Mesoporous Gold: Substrate-Dependent Growth Dynamics, Strain Accumulation, and Electrocatalytic Activity for Biosensing.

Understanding the growth of mesoporous crystalline materials, such as mesoporous metals, on different substrates can provide valuable insights into the crystal growth dynamics and the redox reactions that influence their electrochemical sensing performance. Herein, it is demonstrated how the amorphous nature of the glass substrate can suppress the typical <111> oriented growth in mesoporous Au (mAu) films. The suppressed <111> growth is manifested as an accumulation of strain, leading to the generation of abundant surface defects, which are beneficial for enhancing the electrochemical activity. The fine structuring attained enables dramatically accelerated diffusion and enhances the electrochemical sensing performance for disease-specific biomolecules. As a proof-of-concept, the as-fabricated glass-grown mAu film demonstrates high sensitivity in electrochemical detection of SARS-CoV-2-specific RNA with a limit of detection (LoD) as low as 1 attomolar (aM).

The revelation of glucose adsorption mechanisms on hierarchical metal-organic frameworks using a surface plasmon resonance sensor.

The gold layer on the surface plasmon resonance (SPR) sensor chip cannot detect small molecules, such as glucose without the use of specific receptors. Metal-organic frameworks (MOFs) are useful in biosensing technologies for capturing and co-localizing enzymes and receptors with the target biomolecule. In many previous studies, the properties of the MOFs were often ignored, with these studies focusing on the selection of appropriate receptors. To take advantage of the unique properties of MOFs in biosensors, one must also consider the technique and transducer used because these aspects will strongly influence the detection mechanism. In this work, we have investigated for the first time, the applications of hierarchical metal-BDC (M-BDC) MOFs for glucose detection using the SPR technique without the use of specific receptors. The underlying interactions and adsorption mechanisms were analyzed using adsorption isotherm and kinetic models. The sensing measurements show that the SPR chips functionalized with M-BDC MOFs exhibit higher sensitivity and lower limit of detection (LOD). Specifically, the sensitivity follows the order of Zr-BDC > Cu-BDC > Mn-BDC > Ni-BDC > bare Au SPR chips with the LOD in the order of Zr-BDC < Mn-BDC < Ni-BDC < Cu-BDC < bare Au SPR chips. The selectivity test results reveal that Zr-BDC exhibits a decent selectivity to glucose in the presence of other interfering compounds, such as ascorbic acid, uric acid, maltose, and urea. These results demonstrate the promising potential of MOFs for SPR biosensing.

Carbon nanotube-decorated hierarchical porous nickel/carbon hybrid derived from nickel-based metal-organic framework for enhanced methyl blue adsorption.

This work reports the incorporation of coordinated water into Ni-BTC nanorods (Ni-BTC-O) which induces their structural transformation to Ni-BTC nanofibres (Ni-BTC-F). The carbonization of the Ni-BTC nanofibres at 600 °C results in the formation of carbon nanotube (CNT)-decorated hierarchical porous nickel/carbon hybrid (labelled as Ni/C-600) with enlarged pores. In contrast, the Ni/C hybrid obtained from the carbonization of the original (unmodified) Ni-BTC nanorods (Ni-BTC-O) at 600 °C (labelled as Ni-BTC-O-600) exhibits smaller pore size and does not show the formation of CNTs. The Ni/C-600 hybrid derived from Ni-BTC-F shows a very high adsorption capacity of 686.8 mg g-1 toward methyl blue (MB) dye. This is approximately 4.8 times higher than the adsorption capacity of Ni-BTC-O-600 (144.1 mg g-1). The higher adsorption performance of Ni/C-600 relative to Ni-BTC-O-600 can be attributed to its larger pore volume, hierarchical porosity, and additional adsorption sites provided by the CNTs. In addition, the Ni/C-600 hybrid can maintain 90% of its adsorption capacity after 5 consecutive cycles, demonstrating its potential as an efficient and recyclable adsorbent for MB dye.

Flexible Nanoarchitectonics for Biosensing and Physiological Monitoring Applications.

