Carbon dots enhanced gelatin/chitosan bio-nanocomposite packaging film for perishable foods

Carbon dots(CDs) with intriguing fluorescent property, good biocompatibility, high stability, easy interaction with substrates, are burgeoning carbon nanoparticles with large potential in various applications. Incorporating CDs into the polymer matrix is becoming a popular strategy to endow the complex with new functions. Herein, the green-synthesized CDs was integrated into the mixture of gelatin(derived from waste fish scale) and chitosan, and a multifunctional bio-nanocomposite(defined as Gel...     

Stripping chronopotentiometric analysis of cysteine on nano-silver coat polyquercetin–MWCNT modified platinum electrode

Silver nanoparticles coat polyquercetin (Qu) and multi-walled carbon nanotube (MWCNT) complex films were prepared using an electrochemical coupling strategy on platinum electrode (Ag/Qu/MWCNT/Ch/Pt). The new composite material was characterized by means of field emission scanning electron microscopy, X-ray photoelectron spectroscopy spectra, X-ray diffraction, and electrochemical techniques, which confirmed that polyquercetin plays an important role to obtain a great deal of uniformly dispersed silver nanoparticles and MWCNT complex film with a diameter of 10 ± 6 nm. The resulting Ag/Qu/MWCNT/Ch/Pt electrode shows a significant electrocatalysis for the redox of cysteine (CysH). The stripping chronopotentiometric analysis of CysH has been successfully used with a satisfying effect. A linear range of 1 × 10⁻¹⁰ to 9 × 10⁻⁸ M was obtained with a detection limit of 3 × 10⁻¹¹ M (3σ) and sensitivity of 35 μA/nM. The films were also robust, surviving up to 100 consecutive cyclic voltammograms and sonication.     

The synthesis of free-standing films of polymer/nanocarbon composites using the carbon nanopowder's buoyancy

In this work we report the synthesis of free-standing films of polymer/nanocarbon composites. The method consists in forming a thin film of carbon nanoparticles onto the water's surface. Through the free infiltration of the polymer between the nanoparticles which form the film, after the polymer is cured, we obtain free-standing films of polymer/nanocarbon composites. The composite films are homogeneous; they have 5 wt.% carbon nanoparticles within the polymer matrix and are a few micrometers in thickness.     

Capillary electrophoresis coupled to chemometrics for analysis of carbon dots in nanoparticles mixtures

Since their discovery in 2004, carbon dots (CDs) have attracted attention due to their intrinsic physicochemical properties and the easy synthesis from simple precursors. However, quantification of CDs in mixtures of nanoparticles with similar sizes and surface functionality is still a challenging issue for research applications or regulatory purposes. In this work, CDs and silver nanoparticles were first synthesized under alkaline conditions by using glucose as precursor and capping agent, respectively. Mixtures of these nanoparticles were made at micromolar range, without purification, and then analyzed by CE–DAD, using an electrolyte solution composed of 20 mM sodium borate and 20 mM SDS at pH 8.5, in a total time of <15 min. The three-way electrophoretic data were then decomposed by advanced chemometric models, parallel factor analysis and multivariate curve resolution–alternating least-squares. The explained variances for both models were 95.8% (parallel factor analysis) and 85.3% (multivariate curve resolution–alternating least-squares). In both cases, the quality of the results was verified by the root mean square standard deviation coefficient variation, which resulted lower than 5%, and no significant bias was observed at 95% of statistical confidence. Satisfactory prediction for CDs concentration was obtained with recovery values between 80.0% and 115%.     

Inner filter effect (IFE) as a simple and selective sensing platform for detection of tetracycline using milk-based nitrogen-doped carbon nanodots as fluorescence probe

A simple, selective, and sensitive turn-off fluorescent assay for detecting of tetracycline in pharmaceutical dosage form based on inner filter effect (IFE) sensing platform has been described. In this IFE sensing strategy, N-doped carbon dots (CDs) were prepared by one-pot solvothermal synthesis using milk as a precursor and were directly used as a fluorophore in IFE. The prepared CDs were characterized by common spectroscopic and microscopic techniques. The CDs exhibited excitation-wavelength dependent emission with 10% as the fluorescence quantum yield. The fluorescence of CDs was decreased in correlation to the addition of absorber (tetracycline), as the excitation spectrum of the fluorophore (CDs) matches the absorption spectrum of the absorber. The present IFE-based sensing platform showed a good linear relationship from 2.0 µM to 200 µM (R² = 0.9960) and provided a detection limit of 0.6 µM (signal-to-noise ratio of 3). Additionally, the cytotoxic effects of CDs were determined using normal healthy male Balb/C mice model treated with various doses of CDs and at the end of the study, no mortality or even no sign of toxicity was observed at oral doses of 100 and 200 mg/kg CDs in all treated animals. The proposed nanoprobe assay is a free from interferences, low-cost, biocompatible, and accurate for the detection of tetracycline in pharmaceutical formulation.     

