Highly green fluorescent Nb2C MXene quantum dots for Cu2+ ion sensing and cell imaging

The luminescent Nb2C MXene nanosheet-based whispering gallery mode-enhanced ECL strategy for miRNA-214 detection

MiRNA-214 can regulate the expression of their downstream target genes after post-transcriptional and are involved in the biological processes of triple negative breast cancer (TNBC). In this work, the small-sized luminescent Nb2C nanosheet-based whispering gallery mode-enhanced electrochemiluminescence (ECL) strategy was successfully constructed to detect miRNA-214 in TNBC. Firstly, we have synthesized small-sized luminescent Nb2C nanosheets from Nb2AlC MXene. The Nb2C nanosheets not only exhibited more stable chemical properties and reduced the defects of the large sheet structures, but also possessed the quantum confinement effect with the discrete energy level. As a result, the prepared small-sized Nb2C nanosheets had unique luminescent and electrochemical properties. Furthermore, in order to improve the ECL performance of Nb2C nanosheets, SiO2 microspheres were self-assembled on the electrode surface by gas-liquid interface method to form whispering gallery mode structure. Because the light was continuously reflected at the interface of the microcavity in the whispering gallery mode, the ECL signal of Nb2C luminescent nanosheets was amplified largely. Finally, the whispering gallery mode-based ECL sensing platform was established. The results showed that the biosensor had a good linear correlation between the ECL intensity and the logarithm of concentration of miRNA-214 in the range of 10 fM to 100 nM with a limit of detection of 2.5 fM. The actual detection of miRNA-214 content in clinical TNBC tissue samples was realized successfully.

The potential of MXene-based materials in fluorescence-based sensing/biosensing of ionic and organic contaminants in environment and food samples: Recent advancements and challenges

MXenes belong to one of the recently developed advanced materials with tremendous potential for diverse sensing applications. To date, various types of MXene-based materials have been developed to generate direct/indirect ultrasensitive sensing signals against various forms of analytes via fluorescence quenching or enhancement. In this work, the fluorescence sensing/biosensing capabilities of the MXene-based materials have been explored and evaluated against a list of ionic/emerging pollutants in environment and food matrices. The suitability of an MXene-based sensing approach is also validated through the assessment of the performance based on the basic quality assurance parameters, e.g., limit of detection (LOD), sensing range, and response time. Accordingly, the best performing MXene-based materials are selected and recommended for the given target(s) to help facilitate their scalable applications under real-world conditions.

Ultrasensitive Fluorescence Detection of Ascorbic Acid Using Silver Ion-Modulated High-Quality CdSe/CdS/ZnS Quantum Dots

Improving the sensitivity of the fluorescence method for the detection of bioactive molecules is crucial in biochemical analysis. In this work, an ultrasensitive sensing strategy was constructed for the detection of ascorbic acid (AA) using high-quality 3-mercaptopropionic acid-capped CdSe/CdS/ZnS quantum dots (MPA-CdSe/CdS/ZnS QDs) as the fluorescent probe. The prepared water-soluble QDs exhibited a high photoluminescence quantum yield (PL QY) of up to 96%. Further, the fluorescence intensity of the QDs was intensively quenched through the dynamic quenching of Ag+ ions due to an efficient photoinduced electron transfer progress. While the existence of AA before adding Ag+ ions, Ag+ ions were reduced. Thus, the interaction of the QDs and Ag+ ions was destroyed, which led to the fluorescence distinct recovery. The detection limit of AA could be as low as 0.2 nM using this sensing system. Additionally, most relevant small molecules and physiological ions had no influence on the analysis of AA. Satisfactory results were obtained in orange beverages, showing its great potential as a meaningful platform for highly sensitive and selective AA sensing for clinical analysis.

