin, a novel Si-containing benzoxazine (Si-BOZ) monomer was synthesized using a solvent process and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane as a silane coupling agent. The novel Si-BOZ monomer was subsequently blended with BMI to prepare Si-BOZ/BMI polymer alloys. Furthermore, the effect of Si-BOZ content on the mechanical, tribological, and thermal properties of Si-BOZ/BMI alloys was investigated. The results revealed that the addition of Si-BOZ to BMI improved the mechanical properties and wear resistance of Si-BOZ/BMI; moreover, the glass transition temperature of cured Si-BOZ/BMI alloys was lower than that of pure BMI resin. These results confirmed that the increase in wear resistance of Si-BOZ/BMI alloys can be attributed to the increase in thermal resistance and improvement in mechanical performance owing to the addition of Si-BOZ.

A one-pot synthesis of fluorescent N,P-codoped carbon dots for vitamin B12 determination and bioimaging application

N,P-codoped carbon dots were synthesised using l-arginine and phosphoric acid and explored for the detection of vitamin B₁₂ (VB₁₂) and bioimaging.

Fluorescent “on–off–on” sensor based on N,S co-doped carbon dots from seaweed (Sargassum carpophyllum) for specific detection of Cr(vi) and ascorbic acid

A low-temperature carbonization method using seaweed (Sargassum carpophyllum) as a precursor was applied to prepare nitrogen and sulfur co-doped CDs (N,S-CDs).

Compressible, Flame-Resistant and Thermally Insulating Fiber-Reinforced Polybenzoxazine Aerogel Composites

The preparation of novel polymer aerogel materials with enhanced flame-retardancy, superior thermal insulation and mechanical strength is of great practical significance in energy-savings and fire-prevention for buildings. Herein, we reported the fiber-reinforced polybenzoxazine (PBO) aerogel composites with flame retardance and thermal insulation, which were prepared under room temperature and atmospheric pressure, and using 4,4′-diaminodiphenlymethane (MDA) benzoxazine monomer as the raw material and oxalic acid (OA) as the catalyst. Several outstanding attributes were achieved in the aerogel composites, such as relatively low thermal conductivity (0.069 W/m·K at 10⁵ Pa, 0.031 W/m·K at 5 Pa), high limiting oxygen index (LOI) up to 32.5, and enhanced mechanical properties. It can be compressed to more than 80% of the deformation without obvious cracks, and shows high compressive modulus and specific modulus (20.69 MPa and 5.05 × 10⁴ N·m/Kg, respectively). All the excellent comprehensive properties mean that fiber-reinforced PBO aerogel composites have broad application prospects in the fields of flame retardancy and thermal insulation.

A ratiometric fluorometric ciprofloxacin assay based on the use of riboflavin and carbon dots

Carbon dots (CDs) were hydrothermally synthesized from selenious yeast. They were further coupled with riboflavin to form a dually emitting probe for ciprofloxacin (CIP). Under 370 nm excitation, the probe displays dual (blue and green) emissions with peaks at 443 and 510 nm. When CIP is added, the blue fluorescence of the CDs is enhanced while the green fluorescence remains unaffected. The ratio of the relative fluorescence intensities at 443 and 510 nm increases linearly in the 0.5-200 μM CIP concentration range. The fluorescent probe is selective and has a 0.13 μM detection limit. Satisfactory recoveries (97.9-101.1%) were received when the probe was used to quantify CIP in spiked water and human serum samples. Graphical abstractBlue-emissive carbon dots were prepared from selenious yeast via a hydrothermal method, and then coupled with riboflavin as a ratiometric fluorometric probe for ciprofloxacin determination.

A review on charred traditional Chinese herbs: carbonization to yield a haemostatic effect

Context: Charcoal of Chinese drugs is a kind of special processing product in Chinese medicine and used for treatment of haemoptysis, hematemesis and haemorrhage in the clinic during ancient times. During carbonizing, significant changes occur in chemical constituents and the efficacy of haemostasis will be enhanced. But the quality control standard of 'carbonizing retains characteristics' should be followed. Objective: This review introduces the typical methods of carbonizing, which highlight current research progress on haemostatic substances of charcoal drugs so as to provide a reasonable explanation for the theory of haemostasis treated by charcoal medicine. Methods: English and Chinese literature from 2004 to 2019 was collected from databases including Web of Science, PubMed, Elsevier and CNKI (Chinese). Charcoal drug, chemical constituents, processing, haemostasis and carbon dots were used as the key words. Results: Charcoal drugs mainly play a haemostatic role and the effect can be classified into four types to stop bleeding: removing blood stasis, cooling blood, warming meridians and astringing. Changes in composition lead to changes in pharmacodynamics. Carbonizing methods and basic research on haemostasis material in charcoal drugs have also been summarized. Conclusions: This review summarizes the classification of charcoal drugs and highlights the possible material bases for the haemostatic effect of charcoal drugs in recent years, providing new insights to future research.

Benzoxazine monomer derived carbon dots as a broad-spectrum agent to block viral infectivity

Multiple viruses can cause infection and death of millions annually. Of these, flaviviruses are found to be highly prevalent in recent years with no distinctive antiviral therapies. Therefore, there is a desperate need for broad-spectrum antiviral drugs that can be active against a large number of existing and emerging viruses. Herein, we prepared a kind of benzoxazine monomer derived carbon dots (BZM-CDs) and demonstrated their infection-blocking ability against life-threatening flaviviruses (Japanese encephalitis, Zika, and dengue viruses) and non-enveloped viruses (porcine parvovirus and adenovirus-associated virus). It was found that BZM-CDs could directly bind to the surface of the virion, and eventually the first step of virus-cell interaction was impeded. The developed nanoparticles are active against both flaviviruses and non-enveloped viruses in vitro. Thus, the application of BZM-CDs may constitute an intriguing broad-spectrum approach to rein in viral infections.