Fluorescent Self-Healing Carbon Dot/Polymer Gels

Selective Bacterial Growth Inactivation by pH-Sensitive Sulfanilamide Functionalized Carbon Dots

Carbon dots (CDs) were synthesized hydrothermally by mixing citric acid (CA) and an antifolic agent, sulfanilamide (SNM), employed for pH sensing and bacterial growth inactivation. Sulfanilamide is a prodrug; aromatic hetero cyclization of the amine moiety along with other chemical modifications produces an active pharmacological compound (chloromycetin and miconazole), mostly administered for the treatment of various microbial infections. On the other hand, the efficacy of the sulfanilamide molecule as a drug for antimicrobial activity was very low. We anticipated that the binding of the sulfanilamide molecule on the carbon dot (CD) surface may form antibacterial CDs. Citric acid was hybridized with sulfanilamide during the hydrothermal preparation of the CDs. The molecular fragments of bioactivated sulfanilamide molecule play a crucial role in bacterial growth inactivation for Gram-positive and Gram-negative bacteria. The functional groups of citric acid and sulfanilamide were conserved during the CD formation, facilitating the zwitterionic behavior of CDs associated with its photophysical activity. At low concentrations of CDs, the antibacterial activity was apparent for Gram-positive bacteria only. This Gram-positive bacteria selectivity was also rationalized by zeta potential measurement.

Synthesis of Tough and Fluorescent Self-Healing Elastomers by Scandium-Catalyzed Terpolymerization of Pyrenylethenylstyrene, Ethylene, and Anisylpropylene

The synthesis of fluorescent self-healing polymers by the incorporation of a fluorophore-containing olefin into a polyolefin backbone through catalyst-controlled multicomponent copolymerization is of fundamental interest and practical importance, but such an approach has remained unexplored to date. Herein, we report for the first time the synthesis of tough and fluorescent self-healing polymers by sequence-controlled terpolymerization of 4-[2-(1-pyrenyl)ethenyl]styrene (Pyr), ethylene (E), and anisylpropylene (AP) using a sterically demanding half-sandwich scandium catalyst. The resulting terpolymers consisted of relatively long alternating E-alt-AP sequences, isolated Pyr units, and short E-E blocks, which exhibited excellent tensile strength, remarkable self-healability, and high fluorescence quantum yield. The excellent mechanical and self-healing properties could be attributed to the nanophase separation of the crystalline E-E segments and the hard Pyr aggregates from a flexible E-alt-AP segment matrix, in which the Pyr units not only served as an efficient fluorophore but also played an important role in forming nanodomains and enhancing the polymer mobility. Furthermore, the styrenyl C═C bond of the Pyr unit in the terpolymers could undergo [2 + 2] cycloaddition under photoirradiation, which thus enabled the fabrication of a self-healable fluorescent two-dimensional image on a terpolymer film through photolithography. This work offers an unprecedented efficient protocol for the synthesis of a brand-new family of fluorescent self-healing materials, showcasing the high potential of catalyst-controlled sequence-regular copolymerization of different olefins for the creation of novel functional polymers.

Adsorption of Aldehyde-Functional Diblock Copolymer Spheres onto Surface-Grafted Polymer Brushes via Dynamic Covalent Chemistry Enables Friction Modification

Dynamic covalent chemistry has been exploited to prepare numerous examples of adaptable polymeric materials that exhibit unique properties. Herein, the chemical adsorption of aldehyde-functional diblock copolymer spherical nanoparticles onto amine-functionalized surface-grafted polymer brushes via dynamic Schiff base chemistry is demonstrated. Initially, a series of cis-diol-functional sterically-stabilized spheres of 30-250 nm diameter were prepared via reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization. The pendent cis-diol groups within the steric stabilizer chains of these precursor nanoparticles were then oxidized using sodium periodate to produce the corresponding aldehyde-functional spheres. Similarly, hydrophilic cis-diol-functionalized methacrylic brushes grafted from a planar silicon surface using activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) were selectively oxidized to generate the corresponding aldehyde-functional brushes. Ellipsometry and X-ray photoelectron spectroscopy were used to confirm brush oxidation, while scanning electron microscopy studies demonstrated that the nanoparticles did not adsorb onto a cis-diol-functional precursor brush. Subsequently, the aldehyde-functional brushes were treated with excess small-molecule diamine, and the resulting imine linkages were converted into secondary amine bonds via reductive amination. The resulting primary amine-functionalized brushes formed multiple dynamic imine bonds with the aldehyde-functional diblock copolymer spheres, leading to a mean surface coverage of approximately 0.33 on the upper brush layer surface, regardless of the nanoparticle size. Friction force microscopy studies of the resulting nanoparticle-decorated brushes enabled calculation of friction coefficients, which were compared to that measured for the bare aldehyde-functional brush. Friction coefficients were reasonably consistent across all surfaces except when particle size was comparable to the size of the probe tip. In this case, differences were ascribed to an increase in contact area between the tip and the brush-nanoparticle layer. This new model system enhances our understanding of nanoparticle adsorption onto hydrophilic brush layers.

