Carbon dots embedded nanofiber films: Large-scale fabrication and enhanced mechanical properties

Polysaccharide- and protein-based edible films combined with microwave technology for meat preservation

To reduce food-borne bacterial infection caused by food spoilage, developing highly efficient food packing film is still an urgent need for food preservation. Herein, microwave-assisted antibacterial nanocomposite films CaO2@PVP/EA/CMC-Na (CP/EC) were synthesized using waste eggshell as precursor, egg albumen (EA) and sodium carboxymethylcellulose (CMCNa) as matrix by casting method. The size of CaO2@PVP (CP) nanoparticles with monodisperse spherical structures was 100-240 nm. When microwave and CP nanoparticles (0.05 mg/mL) were treated for 5 min, the mortality of E. coli and S. aureus could reach >97 %. Under microwave irradiation (6 min), the bactericidal rate of 2.5 % CP/EC film against E. coli and S. aureus reached 98.6 % and 97.2 %, respectively. After adding CP nanoparticles, the highest tensile strength (TS) and elongation at break (EB) of CP/EC film reached 19.59 MPa and 583.43 %, respectively. At 18 °C, the proliferation of bacterial colonies on meat can be significantly inhibited by 2.5 % CP/EC film. Detailed characterization showed that the excellent meat preservation activity was due to the synergistic effect of dynamic effect generated by ROS and thermal effect of microwave. This study provides a promising approach for the packaging application of polysaccharide- and protein-based biomass nanocomposite antibacterial edible films.

Covalently cross-linked ultrastrong SiO2-loaded polyvinyl alcohol fibers via microfluidic spinning

Polyvinyl alcohol (PVA) fiber materials have gained immense recognition due to their good biocompatibility and wide applications. However, methods allowing the synergistic enhancement of mechanical strength and toughness of PVA fibers still remain a key challenge. To this end, we developed covalently cross-linked ultrastrong SiO2-loaded polyvinyl alcohol fibers via a microfluidic spinning chemistry strategy. The thermal stretching and annealing processes not only promote the ordered arrangement of molecules, but also facilitate the ring opening reaction and increase crystallinity. Thus, the resulting fiber has a high tensile strength of 866 MPa, a specific toughness of 288 J g-1 and a tensile strain of 80%. This work provides a covalent cross-linking reinforcement method to prepare ultrastrong composite fibers assisted by microfluidic spinning chemistry and thermal stretching, which would lead to the fabrication of mechanically strong fiber materials through a simple pathway.

Carbon Dots and Their Polymeric Nanocomposites: Insight into Their Synthesis, Photoluminescence Mechanisms, and Recent Trends in Sensing Applications

Carbon dots (CDs), a novel class of carbon-based nanoparticles, have received a lot of interest recently due to their exceptional mechanical, chemical, and fluorescent properties, as well as their excellent photostability and biocompatibility. CDs' emission properties have already found a variety of potential applications, in which bioimaging and sensing are major highlights. It is widely acknowledged that CDs' fluorescence and surface conditions are closely linked. However, due to the structural complexity of CDs, the specific underlying process of their fluorescence is uncertain and yet to be explained. Because of their low toxicity, robust and wide optical absorption, high chemical stability, rapid transfer characteristics, and ease of modification, CDs have been recognized as promising carbon nanomaterials for a variety of sensing applications. Thus, following such outstanding properties of CDs, they have been mixed and imprinted onto different polymeric components to achieve a highly efficient nanocomposite with improved functional groups and properties. Here, in this review, various approaches and techniques for the preparation of polymer/CDs nanocomposites have been elaborated along with the individual characteristics of CDs. CDs/polymer nanocomposites recently have been highly demanded for sensor applications. The insights from this review are detailed sensor applications of polymer/CDs nanocomposites especially for detection of different chemical and biological analytes such as metal ions, small organic molecules, and several contaminants.

Free-Boundary Microfluidic Platform for Advanced Materials Manufacturing and Applications

Microfluidics, with its remarkable capacity to manipulate fluids and droplets at the microscale, has emerged as a powerful platform in numerous fields. In contrast to conventional closed microchannel microfluidic systems, free-boundary microfluidic manufacturing (FBMM) processes continuous precursor fluids into jets or droplets in a relatively spacious environment. FBMM is highly regarded for its superior flexibility, stability, economy, usability, and versatility in the manufacturing of advanced materials and architectures. In this review, a comprehensive overview of recent advancements in FBMM is provided, encompassing technical principles, advanced material manufacturing, and their applications. FBMM is categorized based on the foundational mechanisms, primarily comprising hydrodynamics, interface effects, acoustics, and electrohydrodynamic. The processes and mechanisms of fluid manipulation are thoroughly discussed. Additionally, the manufacturing of advanced materials in various dimensions ranging from zero-dimensional to three-dimensional, as well as their diverse applications in material science, biomedical engineering, and engineering are presented. Finally, current progress is summarized and future challenges are prospected. Overall, this review highlights the significant potential of FBMM as a powerful tool for advanced materials manufacturing and its wide-ranging applications.