Advances in MXene-based luminescence sensing strategies

MXenes have attracted the attention of many researchers as one of the latest two-dimensional (2D) materials over the last decade. Their great potential for biosensing has also been fully exploited after the discovery of their unique properties such as superior optical properties, excellent hydrophilicity, good thermal stability, excellent mechanical property, high electrical conductivity, biocompatibility, large surface area, and ease of surface functionalization. In the MXene-based luminescence sensing strategy, MXenes typically appear in the form of nanosheets, quantum dots and modified MXene nanocomposites, and they are utilized as different sensing platforms or as a luminescence source. In this review, we focused on the MXene-based luminescence sensing strategies, including fluorescence, electrochemiluminescence and chemiluminescence sensors and the comparison of their performance. Finally, the perspectives of the MXene-based luminescence sensors are discussed.

An Overview of Electrochemical Sensors Based on Transition Metal Carbides and Oxides: Synthesis and Applications

Sensors play vital roles in industry and healthcare due to the significance of controlling the presence of different substances in industrial processes, human organs, and the environment. Electrochemical sensors have gained more attention recently than conventional sensors, including optical fibers, chromatography devices, and chemiresistors, due to their better versatility, higher sensitivity and selectivity, and lower complexity. Herein, we review transition metal carbides (TMCs) and transition metal oxides (TMOs) as outstanding materials for electrochemical sensors. We navigate through the fabrication processes of TMCs and TMOs and reveal the relationships among their synthesis processes, morphological structures, and sensing performance. The state-of-the-art biological, gas, and hydrogen peroxide electrochemical sensors based on TMCs and TMOs are reviewed, and potential challenges in the field are suggested. This review can help others to understand recent advancements in electrochemical sensors based on transition metal oxides and carbides.

Smart nanoparticles for cancer therapy

Smart nanoparticles, which can respond to biological cues or be guided by them, are emerging as a promising drug delivery platform for precise cancer treatment. The field of oncology, nanotechnology, and biomedicine has witnessed rapid progress, leading to innovative developments in smart nanoparticles for safer and more effective cancer therapy. In this review, we will highlight recent advancements in smart nanoparticles, including polymeric nanoparticles, dendrimers, micelles, liposomes, protein nanoparticles, cell membrane nanoparticles, mesoporous silica nanoparticles, gold nanoparticles, iron oxide nanoparticles, quantum dots, carbon nanotubes, black phosphorus, MOF nanoparticles, and others. We will focus on their classification, structures, synthesis, and intelligent features. These smart nanoparticles possess the ability to respond to various external and internal stimuli, such as enzymes, pH, temperature, optics, and magnetism, making them intelligent systems. Additionally, this review will explore the latest studies on tumor targeting by functionalizing the surfaces of smart nanoparticles with tumor-specific ligands like antibodies, peptides, transferrin, and folic acid. We will also summarize different types of drug delivery options, including small molecules, peptides, proteins, nucleic acids, and even living cells, for their potential use in cancer therapy. While the potential of smart nanoparticles is promising, we will also acknowledge the challenges and clinical prospects associated with their use. Finally, we will propose a blueprint that involves the use of artificial intelligence-powered nanoparticles in cancer treatment applications. By harnessing the potential of smart nanoparticles, this review aims to usher in a new era of precise and personalized cancer therapy, providing patients with individualized treatment options.

Recent Advances in MXene Quantum Dots: A Platform with Unique Properties for General-Purpose Functional Materials with Novel Biomedical Applications

Developing new, high-performance materials is a prerequisite for technological advancement. In comparison to bulk materials, quantum dots have a number of good advantages due to their small size, high surface area, and quantum dimensions. Quantum dots, two-dimensional materials with lateral dimensions less than 100 nm, can be generated by the quantum confinement effect. Mxene quantum dots (MQDs) retain some of their two-dimensional characteristics. They also exhibit novel physicochemical properties, including enhanced dispersibility in aqueous and nonaqueous phases, modification or doping capabilities, and photoluminescence. MQDs, due to their unique and diverse properties, have been receiving a great deal of attention as new members of the Mxene group and wide use for biotechnology, bioimaging, optoelectronics, catalysis, cancer therapy, etc. This review aims to provide an overview of the synthesis of MQDs, their optical properties, and their cancer therapy applications. MQDs exhibit remarkable photothermal and photodynamic features and can be suitable for bioimaging. In addition to obtaining bioimaging, photothermal therapy (PTT) and photodynamic therapy (PDT) effects simultaneously, MQDs have high biocompatibility in vitro and in vivo, providing evidence of their potential clinical utility. Herein, recent developments and future prospects concerning MQDs biomedical applications are discussed.

