Sulfhydryl-functionalized 3D MXene-AuNPs enabled electrochemical sensors for the selective determination of Pb2+, Cu2+ and Hg2+ in grain

Herein, we made 3D MXene-AuNPs by in situ growth of gold nanoparticles (AuNPs) on the surface of MXene by chemical reduction method, and then introduced three sulfhydryl (-SH) compounds as functionalized modifiers attached to the AuNPs to form a highly selective composite material for the detection of Pb2+, Cu2+, and Hg2+, respectively. The doping of AuNPs changes the microstructure of 2D MXene and generates more active sites. On a sensing platform based on ITO array electrodes, the detection system was optimised with sensitivities up to 1.157, 0.846 and 0.799 μA·μg-1Lcm-2 (Pb2+, Cu2+, and Hg2+). The selectivity of MXene@AuNPs was effectively improved by sulfhydryl group modification. In the range of 1-1300 μg L-1, the detection limits of three ions were 0.07, 0.13 and 0.21 μg L-1. In addition, this method can efficiently and accurately detect heavy metal ions in four cereal samples with consistent results with inductively coupled plasma mass spectrometry.

Ti2C3 MXene-based nanocomposite as an intelligent nanoplatform for efficient mild hyperthermia treatment

Photothermal therapy (PTT) has attracted much attention due to its less invasive, controllable and highly effective nature. However, PTT also suffers from intrinsic cancer resistance mediated by cell survival pathways. These survival pathways are regulated by a variety of proteins, among which heat shock protein (HSP) triggers thermotolerance and protects tumor cells from hyperthermia-induced apoptosis. Confronted by this challenge, we propose and validate here a novel MXene-based HSP-inhibited mild photothermal platform, which significantly enhances the sensitivity of tumor cells to heat-induced stress and thus improves the PPT efficacy. The Ti3C2@Qu nanocomposites are constructed by utilizing the high photothermal conversion ability of Ti3C2 nanosheets in combination with quercetin (Qu) as an inhibitor of HSP70. Qu molecules are loaded onto the nanoplatform in a pH-sensitive controlled release manner. The acidic environment of the tumor causes the burst-release of Qu molecules, which deplete the level of heat shock protein 70 (HSP70) in tumor cells and leave the tumor cells out from the protection of the heat-resistant survival pathway in advance, thus sensitizing the hyperthermia efficacy. The nanostructure, photothermal properties, pH-responsive controlled release, synergistic photothermal ablation of tumor cells in vitro and in vivo, and hyperthermia effect on subcellular structures of the Ti3C2@Qu nanocomposites were systematically investigated.

Facile preparation of fatigue-resistant Mxene-reinforced chitosan cryogel for accelerated hemostasis and wound healing

The development of highly effective chitosan-based hemostatic materials that can be utilized for deep wound hemostasis remains a considerable challenge. In this study, a hemostatic antibacterial chitosan/N-hydroxyethyl acrylamide (NHEMAA)/Ti3C2Tx (CSNT) composite cryogel was facilely prepared through the physical interactions between the three components and the spontaneous condensation of NHEMAA. Because of the formation of strong crosslinked network, the CSNT cryogel showed a developed pore structure (~ 99.07 %) and superfast water/blood-triggered shape recovery, enabling it to fill the wound after contacting the blood. Its capillary effect, amino groups, negative charges, and affinity with lipid collectively induced rapid hemostasis, which was confirmed by in vitro and in vivo analysis. In addition, CSNT cryogel showed excellent photothermal antibacterial activities, high biosafety, and in vivo wound healing ability. Furthermore, the presence of chitosan effectively prevented the oxidation of MXene, thus enabling the long-term storage of the MXene-reinforced cryogel. Thus, our hemostatic cryogel demonstrates promising potential for clinical application and commercialization, as it combines high resilience, rapid hemostasis, efficient sterilization, long-term storage, and easy mass production.

Highly elastic, fatigue-resistant, antibacterial, conductive, and nanocellulose-enhanced hydrogels with selenium nanoparticles loading as strain sensors

The fabrication of highly elastic, fatigue-resistant and conductive hydrogels with antibacterial properties is highly desirable in the field of wearable devices. However, it remains challenging to simultaneously realize the above properties within one hydrogel without compromising excellent sensing ability. Herein, we fabricated a highly elastic, fatigue-resistant, conductive, antibacterial and cellulose nanocrystal (CNC) enhanced hydrogel as a sensitive strain sensor by the synergistic effect of biosynthesized selenium nanoparticles (BioSeNPs), MXene and nanocellulose. The structure and potential mechanism to generate biologically synthesized SeNPs (BioSeNPs) were systematically investigated, and the role of protease A (PrA) in enhancing the adsorption between proteins and SeNPs was demonstrated. Additionally, owing to the incorporation of BioSeNPs, CNC and MXene, the synthesized hydrogels showed high elasticity, excellent fatigue resistance and antibacterial properties. More importantly, the sensitivity of hydrogels determined by the gauge factor was as high as 6.24 when a high strain was applied (400-700 %). This study provides a new horizon to synthesize high-performance antibacterial and conductive hydrogels for soft electronics applications.

An ATPase-Mimicking MXene nanozyme pharmacologically breaks the ironclad defense system for ferroptosis cancer therapy

Anticancer nanomedicines used for ferroptosis therapy generally rely on the direct delivery of Fenton catalysts to drive lipid peroxidation in cancer cells. However, the therapeutic efficacy is limited by the ferroptosis resistance caused by the intracellular anti-ferroptotic signals. Herein, we report the intrinsic ATPase-mimicking activity of a vanadium carbide MXene nanozyme (PVCMs) to pharmacologically modulate the nuclear factor erythroid 2-related factor 2 (Nrf2) program, which is the master anti-ferroptotic mediator in the ironclad defense system in triple-negative breast cancer (TNBC) cells. The PVCMs perform high ATPase-like activity that can effectively and selectively catalyze the dephosphorylation of ATP to generate ADP. Through a cascade mechanism initiated by falling energy status, PVCMs can powerfully hinder the Nrf2 program to selectively drive ferroptosis in TNBC cells in response to PVCMs-induced glutathione depletion. This study provides a paradigm for the use of pharmacologically active nanozymes to moderate specific cellular signals and elicit desirable pharmacological activities for therapeutic applications.

Self-reduced MXene-Metal interaction electrochemiluminescence support with synergistic electrocatalytic and photothermal effects for the bimodal detection of ovarian cancer biomarkers

Novel two-dimensional MXene with unique optical and electrical properties has become a new focus in the field of sensing. In particular, their metallic conductivity, good biocompatibility and high anchoring ability to biomaterials make them attractive candidates. Despite such remarkable properties, there are certain limitations, such as low oxidative stability. MXene-Metal interactions are an effective strategy to maintain the long-term stability of MXene, while also improving the electrochemical activity and optical properties. Herein, a series of MXene/Ag nanocomposites including Ti3C2/Ag, Nb2C/Ag and V2C/Ag were designed based on the surface chemistry characteristics of MXene, where MXene served as the substrate for in-situ growth of silver nanoparticles via self-reduction of Ag(NH3)2+. The results showed that V2C MXene has the strongest self-reducing ability due to its multiple variable valence states, larger interlayer space and more reactive groups. Moreover, V2C/Ag exhibited unexpected oxygen reduction reaction catalytic activity and photothermal performance. In view of which, an electrochemiluminescence-photothermal (ECL-photothermal) immunosensor was developed using V2C/Ag as ECL anchor and photothermal reagent for ultrasensitive detection of Lipolysis stimulated lipoprotein receptor. This work not only provides a simple and effective synthesis method of MXene supported metal nanocomposites, but also provides more inspirations for exploring the efficient biosensing strategies.