Flexible and implantable electronics hold tremendous promises for advanced healthcare applications, especially for physiological neural recording and modulations. Key requirements in neural interfaces include miniature dimensions for spatial physiological mapping and low impedance for recognizing small biopotential signals. Herein, a bottom-up mesoporous formation technique and a top-down microlithography process are integrated to create flexible and low-impedance mesoporous gold (Au) electrodes for biosensing and bioimplant applications. The mesoporous architectures developed on a thin and soft polymeric substrate provide excellent mechanical flexibility and stable electrical characteristics capable of sustaining multiple bending cycles. The large surface areas formed within the mesoporous network allow for high current density transfer in standard electrolytes, highly suitable for biological sensing applications as demonstrated in glucose sensors with an excellent detection limit of 1.95 µm and high sensitivity of 6.1 mA cm-2  µM-1 , which is approximately six times higher than that of benchmarking flat/non-porous films. The low impedance of less than 1 kΩ at 1 kHz in the as-synthesized mesoporous electrodes, along with their mechanical flexibility and durability, offer peripheral nerve recording functionalities that are successfully demonstrated in vivo. These features highlight the new possibilities of our novel flexible nanoarchitectonics for neuronal recording and modulation applications.

Hydrogel Nanoarchitectonics: An Evolving Paradigm for Ultrasensitive Biosensing.

The integration of nanoarchitectonics and hydrogel into conventional biosensing platforms offers the opportunities to design physically and chemically controlled and optimized soft structures with superior biocompatibility, better immobilization of biomolecules, and specific and sensitive biosensor design. The physical and chemical properties of 3D hydrogel structures can be modified by integrating with nanostructures. Such modifications can enhance their responsiveness to mechanical, optical, thermal, magnetic, and electric stimuli, which in turn can enhance the practicality of biosensors in clinical settings. This review describes the synthesis and kinetics of gel networks and exploitation of nanostructure-integrated hydrogels in biosensing. With an emphasis on different integration strategies of hydrogel with nanostructures, this review highlights the importance of hydrogel nanostructures as one of the most favorable candidates for developing ultrasensitive biosensors. Moreover, hydrogel nanoarchitectonics are also portrayed as a promising candidate for fabricating next-generation robust biosensors.

Boosting capacitive performance of manganese oxide nanorods by decorating with three-dimensional crushed graphene.

This work reports the rational design of MnOx nanorods on 3D crushed reduced graphene oxide (MnOx/C-rGO) by chemical reduction of Ni-incorporated graphene oxide (GO) followed by chemical etching to remove Ni. The resulting MnOx/C-rGO composite synergistically integrates the electronic properties and geometry structure of MnOx and 3D C-rGO. As a result, MnOx/C-rGO shows a significantly higher specific capacitance (Csp) of 863 F g-1 than MnOx/2D graphene sheets (MnOx/S-rGO) (373 F g-1) and MnOx (200 F g-1) at a current density of 0.2 A g-1. Furthermore, when assembled into symmetric supercapacitors, the MnOx/C-rGO-based device delivers a higher Csp (288 F g-1) than MnOx/S-rGO-based device (75 F g-1) at a current density of 0.3 A g-1. The superior capacitive performance of the MnOx/C-rGO-based symmetric device is attributed to the enlarged accessible surface, reduced lamellar stacking of graphene, and improved ionic transport provided by the 3D architecture of MnOx/C-rGO. In addition, the MnOx/C-rGO-based device exhibits an energy density of 23 Wh kg-1 at a power density of 113 Wkg-1, and long-term cycling stability, demonstrating its promising potential for practical application.

Borophene: Two-dimensional Boron Monolayer: Synthesis, Properties, and Potential Applications.

