A Versatile Multicomponent Assembly via β‐cyclodextrin Host–Guest Chemistry on Graphene for Biomedical Applications

A multi‐component nanosystem based on graphene and comprising individual cyclodextrins at its surface is assembled, creating hybrid structures enabling new and important functionalities: optical imaging, drug storage, and cell targeting for medical diagnosis and treatment. These nanohybrids are part of a universal system of interchangeable units, capable of mutilple functionalities. The surface components, made of individual β‐cyclodextrin molecules, are the “hosts” for functional units, which may be used as imaging agents, for anti‐cancer drug delivery, and as tumor‐specific ligands. Specifically, individual β‐cyclodextrin (β‐CD), with a known capability to host various molecules, is considered a module unit that is assembled onto graphene nanosheet (GNS). The cyclodextrin‐functionalized graphene nanosheet (GNS/β‐CD) enables “host–guest” chemistry between the nanohybrid and functional “payloads”. The structure, composition, and morphology of the graphene nanosheet hybrid have been investigated. The nanohybrid, GNS/β‐CD, is highly dispersive in various physiological solutions, reflecting the high biostability of cyclodextrin. Regarding the host capability, the nanohybrid is fully capable of selectively accommodating various biological and functional agents in a controlled fashion, including the antivirus drug amantadine, fluorescent dye [5(6)‐carboxyfluorescein], and Arg‐Gly‐Asp (RGD) peptide‐targeting ligands assisted by an adamantine linker. The loading ratio of 5(6)‐carboxyfluorescein is as high as 110% with a drug concentration of 0.45 mg mL^?1. The cyclic RGD‐functionalized nanohybrid exhibits remarkable targeting for HeLa cells.     

Recent Advances on Host–Guest Material Systems toward Organic Room Temperature Phosphorescence

The design and characterization of purely organic room-temperature phosphorescent (RTP) materials for optoelectronic applications is currently the focus of research in the field of organic electronics. Particularly, with the merits of preparation controllability and modulation flexibility, host–guest material systems are encouraging candidates that can prepare high-performance RTP materials. By regulating the interaction between host and guest molecules, it can effectively control the quantum efficiency, luminescent lifetime, and color of host–guest RTP materials, and even produce RTP emission with stimuli-responsive features, holding tremendous potential in diverse applications such as encryption and anti-counterfeiting, organic light-emitting diodes, sensing, optical recording, etc. Here a roundup of rapid achievement in construction strategies, molecule systems, and diversity of applications of host–guest material systems is outlined. Intrinsic correlations between the molecular properties and a survey of recent significant advances in the development of host–guest RTP materials divided into three systems including rigid matrix, exciplex, and sensitization are presented. Providing an insightful understanding of host–guest RTP materials and offering a promising platform for high throughput screening of RTP systems with inherent advantages of simple material preparation, low-cost, versatile resource, and controllably modulated properties for a wide range of applications is intended.     

A Modular System for the Design of Stimuli‐Responsive Multifunctional Nanoparticle Aggregates by Use of Host–Guest Chemistry

A self‐assembly approach for the design of multifunctional nanomaterials consisting of different nanoparticles (gold, iron oxide, and lanthanide‐doped LiYF₄) is developed. This modular system takes advantage of the light‐responsive supramolecular host–guest chemistry of β‐cyclodextrin and arylazopyrazole, which enables the dynamic and reversible self‐assembly of particles to spherical nanoparticle aggregates in aqueous solution. Due to the magnetic iron oxide nanoparticles, the aggregates can be manipulated by an external magnetic field leading to the formation of linear structures. As a result of the integration of upconversion nanoparticles, the aggregates are additionally responsive to near‐infrared light and can be redispersed by use of the upconversion effect. By varying the nanoparticle and linker concentrations the composition, size, shape, and properties of the multifunctional nanoparticle aggregates can be fine‐tuned.     