Zinc porphyrin/MXene hybrids with phosphate-induced stimuli-responsive behavior for dual-mode fluorescent/electrochemiluminescent ratiometric biosensing

Highly sensitive ratiometric biosensors have attracted much attention in biomarker detection, but most rely on single-mode signals, which can affect accuracy. The development of new principles and methods for dual-mode ratiometric sensing can enhance detection accuracy. Herein, the zinc(II) meso-tetra(4-carboxyphenyl) porphyrin/MXene (ZnTCPP/Ti3C2Tx) hybrids with phosphate-induced stimuli-responsive behavior are used to develop a novel dual-mode fluorescent/electrochemiluminescent (FL/ECL) ratiometric biosensor. The composites exhibit FL quenching and enhanced ECL behavior involving dissolved O2. The FL quenching of ZnTCPP/Ti3C2Tx is caused by energy transfer (EnT) and photo-induced electron transfer (PET) from ZnTCPP to Ti3C2Tx. While the introduction of MXene compensates for the inadequate conductivity of ZnTCPP, facilitating electron transfer, which further makes the surface ZnTCPP more capable of activating O2 to produce singlet oxygen (1O2), thereby generating enhanced cathodic ECL. Furthermore, phosphate ions (PO43-) can interact with the Ti sites of ZnTCPP/Ti3C2Tx, leading to competition for coordination with ZnTCPP, which in turn detaches ZnTCPP, resulting in enhanced FL and reduced ECL. On the basis of the phosphate-induced stimuli-responsive behavior, the dual-mode FL/ECL ratiometric biosensing of alkaline phosphatase (ALP) is achieved through ALP-catalyzed production of PO43- cascade effect with ZnTCPP/Ti3C2Tx. The linear detection range for ALP is 0.1-50 mU/mL, with a detection limit as low as 0.0083 mU/mL. This proposed ZnTCPP/Ti3C2Tx composites with stimuli-responsive behavior is expected to provide new ideas for the development of high-sensitivity dual-mode ratiometric biosensors with promising applications in the precise detection of important biomarkers.

Ultra-high flux mesh membranes coated with tannic acid-ZIF-8@MXene composites for efficient oil-water separation

Oil/water separation has become a global concern due to the increasing discharge of multi-component harmful oily wastewater. Super wetting membranes have been shown to be an effective material for oil/water separation. Ultra-high flux stainless-steel meshes (SSM) with superhydrophilicity and underwater superoleophobicity were fabricated by tannic acid (TA) modified ZIF-8 nanoparticles (TZIF-8) and two-dimensional MXene materials for oil/water separation. The TZIF-8 increased the interlayer space of MXene, enhancing the flux permeation (69,093 L m-2h-1) and rejection of the composite membrane (TZIF-8@MXene/SSM). The TZIF-8@MXene/SSM membrane showed an underwater oil contact angle of 154.2°. The membrane maintained underwater superoleophobic after stability and durability tests, including various pH solutions, organic solvents, reusability, etc. In addition, the oil/water separation efficiency of TZIF-8@MXene/SSM membranes was higher than 99% after treatment in harsh conditions and recycling. The outstanding anti-fouling, stability, durability, and recyclability properties of TZIF-8@MXene/SSM membrane highlight the remarkable potential of membranes for complex oil/water separation process.

Dendritic-like MXene quantum dots@CuNi as an efficient peroxidase candidate for colorimetric determination of glyphosate

Oxidized MXene quantum dots@CuNi bimetal (MQDs@CuNi) were firstly prepared through a simple hydrothermal method. Compared to the controlled samples, MQDs@CuNi1:1 showed the highest peroxidase-like activity. The catalytic mechanism of MQDs@CuNi1:1 was investigated using a steady-state fluorescence analysis, which showed that MQDs@CuNi1:1 efficiently decomposes H2O2 and produces highly reactive hydroxyl radicals (OH). Furthermore, theoretical calculations showed that the remarkable catalytic activity of MQDs@CuNi1:1 originates from the interaction between CuNi bimetal and MQDs to promote the activation and decomposition of H2O2, making it easier to combine with the hydrogen at the end of 3,3',5,5'-Tetramethylbenzidine (TMB). Accordingly, a sensitive colorimetric sensor is proposed to detect glyphosate (Glyp), displaying a low detection limit of 1.13 µM. The work will provide a new way for the development of high-performance nanozyme and demonstrate potential applicability for the determination of pesticide residues in environment.

Single-and double transition metal atoms anchored C2N as a high-activity catalyst for CO oxidation: A first-principles study

The oxidation of CO has attracted great interest in recent years due to its important role in enhancing the catalyst durability in fuel cells and solving the growing environmental problems caused by CO emissions. Consequently, the catalytic oxidation of CO at double non-noble metal atoms anchored C2N is investigated using density functional theory (DFT) computations. All the screened Ti@C2N and Ti2@C2N are thermodynamically stable based on their binding energy calculations. The electronic characteristics, the natural bond orbital analyses (NBO), Frontier orbital, statistical thermodynamics, projected densities of states (PDOS) characteristics, non-covalent interactions (NCI), and quantum theory of atoms in molecules (QTAIM) descriptors of these systems have been examined to analyze the interaction process. Our comparative study suggested that the newly predicted double-atom catalyst (Ti2@C2N) is highly active for CO oxidation, which is a useful guideline for further development. The calculated static first-order hyperpolarizability (βo) illustrated that the double-atom catalyst under investigation can be considered a potential candidate for non-linear optical behavior and could be used for NLO applications. CO oxidation on Ti2@C2N along the Eley-Rideal (ER) mechanism with a low energy barrier of 0.16 eV, which is smaller than the maximum energy barrier (0.73 eV) of CO oxidation along the Langmuir-Hinshelwood (LH) mechanism. Consequently, the ER mechanism is more favorable both thermodynamically and dynamically. This work can provide useful insights and guidelines for future theoretical and experimental investigations to promote the design and development of highly effective and low-cost non-precious-metal Ti2@C2N nanocatalysts towards CO oxidation at ambient temperature.

Metabolomic analysis to understand the mechanism of Ti3C2Tx (MXene) toxicity in Daphnia magna

Due to their potential release into the environment, the ecotoxicity of Ti3C2Tx (MXene) nanomaterials is a growing concern. Unfortunately, little is known about the toxic effects and mechanisms through which Ti3C2Tx induces toxicity in aquatic organisms. The aim of this study is thus to investigate the toxic effects and mechanisms of Daphnia magna upon exposure to Ti3C2Tx with different sheet sizes (100 nm [Ti3C2Tx-100] and 500 nm [Ti3C2Tx-500]) by employing conventional toxicology and metabolomics analysis. The results showed that exposure to both Ti3C2Tx-100 and Ti3C2Tx-500 at 10 μg/mL resulted in a significant accumulation of Ti3C2Tx in D. magna, but no effects on the mortality or growth of D. magna were observed. However, the metabolomics results revealed that Ti3C2Tx-100 and Ti3C2Tx-500 induced significant changes in up to 265 and 191 differential metabolites in D. magna, respectively, of which 116 metabolites were common for both. Ti3C2Tx-100-induced metabolites were mainly enriched in phospholipid, pyrimidine, tryptophan, and arginine metabolism, whereas Ti3C2Tx-500-induced metabolites were mainly enriched in the glycerol-ester, tryptophan, and glyoxylate metabolism and the pentose phosphate pathway. These results indicated that the toxicity of Ti3C2Tx to D. magna has a size-dependent effect at the metabolic level, and both sheet sizes of Ti3C2Tx can lead to metabolic disturbances in D. magna by interfering with lipid and amino acid metabolism pathways.

Progress and Perspective in harnessing MXene-carbon-based composites (0-3D): Synthesis, performance, and applications

MXene is recognized as a promising catalyst for versatile applications due to its abundant metal sites, physicochemical properties, and structural formation. This comprehensive review offers an in-depth analysis of the incorporation of carbon into MXene, resulting in the formation of MXene-carbon-based composites (MCCs). Pristine MXene exhibits numerous outstanding characteristics, such as its atomically thin 2D structure, hydrophilic surface nature, metallic electrical conductivity, and substantial specific surface area. The introduction of carbon guides the assembly of MCCs through electrostatic self-assembly, pairing positively charged carbon with negatively charged MXene. These interactions result in increased interlayer spacing, reduced ion/electron transport distances, and enhanced surface hydrophilicity. Subsequent sections delve into the synthesis methods for MCCs, focusing on MXene integrated with various carbon structures, including 0D, 1D, 2D, and 3D carbon. Comprehensive discussions explore the distinctive properties of MCCs and the unique advantages they offer in each application domain, emphasizing the contributions and advancements they bring to specific fields. Furthermore, this comprehensive review addresses the challenges encountered by MCCs across different applications. Through these analyses, the review promotes a deeper understanding of exceptional characteristics and potential applications of MCCs. Insights derived from this review can serve as guidance for future research and development efforts, promoting the widespread utilization of MCCs across a broad spectrum of disciplines and spurring future innovations.