Borophene, a monolayer of boron, has risen as a new exciting two-dimensional (2D) material having extraordinary properties, including anisotropic metallic behavior and flexible (orientation-dependent) mechanical and optical properties. This review summarizes the current progress in the synthesis of borophene on various metal substrates, including Ag(110), Ag(100), Au(111), Ir(111), Al(111), and Cu(111), as well as heterostructuring of borophene. In addition, it discusses the mechanical, thermal, magnetic, electronic, optical, and superconducting properties of borophene and the effects of elemental doping, defects, and applied mechanical strains on these properties. Furthermore, the promising potential applications of borophene for gas sensing, energy storage and conversion, gas capture and storage applications, and possible tuning of the material performance in these applications through doping, formation of defects, and heterostructures are illustrated based on available theoretical studies. Finally, research and application challenges and the outlook of the whole borophene's field are given.

Ultrathin nanosheet-assembled nickel-based metal-organic framework microflowers for supercapacitor applications.

Herein, we propose a solvent-assisted approach for preparing Ni-MOF microflowers with high specific capacitance and excellent rate capability as an electrode material for supercapacitors. The high electrochemical performance of this Ni-MOF is attributed to the fast ion transport and low electrical resistance resulting from its hierarchical flower-like structure, and the capacitance contribution from nickel hydroxide species.

Defect-Rich Hierarchical Porous UiO-66(Zr) for Tunable Phosphate Removal.

The introduction of defects into hierarchical porous metal-organic frameworks (HP-MOFs) is of vital significance to boost their adsorption performance. Herein, an advanced template-assisted strategy has been developed to fine-tune the phosphate adsorption performance of HP-MOFs by dictating the type and number of defects in HP-UiO-66(Zr). To achieve this, monocarboxylic acids of varying chain lengths have been employed as template molecules to fabricate an array of defect-rich HP-UiO-66(Zr) derivatives following removal of the template. The as-prepared HP-UiO-66(Zr) exhibits a higher sorption capacity and faster sorption rate compared to the pristine UiO-66(Zr). Particularly, the octanoic acid-modulated UiO-66(Zr) exhibits a high adsorption capacity of 186.6 mg P/g and an intraparticle diffusion rate of 6.19 mg/g·min0.5, which are 4.8 times and 1.9 times higher than those of pristine UiO-66(Zr), respectively. The results reveal that defect sites play a critical role in boosting the phosphate uptake performance, which is further confirmed by various advanced characterizations. Density functional theory (DFT) calculations reveal the important role of defects in not only providing additional sorption sites but also reducing the sorption energy between HP-UiO-66(Zr) and phosphate. In addition, the hierarchical pores in HP-UiO-66(Zr) can accelerate the phosphate diffusion toward the active sorption sites. This work presents a promising route to tailor the adsorption performance of MOF-based adsorbents via defect engineering.

Extracellular Vesicle Nanoarchitectonics for Novel Drug Delivery Applications.

Extracellular vesicles (EVs) can transfer intercellular messages in various (patho)physiological processes and transport biomolecules to recipient cells. EVs possess the capacity to evade the immune system and remain stable over long periods, identifying them as natural carriers for drugs and biologics. However, the challenges associated with EVs isolation, heterogeneity, coexistence with homologous biomolecules, and lack of site-specific delivery, have impeded their potential. In recent years, the amalgamation of EVs with rationally engineered nanostructures has been proposed for achieving effective drug loading and site-specific delivery. With the advancement of nanotechnology and nanoarchitectonics, different nanostructures with tunable size, shapes, and surface properties can be integrated with EVs for drug loading, target binding, efficient delivery, and therapeutics. Such integration may enable improved cellular targeting and the protection of encapsulated drugs for enhanced and specific delivery to target cells. This review summarizes the recent development of nanostructure amalgamated EVs for drug delivery, therapeutics, and real-time monitoring of disease progression. With a specific focus on the exosomal cargo, diverse drug delivery system, and biomimetic nanostructures based on EVs for selective drug delivery, this review also chronicles the needs and challenges of EV-based biomimetic nanostructures and provides a future outlook on the strategies posed.

Solar-Powered Sustainable Water Production: State-of-the-Art Technologies for Sunlight-Energy-Water Nexus.