Recent Progress on Chiral Carbon Dots: Synthetic Strategies and Biomedical Applications

The discovery of chiral carbon dots (Ch-CDs) has opened up an exciting new research direction in the field of carbon dots. It not only retains the chirality of the precursor and exhibits highly symmetric chiral optical properties but also has properties such as chemical stability, antibacterial and antitumor properties, and good biocompatibility of carbon dots. Based on these advantages, the application of Ch-CDs in the biomedical field has attracted significant interest among researchers. However, a comprehensive review of the selection of precursors for Ch-CDs, preparation methods, and applications in biomedical fields is still lacking. Here, we summarize their precursor selection and preparation methods based on recent reports on Ch-CDs and provide the first comprehensive review for specific applications in biomedical engineering, such as biosensing, bioimaging, drug carriers, antibacterial and antibiofilm, and enzyme activity modulation. Finally, we discuss application prospects and challenges that need to be overcome. We hope this review will provide valuable guidance for researchers to prepare novel Ch-CDs and facilitate their application in biomedical engineering.

Deep insights to explain the mechanism of carbon dot formation at various reaction times using the hydrothermal technique: FT-IR, 13C-NMR, 1H-NMR, and UV-visible spectroscopic approaches

A well-explained mechanism for synthesizing carbon dots (CDs) is not yet explored and is still a subject of great debate and challenge. This study used a one-step hydrothermal method to prepare highly efficient, gram-scale, excellent water solubility, and blue fluorescent nitrogen-doped carbon dots (NCDs) with the particle size average distribution of around 5 nm from 4-aminoantipyrine. The effects of varying synthesis reaction times on the structure and mechanism formation of NCDs were investigated using spectroscopic methods, namely FT-IR, 13C-NMR, 1H-NMR, and UV-visible spectroscopies. The spectroscopic results indicated that increasing the reaction time affects the structure of the NCDs. As the hydrothermal synthesis reaction time is extended, the intensity of the peaks in the aromatic region decreases, and new peaks in the aliphatic and carbonyl group regions are generated, which display enhanced intensity. In addition, the photoluminescent quantum yield increases as the reaction time increases. The presence of a benzene ring in 4-aminoantipyrine is thought to contribute to the observed structural changes in NCDs. This is due to the increased noncovalent π-π stacking interactions of the aromatic ring during the carbon dot core formation. Moreover, the hydrolysis of the pyrazole ring in 4-aminoantipyrine results in polar functional groups attached to aliphatic carbons. As the reaction time prolongs, these functional groups progressively cover a larger portion of the surface of the NCDs. After 21 h of the synthesis process, the XRD spectrum of the produced NCDs illustrates a broad peak at 21.1°, indicating an amorphous turbostratic carbon phase. The d-spacing measured from the HR-TEM image is about 0.26 nm, which agrees with the (100) plane lattice of graphite carbon and confirms the purity of the NCD product with a surface covered by polar functional groups. This investigation will lead to a greater understanding of the effect of hydrothermal reaction time on the mechanism and structure of carbon dot synthesis. Moreover, it offers a simple, low-cost, and gram-scale method for creating high-quality NCDs crucial for various applications.

Antibacterial Carbon Dots-Based Composites

The emergence and global spread of bacterial resistance to conventionally used antibiotics have highlighted the urgent need for new antimicrobial agents that might replace antibiotics. Currently, nanomaterials hold considerable promise as antimicrobial agents in anti-inflammatory therapy. Due to their distinctive functional physicochemical characteristics and exceptional biocompatibility, carbon dots (CDs)-based composites have attracted a lot of attention in the context of these antimicrobial nanomaterials. Here, a thorough assessment of current developments in the field of antimicrobial CDs-based composites is provided, starting with a brief explanation of the general synthesis procedures, categorization, and physicochemical characteristics of CDs-based composites. The many processes driving the antibacterial action of these composites are then thoroughly described, including physical destruction, oxidative stress, and the incorporation of antimicrobial agents. Finally, the obstacles that CDs-based composites now suffer in combating infectious diseases are outlined and investigated, along with the potential applications of antimicrobial CDs-based composites.

Facile Access to Fabricate Carbon Dots and Perspective of Large-Scale Applications

Carbon dots (CDs), fluorescent carbon nanoparticles with particle sizes < 10 nm, are constantly being developed for potential large-scale applications. Recently, methods allow CD synthesis to be carried out on large-scale preparation in a controlled fashion are potentially important for multiple disciplines, including bottom-up strategy, top-down method. In this review, the recent progresses in the research of the methods for large-scale production of CDs and their functionalization are summarized. Especially, the methods of CD synthesis, such as large-scale preparation, hydrothermal/solvothermal, microwave-assisted, magnetic hyperthermia microfluidic and other methods, along with functionalization of CDs, are summarized in detail. By promising applications of CDs, there are three aspects have been already reported, such as enhancing mechanical properties, flame retardancy, and energy storage. Also, future development of CDs is prospected.