Room-Temperature Self-Healing Conductive Elastomers for Modular Assembly as a Microfluidic Electrochemical Biosensing Platform for the Detection of Colorectal Cancer Exosomes

Modular components for rapid assembly of microfluidics must put extra effort into solving leakage and alignment problems between individual modules. Here, we demonstrate a conductive elastomer with self-healing properties and propose a modular microfluidic component configuration system that utilizes self-healing without needing external interfaces as an alternative to the traditional chip form. Specifically, dual dynamic covalent bond crosslinks (imine and borate ester bonds) established between Polyurethane (PU) and 2-Formylbenzeneboronic acid (2-FPBA) are the key to a hard room-temperature self-healing elastomeric substrate PP (PU/2-FPBA). An MG (MXene/GO) conductive network with stable layer spacing (Al-O bonds) obtained from MXene and graphene oxide (GO) by in situ reduction of metals confers photothermal conductivity to PP. One-step liquid molding obtained a standardized modular component library of puzzle shapes from PP and MGPP (MG/PP). The exosomes were used to validate the performance of the constructed microfluidic electrochemical biosensing platform. The device has a wide detection range (50-10⁵ particles/μL) and a low limit of detection (LOD) (42 particles/μL) (S/N = 3), providing a disposable, reusable, cost-effective, and rapid analysis platform for quantitative detection of colorectal cancer exosomes. In addition, to our knowledge, this is the first exploration of self-healing conductive elastomers for a modular microfluidic electrochemical biosensing platform.

Polymeric Emissive Materials Based on Dynamic Covalent Bonds

Dynamic covalent polymers, composed of dynamic covalent bonds (DCBs), have received increasing attention in the last decade due to their adaptive and reversible nature compared with common covalent linked polymers. Incorporating the DCBs into the polymeric material endows it with advanced performance including self-healing, shape memory property, and so forth. However, the emissive ability of such dynamic covalent polymeric materials has been rarely reviewed. Herein, this review has summarized DCBs-based emissive polymeric materials which are classified according to the different types of DCBs, including imine bond, acylhydrazone bond, boronic ester bond, dynamic C-C bond, as well as the reversible bonds based on Diels–Alder reaction and transesterification. The mechanism of chemical reactions and various stimuli-responsive behaviors of DCBs are introduced, followed by typical emissive polymers resulting from these DCBs. By taking advantage of the reversible nature of DCBs under chemical/physical stimuli, the constructed emissive polymeric materials show controllable and switchable emission. Finally, challenges and future trends in this field are briefly discussed in this review.

Synthesis and Processing of Dynamic Covalently Crosslinked Polydextran/Carbon Dot Nanocomposite Hydrogels with Tailorable Microstructures and Properties

Using functionalized nanoparticles to crosslink hydrophilic polymers is a growing theme of directly constructing nanocomposite (NC) hydrogels. Employing dynamic covalent chemistry at the nanoparticle-polymer interface is particularly attractive due to the spontaneous formation and reversible manner of dynamic covalent bonds. However, the structure and property modulation of the dynamic covalently crosslinked NC hydrogels has not been thoroughly discussed. Here, we fabricated NC hydrogels by using amine-functionalized carbon dots (CDs) to crosslink polydextran aldehyde (PDA) polymers through imine bond formation. The role of PDA with different oxidation degrees (i.e., PDA10, PDA30, and PDA50) in affecting the microstructures and properties of PDA@CD hydrogels was systematically investigated, showing that the PDA50@CD hydrogel presented the densest structure and the highest mechanical strength among the three PDA@CD hydrogels. The pH-responsiveness, 3D printing, electrospinning, and biocompatibility of PDA@CD hydrogels were also demonstrated, showing the great promise of using PDA@CD hydrogels for applications in biomedicine and biofabrication.