Bio-inspired Two-dimensional Nanofluidic Ionic Transistor for Neuromorphic Signal Processing

Voltage-gated ion channels prevalent in neurons play important roles in generating action potential and information transmission by responding to transmembrane potential. Fabricating bio-inspired ionic transistors with ions as charge carriers will be crucial for realizing neuro-inspired devices and brain-liking computing. Here, we reported a two-dimensional nanofluidic ionic transistor based on a MXene membrane with sub-1 nm interlayer channels. By applying a gating voltage on the MXene nanofluidic, a transmembrane potential will be generated to active the ionic transistor, which is similar to the transmembrane potential of neuron cells and can be effectively regulated by changing membrane parameters, e.g., thickness, composition, and interlayer spacing. For the symmetric MXene nanofluidic, a high on/off ratio of ~2000 can be achieved by forming an ionic depletion or accumulation zone, contingent on the sign of the gating potential. An asymmetric PET/MXene-composited nanofluidic transitioned the ionic transistor from ambipolar to unipolar, resulting in a more sensitive gate voltage characteristic with a low subthreshold swing of 560 mV/decade. Furthermore, ionic logic gate circuits, including the "NOT", "NAND", and "NOR" gate, were implemented for neuromorphic signal processing successfully, which provides a promising pathway towards highly parallel, low energy consumption, and ion-based brain-like computing.

Reversible pH-Gated MXene Membranes with Ultrahigh Mono-/Divalent-Ion Selectivity

Artificial ion channel membranes hold high promise in water treatment, nanofluidics, and energy conversion, but it remains a great challenge to construct such smart membranes with both reversible ion-gating capability and desirable ion selectivity. Herein, we constructed a smart MXene-based membrane via p-phenylenediamine functionalization (MLM-PPD) with highly stable and aligned two-dimensional subnanochannels, which exhibits reversible ion-gating capability and ultrahigh metal ion selectivity similar to biological ion channels. The pH-sensitive groups within the MLM-PPD channel confers excellent reversible Mg2+-gating capability with a pH-switching ratio of up to 100. The mono/divalent metal-ion selectivity up to 1243.8 and 400.9 for K+/Mg2+ and Li+/Mg2+, respectively, outperforms other reported membranes. Theoretical calculations combined with experimental results reveal that the steric hindrance and stronger PPD-ion interactions substantially enhance the energy barrier for divalent metal ions passing through the MLM-PPD, and thus leading to ultrahigh mono/divalent metal-ion selectivity. This work provides a new strategy for developing artificial-ion channel membranes with both reversible ion-gating functionality and high-ion selectivity for various applications.

Ti3C2 MXene-based nanozyme as coreaction accelerator for enhancing electrochemiluminescence of glucose biosensing

Delamination of the exfoliated multilayer MXenes with electro-catalysts, not only leads to increasing surface area for high electrochemiluminescent (ECL) signal tracer loading but also provides highly sensitive achievements in a coreaction accelerator manner. To this end, herein, we used bromophenol blue (BPB)-delaminated multilayer Ti3C2 MXene as both a coreaction accelerator to promote the electrochemiluminescent (ECL) reaction rate of luminol (LUM) and the co-reactant H2O2 and a substrate for retaining high loading of glucose oxidase (GOx)-conjugated polyethylene imine (PEI) along with luminophore species into more open structure of Ti3C2 MXene for sensitive detection of glucose. In the presence of glucose, in situ generating H2O2 product through a GOx-catalyzed process could produce abundant •OH radicals via the peroxidase-like activity of the BPB@Ti3C2 in the LUM ECL reaction. Moreover, decreasing the distance between the high-content LUM into the BPB@Ti3C2 and the generated •OH, minimizes the decomposition of highly active •OH, providing a superb ECL signal. Last, the proximity of incorporated GOx into the delaminated Ti3C2 MXene near the electrode allows efficient electron transfer between the electrode and enzyme. The integration of such amplifying effects endowed high sensitivity and excellent selectivity for glucose with a low limit of detection of 0.02 μM in the wide range of 0.01 μM-40,000 μM, enabling the feasibility of the glucose analysis in human serum samples. Overall, the enhanced ECL based on the BPB@Ti3C2 opens a new horizon to develop highly sensitive MXene-based ECL toward the field of biosensors.

Vertically aligned MXene bioelectrode prepared by freeze-drying assisted electrophoretic deposition for sensitive electrochemical protein detection

Two-dimensional (2D) carbides, MXenes, have attracted attention as electrode materials of electrochemical biosensors because of their metallic conductivity, hydrophilicity, and mechanical stability. However, when fabricating electrodes, the nanosheets tend to re-stack and generally align horizontally with respect to the current collector due to the highly anisotropic nature of MXene, resulting in low porosity and poor utilization of the MXene surface. Here we report the electrochemical biosensing of antibody-antigen reactions with a vertically aligned Ti3C2Tx MXene (VA-MXene) electrode prepared by freeze-drying assisted electrophoretic deposition. The macroporous VA-MXene electrode exhibited a better electrochemical response towards the immunoreaction between the allergenic buckwheat protein (BWp16) and the antibody compared to a non-porous, horizontally (in-plane) stacked MXene (HS-MXene) and the sensors reported in the literature. The sensor responsiveness, defined as the ratio of the obtained current density of the electrode to the antigen concentration, was much higher for the VA-MXene electrode (238 μA cm-2 (ng mL-1) -1) than for the HS-MXene electrode. The proposed technique is applicable to other exfoliated nanosheets, and will open a new avenue for porous nanosheet electrodes to improve the sensing characteristics of electrochemical biosensors.

A water transfer printing method for contact lenses surface 2D MXene modification to resist bacterial infection and inflammation

Contact lenses (CLs) are prone to adhesion and invasion by pollutants and pathogenic bacteria, leading to infection and inflammatory diseases. However, the functionalization of CL (biological functions such as anti-fouling, antibacterial, and anti-inflammatory) and maintaining its transparency still face great challenges. In this work, as a member of the MXenes family, vanadium carbide (V2C) is modified onto CL via a water transfer printing method after the formation of a tightly arranged uniform film at the water surface under the action of the Marangoni effect. The coating interface is stable owing to the electrostatic forces. The V2C-modified CL (V2C@CL) maintains optical clarity while providing good biocompatibility, strong antioxidant properties, and anti-inflammatory activities. In vitro antibacterial experiments indicate that V2C@CL shows excellent performance in bacterial anti-adhesion, sterilization, and anti-biofilm formation. Last, V2C@CL displays notable advantages of bacteria elimination and inflammation removal in infectious keratitis treatment.

Self-assembly of a AuNPs/Ti3C2 MXene hydrogel for cascade amplification of microRNA-122 biosensing

A three-dimensional (3D) self-assembled AuNPs/Ti3C2 MXene hydrogel (AuNPs/Ti3C2 MXH) nanocomposite was prepared for the fabrication of a novel microRNA-122 electrochemical biosensor. The 3D hydrogel structure was gelated from two-dimensional MXene nanosheets with the assistance of graphite oxide and ethylenediamine. MXene hydrogels supported the in situ formation of Au nanoparticles (AuNPs) that predominantly exploring the (111) facet, and these AuNPs are utilized as carriers for hairpin DNA (hpDNA) probes, facilitating DNA hybridization. MXene acted as both a reductant and stabilizer, significantly improving the electrochemical signal. In addition, the conjugation of PAMAM dendrimer-encapsulated AuNPs and H-DNA worked as an ideal bridge to connect targets and efficient electrochemical tags, providing a high amplification efficiency for the sensing of microRNA-122. A linear relationship between the peak currents and the logarithm of the concentrations of microRNA-122 from 1.0 × 10-2 to 1.0 × 102 fM (I = 1.642 + 0.312 lgc, R2 = 0.9891), is obtained. The detection limit is  0.8 × 10-2 fM (S/N = 3). The average recovery for human serum detection ranged from 97.32 to 101.4% (RSD < 5%).

The Role of MXene Surface Terminations on Peptide Transportation in Nanopore Sensing

Nanopores with two-dimensional materials have various advantages in sensing, but the fast translocation of molecules hinders their scale-up applications. In this work, we investigate the influence of -F, -O, and -OH surface terminations on the translocation of peptides through MXene nanopores. We find that the longest dwell time always occurs when peptides pass through the Ti3C2O2 nanopores. This elongated dwell time is induced by the strongest interaction between peptides and the Ti3C2O2 membrane, in which the van der Waals interactions dominate. Compared to the other two MXene nanopores, the braking effect is indicated during the whole translocation process, which evidence the advantage of Ti3C2O2 in nanopore sensing. Our work demonstrates that membrane surface chemistry has a great influence on the translocation of peptides, which can be introduced in the design of nanopores for a better performance.