Crafting two-dimensional materials for contrast agents, drug, and heat delivery applications through green technologies

The development of two-dimensional (2D) materials for biomedical applications has accelerated exponentially. Contrary to their bulk counterparts, the exceptional properties of 2D materials make them highly prospective for contrast agents for bioimage, drug, and heat delivery in biomedical treatment. Nevertheless, empty space in the integration and utilisation of 2D materials in living biological systems, potential toxicity, as well as required complicated synthesis and high-cost production limit the real application of 2D materials in those advance medical treatments. On the other hand, green technology appears to be one of strategy to shed a light on the blurred employment of 2D in medical applications, thus, with the increasing reports of green technology that promote advanced technologies, here, we compile, summarise, and synthesise information on the biomedical technology of 2D materials through green technology point of view. Beginning with a fundamental understanding, of crystal structures, the working mechanism, and novel properties, this article examines the recent development of 2D materials. As well as 2D materials made from natural and biogenic resources, a recent development in green-related synthesis was also discussed. The biotechnology and biomedical-related application constraints are also discussed. The challenges, solutions, and prospects of the so-called green 2D materials are outlined.

State-of-the-art: MXene structures in nano-oncology

Cancer nanomedicine has been investigated widely and boomed in the last two decades, resulting in designing nanostructures with biofunctionalization, giving rise to an "All-in-One" multifunctional platform. The development of rational design technology with extended functionalities brought interdisciplinary researchers to work continuously, aiming to find a prevent or effectively treat the deadly disease of the century. Thus, it led to some Food and Drug Administration (FDA)-approving nano-based formulations for cancer treatment and opening a vast area of promising discoveries by exploiting different nanomaterials. Two-dimensional (2D) materials have recently gained tremendous interest among scientists because of their outstanding structural, optical, electronic, thermal, and mechanical characteristics. Among various 2D nanomaterials, MXenes are a widely studied nanosystem because of their close similarity to graphene analogs. So, it is synthesized using multiple approaches and exploits their inherited properties. But in most cases, surface functionalization techniques are carried out for targeting, site-specific drug clearance, renal clearance, and biocompatible with healthy cells. Thus, fabricating a multimodal agent for mono or combined therapies is also an image-guided diagnostic agent. This review will explain the recent and emerging advancements of MXenes-based composites as a multifunctional theragnostic agent and discuss the possibilities of transferring laboratory research to clinical translation.

Latest advances on MXenes in biomedical research and health care

The unique combination of physical and chemical properties of MXenes has propelled a growing number of applications in biomedicine and healthcare. The expanding library of MXenes with tunable properties is paving the way for high-performance, application-specific MXene-based sensing and therapeutic platforms. In this article, we highlight the emerging biomedical applications of MXenes with specific emphasis on bioelectronics, biosensors, tissue engineering, and therapeutics. We present examples of MXenes and their composites enabling novel technological platforms and therapeutic strategies, and elucidate potential avenues for further developments. Finally, we discuss the materials, manufacturing, and regulatory challenges that need to be synergistically addressed for the clinical translation of MXene-based biomedical technologies.

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Towards Greener and More Sustainable Synthesis of MXenes: A Review

The unique properties of MXenes have been deemed to be of significant interest in various emerging applications. However, MXenes provide a major drawback involving environmentally harmful and toxic substances for its general fabrication in large-scale production and employing a high-temperature solid-state reaction followed by selective etching. Meanwhile, how MXenes are synthesized is essential in directing their end uses. Therefore, making strategic approaches to synthesize greener, safer, more sustainable, and more environmentally friendly MXenes is imperative to commercialize at a competitive price. With increasing reports of green synthesis that promote advanced technologies and non-toxic agents, it is critical to compile, summarize, and synthesize the latest development of the green-related technology of MXenes. We review the recent progress of greener, safer, and more sustainable MXene synthesis with a focus on the fundamental synthetic process, the mechanism, and the general advantages, and the emphasis on the MXene properties inherited from such green synthesis techniques. The emerging use of the so-called green MXenes in energy conversion and storage, environmental remediation, and biomedical applications is presented. Finally, the remaining challenges and prospects of greener MXene synthesis are discussed.