Multicolor Nitrogen-Doped Carbon Quantum Dots for Environment-Dependent Emission Tuning

Carbon quantum dots (CQDs) have potential applications in many fields such as light-emitting devices, photocatalysis, and bioimaging due to their unique photoluminescence (PL) properties and environmental benignness. Here, we report the synthesis of nitrogen-doped carbon quantum dots (NCQDs) from citric acid and m-phenylenediamine using a one-pot hydrothermal approach. The environment-dependent emission changes of NCQDs were extensively investigated in various solvents, in the solid state, and in physically assembled PMMA-PnBA-PMMA copolymer gels in 2-ethyl-hexanol. NCQDs display bright emissions in various solvents as well as in the solid state. These NCQDs exhibit multicolor PL emission across the visible region upon changing the environment (solutions and polymer matrices). NCQDs also exhibit excitation-dependent PL and solvatochromism, which have not been frequently investigated in CQDs. Most CQDs are nonemissive in the aggregated or solid state due to the aggregation-caused quenching (ACQ) effect, limiting their solid-state applications. However, NCQDs synthesized here display a strong solid-state emission centered at 568 nm attributed to the presence of surface functional groups that restrict the π-π interaction between the NCQDs and assist in overcoming the ACQ effect in the solid state. NCQD-containing gels display significant fluorescence enhancement in comparison to the NCQDs in 2-ethyl hexanol, likely because of the interaction between the polar PMMA blocks and NCQDs. The application of NCQDs-Gel as a solid/gel state fluorescent display has been presented. This research facilitates the development of large-scale, low-cost multicolor phosphor for the fabrication of optoelectronic devices, sensing, and bioimaging applications.

Injectable Self-Healing First-Aid Tissue Adhesives with Outstanding Hemostatic and Antibacterial Performances for Trauma Emergency Care

Soft-tissue trauma emergency caused by natural disasters and traffic accidents is highly prevalent, which can result in massive bleeding, pathogen infection, and even death. Although numerous tissue adhesives can bind to tissue surfaces and cover wounds, most of them still have several deficiencies, including long gelation time, poor adhesive strength, and anti-infection, making them inappropriate for use as first-aid bandages. Herein, injectable and self-healing four-arm-PEG-CHO/polyethyleneimine (PEI) tissue adhesives as liquid first-aid supplies are developed via the dynamic Schiff base reaction for trauma emergency. It is found that the prepared hydrogel adhesives exhibit short and controlled gelation time (9∼88 s), strong adhesive strength, and excellent antibacterial ability. Their hemostatic and antimicrobial performances can be tailored by the mass ratio of four-arm-PEG-CHO/PEI. Moreover, in vitro biological assays display that the developed tissue adhesives possess satisfactory cyto/hemocompatibility. Importantly, in vivo the designed adhesives show fast hemostatic capacity and excellent anti-infection as compared to commercial Prontosan gel. Thus, this work indicates that the four-arm-PEG-CHO/PEI first-aid tissue adhesives display great potential for wound emergency management.

Soft-Hard Segment Combined Carbonized Polymer Dots for Flexible Optical Film with Superhigh Surface Hardness

The rapid development of optical and electronic devices has driven up the demand of high performance optical protective films to avoid exterior influence and extend the service life. But it is not easy to obtain an ideal coating film with high transmittance, high hardness, and good flexibility. Herein, by taking advantage of the special core-shell structure of carbonized polymer dots (CPDs), we propose a strategy to build up a nanoscale soft-hard segment microstructure for optical protective coating materials. The CPDs with hard core and soft polymer chain shell are prepared from citric acid and (3-aminopropyl)triethoxysilane. The as-prepared CPDs can be converted directly to the coating film by the dehydration and cross-linking. In addition to the good optical transmittance, the final film exhibits simultaneously ultrahigh 9H pencil hardness to stand 4000 cycles of a steel-wool wear test, and excellent flexibility to stand bending and rolling-up.