Conductive and Enhanced Mechanical Strength of Mo2Ti2C3 MXene-Based Hydrogel Promotes Neurogenesis and Bone Regeneration in Bone Defect Repair

Bone defects are common with increasing high-energy fractures, tumor bone invasion, and implantation revision surgery. Bone is an electroactive tissue that has electromechanical interaction with collogen, osteoblasts, and osteoclasts. Hydrogel provides morphological plasticity and extracellular matrix (ECM) 3D structures for cell survival, and is widely used as a bone engineering material. However, the hydrogels have poor mechanical intensity and lack of cell adhesion, slow gelation time, and limited conductivity. MXenes are novel nanomaterials with hydrophilic groups that sense cell electrophysiology and improve hydrogel electric conductivity. Herein, gelatin had multiple active groups (NH2, OH, and COOH) and an accelerated gelation time. Acrylamide has Schiff base bonds to cross-link with gelatin and absorb metal ions. Deacetylated chitosan improved cell adhesion and active groups to connect MXene and acrylamide. We constructed Mo2Ti2C3 MXene hydrogel with improved elastic modulus and viscosity, chemical cross-linking structure, electric conductivity, and good compatibility. Mo2Ti2C3 MXene hydrogel exhibits outstanding osteogenesis in vitro. Mo2Ti2C3 MXene hydrogel promotes osteogenesis via alkaline phosphatase (ALP) and alizarin red S (ARS) staining, improving osteogenic marker genes and protein expressions in vitro. Mo2Ti2C3 MXene hydrogel aids new bone formation in the in vivo calvarial bone defect model via micro-CT and histology. Mo2Ti2C3 MXene hydrogel facilitates neurogenesis factors nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) expression, and aids newly born neuron marker Tuj-1 and sensory neuron marker serotonin (5-HT) and osteogenesis pathway proteins, runt-related transcription factor 2 (Runx2), osteocalcin (OCN), SMAD family member 4 (SMAD4), and bone morphogenetic protein-2 (BMP2) in the bone defect repair process. Mo2Ti2C3 MXene hydrogel promotes osteogenesis and neurogenesis, which extends its biomedical application in bone defect reconstruction.

Multifunctional MXene-Based Platforms for Soft and Bone Tissue Regeneration and Engineering

MXenes and their composites hold great promise in the field of soft and bone tissue regeneration and engineering (TRE). However, there are challenges that need to be overcome, such as ensuring biocompatibility and controlling the morphologies of MXene-based scaffolds. The future prospects of MXenes in TRE include enhancing biocompatibility through surface modifications, developing multifunctional constructs, and conducting in vivo studies for clinical translation. The purpose of this perspective about MXenes and their composites in soft and bone TRE is to critically evaluate their potential applications and contributions in this field. This perspective aims to provide a comprehensive analysis of the challenges, advantages, limitations, and future prospects associated with the use of MXenes and their composites for soft and bone TRE. By examining the existing literature and research, the review seeks to consolidate the current knowledge and highlight the key findings and advancements in MXene-based TRE. It aims to contribute to the understanding of MXenes' role in promoting soft and bone TRE, addressing the challenges faced in terms of biocompatibility, morphology control, and tissue interactions.

Novel 2D MXene Cobalt Ferrite (CoF@Ti3C2) Composite: A Promising Photothermal Anticancer In Vitro Study

In search of materials with superior capability of light-to-heat (photothermal) conversion, biocompatibility, and confinement of active photothermal materials within the cells, novel magnetic MXene-based nanocomposites are found to possess all of these criteria. The CoF@Ti3C2 composite is fabricated by a simple two-step method, including an exfoliation strategy followed by sonochemical method. MXene composite has been modified with polyvinylpyrrolidone (PVP) to improve the stability in physiological conditions. The synthesized composite was characterized with multiple analytical tools. In vitro photothermal conversion efficiency of composite was determined by the time constant method and achieved η = 34.2% with an NIR 808 nm laser. In vitro, cytotoxicity studies conducted on human malignant melanoma (Ht144) and cells validated the photothermal property of the CoF@Ti3C2-PVP composite in the presence of an NIR laser (808 nm, 1.0 W cm-2), with significantly increased cytotoxicity. Calculated IC50 values were 86 μg/mL with laser, compared to 226 μg/mL without the presence of NIR laser. Microscopic results demonstrated increased apoptosis in the presence of NIR laser. Additionally, hemolysis assay confirmed biocompatibility of CoF@Ti3C2-PVP composite for intravenous applications at the IC50 concentration. The research described in this work expands the potential applications of MXene-based nanoplatforms in the biomedical field, particularly in photothermal therapy (PTT). Furthermore, the addition of cobalt ferrite serves as a magnetic nanocomposite, which eventually helps to confine therapeutic photothermal materials inside the cells, provides enhanced photothermal conversion efficiency, and creates externally controlled theranostic nanoplatforms for cancer therapy.

Transition Metal Ru(II) Catalysts Immobilized Nanoreactors for Conditional Bioorthogonal Catalysis in Cells

Employing transition metal catalysts (TMCs) to perform bioorthogonal activation of prodrugs and pro-fluorophores in biological systems, particularly in a conditional fashion, remains a challenge. Here, we used a mesoporous organosilica nanoscaffold (RuMSN), which localizes Ru(II) conjugates on the pore wall, enabling the biorthogonal photoreduction reactions of azide groups. Due to easily adjustable surface charges and pore diameter, this efficiently engineering RuMSN catalyst, with abundant active sites on the inner pore well, could spontaneously repel or attract substrates with different molecular sizes and charges and thus ensure selective bioorthogonal catalysis. Depending on it, engineering RuMSN nanoreactors showed fascinating application scales from conditional bioorthogonal activation of prodrugs and pro-fluorophores in either intra- or extracellular localization to performing intracellular concurrent and tandem catalysis together with natural enzymes.

Self-healing and adhesive MXene-polypyrrole/silk fibroin/polyvinyl alcohol conductive hydrogels as wearable sensor

Conductive hydrogels become increasing attractive for flexible electronic devices and biosensors. However, challenges still remain in fabrication of flexible hydrogels with high electrical conductivity, self-healing capability and adhesion property. Herein, a conductive hydrogel (PSDM) was prepared by solution-gel method using MXene and dopamine modified polypyrrole as conductive enhanced materials, polyvinyl alcohol and silk fibroin as gel networks, and borax as cross-linking agent. Notably, the PSDM hydrogels not only showed high permeability (13.82 mg∙cm-2∙h-1), excellent stretch ability (1235 %), high electrical conductivity (11.3 S/m) and long-term stability, but also exhibited high adhesion performance and self-healing properties. PSDM hydrogels displayed outstanding sensing performance and durability for monitoring human activities including writing, finger bending and wrist bending. The PSDM hydrogel was made into wearable flexible electrodes and realized accurate, sensitive and reliable detection of human electromyographic and electrocardiographic signals. The sensor was also applied in human-computer interaction by collecting electromyography signals of different gestures for machine learning and gesture recognition. According to 480 groups of data collected, the recognition accuracy of gestures by the electrodes was close to 100 %, indicating that the PSDM hydrogel electrodes possessed excellent sensing performance for high precision data acquisition and human-computer interaction interface.

MOF/MXene-loaded PVA/chitosan hydrogel with antimicrobial effect and wound healing promotion under electrical stimulation and improved mechanical properties

Electrical stimulation modulates cell behavior and influences bacterial activity, so highly conductive, antimicrobial hydrogels are suitable for promoting wound healing. In this study, highly conductive and antimicrobial Ti3C2Tx (MXene) hydrogels composed of chitosan and poly(vinyl alcohol) and AgCu- H2PYDC MOF were developed. In PVACS/MOF/MXene (PCMM) hydrogels, the MXene layer acts as an electrical conductor. The electrical conductivity is 0.61 ± 0.01 S·cm-1. PCMM hydrogels modulate cell behavior and provide ES antimicrobial capacity under ES at 1 V. The metal ions of MOF form coordination with chitosan molecules and increase the cross-linking density between chitosan molecules, thus improving the mechanical properties of the hydrogel (tensile strength 0.088 ± 0.04 MPa, elongation at break 233 ± 11 %). The PCMM gels had good biocompatibility. The PCMM hydrogels achieved 100 % antibacterial activity against E. coli and S. aureus for 12 h. 1 V electrical stimulation of PCMM hydrogel accelerated the wound healing process in mice by promoting cell migration and neovascularization, achieving 97 ± 0.4 % wound healing on day 14. The hydrogel dressing PCMM-0.1 with MOF addition of 0.1 % had the best wound healing promoting effect and which is a promising dressing for promoting wound healing and is a therapeutic strategy worth developing.

