Coffee Ring-Inspired Approach toward Oriented Self-Assembly of Biomimetic Murray MOFs as Sweat Biosensor

Rise of Metal-Organic Frameworks: From Synthesis to E-Skin and Artificial Intelligence

Metal-organic frameworks (MOFs) have attained broad research attention in the areas of sensors, resistive memories, and optoelectronic synapses on the merits of their intriguing physical and chemical properties. In this review, recent progress on the synthesis of MOFs and their electronic applications is introduced and discussed. Initially, the crystal structures and properties of MOFs encompassing optical, electrical, and chemical properties are discussed in brief. Subsequently, advanced synthesis methods for MOFs are introduced, categorized into hydrothermal approach, microwave synthesis, mechanochemical synthesis, and electrochemical deposition. After that, the various roles of MOFs in widespread applications, including sensing, information storage, optoelectronic synapses, machine learning, and artificial intelligence, are discussed, highlighting their versatility and the innovative solutions they provide to long-standing challenges. Finally, an outlook on remaining challenges and a future perspective for MOFs are proposed.

Evaporative self-assembly in colloidal droplets: Emergence of ordered structures from complex fluids

Colloidal droplet evaporation is an intriguing and intricate phenomenon that has captured the interest of scientists across diverse disciplines, including physical chemistry, fluid dynamics, and soft matter science, over the past two decades. Despite being a non-equilibrium system with inherent challenges posed by coffee ring formation and Marangoni effects, which hinder the precise control of deposition patterns, evaporative self-assembly presents a convenient and cost-effective approach for generating arrays of well-ordered structures and functional patterns with wide-ranging applications in inkjet printing, photonic crystals, and biochemical assays. In the realm of printed electronics and photonics, effectively mitigating coffee rings while achieving uniformity and orderliness has emerged as a critical factor in realising the next generation of large-area, low-cost, flexible devices that are exceptionally sensitive and high-performance. This review highlights the evaporative self-assembly process in colloidal droplets with a focus on the intricate mechanical environment, self-assembly at diverse interfaces, and potential applications of these assembling ordered structures.

Unlocking Efficiency: Minimizing Energy Loss in Electrocatalysts for Water Splitting

Catalysts play a crucial role in water electrolysis by reducing the energy barriers for hydrogen and oxygen evolution reactions (HER and OER). Research aims to enhance the intrinsic activities of potential catalysts through material selection, microstructure design, and various engineering techniques. However, the energy consumption of catalysts has often been overlooked due to the intricate interplay among catalyst microstructure, dimensionality, catalyst-electrolyte-gas dynamics, surface chemistry, electron transport within electrodes, and electron transfer among electrode components. Efficient catalyst development for high-current-density applications is essential to meet the increasing demand for green hydrogen. This involves transforming catalysts with high intrinsic activities into electrodes capable of sustaining high current densities. This review focuses on current improvement strategies of mass exchange, charge transfer, and reducing electrode resistance to decrease energy consumption. It aims to bridge the gap between laboratory-developed, highly efficient catalysts and industrial applications regarding catalyst structural design, surface chemistry, and catalyst-electrode interplay, outlining the development roadmap of hierarchically structured electrode-based water electrolysis for minimizing energy loss in electrocatalysts for water splitting.

Universal Murray's law for optimised fluid transport in synthetic structures

Materials following Murray's law are of significant interest due to their unique porous structure and optimal mass transfer ability. However, it is challenging to construct such biomimetic hierarchical channels with perfectly cylindrical pores in synthetic systems following the existing theory. Achieving superior mass transport capacity revealed by Murray's law in nanostructured materials has thus far remained out of reach. We propose a Universal Murray's law applicable to a wide range of hierarchical structures, shapes and generalised transfer processes. We experimentally demonstrate optimal flow of various fluids in hierarchically planar and tubular graphene aerogel structures to validate the proposed law. By adjusting the macroscopic pores in such aerogel-based gas sensors, we also show a significantly improved sensor response dynamics. In this work, we provide a solid framework for designing synthetic Murray materials with arbitrarily shaped channels for superior mass transfer capabilities, with future implications in catalysis, sensing and energy applications.