Alternative water resources (seawater, brackish water, atmospheric water, sewage, etc.) can be converted into clean freshwater via high-efficiency, energy-saving, and cost-effective methods to cope with the global water crisis. Herein, we provide a comprehensive and systematic overview of various solar-powered technologies for alternative water utilization (i.e., "sunlight-energy-water nexus"), including solar-thermal interface desalination (STID), solar-thermal membrane desalination (STMD), solar-driven electrochemical desalination (SED), and solar-thermal atmospheric water harvesting (ST-AWH). Three strategies have been proposed for improving the evaporation rate of STID systems above the theoretical limit and designing all-weather or all-day operating STID systems by analyzing the energy transfer of the evaporation and condensation processes caused by solar-thermal conversion. This review also introduces the fundamental principles and current research hotspots of two other solar-driven seawater or brackish water desalination technologies (STMD and SED) in detail. In addition, we also cover ST-AWH and other solar-powered technologies in terms of technology design, materials evolution, device assembly, etc. Finally, we summarize the content of this comprehensive review and discuss the challenges and future outlook of different types of solar-powered alternative water utilization technologies.

Nanoarchitectured Porous Conducting Polymers: From Controlled Synthesis to Advanced Applications.

Conductive polymers (CPs) integrate the inherent characteristics of conventional polymers and the unique electrical properties of metals. They have aroused tremendous interest over the last decade owing to their high conductivity, robust and flexible properties, facile fabrication, and cost-effectiveness. Compared to bulk CPs, porous CPs with well-defined nano- or microstructures possess open porous architectures, high specific surface areas, more exposed reactive sites, and remarkably enhanced activities. These attractive features have led to their applications in sensors, energy storage and conversion devices, biomedical devices, and so on. In this review article, the different strategies for synthesizing porous CPs, including template-free and template-based methods, are summarized, and the importance of tuning the morphology and pore structure of porous CPs to optimize their functional performance is highlighted. Moreover, their representative applications (energy storage devices, sensors, biomedical devices, etc.) are also discussed. The review is concluded by discussing the current challenges and future development trend in this field.

Fabrication of highly and poorly oxidized silver oxide/silver/tin(IV) oxide nanocomposites and their comparative anti-pathogenic properties towards hazardous food pathogens.

Herein, we report the fabrication of highly oxidized silver oxide/silver/tin(IV) oxide (HOSBTO or Ag3+-enriched AgO/Ag/SnO2) nanocomposite under a robust oxidative environment created with the use of concentrated nitric acid. Tin(IV) hydroxide nanofluid is added to the reaction mixture as a stabilizer for the Ag3+-enriched silver oxide in the nanocomposite. The formation of Ag nanoparticles in this nanocomposite originates from the decomposition of silver oxides during calcination at 600 °C. For comparison, poorly oxidized silver oxide/silver/tin(IV) oxide (POSBTO with formula AgO/Ag/SnO2) nanocomposite has also been prepared by following the same synthetic procedures, except for the use of concentrated nitric acid. Finally, we studied in detail the anti-pathogenic capabilities of both nanocomposites against four hazardous pathogens, including pathogenic fish bacterium (Stenotrophomonas maltophilia stain EP10), oomycete (Phytophthora cactorum strain P-25), and two different strains of pathogenic strawberry fungus, BRSP08 and BRSP09 (Collectotrichum siamense). The bioassays reveal that the as-prepared HOSBTO and POSBTO nanocomposites exhibit significant inhibitory activities against the tested pathogenic bacterium, oomycete, and fungus in a dose-dependent manner. However, the degree of dose-dependent effectiveness of the two nanocomposites against each pathogen largely varies.

Mesoporous TiO2-based architectures as promising sensing materials towards next-generation biosensing applications.