Quantum Dots-Loaded Self-Healing Gels for Versatile Fluorescent Assembly

From the perspective of applied science, methods that allow the simple construction of versatile quantum dots (QDs)-loaded gels are highly desirable. In this work, we report the self-healing assembly methods for various fluorescent QDs-loaded gels. Firstly, we employed horizontal frontal polymerization (FP) to fabricate self-healing gels within several minutes using a rapid and energy-saving means of preparation. The as-prepared gels showed pH sensitivity, satisfactory mechanical properties and excellent self-healing properties and the healing efficiency reached 90%. The integration of the QDs with the gels allowed the generation of fluorescent composites, which were successfully applied to an LED device. In addition, by using the self-healing QDs-loaded gels as building blocks, the self-healing assembly method was used to construct complex structures with different fluorescence, which could then be used for sensing and encoding. This work offers a new perspective on constructing various fluorescent assemblies by self-healing assembly, and it might stimulate the future application of self-healing gels in a self-healing assembly fashion.

Multistimuli-Responsive and Antifreeze Aggregation-Induced Emission-Active Gels Based on CuNCs

Multistimuli-responsive fluorescent gelsbased small molecular gelator by supramolecular assembly, possessing excellent dynamic and reversible characteristic, have caused much concern. In this article, aggregation-induced emission-active fluorescence gels (AIE-gels) with chirality were developed by combining Cu nanoclusters (CuNCs) and natural amino acids, l-tryptophan (l-Trp) or d-Tryptophan (d-Trp). In DMSO/H₂O mixed solvents, CuNCs can self-assemble to form intertwined fibersbased nanoparticles with numerous pores by introducing Zn²⁺. Fibers as second networks of heteronetwork structures are characterized with the participation of l-Trp or d-Trp for cross-linking to reinforce mechanical strength and chiral regulation of gel networks. Aggregation-induced emission enhancement (AIEE) of CuNCs endows the gels with excellent fluorescent properties by introducing solvents and gelation process. The fluorescent gels exhibit sufficient fluorescence intensity (FI) at -20 °C to -80 °C and possess sensitive responsibility including gel-sol transition and fluorescence behavior for stimuli of mechanical force, heating, pH, H₂O₂, and ethylene diamine tetraacetic acid (EDTA).

In Vivo Biodistribution, Clearance, and Biocompatibility of Multiple Carbon Dots Containing Nanoparticles for Biomedical Application

Current research on the use of carbon dots for various biological systems mainly focuses on the single carbon dots, while particles that contain multiple carbon dots have scarcely been investigated. Here, we assessed multiple carbon dots-crosslinked polyethyleneimine nanoparticles (CDs@PEI) for their in vivo biodistribution, clearance, biocompatibility, and cellular uptake. The in vivo studies demonstrate three unique features of the CDs@PEI nanoparticles: (1) the nanoparticles possess tumor-targeting ability with steady and prolonged retention time in the tumor region. (2) The nanoparticles show hepatobiliary excretion and are clear from the intestine in feces. (3) The nanoparticles have much better biocompatibility than the polyethyleneimine passivated single carbon dots (PEI-CD). We also found that pegylated CDs@PEI nanoparticles can be effectively taken up by the cells, which the confocal laser scanning microscope can image under different excitation wavelengths (at 405, 488, and 800 nm). These prior studies provide invaluable information and new opportunities for this new type of intrinsic photoluminescence nanoparticles in carbon dot-based biomedical applications.

Carbon Dot/Polymer Composites with Various Precursors and Their Sensing Applications: A Review