A Review on Recent Trends and Future Developments in Electrochemical Sensing

Electrochemical methods and devices have ignited prodigious interest for sensing and monitoring. The greatest challenge for science is far from meeting the expectations of consumers. Electrodes made of two-dimensional (2D) materials such as graphene, metal-organic frameworks, MXene, and transition metal dichalcogenides as well as alternative electrochemical sensing methods offer potential to improve selectivity, sensitivity, detection limit, and response time. Moreover, these advancements have accelerated the development of wearable and point-of-care electrochemical sensors, opening new possibilities and pathways for their applications. This Review presents a critical discussion of the recent developments and trends in electrochemical sensing.

Electrochemical aptasensor based on the engineered core-shell MOF nanostructures for the detection of tumor antigens

It is essential to develop ultrasensitive biosensors for cancer detection and treatment monitoring. In the development of sensing platforms, metal-organic frameworks (MOFs) have received considerable attention as potential porous crystalline nanostructures. Core-shell MOF nanoparticles (NPs) have shown different diversities, complexities, and biological functionalities, as well as significant electrochemical (EC) properties and potential bio-affinity to aptamers. As a result, the developed core-shell MOF-based aptasensors serve as highly sensitive platforms for sensing cancer biomarkers with an extremely low limit of detection (LOD). This paper aimed to provide an overview of different strategies for improving selectivity, sensitivity, and signal strength of MOF nanostructures. Then, aptamers and aptamers-modified core-shell MOFs were reviewed to address their functionalization and application in biosensing platforms. Additionally, the application of core-shell MOF-assisted EC aptasensors for detection of several tumor antigens such as prostate-specific antigen (PSA), carbohydrate antigen 15-3 (CA15-3), carcinoembryonic antigen (CEA), human epidermal growth factor receptor-2 (HER2), cancer antigen 125 (CA-125), cytokeratin 19 fragment (CYFRA21-1), and other tumor markers were discussed. In conclusion, the present article reviews the advancement of potential biosensing platforms toward the detection of specific cancer biomarkers through the development of core-shell MOFs-based EC aptasensors.

A controllable SERS biosensor for ultrasensitive detection of miRNAs based on porous MOFs and subject-object recognition ability

In this work, a simple and sensitive SERS-based miRNA biosensor was constructed based on porous MOFs nanoparticles and efficient subject-object recognition ability. MOFs as a container can package lots of signal probe neutral red (NR) for the advantages of three dimensional structure and porosity. The partially complementary duplex DNA can as a "lock" to lock up the hole for obtaining a weak Raman signal. In the present of miRNA, miRNA just like a "key" to open the duplex structure with the results of releasing NR. At this time, the released NR can be captured by SERS substrate AuNS@CB[7] for the subject-object recognition ability to produce a strong Raman signal which was positive correlation to target miRNA. By this way, the proposed SERS biosensor can achieve sensitively and selectively detect miRNA with a detection limit of 0.562 fM. This MOF-based SERS biosensor also be hopeful application for clinical diagnostics.

What Is Left for Real-Life Lactate Monitoring? Current Advances in Electrochemical Lactate (Bio)Sensors for Agrifood and Biomedical Applications

Monitoring of lactate is spreading from the evident clinical environment, where its role as a biomarker is notorious, to the agrifood ambit as well. In the former, lactate concentration can serve as a useful indicator of several diseases (e.g., tumour development and lactic acidosis) and a relevant value in sports performance for athletes, among others. In the latter, the spotlight is placed on the food control, bringing to the table meaningful information such as decaying product detection and stress monitoring of species. No matter what purpose is involved, electrochemical (bio)sensors stand as a solid and suitable choice. However, for the time being, this statement seems to be true only for discrete measurements. The reality exposes that real and continuous lactate monitoring is still a troublesome goal. In this review, a critical overview of electrochemical lactate (bio)sensors for clinical and agrifood situations is performed. Additionally, the transduction possibilities and different sensor designs approaches are also discussed. The main aim is to reflect the current state of the art and to indicate relevant advances (and bottlenecks) to keep in mind for further development and the final achievement of this highly worthy objective.