Analytical methods to determine and sense heavy metal pollutants using MXene and MXene-based composites: Mechanistic prophecy into sensing properties

The presence of heavy metal ions in the biosphere is of grave concern, as these are toxic and impact living organisms. Lack of pure drinking water can spread waterborne diseases like cholera, dysentery, typhoid, etc. The presence of heavy metals like arsenic and radioactive materials can cause cancer. The detection and removal of these heavy metals are important for sustaining life. Herein, MXene comes to the rescue as a crucial and potential material, which can sense and adsorb heavy metal ions. Developed in 2011, MXenes are an emerging class of 2D nanomaterials that are appropriate substitutes for existing heavy metal ions sensing materials and have shown excellent efficiency due to their better hydrophilicity, capacity of transportation of electrons, functionalization, and a great variety in compositions as compared to the other nanomaterials properties. This work gives an insight into the chemistry and synthesis of MXenes for further utilization as a sensor in heavy metal ions toxicity and underlines the key future challenges to knowing the full prospective of MXenes in environmental systems.

Quantum Dots Compete at the Acme of MXene Family for the Optimal Catalysis

It is well known that two-dimensional (2D) MXene-derived quantum dots (MQDs) inherit the excellent physicochemical properties of the parental MXenes, as a Chinese proverb says, "Indigo blue is extracted from the indigo plant, but is bluer than the plant it comes from." Therefore, 0D QDs harvest larger surface-to-volume ratio, outstanding optical properties, and vigorous quantum confinement effect. Currently, MQDs trigger enormous research enthusiasm as an emerging star of functional materials applied to physics, chemistry, biology, energy conversion, and storage. Since the surface properties of small-sized MQDs include the type of surface functional groups, the functionalized surface directly determines their performance. As the Nobel Laureate Wolfgang Pauli says, "God made the bulk, but the surface was invented by the devil," and it is just on the basis of the abundant surface functional groups, there is lots of space to be thereof excavated from MQDs. We are witnessing such excellence and even more promising to be expected. Nowadays, MQDs have been widely applied to catalysis, whereas the related reviews are rarely reported. Herein, we provide a state-of-the-art overview of MQDs in catalysis over the past five years, ranging from the origin and development of MQDs, synthetic routes of MQDs, and functionalized MQDs to advanced characterization techniques. To explore the diversity of catalytic application and perspectives of MQDs, our review will stimulate more efforts toward the synthesis of optimal MQDs and thereof designing high-performance MQDs-based catalysts.

Biomedical engineering of two-dimensional MXenes

The emergence of two-dimensional (2D) transition metal carbides, carbonitrides and nitrides, referred to MXenes, with a general chemical formula of M_n+1X_nT_x have aroused considerable interest and shown remarkable potential applications in diverse fields. The unique ultrathin lamellar structure accompanied with charming electronic, optical, magnetic, mechanical and biological properties make MXenes as a kind of promising alternative biomaterials for versatile biomedical applications, as well as uncovering many new fundamental scientific discoveries. Herein, the current state-of-the-art advances of MXenes-related biomaterials are systematically summarized in this comprehensive review, especially focusing on the synthetic methodologies, design and surface engineering strategies, unique properties, biological effects, and particularly the property-activity-effect relationship of MXenes at the nano-bio interface. Furthermore, the elaborated MXenes for varied biomedical applications, such as biosensors and biodevices, antibacteria, bioimaging, therapeutics, theranostics, tissue engineering and regenerative medicine, are illustrated in detail. Finally, we discuss the current challenges and opportunities for future advancement of MXene-based biomaterials in-depth on the basis of the present situation, aiming to facilitate their early realization of practical biomedical applications.