Carbon dots (CDs) have generated much interest because of their significant fluorescence (FL) properties, extraordinary photophysical attributes, and long-term colloidal stability. CDs have been regarded as a prospective carbon nanomaterial for various sensing applications because of their low toxicity, strong and broad optical absorption, high chemical stability, rapid transfer properties, and easy modification. To improve their functionality, CD/polymer composites have been developed by integrating polymers into CDs. CD/polymer composites have diversified because of their easy preparation and applications in sensing, optoelectronics, semiconductors, molecular delivery, and various commercial fields. Many review articles are available regarding the preparation and applications of CDs. Some review articles describing the production and multiple applications of the composites are available. However, no such article has focused on the types of precursors, optical properties, coating characteristics, and specific sensing applications of CD/polymer composites. This review aimed to highlight and summarize the current progress of CD/polymer composites in the last five years (2017–2021). First, we overview the precursors used for deriving CDs and CD/polymer composites, synthesis methods for preparing CDs and CD/polymer composites, and the optical properties (absorbance, FL, emission color, and quantum yield) and coating characteristics of the composites. Most carbon and polymer precursors were dominated by synthetic precursors, with citric acid and polyvinyl alcohol widely utilized as carbon and polymer precursors, respectively. Hydrothermal treatment for CDs and interfacial polymerization for CDs/polymers were frequently performed. The optical properties of CDs and CD/polymer composites were almost identical, denoting that the optical characters of CDs were well-maintained in the composites. Then, the chemical, biological, and physical sensing applications of CD/polymer composites are categorized and discussed. The CD/polymer composites showed good performance as chemical, biological, and physical sensors for numerous targets based on FL quenching efficiency. Finally, remaining challenges and future perspectives for CD/polymer composites are provided.

Nanoscale Carbon-Polymer Dots for Theranostics and Biomedical Exploration

In recent years, new carbonized nanomaterials have emerged in imaging, sensing, and various biomedical applications. Published literature shows that carbon dots (CDs) have been explored more extensively than any other nanomaterials. However, its polymeric version, carbon polymer dots (CPDs), did not get much attention. The non-conjugated and single-particle CPDs have all the merits of polymer and CDs, such as photoluminescent properties. The partially carbonized CPDs can be applied like CDs without surface passivation and functionalization. This merit can be further enhanced through the selection of desired precursors and control of carbonization synthesis. CPDs can absorb UV-visible-NIR light and can enhance the photoresponsive chemical and biochemical interactions. This review aims to introduce this area of renewed interest and provide insights into current developments of CPDs nanoparticles and present an overview of chemical, biological, and therapeutic applications.

Mussel-inspired in situ fabrication of a photothermal composite hydrogel for MR-guided localized tumor ablation

Photothermal ablation could be considered an effective treatment for tumors, but accurate administration and enrichment of photothermal agents remain a huge challenge. Herein, a mussel-inspired photothermal polymeric hydrogel (PPH) was synthesized through a ferric iron-triggered simultaneous metal–catechol coordination reaction and oxidative polymerization of covalently linked pyrrole. The PPH with rapid gelation (less than 10 s) exhibited high photothermal conversion efficiency (49.3%), which enabled effective hyperthermal therapy in situ. Besides, the introduced iron could be used as a T₂-weighted contrast agent for real-time MR imaging to explore the retention and bio-degradation of PPH in vivo. Overall, our findings evidence that the resultant PPH, which possesses potential application in tumor ablation in situ, and metal–catechol coordination strategy inspired by mussel adhesion may stimulate biomedical hydrogel development.

A mussel-inspired photothermal polymeric hydrogel (PPH) was synthesized has been successfully used in tumor ablation in situ.

Applications of Carbon Dots in Optoelectronics

Carbon dots (CDs) are an attractive class of nanomaterials due to the ease of their synthesis, biocompatibility, and superior optical properties. The electronic structure of CDs and hence their optical transitions can be controlled and tuned over a wide spectral range via the choice of precursors, adjustment of the synthetic conditions, and post-synthetic treatment. We summarize recent progress in the synthesis of CDs emitting in different colors in terms of morphology and optical properties of the resulting nanoparticles, with a focus on the synthetic approaches allowing to shift their emission to longer wavelengths. We further consider formation of CD-based composite materials, and review approaches used to prevent aggregation and self-quenching of their emission. We then provide examples of applications of CDs in optoelectronic devices, such as solar cells and light-emitting diodes (LEDs) with a focus on white LEDs.