Functionalized carbon dots as sensors for gold nanoparticles in spiked samples: Formation of nanohybrids

This paper reports the synthesis, passivation and functionalization of luminescent carbon dots (CDs) possessing surface thiol ending groups. A simple procedure involving amidation of passivated carbon dots (p-CDs) with cysteamine boosts their photoluminescent properties and enables their use as easily controlled fluorescent nanosensors for determining citrate–gold nanoparticles (AuNPs). The mechanism behind the quenching phenomenon was established from fluorescence measurements at high temperatures and lifetime tests, and found to involve static quenching leading to the formation of CD–AuNP nanohybrids. A method for determining AuNPs in complex matrices was developed and validated by application to spiked drinking water and mussel tissues. The limits of detection and quantitation for AuNPs thus obtained were 0.20 and 0.66 nmol L^–1, respectively.     

Red,green and blue aggregation‐induced emissive carbon dots

As one of the most promising fluorescent nanomaterials, carbon dots (CDs) have been extensively studied for their fluorescent properties in solution. However, research on the synthesis of multicolor solid-state fluorescence (SSF) CDs (from blue to red) is rarely reported. Herein, we used o-phenylenediamine, m-phenylenediamine and p-phenylenediamine with dithiosalicylic acid (DTSA) in the solvothermal reaction using acetic acid as a solvent to obtain aggregation-induced emissive (AIE) CDs of red (620 nm), green (520 nm), and blue (478 nm), respectively. XPS spectra and TEM image show that with the red-shift of luminescence, the particle size and content of C=O of the CDs gradually increases. Finally, based on the non-matrix solid-state multicolor luminescence characteristics of CDs, the application of white light LED devices is realized. Besides, based on the fat-soluble properties of CDs, fingerprint detection applications are realized.     

Comparative study for N and S doped carbon dots: Synthesis,characterization and applications for Fe probe and cellular imaging

A facile and eco-friendly approach to prepare nitrogen(N)- and sulfur(S)-doped carbon dots (CDs) by one step microwave-assisted pyrolysis of the precursors with dl-malic acid as carbon source, ethanolamine and ethane-sulfonic acid as N and S dopants, respectively, was reported. Through the extensive investigation on morphology, chemical structures and optical properties of the carbon dots, it was found that the obtained CDs exhibited good luminescence stability, high resistance to photo bleaching and favorite solubility. Compared with undoped CDs, adding the N or S dopant could give rise to a slightly smaller particle size and a long fluorescence lifetime of CDs. Moreover, the optimal N-CDs was successfully employed as good multicolor cell imaging probes due to its fine dispersion in water, excitation-dependent emission, excellent biocompatibility and low toxicity. Besides, such N-CDs showed a wide detection range and excellent accuracy as fluorescent probe for Fe³⁺ ions. This probe enabled the selective detection of Fe³⁺ ions with a linear range of 6.0–200 μM and a limit of detection of 0.80 μM.     

Synthesis of Fluorescent Carbon Dots and Their Application in Ascorbic Acid Detection

Water-soluble fluorescent carbon dots (CDs) were synthesized by a hydrothermal method using citric acid as the carbon source and ethylenediamine as the nitrogen source. The repeated and scale-up synthetic experiments were carried out to explore the feasibility of macroscopic preparation of CDs. The CDs/Fe³⁺ composite was prepared by the interaction of the CDs solution and Fe³⁺ solution. The optical properties, pH dependence and stability behavior of CDs or the CDs/Fe³⁺ composite were studied by ultraviolet spectroscopy and fluorescence spectroscopy. Following the principles of fluorescence quenching after the addition of Fe³⁺ and then the fluorescence recovery after the addition of asorbic acid, the fluorescence intensity of the carbon dots was measured at λex = 360 nm, λem = 460 nm. The content of ascorbic acid was calculated by quantitative analysis of the changing fluorescence intensity. The CDs/Fe³⁺ composite was applied to the determination of different active molecules, and it was found that the composite had specific recognition of ascorbic acid and showed an excellent linear relationship in 5.0–350.0 μmol·L⁻¹. Moreover, the detection limit was 3.11 μmol·L⁻¹. Satisfactory results were achieved when the method was applied to the ascorbic acid determination in jujube fruit. The fluorescent carbon dots composites prepared in this study may have broad application prospects in a rapid, sensitive and trace determination of ascorbic acid content during food processing.     