Layer-by-Layer Assembly of Polyelectrolytes on Urchin-like MnO2 for Extraction of Zn2+, Cu2+ and Pb2+ from Alkaline Solutions

Three-dimensional (3D) urchin-like MnO2@poly (sodium 4-styrene sulfonate) (PSS)/poly (diallyl dimethylammonium chloride) (PDDA)/PSS particles were prepared via the layer-by-layer (LBL) assembly of polyelectrolytes for the extraction of Zn2+ from alkaline media. The adsorption performance of Zn2+ on MnO2, MnO2@PSS/PDDA/PSS, and MnO2@(PSS/PDDA)3/PSS was investigated in batch experiments. The adsorption of Zn2+ on MnO2@PSS/PDDA/PSS has been studied under various conditions, such as initial Zn2+ concentration, adsorbent dosage, the solution’s pH, and reaction time. The Zn2+ adsorption process is well represented by the pseudo-second-order kinetic model, and the equilibrium data fit the Freundlich isotherm well. MnO2@PSS/PDDA/PSS also showed high efficiency for Pb2+ and Cu2+ removal from slightly alkaline water. Thus, our research provides a deep insight into the preparation of 3D manganese oxides with polyelectrolyte films for the extraction of heavy metal ions, such as Pb2+, Cu2+, and Zn2+, from slightly alkaline wastewater.

MXene-based hybrid system exhibits excellent synergistic antibiosis

MXenes are a group of inorganic two-dimensional (2D) nanomaterial, and have raised significant interests in biomedical areas. Ti₃C₂T_x, as an important member of MXene family, is widely studied because of its biodegradability and low-cytotoxicity. However, their single antibacterial mechanism and poor stability in aqueous solution need to be improved, especially for the antimicrobial applications. In this work, a MXene-based hybrid antibacterial system (M-HAS) was developed and its synergistic antibacterial activity was investigated. In the M-HAS, 2D few-layer Ti₃C₂T_x(FL-Ti₃C₂T_x) was modified with hydrophilic polymers and thereby used as carriers for silver nanoparticles (Ag NPs). By assembling these two substrates, photodynamic performance of the prepared system is significantly improved with a large amount of reactive oxygen species produced under 660 nm laser. Antibacterial effects of the M-HAS are enhanced by over 4 times with irradiation. In another word, the developed hybrid system displays excellent photodynamic antibacterial synergistic properties. This work takes advantage of the photodynamic properties of each component in the M-HAS to achieve efficient antibacterial activity and proposes an innovative approach to develop the 2D FL-Ti₃C₂T_x-based antibacterial platform.

Quantum dots in cell imaging and their safety issues

When quantum dots are used as fluorescent probes or drug tracers for in vivo imaging, the quantum dots in the blood will come into direct contact with vascular endothelial cells. Thus, it is necessary to study whether quantum dots can affect endothelial function after being injected into blood vessels as imaging agents. In recent years, there have been numerous studies on the toxicity of quantum dots. Herein, we focused on five types of quantum dots (Cd-containing quantum dots, CuInS2 quantum dots, black phosphorus quantum dots, MXene quantum dots, and carbon-based quantum dots) for cell imaging and their toxicity in vivo and in vitro. Although current research on the toxicity of quantum dots has not reached a consistent conclusion, it can guide the next step in evaluating their cytotoxicity.

2D Transition Metal Carbides (MXene) for Electrochemical Sensing: A Review

MXene, a novel class of 2-dimensional transition metal carbides has evolved as a promising material for various applications owing to its outstanding characteristics such as hydrophilicity, high electrical conductivity, surface area, and attractive topological structure. MXenes can form dispersion in common solvents and constitute composite with other nanomaterials, which can be utilized as effective transducers for molecular sensing. MXene-modified support materials, thus provide an intriguing platform for immobilization of target molecules onto their surface. The literature reveals that it has been increasingly utilized in the sensing of diverse types of analytes including glucose, pharmaceuticals, metals and dyes, cancer markers, pesticides, neurotransmitters, small valuable molecules, and so on. In this review, we summarize the recent updates in the MXene modified materials for sensing. For the convenience of our audience, we have distributed the analytes into categories and discussed them comprehensively. Not only we present the synthesis approach, electrochemical properties and surface chemistry of MXenes but also discussed briefly the current challenges and an outlook for future research in the related area.