Cooperative Treatment of Metastatic Breast Cancer Using Host–Guest Nanoplatform Coloaded with Docetaxel and siRNA

Conventional chemotherapy shows moderate efficiency against metastatic cancer since it targets only part of the mechanisms regulating tumor growth and metastasis. Here, gold nanorod (GNR)‐based host‐guest nanoplatforms loaded with docetaxel (DTX) and small interfering RNA (siRNA)‐p65 (referred to as DTX‐loaded GNR (GDTX)/p65) for chemo‐, RNA interference (RNAi), and photothermal ablation (PTA) cooperative treatment of metastatic breast cancer are reported. To prepare the nanoplatform, GNRs are first coated with cyclodextrin (CD)‐grafted polyethylenimine (PEI) and then loaded with DTX and siRNA through host–guest interaction with CD and electrostatic interaction with PEI, respectively. Upon near‐infrared laser irradiation, GNRs generate a significant hyperthermia effect to trigger siRNA and DTX release. DTX reduces tumor growth by inhibiting mitosis of cancer cells. Meanwhile, siRNA‐p65 suppresses lung metastasis and proliferation of cancer cells by blocking the nuclear factor kappa B (NF‐κB) pathway and downregulating the downstream genes matrix metalloproteinase‐9 (MMP‐9) and B cell lymphoma‐2 (Bcl‐2). It is demonstrated that GDTX/p65 in combination with laser irradiation significantly inhibits the growth and lung metastasis of 4T1 breast tumors. The antitumor results suggest promising potential of the host–guest nanoplatform for combinational treatment of metastatic cancer by using RNAi, chemotherapy, and PTA.     

A Solid‐State Fibriform Supercapacitor Boosted by Host–Guest Hybridization between the Carbon Nanotube Scaffold and MXene Nanosheets

Fiber‐shaped supercapacitors with improved specific capacitance and high rate capability are a promising candidate as power supply for smart textiles. However, the synergistic interaction between conductive filaments and active nanomaterials remains a crucial challenge, especially when hydrothermal or electrochemical deposition is used to produce a core (fiber)–shell (active materials) fibrous structure. On the other hand, although 2D pseudocapacitive materials, e.g., Ti₃C₂T _x (MXene), have demonstrated high volumetric capacitance, high electrical conductivity, and hydrophilic characteristics, MXene‐based electrodes normally suffer from poor rate capability owing to the sheet restacking especially when the loading level is high and solid‐state gel is used as electrolyte. Herein, by hosting MXene nanosheets (Ti₃C₂T _x ) in the corridor of a scrolled carbon nanotube (CNT) scaffold, a MXene/CNT fiber with helical structure is successfully fabricated. These features offer open spaces for rapid ion diffusion and guarantee fast electron transport. The solid‐state supercapacitor based on such hybrid fibers with gel electrolyte coating exhibits a volumetric capacitance of 22.7 F cm⁻³ at 0.1 A cm⁻³ with capacitance retention of 84% at current density of 1.0 A cm⁻³ (19.1 F cm⁻³), improved volumetric energy density of 2.55 mWh cm⁻³ at the power density of 45.9 mW cm⁻³, and excellent mechanical robustness.     

Reversible Ion‐Conducting Switch in a Novel Single‐Ion Supramolecular Hydrogel Enabled by Photoresponsive Host–Guest Molecular Recognition

A novel ion‐conducting supramolecular hydrogel with reversible photoconductive properties in which the azobenzene motif, α‐cyclodextrin (α‐CD), and ionic liquid are grafted onto the gel matrix is reported. Host–guest interactions with different association constants between α‐CD and azobenzene or the anionic part of the ionic liquid can be readily tuned by photoinduced trans–cis isomerization of the azobenzene unit. When irradiated by 365 nm light, α‐CD prefers to form a complex with the anionic part of the ionic liquid, resulting in decreased ionic mobility and thus high resistance of the hydrogel. However, under 420 nm light irradiation, a more stable complex is again formed between α‐CD and trans‐azobenzene, thereby releasing the bound anions to regenerate the low‐resistive hydrogel. As such, remote control of the ionic conductivity of the hydrogel is realized by simple host–guest chemistry. With the incorporation of a logic gate, this hydrogel is able to reversibly switch an electric circuit on and off by light irradiation with certain wavelengths. The concept of photoswitchable ionic conductivity of a hydrogel mediated by competitive molecular recognition is potentially promising toward the fabrication of optoelectronic devices and applications in bioelectronic technology.     