In the past two decades, mesoporous TiO2 has emerged as a promising material for biosensing applications. In particular, mesoporous TiO2 materials with uniform, well-organized pores and high surface areas typically exhibit superior biosensing performance, which includes high sensitivity, broad linear response, low detection limit, good reproducibility, and high specificity. Therefore, the development of biosensors based on mesoporous TiO2 has significantly intensified in recent years. In this review, the expansion and advancement of mesoporous TiO2-based biosensors for glucose detection, hydrogen peroxide detection, alpha-fetoprotein detection, immobilization of enzymes, proteins, and bacteria, cholesterol detection, pancreatic cancer detection, detection of DNA damage, kanamycin detection, hypoxanthine detection, and dichlorvos detection are summarized. Finally, the future perspective and research outlook on the utilization of mesoporous TiO2-based biosensors for the practical diagnosis of diseases and detection of hazardous substances are also given.

Highly dispersed secondary building unit-stabilized binary metal center on a hierarchical porous carbon matrix for enhanced oxygen evolution reaction.

Restricting the aggregation and rationally adjusting the electronic structure of binary metal centers in metal-organic framework (MOF) precursors are important for optimizing their performance as electrocatalysts for the oxygen evolution reaction (OER) and achieving low overpotential and high stability in such applications. Herein, we demonstrate the possibility of enhancing the electrochemical activity of MOF-derived binary metal center catalysts by controlling the form of the Fe species. The introduction of Fe-SBU (iron 2,5-dihydroxyterephthalic acid) into ZIF-67 is found to induce a distinct confinement effect and this can be exploited to improve the electroconductivity of binary metal center catalysts, and therefore, to reduce the OER reaction barrier (OOH* → O*). When applied as an OER catalyst in 1 M KOH solution, the Fe-SBU@Co-Matrix catalyst exhibits a low overpotential of 249 mV to reach a current density of 10 mA cm-2 and high stability for over 40 h. This work describes the secondary growth treatment of MOF-derived porous carbons to promote their application as catalysts in energy conversion reactions.

Mesoporous gold-silver alloy films towards amplification-free ultra-sensitive microRNA detection.

Herein, we report the preparation of mesoporous gold (Au)-silver (Ag) alloy films through the electrochemical micelle assembly process and their applications as microRNA (miRNA) sensors. Following electrochemical deposition and subsequent removal of the templates, the polymeric micelles can create uniformly sized mesoporous architectures with high surface areas. The resulting mesoporous Au-Ag alloy films show high current densities (electrocatalytic activities) towards the redox reaction between potassium ferrocyanide and potassium ferricyanide. Following magnetic isolation and purification, the target miRNA is adsorbed directly on the mesoporous Au-Ag film. Electrochemical detection is then enabled by differential pulse voltammetry (DPV) using the [Fe(CN)6]3-/4- redox system (the faradaic current for the miRNA-adsorbed Au-Ag film decreases compared to the bare film). The films demonstrate great advantages towards miRNA sensing platforms to enhance the detection limit down to attomolar levels of miR-21 (limit of detection (LOD) = 100 aM, s/n = 3). The developed enzymatic amplification-free miniaturized analytical sensor has promising potential for RNA-based diagnosis of diseases.

Assembling well-arranged covalent organic frameworks on MOF-derived graphitic carbon for remarkable formaldehyde sensing.

Constructing heterostructures with advanced architectures is an effective strategy for enhancing the crystallinity and functional performance of covalent organic frameworks (COFs). Herein, a novel core-shell heterostructure integrating a metal-organic framework (MOF)-derived graphitic carbon core (GC) and a well-arranged COF shell, termed MOF-GC@COF, is reported. ZIF-67 dodecahedra are first chemically etched with a weak organic acid and further converted to MOF-GC via thermal pyrolysis. In the subsequent step, ß-ketoenamine-linked COF nanofibers are vertically assembled on the surface of the MOF-GC cores to generate the MOF-GC@COF heterostructure. As a proof-of-concept application, the as-prepared MOF-GC@COF heterostructure is used as an effective quartz crystal microbalance (QCM) sensor for the adsorption of formaldehyde. Benefiting from the synergistic effect of the hybrid composition and the advantages of the core-shell heterostructure, the newly prepared MOF-GC@COF heterostructure exhibits excellent sensing performance toward formaldehyde with rapid adsorption kinetics, high sensitivity, and superior selectivity.

Self-assembly of block copolymers towards mesoporous materials for energy storage and conversion systems.