Synthesis of highly luminescent carbon dots from postconsumer waste silk cloth and investigation of its electron transfer dynamics with methyl viologen dichloride

Synthesis of luminescent carbon dots (CDs) from biological waste materials is gaining more attention in the present-day scenario. We have synthesized highly luminescent (luminescence quantum yield, φ ​= ​19.1%), water-soluble CDs from a postconsumer waste silk cloth via a facile hydrothermal synthetic method. The resulting CDs are characterized and their photophysical properties are studied in detail. The electron transfer dynamics of CDs in presence of methyl viologen dichloride hydrate (MV²⁺) is systematically investigated in this work. Knowledge of the electron transfer dynamics of CDs is essential in the structural elucidation of CDs, prediction of sensing mechanisms and utilizing the CDs in energy storage devices.     

Co-extrusion of multilayer poly(m-xylylene adipimide) nanocomposite films for high oxygen barrier packaging applications

Multilayer packaging films incorporating a montmorillonite layered silicate (MLS)/poly(m-xylylene adipimide) (MXD6) nanocomposite as the oxygen barrier layer and low-density polyethylene (LDPE) as the moisture resistant layer were produced through the co-extrusion process at the laboratory and pilot scale level. Extrusion screw speeds were varied from 30 to 130 rpm in order to produce samples with varying layer thicknesses. The multilayer film structure was scaled up from the laboratory scale to the pilot-level scale based on oxygen transmission data obtained from the laboratory-scale process parameters. Laboratory-scale film results indicated that the film which demonstrated an optimal oxygen transmission rate (OTR) of 0.3 cm³/(m² day) at 60%RH and water vapor transmission rate (WvTR) of 1.4 g/(m² day) at 90%RH had a structure that contained a core barrier film layer of nanocomposite MXD6 that makes up roughly 34% of the total film thickness, with the remainder of the film material consisting of maleic anhydride grafted polyolefin tie layers and LDPE skin layers. The OTR of the films changed as the relative humidity of the test environment was varied from 0 to 90%. However, for the pilot-scale trial it was necessary to reduce the target thickness of the core nylon barrier layer to 22% due to layer-to-layer melt flow instabilities that occurred during processing. The barrier properties of the multi-layer co-extruded films were highly dependant on overall film thickness. The highest performing oxygen barrier pilot-scale film had an OTR of 0.3 cm³/(m² day) (60%RH) and a WvTR of 2.4 g/(m² day) (90%RH) with a core nylon layer of 1.5 mil and a total thickness of 7.7 mil. Correlation of the layer thicknesses to the barrier and mechanical properties of the pilot-scale multilayer films indicated that an increased nanocomposite core layer thickness improved the oxygen barrier performance and decreased film elongation while improving the tear resistance of the films.     

Environmentally friendly cleaner water-soluble fluorescent carbon dots coated with chitosan: synthesis and its application for sensitivity determination of Cr(VI) ions

In the current work, novel environmentally friendly water-soluble fluorescent carbon dots coated with chitosan (CDs/CTS) were successively synthesized via a facile and green preparation procedure. The fluorescent carbon dots were prepared through a simple, convenient and one-step hydrothermal method in the presence of cellulose as a raw material. The CDs/CTS were connected together via intermolecular hydrogen bonds interaction and chemical bonds between hydroxyl and amino groups in the chitosan polymeric chains and hydroxyl groups of fluorescent carbon dots. This approach can be applied for milligram-scale preparation of these water-soluble particles. The CDs/CTS material showed blue fluorescence under UV exposure. The structure and morphology of as-prepared CDs/CTS were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. The as-prepared CDs/CTS exhibited excellent fluorescent property and good stability. The fluorescence of as-prepared CDs/CTS could be quenched by the Cr(VI) ions. The effects of environmental factors on the fluorescence intensity were investigated in detail, and the obtained results showed that the optimum conditions for the Cr(VI) ions determination were as follows: 1:3 of mass ratio of CDs/CTS, 9.5 of pH and 20 min of reaction time. Under optimized experimental conditions, a novel fluorescent probe was developed for the detection of Cr(VI) ions, which exhibited wide linear ranges (0–600 μmol/L) and excellent selectivity. The proposed method was directly applied for the determination of Cr(VI) ions in water and soil samples with satisfactory results.     