Platforms of graphene/MXene heterostructure for electrochemical monitoring of rutin in drug and Tartary buckwheat tea

The use of two-dimensional heterostructure composite as electrode modification material has become a new strategy to improve the electrocatalytic activity and electroactive sites of electrochemical sensor. Herein, a soluble heterostructure, namely rGO-PSS@MXene, was designed and synthesized by integrating poly (sodium p-styrenesulfonate)-functionalized reduced graphene oxide into MXene nanosheets via ultrasonic method. The interactive heterostructure can effectively alleviate the self-stacking of MXene and rGO, endowing them with superior electron transfer capacity and large specific surface area, thereby producing prominent synergistic electrocatalytic effect towards rutin. In addition, the excellent enrichment effect of rGO-PSS@MXene for rutin also plays an important role through the electrostatic and π-π stacking interactions. The electrochemical characteristics of rutin on the sensor were examined in detail and a sensitive sensing method was proposed. Under optimized conditions, the method showed satisfactory linear relationship for rutin in the concentration range of 0.005-10.0 μM, with limit of detection of 1.8 nM (S/N = 3). The quantitative validation results in herbal medicine and commercial Tartary buckwheat tea were highly consistent with the labeled quantity and the results of HPLC determination, respectively, suggesting the sensor possessed excellent selectivity and accuracy. This proposed strategy for rutin determination is expected to expand the application of MXene heterostructure in electrochemical sensors, and is envisioned as a promising candidate for quality monitoring of drugs and foods.

Structural/surface characterization of transition metal element-doped H-ZSM-5 adsorbent for CH3SH removal: identification of active adsorption sites and deactivation mechanism

CH3SH is a potential hazard to both chemical production and human health, so controlling its emissions is an urgent priority. In this work, a series of transition metal-loaded H-ZSM-5 adsorbents (Si/Al = 25) (Cu, Fe, Co, Ni, Mn, and Zn) were synthesized through the wet impregnation method and tested for CH3SH physicochemical adsorption at 60 °C. It was shown that the Cu-modified H-ZSM-5 adsorbent was much more active for CH3SH removal due to its abundant strong acid sites than other transition metal-modified H-ZSM-5 adsorbents. The detailed physicochemical properties of various modified H-ZSM-5 adsorbents were characterized by SEM, XRD, N2 physisorption, XPS, H2-TPR, and NH3-TPD. The effects of metal loading mass ratio, calcination temperature, and acid or alkali modification on the performance of the adsorbent were also investigated, and finally 20% Cu/ZSM-5 was found to have the best adsorption capacity after calcined at 350 °C. Additionally, the Cu/ZSM-5 adsorbent modified by sodium bicarbonate could expose more active components, which improved the adsorbent's stability. However, the consumption and reduction of the active component Cu2+ and the accumulation of sulfate during the adsorption process are the main reasons for the deactivation of the adsorbent. In addition, the simultaneous purging of N2 + O2 can effectively restore the adsorption capacity of the deactivated adsorbent and can be used as a potential strategy to regenerate the adsorbent.

Electrochemical biosensor based on PAMAM functionalized MXene nanoplatform for detection of folate receptor

The level of folate receptor (FR) has become one of the independent factors for measuring human tumor diseases. The precise quantification of FR is helpful for the early diagnosis and subsequent treatment of tumors. The modification of electrodes is a key issue in ensuring and enhancing the electrochemical biosensing ability. In this study, we in-situ synthesized a nanocomposite material with excellent conductivity and stability by grafting first-generation poly(amidoamine) dendrimers onto the MXene (Ti3C2TX) as the immobilized matrix (PAMAM@MXene). An electrochemical sensor was developed for FR monitor by loading the PAMAM@MXene on screen-printed carbon electrodes (SPCEs). Scanning electron microscopy (SEM) supported the effective synthesis of PAMAM@MXene. Under optimal conditions, the prepared sensor achieved the quantification of FR with a wide range of concentrations from 10 ng/mL to 1000 ng/mL with a detection limit (LOD) of 5.6 ng/mL. It also exhibited satisfactory selectivity, reproducibility, and stability, which provided the possibility for expanding new pathways in the detection of clinical FR.

Bismuth oxide modified V2C MXene as a Schottky catalyst with enhanced photocatalytic oxidation for photo-denitration activities

In this work, a new composite photocatalyst was synthesized by flower-like Bi2O3 and two-dimensional multilayer V2C using a facile hydrothermal method. Compared with the pristine sample, the specific surface area of Bi2O3/V2C MXene composite is significantly increased, which is favourable to improve the photocatalytic efficiency. The analysis of the UV-vis absorption spectrum and band gap energy shows that the construction of heterojunction broadens the light response range, improves the light absorption capacity, and obtains a narrower band gap than any of the single component, which is beneficial to the utilization of light. PL, TPC and EIS analysis revealed that Bi2O3/V2C MXene composite had stronger carrier mobility, which further confirmed that the photocatalytic oxidation performance of the system was the dominant reason in the photocatalytic NO pollutant removal process. This study provides a new idea for better understanding the two-dimensional MXene material-based photocatalyst and improving the NO removal efficiency.

Skeletal muscle regeneration with 3D bioprinted hyaluronate/gelatin hydrogels incorporating MXene nanoparticles

There has been significant progress in the field of three-dimensional (3D) bioprinting technology, leading to active research on creating bioinks capable of producing structurally and functionally tissue-mimetic constructs. Ti3C2Tx MXene nanoparticles (NPs), promising two-dimensional nanomaterials, are being investigated for their potential in muscle regeneration due to their unique physicochemical properties. In this study, we integrated MXene NPs into composite hydrogels made of gelatin methacryloyl (GelMA) and hyaluronic acid methacryloyl (HAMA) to develop bioinks (namely, GHM bioink) that promote myogenesis. The prepared GHM bioinks were found to offer excellent printability with structural integrity, cytocompatibility, and microporosity. Additionally, MXene NPs within the 3D bioprinted constructs encouraged the differentiation of C2C12 cells into skeletal muscle cells without additional support of myogenic agents. Genetic analysis indicated that representative myogenic markers both for early and late myogenesis were significantly up-regulated. Moreover, animal studies demonstrated that GHM bioinks contributed to enhanced regeneration of skeletal muscle while reducing immune responses in mice models with volumetric muscle loss (VML). Our results suggest that the GHM hydrogel can be exploited to craft a range of strategies for the development of a novel bioink to facilitate skeletal muscle regeneration because these MXene-incorporated composite materials have the potential to promote myogenesis.

Green Synthesis and Biosafety Assessment of MXene

The rise of MXene-based materials with fascinating physical and chemical properties has attracted wide attention in the field of biomedicine, because it can be exploited to regulate a variety of biological processes. The biomedical applications of MXene are still in its infancy, nevertheless, the comprehensive evaluation of MXene's biosafety is desperately needed. In this review, the composition and the synthetic methods of MXene materials are first introduced from the view of biosafety. The evaluation of the interaction between MXene and cells, as well as the safety of different forms of MXene applied in vivo are then discussed. This review provides a basic understanding of MXene biosafety and may bring new inspirations to the future applications of MXene-based materials in biomedicine.

Near-Infrared Absorbing Para-Azaquinodimethane Conjugated Polymers Synthesized via the Transition-Metal-Free Route toward Efficient Photothermal Conversion

Conjugated polymers with strong absorption in the second near-infrared (NIR-II) window have multiple applications. However, the development of new type of NIR-II conjugated polymers via facile and green methods remains challenging. Herein, this work reports a mild and convenient transition-metal-free method to synthesize near-infrared absorbing quinoidal conjugated polymers containing para-azaquinodimethane (AQM) moieties. The AQM quinoidal conjugated polymers with unique molecular structures and tunable optoelectronic properties can be synthesized by combining the Knoevenagel polycondensation of aromatic dialdehyde monomers with commercially available 1,4-diacetyl-2,5-piperazinedione and the following alkylation reaction. The resultant polymer PQ-DPP shows remarkable NIR-II absorption with a narrow band gap of about 1.08 eV. PQ-DPP nanoparticles exhibit high photothermal conversion efficiency of up to 48% under 1064 nm laser irradiation (1 W cm-2) endowing this polymer with potential in bio-related applications.