The synthesis of a chemically reactive and polymeric luminescent gel

In the past, chemically reactive polymeric interfaces have been considered to be of potential interest for developing functional materials for a wide range of practical applications. Furthermore, the rational incorporation of luminescence properties into such chemically reactive interfaces could provide a basis for extending the horizon of their prospective utility. In this report, a simple catalyst-free chemical approach is introduced to develop a chemically reactive and optically active polymeric gel. Branched-polyethyleneimine (BPEI)-derived, inherently luminescent carbon dots (BPEI-CDs) were covalently crosslinked with pentaacrylate (5Acl) through a 1,4-conjugate addition reaction under ambient conditions. The synthesized polymeric gel was milky white under visible light; however, it displayed fluorescence under UV light. Additionally, the residual acrylate groups in the synthesized fluorescent gel allowed its chemical functionality to be tailored through facile, robust 1,4-conjugate addition reactions with primary-amine-containing small molecules under ambient conditions. The chemical reactivity of the luminescent gel was further employed for a proof-of-concept demonstration of portable and parallel 'ON'/'OFF' toxic chemical sensing (namely, the sensing of nitrite ions as a model analyte). First, the chemically reactive luminescent gel derived from BPEI-CDs was covalently post-modified with aniline for the selective synthesis of a diazo compound in the presence of nitrite ions. During this process, the color of the gel under visible light changed from white to yellow and, thus, the colorimetric mode of the sensor was turned 'ON'. In parallel, the luminescence of the gel under UV light was quenched, which was denoted as the 'OFF' mode of the sensor. This parallel and unambiguous 'ON'/'OFF' sensing of a toxic chemical (nitrite ions, with a detection limit of 3 μM) was also achieved even in presence of other relevant interfering ions and at concentrations well below the permissible limit (65 μM) set by the World Health Organization (WHO). Furthermore, this chemically reactive luminescent gel could be of potential interest in a wide range of basic and applied contexts.

In Situ-Grown Cdot-Wrapped Boehmite Nanoparticles for Cr(VI) Sensing in Wastewater and a Theoretical Probe for Chromium-Induced Carcinogen Detection

In modern society, massive industrialization escalates environmental degradation by liberating various contaminants into the environment. Hexavalent chromium is a heavy metal that is being discharged from tannery and other industries, resulting in various carcinogenic diseases. This study reports a carbon dot (cdot)-based fluorometric probe for detecting hexavalent chromium in water. This is the very first time that cdots are tailored over the boehmite nanoparticle's surface using an in situ approach. Validation of formation of the nanocomposite has been discussed in detail employing the Rietveld refinement-based X-ray crystallography method. Vibrational spectroscopy and electron microscopy of the sample authenticate the nucleation process and the growth mechanism. The Stern-Volmer approach and time-resolved fluorescence measurements justify the sensitivity of the sensor (∼58 nM), and selectivity is analyzed by exposing the material to different ionic environments. Density functional theory (DFT) is applied herein to analyze the origin of fluorescence and the sensing mechanism of the probe, which shows that photoinduced electron transfer is responsible for the turn-off-based sensing of Cr(VI). The molecular docking simulation is carried out to ensure the binding of cdots to the binding pocket of the glutathione enzyme, which is responsible for treating reactive oxygen species-mediated DNA damage due to elements such as hexavalent chromium. Time-dependent density functional calculations show that the fluorometric probe is capable of detecting Cr(VI) in living cells making it an early stage chromium-mediated carcinogen detector.

Diselenide-Bridged Carbon-Dot-Mediated Self-Healing, Conductive, and Adhesive Wireless Hydrogel Sensors for Label-Free Breast Cancer Detection

Recently, a great deal of research has focused on the study of self-healing hydrogels possessing electronic conductivity due to their wide applicability for use in biosensors, bioelectronics, and energy storage. The low solubility, poor biocompatibility, and lack of effective stimuli-responsive properties of their sp² carbon-rich hybrid organic polymers, however, have proven challenging for their use in electroconductive self-healing hydrogel fabrication. In this study, we developed stimuli-responsive electrochemical wireless hydrogel biosensors using ureidopyriminone-conjugated gelatin (Gel-UPy) hydrogels that incorporate diselenide-containing carbon dots (dsCD) for cancer detection. The cleavage of diselenide groups of the dsCD within the hydrogels by glutathione (GSH) or reactive oxygen species (ROS) initiates the formation of hydrogen bonds that affect the self-healing ability, conductivity, and adhesiveness of the Gel-UPy/dsCD hydrogels. The Gel-UPy/dsCD hydrogels demonstrate more rapid healing under tumor conditions (MDA-MB-231) compared to that observed under physiological conditions (MDCK). Additionally, the cleavage of diselenide bonds affects the electrochemical signals due to the degradation of dsCD. The hydrogels also exhibit excellent adhesiveness and in vivo cancer detection ability after exposure to a high concentration of GSH or ROS, and this is comparable to results observed in a low concentration environment. Based on the combined self-healing, conductivity, and adhesiveness properties of the Gel-UPy/dsCD, this hydrogel exhibits promise for use in biomedical applications, particularly those that involve cancer detection, due to its selectivity and sensitivity under tumor conditions.