Solid‐phase microextraction based on an agarose‐chitosan‐multiwalled carbon nanotube composite film combined with HPLC–UV for the determination of nonsteroidal anti‐inflammatory drugs in aqueous samples

We describe the preparation, characterization, and application of a composite film adsorbent based on blended agarose‐chitosan‐multiwalled carbon nanotubes for the preconcentration of selected nonsteroidal anti‐inflammatory drugs in aqueous samples before determination by high performance liquid chromatography with ultraviolet detection. The composite film showed a high surface area (4.0258 m²/g) and strong hydrogen bonding between the multiwalled carbon nanotubes and agarose/chitosan matrix, which prevent adsorbent deactivation and ensure long‐term stability. Several parameters, such as sample pH, addition of salt, extraction time, desorption solvent, and concentration of multiwalled carbon nanotubes in the composite film were optimized using a one‐factor‐at‐time approach. The optimum extraction conditions obtained were as follows: isopropanol as conditioning solvent, 10 mL of sample solution at pH 2, extraction time of 30 min, stirring speed of 600 rpm, 100 μL of isopropanol as desorption solvent, desorption time of 5 min under ultrasonication, and 0.4% w/v of composite film. Under the optimized conditions, the calibration curve showed good linearity in the range of 1–500 ng/mL (r² = 0.997–0.999), and good limits of detection (0.89–8.05 ng/mL) were obtained with good relative standard deviations of < 4.59% (n = 3) for the determination of naproxen, diclofenac sodium salt, and mefenamic acid drugs.     

Yellow emissive carbon dots in ludox silica matrix with anticancer activity for enhanced imaging of developed sweat latent fingermarks

The recognition of fingermarks plays a vital role during a criminal investigation. In the current scenario, fluorescent nano-powders emerged as a potential candidate for latent fingermark detection. We pioneer the use of microwave technology for the synthesis of carbon dots (CDs) with the cationic surfactant (cetylpyridinium chloride). The surfactant-derived CDs exhibit yellow fluorescence and emission at 545 nm with high quantum yield of (QY～34%). The prepared CDs also demonstrated amphiphilic properties. These luminous CDs were combined with ludox HS-30 to develop fluorescent hybrid nano-powders for the detection of sweat latent fingermarks on a non-porous surface. The ludox@CDs accumulate particle size 11.36 ± 1.235 nm and surface area 111 cm³/g^?1. The fluorescent hybrid nano-powders emerged to be successful in creating high contrast and accurate latent fingermark images. Furthermore, cytotoxicity studies on breast cell lines (fR-2 and MCF-7) were conducted by using ludox@CDs. The results revealed that ludox@CDs were less toxic and biocompatible in comparison to the commercialized dusting reagents. Fortunately, ludox@CDs demonstrated anticancer efficacy against MCF-7 breast cancer cell lines. Thus, our findings herald a new age for fluorescent hybrid nano-powders in criminal investigation and biomedical applications.     

Eco friendly synthesis of fluorescent carbon dots for the sensitive detection of ferric ions and cell imaging

This study established a ferric ion (Fe³⁺) detection method as a result of the fluorescence quenching effect of Fe³⁺ on carbon dots (CDs). Specifically, we proposed, a green microwave synthesis route towards fluorescent CDs that requires only the brewer’s spent grain as starting materials. Transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectra and X-ray photoelectron spectroscopy were performed to investigate the CDs characteristic: morphology, size distribution, functional groups, and composition, respectively. The experimental results, which were run under optimal experimental conditions, indicated that the fluorescence intensity and concentration of Fe³⁺ were within the desired linear range (0.3–7 μM). The detection limit of this assay towards Fe³⁺ was 95 nM. The proposed method showed significant selectivity with respect to interfering ions. We evaluated the potential application of this method with tap water, lake water and fetal bovine serum as real samples. Additionally, the CDs could be served as superior bioimaging probes in Hela cells as a result of their excellent optical stability and good biocompatibility. In a word, the present study provides a new idea for CDs derived from the waste of agricultural products for detecting food or environmental contaminants and cell imaging.     

Improvement of mechanical and oxygen barrier properties of cellulose films by controlling drying conditions of regenerated cellulose hydrogels

Mechanical, thermal and oxygen barrier properties of regenerated cellulose films prepared from aqueous cellulose/alkali/urea solutions can be markedly improved by controlling the drying conditions of the films. By pre-pressing followed by vacuum drying under compression, the tensile strength, Young’s modulus, coefficient of thermal expansion and oxygen permeability of the dried films reached 263 MPa, 7.3 GPa, 10.3 ppm K⁻¹ and 0.0007 ml μm m⁻² day⁻¹ kPa⁻¹, respectively. Thus, films produced in this way show the highest performance of regenerated cellulose films with no orientation of cellulose chains reported to date. These improved properties are accompanied by a clear increase in cellulose II crystallinity from 50 to 62% during pre-pressing/press-vacuum drying process. At the same time, the film density increased from 1.45 to 1.57 g cm⁻³, and the moisture content under equilibrium conditions decreased from 14.1 to 9.8%. Hence, the aqueous alkali/urea solvent system has potential applications in producing new and environmentally friendly cellulose films with high performances through control of the drying conditions.     