Recent Progress in Aptamer-Functionalized Metal-Organic Frameworks-Based Optical and Electrochemical Sensors for Detection of Mycotoxins

Mycotoxin contamination in foodstuffs and agricultural products has posed a serious hazard to human health and raised international concern. The progress of cost-effective, facile, rapid and reliable analytical tools for mycotoxin determination is in urgent need. In this regard, the potential utility of metal-organic frameworks (MOFs) as a class of crystalline porous materials has sparked immense attention due to their large specific surface area, adjustable pore size, nanoscale framework structure and good chemical stability. The amalgamation of MOFs with high-affinity aptamers has resulted in the progress of advanced aptasensing methods for clinical and food/water safety diagnosis. Aptamers have many advantages over classical approaches as exceptional molecular recognition constituents for versatile bioassays tools. The excellent sensitivity and selectivity of the MOF-aptamer biocomposite nominate them as efficient lab-on-chip tools for portable, label-free, cost-effective and real-time screening of mycotoxins. Current breakthroughs in the concept, progress and biosensing applications of aptamer functionalized MOFs-derived electrochemical and optical sensors for mycotoxins have been discussed in this study. We first highlighted an overview part, which provides some insights into the functionalization mechanisms of MOFs with aptamers, offering a foundation to create MOFs-based aptasensors. Then, we discuss various strategies to design high-performance MOFs-based aptamer scaffolds, which serve as either signal nanoprobe carriers or signal nanoprobes and their applications. We perceived that applications of optical aptamers are in their infancy in comparison with electrochemical MOFs-derived aptasensors. Finally, current challenges and prospective trends of MOFs-aptamer sensors are discussed.

Tunable coffee-ring formation of halloysite nanotubes by evaporating sessile drops

Halloysite nanotubes (HNTs) are one-dimensional clay nanomaterials with a length of 200-1000 nm and a diameter of ∼50 nm. Understanding the self-assembly behavior of such unique nanoparticles is important to develop their applications in functional devices. In this study, the "coffee-ring" patterns of HNTs are investigated which are formed by evaporation of the sessile droplets of HNT aqueous dispersion on different substrates. The coffee-ring pattern with various dimensions was characterized using a polarizing microscope (POM), a scanning electron microscope (SEM), and a 3D optical profilometer. The diameter, height, and area of the coffee-ring patterns depend on the concentration of HNT dispersion, the droplet volume, and surface wettability. POM and SEM results suggested that the nanotubes were highly ordered in the edge and the middle of the coffee-ring. The coffee-ring effect of HNTs could be suppressed by increasing the evaporation temperature of substrates or adding polymer additives. In addition, multiple-ring patterns consistent with protein rings surrounding HNT rings were formed, which can be utilized to detect the presence of proteins in biological samples. This work illustrated the relationship between the formation of coffee-ring patterns and the experimental conditions, which provided an additional research chance and allowed application development for HNTs using the liquid droplet self-assembly.

Hierarchy in materials for maximized efficiency

This perspective article gives the future research direction on the application of the generalized Murray's law for the design of porous hierarchy in materials and the establishment of a general materials design theory 'law of hierarchy' taking four types of hierarchy into account.

Nanoimprint Lithography-Directed Self-Assembly of Bimetallic Iron-M (M=Palladium, Platinum) Complexes for Magnetic Patterning

Self-assembly of d⁸ metal polypyridine systems is a well-established approach for the creation of 1D organometallic assemblies but there are still challenges for the large-scale construction of nanostructured patterns from these building blocks. We describe herein the use of high-throughput nanoimprint lithography (NIL) to direct the self-assembly of the bimetallic complexes [4'-ferrocenyl-(2,2':6',2''-terpyridine)M(OAc)]⁺ (OAc)^- (M=Pd or Pt; OAc=acetate). Uniform nanorods are fabricated from the molecular self-organization and evidenced by morphological characterization. More importantly, when top-down NIL is coupled with the bottom-up self-assembly of the organometallic building blocks, regular arrays of nanorods can be accessed and the patterns can be controlled by changing the lithographic stamp, where the mold imposes a confinement effect on the nanorod growth. In addition, patterns consisting of the products formed after pyrolysis are studied. The resulting arrays of ferromagnetic FeM alloy nanorods suggest promising potential for the scalable production of ordered magnetic arrays and fabrication of magnetic bit-patterned media.

Applications of Functional Metal-Organic Frameworks in Biosensors

In recent decades, fast advancements in the fields of metal-organic frameworks (MOFs) are providing unprecedented opportunities for the development of novel functional MOFs for various biosensing applications. Exciting progress is achieved due to the combination of MOFs with various functional components, which introduces novel structures and new features to the MOFs-based biosensing applications, such as higher stability, higher sensitivity, higher flexibility, and higher specificity. This review aims to be a comprehensive summary of the most recent advances in the development of functional MOFs for various biosensing applications, placing special attention on important contributions in recent 3 years. In this review, the most recent developments in design and synthesis of functional MOFs for biosensing applications are summarized. MOFs-based biosensing applications are outlined according to the central roles of MOFs in biosensors, which include carriers of sensitive elements, enzyme-mimic elements, electrochemical signaling, optical signaling, and gas sensing. Finally, the current challenges and future development trends of functional MOFs for biosensing applications are proposed and discussed.