Self-Assembly of Hydrophobic and Self-Healing Bionanocomposite-Coated Controlled-Release Fertilizers

Self-healing materials have received increased attention because of their automatic detecting and repairing damage function. In this paper, a novel self-assembly and self-healing bionanocomposite was developed as a coating material for controlled release fertilizers. This nanotechnology-enabled coating is environmentally friendly and highly efficient and possesses a tunable nutrient-releasing characteristic. In the synthesis process, bio-based polyurethane coated urea (BPCU) was prepared by the reaction of bio-polyols with isocyanate. The BPCU was then modified by the layer-by-layer technology to prepare self-assembling modified BPCU (SBPCU). Last, hollow nano-silica (HNS) particles loaded with the sodium alginate (SA) were used to modify SBPCU to fabricate of self-assembling and self-healing BPCU (SSBPCU). The results show that the self-assembled materials were synthesized through electrostatic adsorption. The self-healing was observed through scanning electron microscopy and 3D-X-ray computed tomography, revealing the mechanism was that the repair agent released from HNS reacted with the curing agent to block the pore channels and cracks of the coating. As a result, the SSBPCU exhibited the highest hydrophobicity and surface roughness and thus the slowest release rate. For the first time, this work has designed a novel strategy to solve the bottleneck problem that restricts the development of a controlled-release fertilizer.

Self-Healing and Highly Stretchable Gelatin Hydrogel for Self-Powered Strain Sensor

Hydrogels that electronically respond to mechanical changes can be used as strain sensors. However, these systems usually require external power to convert changes in strain into electrical signals. Here, a self-powered strain sensor is developed based on a gelatin-based hydrogel and a galvanic cell. In the hydrogel matrix, hydrophobic interactions and hydrogen bonding between tannic acid and gelatin give the prepared hydrogel great potential for elongation (1600%). The hydrogel also has a rapid self-healing ability (within 0.65 s) and high self-healing efficiency (95%). The hydrogel operates as an efficient electrolyte material and forms a hydrogel battery when assembled with a thin layer of zinc and an air electrode. This device had excellent tolerance to large compressional strain without sacrificing open-circuit voltage. On the basis of this hydrogel battery, we fabricated a self-powered strain sensor by connecting the hydrogel battery to a fixed resistor to form a closed loop. By converting its chemical energy into electrical energy, the self-powered sensor efficiently converted resistance changes, caused by stretching or compression of the hydrogel, into changes in the voltage output signals without external power. Owing to the stretchability of the hydrogel, the self-powered sensor exhibited good response and flexibility. Self-healing and continuous cycling tests confirmed the long-term stability of the device. These properties suggest that our self-powered sensor has a potential for applications to portable and wearable electronic devices.

Multiresponsive and Self-Healing Hydrogel via Formation of Polymer-Nanogel Interfacial Dynamic Benzoxaborole Esters at Physiological pH

Nanocomposite hydrogels with multiresponsiveness and self-healing property are attracting extensive interest due to their enhanced performance for a wide range of applications. In this work, we have successfully developed novel hydrogels based on interfacial polymer-nanogel benzoxaborolate cross-linking at physiological pH. Temperature-sensitive nanogels (NG-Gal) containing galactose residues on the nanosurface were prepared and subsequently used as macro-cross-linkers to form a hydrogel network through formation of dynamic adducts with benzoxaborole groups of a hydrophilic copolymer poly(DMA-st-MAABO). Benefiting from the low pK_a value of benzoxaborole (∼7.2), hydrogels can be constructed rapidly at physiological pH, which is of great significance for biomedical applications. Changing the molar ratio between benzoxaborole and galactose was found to alter the mechanical properties of hydrogels as confirmed by rheological measurements. The dynamic nature of benzoxaborole esters endowed the hydrogel with moldability and self-healing ability after disruption. Moreover, the hydrogel showed multiresponsiveness toward pH, sugar, adenosine triphosphate (ATP), hydrogen peroxide (H₂O₂), and temperature. Therefore, the novel nanocomposite hydrogel we demonstrated here exhibits great potential for biomedical applications such as tissue engineering and controlled drug delivery.