Construction of MXene-mediated inorganic-organic quaternary ammonium salt-hybrid coating for fire safety and multi-mode synergistic antibacterial of cotton fabric

With the continuous development of the society, there is a growing demand for the durability, versatility and multifunction of cott fabrics. In this work, the cotton fabric is coated with multifunctional coating via dip-coating of transition metal carbide (MXene) and then encapsulation of dimethyloctadecyl [3-trimethoxysilopropyl] ammonium chloride (QAS). In view of MXene with excellent light absorption and photothermal conversion efficiency, the controllable antibacterial performance of the cotton fabric is further improved. Benefiting from the encapsulation of QAS, CF@P@M@QAS fabric shows mechanical stability (24 h washing, 1000 cycles folding test and 100 cyclic abrasion) and hydrophobicity. Meantime, the QAS on the surface of multifunctional cotton fabric significantly increases antibacterial activity, and the antibacterial rate can reach to 100 % against Staphylococcus aureus (S. aureus) and 98 % Escherichia coli (E. coli). Besides, CF@P@M@QAS cotton fabric also integrates functions of fire safety and physical therapy. Thus, this multifunctional cotton fabric based MXene offers a novel solution for extending its application in medical electronics and physical therapy.

Functionalized lignin nanoparticles assembled with MXene reinforced polypropylene with favorable UV-aging resistance, electromagnetic shielding effects and superior fire-safety

Deterioration in mechanical performances and aging resistance due to the introduction of flame retardants is a major obstacle for bio-based fire-safety polypropylene (PP). Herein, we reported a kind of functionalized lignin nanoparticles assembled with MXene (MX@LNP), and applied it to construct the flame-retardant PP composites (PP-MA) with superior fire safety, excellent mechanical performance, electromagnetic shielding effects and aging resistance. Specifically, the PP-MA doped with only 18 wt% flame-retardant additives (PP-MA18) achieved the UL-94 V-0 rating. In comparison to pure PP, PP-MA18 presented a greatly decreased peak of heat release rate (pHRR), total heat rate (THR), and peak smoke production rate (pSPR) by 79.7 %, 69.0 % and 75.8 %, respectively, and satisfactory decrease in total flammable and toxic volatiles evolved. The formed fine solid microstructure of carbon residuals effectively promoted the compactness of char layers. More importantly, the nano-effect and the strong interface interaction between the complexed MX@LNP and PP enhanced the tensile strength (45.78 MPa) and elongation at break (725.95 %) of PP-MA. Additionally, the significant ultraviolet absorption and electromagnetic wave dissipation performance of MXene and lignin enabled excellent aging resistance and electromagnetic shielding effects of PP-MA compared with PP. This achieved MX@LNP afforded a novel approach for developing flame retardant materials with excellent application performance.

Multifunctional Ti3C2Tx MXene-reinforced thermoplastic starch nanocomposites for sustainable packaging solutions

Starch-derived films exhibit significant potential for packaging applications owing to their low cost, biodegradable characteristics, and natural abundance. Nonetheless, there is a demand to enhance their mechanical properties and moisture resistance to broaden their use. In this study, high performing sorbitol-plasticized starch/Ti3C2Tx MXene nanocomposites, reinforced with ultra-low filler contents, were fabricated for the first time in literature. The MXene nanoplatelets were well-dispersed within the starch matrix while there was a tendency for the fillers to align in-plane, as revealed by polarized Raman spectroscopy. The produced nanocomposite films demonstrate remarkable effectiveness in blocking UV light, offering an additional valuable attribute in food packaging. The Young's modulus and tensile strength of starch films containing 0.75 wt% MXene increased from 439.9 and 11.0 MPa to 764.3 and 20.8 MPa, respectively. The introduction of 1 wt% MXene nanoplatelets reduced the water vapour permeability of starch films from 2.78 × 10-7 to 1.80 × 10-7 g/m h Pa due to the creation of highly tortuous paths for water molecules. Micromechanical theories were also implemented to understand further the reinforcing mechanisms in the biobased nanocomposites. The produced starch nanocomposites not only capitalize on the biodegradable and renewable nature of starch but also harness the unique properties of nanomaterials, paving the way for sustainable and high-performance packaging solutions that align with both consumer and environmental demands.

MXene-supported MIL-88A(Fe) as persulfate activator for removal of tetracycline

The poor conductivity, poor stability, and agglomeration of iron-based metal organic framework MIL-88A(Fe) limit its application as persulfate (PS) activator in water purification. Herein, MXene-supported MIL-88A(Fe) composites (M88A/MX) were synthesized to enhance its adsorption and catalytic capability for tetracycline (TC) removal. Scanning electron microscope (SEM), X-ray diffractometer (XRD), Fourier transform infrared spectrometer (FT-IR), and X-ray photoelectron spectroscopy (XPS) were used to characterize prepared materials, confirming the successful attachment of MIL-88A(Fe) to the surface of MXene. M88A/MX-0.2 composites, prepared with 0.2 g MXene addition, exhibit optimal degradation efficiency, reaching 98% under conditions of 0.2 g/L M88A/MX-0.2, 1.0 mM PS, 20 ppm TC, and pH 5. The degradation rate constants of M88A/MX-0.2 were 0.03217 min-1, which was much higher than that of MIL-88A(Fe) (0.00159 min-1) and MXene (0.00626 min-1). The removal effects of reaction parameters, such as dosage of M88A/MX-0.2 and PS; initial solution pH; and the presence of the common co-existing constituents (humic acid and the inorganic anions) were investigated in detail. Additionally, the reuse of M88A/MX-0.2 showed that the composites had good cycling stability by recurrent experiments. The results of electron paramagnetic resonance (EPR) and quenching experiments indicated that ·OH, ·SO4-, and ·O2- were involved in the M88A/MX-0.2/PS system where persulfate oxidation process was activated with prepared M88A/MX-0.2. In addition, the intermediates of photocatalytic degradation were determined by HPLC-MS, and the possible degradation pathways of the target molecules were inferred. This study offered a new avenue for sulfate-based degradation of Fe-based metal organic framework.

A ratiometric molecular imprinted electrochemiluminescence sensor based on enhanced luminescence of CdSe@ZnS quantum dots by MXene@NaAsc for detecting uric acid

An unlabeled ratiometric molecular imprinted electrochemiluminescence sensor was developed for the determination of trace uric acid, based on MXene@NaAsc nanocomposites, CdSe@ZnS quantum dots and molecularly imprinted polymer composites modified glass carbon electrode. MXene@NaAsc stably enhanced the electron transfer and improved electrochemiluminescence intensity by acting as a base platform and signal amplifier for CdSe@ZnS quantum dots. Specific molecular imprinting cavities based on electropolymerization with o-phenylenediamine were formed to specifically identify uric acid. Combining the good sensitivity of electrochemiluminescence and the excellent selectivity of molecularly imprinted polymer, the ratio of optical signal and electrical signal was used as a comprehensive signal to achieve the detection of uric acid. Based on this, uric acid was detected in the range from 1 × 10-10 to 1 × 10-4 mol/L with the LOD of 18.13 pmol/L (S/N = 3). The developed sensor with easy preparation, great selectivity and excellent sensitivity could successfully detect uric acid in human serum.

Flexible cellulose nanofibers/MXene composite films for UV-shielding packaging

Cellulose nanofibers (CNF) based films are promising packaging materials, but the lack of special functions (especially UV-shielding property) usually restrict their further applications. In this work, MXene was incorporated into the CNF film by a direct solvent volatilization induced film forming method to study its UV-shielding property for the first time, which avoided the using of a vacuum filtration equipment. The composite films containing glycerin could be folded repeatedly without breaking, showing good flexibility. The structure and properties of MXene/CNF composite films (CMF) were characterized systematically. The results showed that MXene distributed uniformly in the CNF film matrix and there was strong hydrogen bonding interaction between CNF and MXene. The tensile strength and Young's modulus of the composite films could reach 117.5 MPa and 2.23 GPa, which was 54.1 % and 59.2 % higher than those of pure CNF film, respectively. With the increase of MXene content, both the UVA and UVB shielding percentages increased significantly from 17.2 % and 25.5 % to 100.0 %, showing excellent UV-shielding property. Moreover, CMF exhibited a low oxygen permeability (OP) value of 0.39 cc μm d-1 m-2 kPa-1, a low water vapor permeability (WVP) value of 5.13 × 10-11 g-1s-1Pa-1 and a high antibacterial rate against E. coli (94.1 % at 24 h), showing potential application in the packaging field.