Wettability Control in Tree Structure-Based 1D Fiber Assemblies for Moisture Wicking Functionality

One of the fundamental properties of natural systems is their water transport ability, and living systems have efficient moisture management features. Here, a unique structure, inspired by the water transfer behavior in trees, was designed for one-dimensional (1D) fiber assemblies. In this 1D fiber assembly structure, a differential capillary effect enabling rapid water transfer at the interface between traditional cotton fibers and electrospun nanofibers was explored. A tree-like structure yarn was constructed successfully by novel electrospinning technology, and the effect was quantitatively controlled by precisely regulating the fibers' wettability. Fabrics based on these tree-like core-spun yarns possessed advanced moisture-wicking performance, a high one-way transport index (R) of 1034.5%, and a desirable overall moisture management capability of 0.88, which are over two times higher than those of conventional fabrics. This moisture-wicking regime endowed these 1D fiber assemblies with unique water transfer channels, providing a new strategy for moisture-heat transmission, microfluidics, and biosensor applications.

Assembling Metal-Organic Frameworks into the Fractal Scale for Sweat Sensing

Many natural organizations with some special functional properties possess fractal tissues which display nearly the same at every scale. The benefit of mimicking fractal structure in synthetic functional materials warrants further exploration. To tackle this challenge, we assemble metal-organic frameworks (MOFs) into fractal structures by using a bottom-up approach inspired from evaporation-driven crystallization. Such hierarchically branched MOFs exhibit some unexpected performances in electrochemistry, and can be a versatile biosensor for sweat analysis. Our work provides an interesting and efficient example for fabricating fractal MOFs as well as uncovering their new properties. This fractal-guided strategy can be extended to synthesize and explore new characteristics of other materials, holding potential in various applications including sensors, catalysis, and energy storage.

Ferrocene-Encapsulated Zn Zeolitic Imidazole Framework (ZIF-8) for Optical and Electrochemical Sensing of Amyloid-β Oligomers and for the Early Diagnosis of Alzheimer's Disease

In this work, the ferrocene-encapsulated Zn zeolitic imidazole framework (ZIF-8) was prepared by the self-assembly of Zn ions and 2-methylimidazole and used for the dual detection of amyloid-beta oligomers (AβO), which is the main neuropathological hallmark of Alzheimer's disease. Ferrocene is an optically and electrochemically active signal which was successfully encapsulated inside of the ZIF-8 and released by the competitive coordination between Zn ions and AβO after being treated with AβO. The released ferrocene content was monitored by ultraviolet/visible spectrophotometry and cyclic voltammetry. The dual determination of AβO played a synergetic role in the quick qualitative and precise quantitative analyses in a wide detection range of 10^-5 to 10² μM and good feasibility in artificial cerebrospinal fluid.

Biomimetic Fibrous Murray Membranes with Ultrafast Water Transport and Evaporation for Smart Moisture-Wicking Fabrics

Both antigravity directional water transport and ultrafast evaporation are critical to achieving a high-performance moisture-wicking fabric. The transpiration in vascular plants possess both of these features, which is due to their optimized hierarchical structure composed of multibranching porous networks following Murray's law. However, it remains a great challenge to simultaneously realize the ultrafast water transport and evaporation by mimicking nature's Murray networks in the synthetic materials. Here, we report a synergistic assembly strategy to create a biomimetic micro- and nanofibrous membrane with antigravity directional water transport and quick-dry performance by combining a multibranching porous structure and surface energy gradient, overcoming previous limitations. The resulting fiber-based porous Murray membranes exhibit an ultrahigh one-way transport capability ( R) of 1245%, a desired overall moisture management capability (OMMC) of 0.94, and an outstanding water evaporation rate of 0.67 g h^-1 (5.8 and 2.1 times higher than the cotton fabric and Coolmax fabric, respectively). Overall, the successful synthesis of these biomimetic porous Murray membranes should serve as a source of inspiration for the development of moisture-wicking technologies, providing personal comfort in hot or humid environments.