Design, Synthesis, and Functionalization Strategies of Tailored Carbon Nanodots

Over the past decades, considerable efforts have been devoted to synthesizing nanostructured materials with specific properties that ultimately shape their function. In the carbon nanotechnology era, for nanomaterials such as fullerenes, carbon nanotubes, and graphene, the main focus has been on the organic functionalization of these nanostructures, in order to tailor their processability and applicability. Carbon-based dots, quasi-spherical nanoparticles with a shape under 10 nm, have popped up into this context especially due to their versatile synthesis and intriguing properties, mainly their fluorescence emission. Even though they were discovered through the top-down route of cutting large carbon nanostructures, in recent years the ease and flexibility of the bottom-up synthesis have allowed this carbon-based class of nanomaterials to advance at a striking pace. However, the fast speed of research and publication rate have caused a few issues that affect their classification, purity criteria, and fluorescence mechanisms. As these are being progressively addressed, the true potential and applicability of this nanomaterial has started to unravel. In this Ariticle, we describe our efforts toward the synthesis, purification, characterization, and applications of carbon nanodots. Special attention was dedicated to designing and customizing the optoelectronic properties of these nanomaterials, as well as their applications in hybrid and composite systems. Our approach is centered on a bottom-up, microwave-assisted hydrothermal synthesis. We have successfully exploited a multicomponent synthetic approach, using arginine and ethylenediamine as starting materials. By controlling the reaction conditions, in just 3 min, blue-emitting carbon nanodots become accessible. We have improved this approach by designing and tuning the emissive, electrochemical, and chiroptical properties of these nanoforms. On the other hand, we have used postfunctionalization reactions as a tool for conjugation with suitable partners and for further tuning the surface chemistry. The combination of these two approaches has produced a number of carbon nanodots that can be investigated in fields ranging from biology to materials chemistry and in applications spanning from nanomedicine to energy conversion.

Aggregation-Caused Quenching-Type Naphthalimide Fluorophores Grafted and Ionized in a 3D Polymeric Hydrogel Network for Highly Fluorescent and Locally Tunable Emission

Polymer hydrogels with intense yet tunable fluorescence are of great research interest due to their wide potential use in biological imaging, sensing, information storage, etc. However, the conventional fluorophores such as naphthalimide and its derivatives are usually not recommended to prepare highly fluorescent hydrogels because of their aggregation-caused quenching (ACQ) nature and spontaneous tendency to undergo fluorescence self-quenching in quasi-solid-state hydrogel systems. Additionally, local regulation over fluorescent behavior of hydrogels, despite being important, still remains underdeveloped. Herein, we report highly fluorescent polymeric hydrogels based on conventional ACQ-type naphthalimide fluorophores, followed by spatial and temporal control of their fluorescent behavior. The hydrogels were prepared by one-pot radical copolymerization of naphthalimide-containing monomer and acrylamide in chitosan-acetic acid solution. Their intense emission comes from synergetic anchoring and diluting effect of the protonated naphthalimide moieties grafted on polymer chains, which result in the electrostatic repulsion among ACQ luminogens and reduced PET (photoinduced electron transfer) effect from adjacent dimethylamine groups to naphthalimide fluorophores. After being deprotonated in alkaline conditions, both PET and the ACQ effect work again to greatly quench fluorescence, endowing the hydrogels with pH-sensitive emission behavior. These properties encourage us to develop a diffusion-reaction (D-R) method to spatially and temporally control their fluorescent behavior. Based on these results, the ion-transfer-printing-assisted D-R method was further developed to fabricate many high-precision and meaningful fluorescent patterns on hydrogels. These fluorescent patterns are invisible under daylight but become vivid under specific UV light illumination, suggesting their wide potential applications in information security and transmission.