CuO/TiO2/MXene-Based Sensor and SMS-TENG Array Integrated Inspection Robots for Self-Powered Ethanol Detection and Alarm at Room Temperature

In this study, a high-precision CuO/TiO2/MXene ethanol sensor operating at room temperature was prepared. The sensor exhibits excellent response value (95% @1 ppm ethanol), extremely low detection limit (0.3 ppm), fast response/recovery time (16/13 s), and remarkable long-term stability for trace detection of ethanol gas at room temperature, attributed to the p-n heterojunction formed by CuO and TiO2, as well as the rich functional groups and large specific surface area of MXene. Furthermore, a high-performance triboelectric nanogenerator (SMS-TENG) was developed through the introduction of the silicone/Mxene@silicone dual dielectric layer as the triboelectric layer, which improves the charge storage capacity of the dielectric layer and greatly enhances the output performance of the TENG. At the optimal doping ratio, the open-circuit voltage of the SMS-TENG can reach 1160 V, which is sufficient to light 720 LEDs. By combining the sensor and SMS-TENG, the resistive response of ethanol sensing is converted to a voltage response, which amplifies the response value up to 15.8 times. Finally, the designed SMS-TENGs are expected to be arrayed on an inspection robot as energy supply and combined with the CuO/TiO2/Mxene ethanol sensor to build a self-powered ethanol detection alarm system, endowing the inspection robot with the capability of self-powered ethanol detection at ppb level. This work provides an effective pathway for the intelligence of ethanol detection.

Fully Transient 3D Origami Paper-Based Ammonia Gas Sensor Obtained by Facile MXene Spray Coating

Developing high-performance chemiresistive gas sensors with mechanical compliance for environmental or health-related biomarker monitoring has recently drawn increasing research attention. Among them, two-dimensional MXene materials hold great potential for room-temperature hazardous gas (e.g., NH3) monitoring regardless of the complicated fabrication process, insufficient 2D/3D flexibilities, and poor environmental sustainability. Herein, a Ti3C2Tx MXene/gelatin ink was developed for patterning electrodes through a facile spray coating. Particularly, the patterned Ti3C2Tx-based coating exhibited good adhesion on the paper substrate against repeated peeling-off and excellent mechanical flexibility against 1000 cyclic stretching. The porous morphology of the coating facilitated the NH3 sensing ability. As a result, the 2D kirigami-shaped NH3 sensor exhibited a good response of 7% to 50 ppm of NH3 with detectable concentrations ranging from 5-500 ppm, decent selectivity over interferences, etc., which could be well-maintained even at 50% stretched state. In addition, with the help of mechanically guided compressive buckling, 3D mesostructured MXene origamis could be obtained, holding promise for detecting the coming direction and height distribution of hazardous gas, e.g., the NH3. More importantly, the as-fabricated MXene/gelatin origami paper could be fully degraded in PBS/H2O2/cellulase solution within 19 days, demonstrating its potential as a high-performance, shape morphable, and environmentally friendly wearable gas sensor.

Selective Detection of NH3 Gas by Ti3C2Tx Sensors with the PVDF-ZIF-67 Overlayer at Room Temperature

In the realm of NH3 gas-sensing applications, the electrically conductive nature of Ti3C2Tx MXene, adorned with surface terminations such as -O and -OH groups, renders it a compelling material. However, the inherent challenges of atmospheric instability and selectivity in the presence of gas mixtures have prompted the exploration of innovative solutions. This work introduces a strategic solution through the deposition of a mixed-matrix membrane (MMM) composed of poly(vinylidene fluoride) (PVDF) as the matrix and zeolitic imidazolate framework-67 (ZIF-67) as the filler. This composite membrane acts as a selective filter, permitting the passage of a specific gas, namely NH3. Leveraging the hydrophobic and chemically inert nature of PVDF, the MMM enhances the atmospheric stability of Ti3C2Tx by impeding water molecules from interacting with the MXene. Furthermore, ZIF-67 is selective to NH3 gas via acid-base interactions within the zeolite group and selective pore size. The Ti3C2Tx sensor embedded in the MMM filter exhibits a modest 1.3% change in the sensing response to 25 ppm of NH3 gas compared to the response without the filter. This result underscores the filter's effectiveness in conferring selectivity and diffusivity, particularly at 35% relative humidity (RH) and 25 °C. Crucially, the hydrophobic attributes of PVDF impart heightened stability to the Ti3C2Tx sensor even amidst varying RH conditions. These results not only demonstrate effective NH3 detection but also highlight the sensor's adaptability to diverse environmental conditions, offering promising prospects for practical applications.

Highly electrochemically active Ti3C2Tx MXene/MWCNT nanocomposite for the simultaneous sensing of paracetamol, theophylline, and caffeine in human blood samples

The facile fabrication is reported of highly electrochemically active Ti3C2Tx MXene/MWCNT (3D/1D)-modified screen-printed carbon electrode (SPE) for the efficient simultaneous electrochemical detection of paracetamol, theophylline, and caffeine in human blood samples. 3D/1D Ti3C2Tx MXene/MWCNT nanocomposite was synthesized using microwave irradiation and ultrasonication processes. Then, the Ti3C2Tx/MWCNT-modified SPE electrode was fabricated and thoroughly characterized towards its physicochemical and electrochemical properties using XPS, TEM, FESEM, XRD, electrochemical impedance spectroscopy, cyclic voltammetry, and differential pulse voltammetry techniques. As-constructed Ti3C2Tx-MWCNT/SPE offers excellent electrochemical sensing performance with good detection limits (0.23, 0.57, and 0.43 µM) and wide linear ranges (1.0 ~ 90.1, 2.0 ~ 62.0, and 2.0-90.9 µM) for paracetamol, caffeine, and theophylline, respectively,  in the human samples. Notably, the non-enzymatic electroactive nanocomposite-modified electrode has depicted a semicircle Nyquist plot with low charge transfer resistance (Rct∼95 Ω), leading to high ionic diffusion and facilitating an excellent electron transfer path. All the above results in efficient stability, reproducibility, repeatability, and sensitivity compared with other reported works, and thus, it claims its practical utilization in realistic clinical applications.

Streamlined fabrication of AuPtRh trimetallic nanoparticles supported on Ti3C2MXene for enhanced photocatalytic activity in cephalosporins degradation

The escalating prevalence of cephalosporin antibiotics in wastewater poses a serious threat to public health and environmental balance. Thus, it is crucial to develop effective methods for removing cephalosporin antibiotics from water sources. Herein, we propose the use of AuPtRh trimetallic nanoparticles supported on Ti3C2MXene as a photocatalyst for the degradation of cephalosporin antibiotics. Initially, AuPtRh nanoparticles were uniformly grown onto Ti3C2MXene sheets using one-step reduction technique. The prepared AuPtRh/Ti3C2MXene exhibited a complete degradation of cefixime and ceftriaxone sodium, while an impressive degradation efficiency of 91.58 % for cephalexin was achieved after 60 min of exposure to visible light, surpassing the performance of its individual AuPtRh nanoparticles and Ti3C2MXene. The enhanced photoactivity of AuPtRh/Ti3C2MXene was resulted from improved light absorption capacity and efficient generation, separation, and transfer of charge carriers driven by the formation of heterojunction between AuPtRh and Ti3C2MXene. Electron paramagnetic resonance and radicals trapping experiments results revealed that •O2- and h+ are the principal reactive species governing the degradation of cephalosporins. The photocatalyst exhibited excellent stability and could be reused four times without significant loss in efficiency. Our study highlights the potential of MXene composites for environmental remediation, offering insights into designing sustainable AuPtRh/Ti3C2MXene photocatalyst for water pollutant degradation.

Highly stable glucose oxidase polynanogel@MXene/chitosan electrochemical biosensor based on a multi-stable interface structure for glucose detection

It is a challenging and meaningful task to design an enzyme electrochemical biosensor that can maintain high sensitivity while improving stability. In this study, we constructed an enzyme electrochemical biosensor by preparing nanocomposites with multi-stable interface structures. Specifically, the nanocomposite (PGOx@MXene/CS) was prepared by efficient electrostatic assembly of GOx polynanogel (PGOx) onto MXene nanosheets. PGOx could enhance enzyme stability, while the extensive the large specific surface area of MXene could realize the efficient loading of nanocapsules (PGOx) and catalyze the decomposition of toxic intermediate H2O2, thereby reducing its influence on the stability of enzyme. The linear range of the constructed glucose sensor was 0.03-16.5 mM, the sensitivity was 48.98 μA mM-1·cm-2, and the detection limit was 3.1 μM. After 200 cycles, the current still remained at 85.83% of the initial current value. The high sensitivity, excellent selectivity and great reproducibility verified the effectiveness of the system we constructed. The multi-stable enzyme electrochemical biosensor had a wide application prospect in stable and continuous blood glucose detection.