Self-assembly of block copolymers (BCPs) provides a versatile strategy for controllable preparation of a broad range of functional materials with different ordered structures. In recent decades, this soft-templating strategy has been widely utilized for preparing a wide range of mesoporous materials. These porous materials have attracted tremendous interest in energy storage and conversion (ESC) applications in view of their ability to absorb, store, and interact with guest species on their exterior/interior surfaces and in the pore space. Compared with other synthetic approaches, such as template-free and hard-templating methods, BCP soft-templating protocols show great advantages in the construction of large mesopores with diameters between 10-60 nm, which are suitable for applications requiring the storage or hosting of large-sized species/molecules. In addition, this strategy shows incomparable merits in the flexible control of pore size/architecture/wall thickness, which determines the final performance of mesoporous materials in ESC devices. In the last decade, rapid development has been witnessed in the area of BCP-templated mesoporous materials. In this review paper, we overview the progress of this field over the past 10 years, with an emphasis on the discussions of synthetic methodologies, the control of materials structures (including morphology and pore size/shape), and potential applications particularly in rechargeable batteries, supercapacitors, electro-/photocatalysis, solar cells, etc.

Pseudocapacitive Lithium Storage of Cauliflower-Like CoFe2 O4 for Low-Temperature Battery Operation.

Binary transition-metal oxides (BTMOs) with hierarchical micro-nano-structures have attracted great interest as potential anode materials for lithium-ion batteries (LIBs). Herein, we report the fabrication of hierarchical cauliflower-like CoFe2 O4 (cl-CoFe2 O4 ) via a facile room-temperature co-precipitation method followed by post-synthetic annealing. The obtained cauliflower structure is constructed by the assembly of microrods, which themselves are composed of small nanoparticles. Such hierarchical micro-nano-structure can promote fast ion transport and stable electrode-electrolyte interfaces. As a result, the cl-CoFe2 O4 can deliver a high specific capacity (1019.9 mAh g-1 at 0.1 A g-1 ), excellent rate capability (626.0 mAh g-1 at 5 A g-1 ), and good cyclability (675.4 mAh g-1 at 4 A g-1 for over 400 cycles) as an anode material for LIBs. Even at low temperatures of 0 °C and -25 °C, the cl-CoFe2 O4 anode can deliver high capacities of 907.5 and 664.5 mAh g-1 at 100 mA g-1 , respectively, indicating its wide operating temperature. More importantly, the full-cell assembled with a commercial LiFePO4 cathode exhibits a high rate performance (214.2 mAh g-1 at 5000 mA g-1 ) and an impressive cycling performance (612.7 mAh g-1 over 140 cycles at 300 mA g-1 ) in the voltage range of 0.5-3.6 V. Kinetic analysis reveals that the electrochemical performance of cl-CoFe2 O4 is dominated by pseudocapacitive behavior, leading to fast Li+ insertion/extraction and good cycling life.

Practical MOF Nanoarchitectonics: New Strategies for Enhancing the Processability of MOFs for Practical Applications.

Over the past decades, the development of porous materials has directly or indirectly affected industrial production methods. Metal-organic frameworks (MOFs) as an emerging class of porous materials exhibit some unique advantages, including controllable composition, a large surface area, high porosity, and so on. These attractive characteristics of MOFs have led to their potential applications in energy storage and conversion devices, drug delivery, adsorption and storage, sensors, and other areas. However, powdered MOFs have limited practical applications owing to poor processability, safety hazards from dust formation, and poor recyclability. In addition, the inherent micro/mesoporosities of MOFs also reduce the accessibility and diffusion kinetics for large molecules. To improve their processability for practical applications, MOFs are often deposited as MOF layers or films (i.e., MOF-coated composites) on supporting materials or are formed into 3D structured composites, such as aerogels and hydrogels. In this article, we review recent researches on these MOF composites, including their synthetic methods and potential applications in energy storage devices, heavy metal ion adsorption, and water purification. Finally, the future outlook and challenges associated with the large-scale fabrication of MOF-based composites for practical applications are discussed.