Rapid and Large‐Scale Production of Multi‐Fluorescence Carbon Dots by a Magnetic Hyperthermia Method

The intrinsic low yield of carbon dots (CDs) is a barrier that limits practical application. Now, a magnetic hyperthermia (MHT) method is used to synthesize fluorescent CDs on a large scale (up to 85 g) in one hour (yield ca. 60 %). The reaction process is intensified by MHT since the efficient heating system enhances the energy transfer. CDs with blue, green, and yellow luminescence are synthesized by using carbamide and citrate with three different cations (Zn²⁺, Na⁺, K⁺), respectively. The CDs exhibit bright fluorescence under UV light and show excellent monodispersity and solubility in water. The alternation of photoluminescence (PL) emissions of these CDs is probably due to the difference in particle sizes and surface state. A bar coating technique is used to construct large‐area emissive polymer/CDs films. CDs can insert themselves into the polymer chains by hydrogen bonding and electrostatic interactions. Wound healing efficiency can be enhanced by the Zn‐CDs/PCL nanofibrous scaffold.     

Single-material solvent-sensitive fluorescent actuator from carbon dots inverse opals based on gradient dewetting

A novel solvent-sensitive fluorescent actuator with reversibility has been obtained from carbon dots(CDs) inverse opals, which is prepared via infiltrating CDs solution into the interstice of colloidal crystal template, thermal polymerization of CDs materials and removing the colloidal template. The as-prepared CDs inverse opal actuator shows a bending angle of75° in 10.2 s, bending rate of 7.35(°) × s-1. In particular, the fluorescence intensity of the films varies during the actuating process. The actuating behavior is attributed to the inhomogeneous swelling/shrinking of the film, which originates from the gradient dewetting by solvent evaporation and hydrogen-bonding interaction between the solvent molecules and oxygen/hydrogen ions of CDs side chain. The CDs inverse opal actuator has the advantages of quick response, good repeatability and strong fluorescence, which gives an important insight into the design and manufacture of novel and advanced solvent-actuators.     

Triphenylamine-Derived Solid-State Emissive Carbon Dots for Multicolor High-Efficiency Electroluminescent Light-Emitting Diodes

Two kinds of triphenylamine-derived solid-state emissive carbon dots (CDs) with orange and yellow color are facilely synthesized through solvothermal treatment, taking advantage of the nonplanar structure and good carrier mobility of triphenylamine unit. Theoretical calculations show that the triphenylamine structure could greatly inhibit the direct π–π stacking of aromatic skeletons and enhance the fluorescence properties of CDs in aggregation state. By adopting the CDs as single emissive layer, high-performance orange-color and green-color electroluminescent light-emitting diodes (LEDs) are successfully fabricated, with maximum brightness of 9450/4236 cd m⁻², high current efficiency of 1.57/2.34 cd A⁻¹ and low turn-on voltage of 3.1/3.6 eV are respectively achieved. Significantly, white-color LED device is further prepared. This work provides a universal platform for the construction of novel solid-state emissive CDs with significant applications in photoelectric device.     

Composite film of carbon nanotubes and chitosan for preparation of amperometric hydrogen peroxide biosensor

A new amperometric biosensor for hydrogen peroxide was developed based on cross-linking horseradish peroxidase (HRP) by glutaraldehyde with multiwall carbon nanotubes/chitosan (MWNTs/chitosan) composite film coated on a glassy carbon electrode. MWNTs were firstly dissolved in a chitosan solution. Then the morphology of MWNTs/chitosan composite film was characterized by field-emission scanning electron microscopy. The results showed that MWNTs were well soluble in chitosan and robust films could be formed on the surface. HRP was cross-linked by glutaraldehyde with MWNTs/chitosan film to prepare a hydrogen peroxide biosensor. The enzyme electrode exhibited excellent electrocatalytic activity and rapid response for H₂O₂ in the absence of a mediator. The linear range of detection towards H₂O₂ (applied potential: −0.2 V) was from 1.67 × 10⁻⁵ to 7.40 × 10⁻⁴ M with correction coefficient of 0.998. The biosensor had good repeatability and stability for the determination of H₂O₂. There were no interferences from ascorbic acid, glucose, citrate acid and lactic acid.