Fast gelling, high performance MXene hydrogels for wearable sensors

Hydrogel-based functional materials had attracted great attention in the fields of artificial intelligence, soft robotics, and motion monitoring. However, the gelation of hydrogels induced by free radical polymerization typically required heating, light exposure, and other conditions, limiting their practical applications and development in real-life scenarios. In this study, a simple and direct method was proposed to achieve rapid gelation at room temperature by incorporating reductive MXene sheets in conjunction with metal ions into the chitosan network and inducing the formation of a polyacrylamide network in an extremely short time (10 s). This resulted in a dual-network MXene-crosslinked conductive hydrogel composite that exhibited exceptional stretchability (1350 %), remarkably low dissipated energy (0.40 kJ m-3 at 100 % strain), high sensitivity (GF = 2.86 at 300-500 % strain), and strong adhesion to various substrate surfaces. The study demonstrated potential applications in the reliable detection of various motions, including repetitive fine movements and large-scale human body motions. This work provided a feasible platform for developing integrated wearable health-monitoring electronic systems.

Removal of heavy metals from wastewater by aerogel derived from date palm waste

Cellulose that has been sourced from date palm leaves as a primary component was utilised. This cellulose served as the foundational material for the development of an aerogel composite. During this process, MXene (Ti3C2Tx) played a pivotal role in enhancing the overall composition of the aerogel. To ensure the stability and durability of the resulting aerogel structure, calcium ions were introduced to the mix. These ions facilitated the cross-linking process of sodium alginate molecules, ultimately leading to the formation of calcium alginate. This cross-linking step is crucial for the enhanced mechanical and chemical stability of the aerogel. Incorporating alginate and Ti3C2Tx into the cellulose aerogel enhanced its structural integrity in aqueous conditions and increased its adsorption capacity. When evaluated with synthetic wastewater, this composite exhibited remarkable adsorption capacities of 72.9, 114.4, 92.9, and 123.9 mg/g for As, Cd, Ni, and Zn ions, respectively. A systematic study was carried out to see the effect of various parameters, including contact time, MXene concentration, pH, and temperature on the adsorption of these elements. Peak adsorption was achieved at 60 min, favoring a pH range between 6 and 8 and exhibited optimal sorption efficiency at lower temperatures. The adsorption kinetics adhered closely to a pseudo-second-order, while the Freundlich model adeptly described the adsorption isotherms. An interesting result of this research was the aerogel's regenerative potential. After undergoing a basic acid treatment, the MXene/cellulose/alginate aerogel composite could be restored and reused for up to three cycles, all while maintaining its core performance capabilities even after the rigorous cross-linking processes. In three consecutive cycles, the removal percentages for As, Cd, Ni, and Zn were 48.15%, 80.38%, 56.51%, and 86.12% in cycle 1; 37.35%, 65.63%, 45.97%, and 78.42% in cycle 2; and 28.60%, 56.22%, 34.70%, and 65.83% in cycle 3, respectively. The composite was tested in conditions resembling seawater salinity. Impressively, the aerogel continued to demonstrate a significant ability to adsorb metals, reinforcing its potential utility in real-world aquatic scenarios. These findings suggest that the composite aerogel, integrating MXene, cellulose, and alginate, is an effective medium for the targeted removal of heavy metals from aquatic environments.

Injectable Bombyx mori (B. mori) silk fibroin/MXene conductive hydrogel for electrically stimulating neural stem cells into neurons for treating brain damage

Brain damage is a common tissue damage caused by trauma or diseases, which can be life-threatening. Stem cell implantation is an emerging strategy treating brain damage. The stem cell is commonly embedded in a matrix material for implantation, which protects stem cell and induces cell differentiation. Cell differentiation induction by this material is decisive in the effectiveness of this treatment strategy. In this work, we present an injectable fibroin/MXene conductive hydrogel as stem cell carrier, which further enables in-vivo electrical stimulation upon stem cells implanted into damaged brain tissue. Cell differentiation characterization of stem cell showed high effectiveness of electrical stimulation in this system, which is comparable to pure conductive membrane. Axon growth density of the newly differentiated neurons increased by 290% and axon length by 320%. In addition, unfavored astrocyte differentiation is minimized. The therapeutic effect of this system is proved through traumatic brain injury model on rats. Combined with in vivo electrical stimulation, cavities formation is reduced after traumatic brain injury, and rat motor function recovery is significantly promoted.

Flexible and Simply Degradable MXene-Methylcellulose Piezoresistive Sensor for Human Motion Detection

Flexible pressure sensors are intensively demanded in various fields such as electronic skin, medical and health detection, wearable electronics, etc. MXene is considered an excellent sensing material due to its benign metal conductivity and adjustable interlayer distance. Exhibiting both high sensitivity and long-term stability is currently an urgent pursuit in MXene-based flexible pressure sensors. In this work, high-strength methylcellulose was introduced into the MXene film to increase the interlayer distance of 2D nanosheets and fundamentally overcome the self-stacking problem. Thus, concurrent improvement of the sensing capability and mechanical strength was obtained. By appropriately modulating the ratio of methylcellulose and MXene, the obtained pressure sensor presents a high sensitivity of 19.41 kPa-1 (0.88-24.09 kPa), good stability (10000 cycles), and complete biodegradation in H2O2 solution within 2 days. Besides, the sensor is capable of detecting a wide range of human activities (pulse, gesture, joint movement, etc.) and can precisely recognize spatial pressure distribution, which serves as a good candidate for next-generation wearable electronic devices.

Potential application of 2D nano-layered MXene in analysing and remediating endocrine disruptor compounds and heavy metals in water

With the advancement of technologies and growth of the economy, it is inevitable that more complex processes are deployed, producing more heterogeneous wastewater that comes from biomedical, biochemical and various biotechnological industries. While the conventional way of wastewater treatment could effectively reduce the chemical oxygen demand, pH and turbidity of wastewater, trace pollutants, specifically the endocrine disruptor compounds (EDCs) that exist in µg L-1 or ng L-1 have further hardened the detection and removal of these biochemical pollutants. Even in small amounts, EDC could interfere human's hormone, causing severe implications on human body. Hence, this review elucidates the recent insights regarding the effectiveness of an advanced 2D material based on titanium carbide (Ti3C2Tx), also known as MXene, in detecting and removing EDCs. MXene's highly tunable feature also allows its surface chemistry to be adjusted by adding chemicals with different functional groups to adsorb different kinds of EDCs for biochemical pollution mitigation. At the same time, the incorporation of MXene into sample matrices also further eases the analysis of trace pollutants down to ng L-1 levels, thereby making way for a more cleaner and comprehensive wastewater treatment. In that sense, this review also highlights the progress in synthesizing MXene from the conventional method to the more modern approaches, together with their respective key parameters. To further understand and attest to the efficacy of MXene, the limitations and current gaps of this potential agent are also accentuated, targeting to seek resolutions for a more sustainable application.

A Wearable Electrochemical Biosensor Utilizing Functionalized Ti3C2Tx MXene for the Real-Time Monitoring of Uric Acid Metabolite

Wearable, noninvasive sensors enable the continuous monitoring of metabolites in sweat and provide clinical information related to an individual's health and disease states. Uric acid (UA) is a key indicator highly associated with gout, hyperuricaemia, hypertension, kidney disease, and Lesch-Nyhan syndrome. However, the detection of UA levels typically relies on invasive blood tests. Therefore, developing a wearable device for noninvasive monitoring of UA concentrations in sweat could facilitate real-time personalized disease prevention. Here, we introduce 1,3,6,8-pyrene tetrasulfonic acid sodium salt (PyTS) as a bifunctional molecule functionalized with Ti3C2Tx via π-π conjugation to design nonenzymatic wearable sensors for sensitive and selective detection of UA concentration in human sweat. PyTS@Ti3C2Tx provides many oxidation-reduction active groups to enhance the electrocatalytic ability of the UA oxidation reaction. The PyTS@Ti3C2Tx-based electrochemical sensor demonstrates highly sensitive detection of UA in the concentration range of 5 μM-100 μM, exhibiting a lower detection limit of 0.48 μM compared to the uricase-based sensor (0.84 μM). In volunteers, the PyTS@Ti3C2Tx-based wearable sensor is integrated with flexible microfluidic sweat sampling and wireless electronics to enable real-time monitoring of UA levels during aerobic exercise. Simultaneously, it allows for comparison of blood UA levels via a commercial UA analyzer. Herein, this study provides a promising electrocatalyst strategy for nonenzymatic electrochemical UA sensor, enabling noninvasive real-time monitoring of UA levels in human sweat and personalized disease prevention.