Semiconducting Polymer Nanocavities: Porogenic Synthesis,Tunable Host–Guest Interactions,and Enhanced Drug/siRNA Delivery

Nanocavities composed of lipids and block polymers have demonstrated great potential in biomedical applications such as sensors, nanoreactors, and delivery vectors. However, it remains a great challenge to produce nanocavities from fluorescent semiconducting polymers owing to their hydrophobic rigid polymer backbones. Here, we describe a facile, yet general strategy that combines photocrosslinking with nanophase separation to fabricate multicolor, water‐dispersible semiconducting polymer nanocavities (PNCs). A photocrosslinkable semiconducting polymer is blended with a porogen such as degradable macromolecule to form compact polymer dots (Pdots). After crosslinking the polymer and removing the porogen, this approach yields semiconducting polymer nanospheres with open cavities that are tunable in diameter. Both small molecules and macromolecules can be loaded in the nanocavities, where molecular size can be differentiated by the efficiency of the energy transfer from host polymer to guest molecules. An anticancer drug doxorubicin (Dox) is loaded into the nanocavities and the intracellular release is monitored in real time by the fluorescence signal. Finally, the efficient delivery of small interfering RNA (siRNA) to silence gene expression without affecting cell viability is demonstrated. The combined features of bright fluorescence, tunable cavity, and efficient drug/siRNA delivery makes these nanostructures promising for biomedical imaging and drug delivery.     

Bioadhesive Polymersome for Localized and Sustained Drug Delivery at Pathological Sites with Harsh Enzymatic and Fluidic Environment via Supramolecular Host–Guest Complexation

Targeted and sustained delivery of drugs to diseased tissues/organs, where body fluid exchange and catabolic activity are substantial, is challenging due to the fast cleansing and degradation of the drugs by these harsh environmental factors. Herein, a multifunctional and bioadhesive polycaprolactone‐β‐cyclodextrin (PCL‐CD) polymersome is developed for localized and sustained co‐delivery of hydrophilic and hydrophobic drug molecules. This PCL‐CD polymersome affords multivalent crosslinking action via surface CD‐mediated host–guest interactions to generate a supramolecular hydrogel that exhibits evident shear thinning and efficient self‐healing behavior. The co‐delivery of small molecule and proteinaceous agents by the encapsulated PCL‐CD polymersomes enhances the differentiation of stem cells seeded in the hydrogel. Furthermore, the PCL‐CD polymersomes are capable of in situ grafting to biological tissues via host–guest complexation between surface CD and native guest groups in the tissue matrix both in vitro and in vivo, thereby effectively extending the retention of loaded cargo in the grafted tissue. It is further demonstrated that the co‐delivery of small molecule and proteinaceous drugs via PCL‐CD polymersomes averts cartilage degeneration in animal osteoarthritic (OA) knee joints, which are known for their biochemically harsh and fluidically dynamic environment.     

Optochemically Responsive 2D Nanosheets of a 3D Metal–Organic Framework Material

Outstanding functional tunability underpinning metal–organic framework (MOF) confers a versatile platform to contrive next‐generation chemical sensors, optoelectronics, energy harvesters, and converters. A rare exemplar of a porous 2D nanosheet material constructed from an extended 3D MOF structure is reported. A rapid supramolecular self‐assembly methodology at ambient conditions to synthesize readily exfoliatable MOF nanosheets, functionalized in situ by adopting the guest@MOF (host) strategy, is developed. Nanoscale confinement of light‐emitting molecules (as functional guest) inside the MOF pores generates unusual combination of optical, electronic, and chemical properties, arising from the strong host–guest coupling effects. Highly promising photonics‐based chemical sensing opened up by the new guest@MOF composite systems is shown. By harnessing host–guest optochemical interactions of functionalized MOF nanosheets, detection of an extensive range of volatile organic compounds and small molecules important for many practical applications has been accomplished.     

A Metal–Organic Framework with Optimized Porosity and Functional Sites for High Gravimetric and Volumetric Methane Storage Working Capacities

Extensive research has been devoted to developing new porous materials with high methane storage capacity. While great progress has been made in recent years, it still remains very challenging to target simultaneously high gravimetric and volumetric methane (CH₄) working capacities (deliverable amount between 5.8 and 65 bar) in a single material. Here, a novel metal–organic framework (termed as UTSA‐110a) constructed by an extended linker containing a high density of functional nitrogen sites, exhibiting both very high gravimetric and volumetric working capacities of 317 cm³ (STP: 273.15 K, 1 atm) g^?1 and 190 cm³ (STP) cm^?3, respectively, for robust MOFs, is reported. Both of these values are higher than those of two benchmark materials: HKUST‐1 (207 cm³ (STP) g^?1 or 183 cm³ (STP) cm^?3) and UTSA‐76a (267 cm³ (STP) g^?1 or 187 cm³ (STP) cm^?3). Computational studies reveal that it is the combination of optimized porosity and favorable binding sites that leads to the simultaneously high gravimetric and volumetric working capacities in this material.