Search

DNA nanostructures have recently attracted increasing interest in biological and biomedical applications by virtue of their unique properties, such as structural programmability, multi-functionality, stimuli-responsive behaviors, and excellent biocompatibility. In particular, the intelligent responsiveness of smart DNA nanostructures to specific stimuli has facilitated their extensive development in the field of high-performance biosensing and controllable drug delivery. This minireview begins with different self-assembly strategies for the construction of various DNA nanostructures, followed by the introduction of a variety of stimuli-responsive functional DNA nanostructures for assembling metastable soft materials and for facilitating amplified biosensing. The recent achievements of smart DNA nanostructures for controllable drug delivery are highlighted. Finally, the current challenges and possible developments of this promising research are discussed in the fields of intelligent nanomedicine.

This Minireview summarizes the recent progress of stimuli-responsive purely organic phosphorescence materials. Organic phosphorescence is closely related to the intermolecular interactions, because such interactions are beneficial to promote spin orbital coupling (SOC) and boost intersystem cross (ISC) efficiency and finally are conducive to satisfactory phosphorescence. It is found that the intermolecular interactions, which are essential for organic phosphorescence, are easily disturbed by external stimuli such as mechanical force, photon, acid, chemical vapor, leading to the luminescence change. According to this principle, various purely organic phosphorescence materials sensitive to external stimuli have been developed. This Minireview categorizes reported stimuli-responsive purely organic phosphorescence materials on the basis of different stimuli, including mechanochromism, mechanoluminescence, photoactivity, acid-responsiveness and other stimuli. Some prospective strategies for constructing stimuli-responsive purely organic phosphorescence molecules are provided.

Advancements in the field of liposomal drug carriers have culminated in greatly improved delivery properties. An important aspect of this work entails development of designer liposomes for release of contents triggered by environmental changes. The majority of these systems are driven by chemical reactions in the presence of different stimuli. However, a promising new paradigm instead focuses on molecular recognition events as the impetus for content release. In certain cases, these platforms exploit synthetic lipid switches designed to undergo conformational changes upon binding to target ions or molecules that perturb membrane assembly, thereby triggering cargo release. Examples of this approach reported thus far showcase how rational design of lipid switches can result in dramatic changes in lipid assembly properties. These strategies show great promise for opening up new pathophysiological stimuli that can be harnessed for programmed content release in drug delivery applications.

The cavities of metallosupramolecular cages can be used to mimic the central spaces of naturally occurring proteins and bind a wide variety of molecular guests. A range of potential applications have arisen from this capacity for host-guest chemistry. However, to truly harness the opportunities thus afforded, methodologies to controllably allow the release and reuptake of guests from the cavities of metallosupramolecular cages are required. Methods to accomplish this have centered upon reversibly altering the character of either the guest or host. This minireview outlines the current approaches used to carry out the binding and release of guests from metallosupramolecular hosts using important examples from the field.

The design of multifunctional nanomaterials that respond to external stimuli and mimic the capacity of biological materials to respond and adapt to their environment has become a focus of interest in nanotechnology. In this Concept, we describe the development of supramolecular nanoparticle assemblies constructed by use of host-guest interactions between cyclodextrins and suitable guest molecules. The nanoparticle assembly is reversible and can be directed by applying different stimuli that act either on the guest molecules or the nanoparticles. This strategy can be extended to mesoscale assembly of microparticles. We highlight the newest research work in this field of nanochemistry and point out future perspectives and opportunities.

Crosslinking is an essential architecture for polymers to improve mechanical and thermal properties and to form three-dimensional (3D) structures. Although conventional synthetic crosslinkers usually only serve as bridges between different polymeric chains, biological crosslinkers are multifunctional. Recently, crosslinkers with active functionality after polymerization are promising a new dimension of molecular design for generating smart materials as they may exhibit dramatic changes in structures and properties in response to external stimuli. This concept article introduces several different designs of hyper-crosslinkers (i.e., multifunctional crosslinkers that provide three or more sites for generating networks) and their applications in tailoring stimuli-responsive and self-healing soft materials. Particularly, the polymeric materials that contain functional hyper-crosslinkers are exhibiting anti-intuitive redox or thermal-pH responses. The goal of this article is to illustrate the concept that functional hyper-crosslinkers not only improve the physical and chemical performance of the polymers, but more importantly, may introduce new architectures and functionalities for soft materials.

The ligands 3,6-di(pyridin-4-yl)-1,4-dihydro-1,2,4,5-tetrazine (H2 DPT), as a pillar spacer, and 4,4'-oxybis(benzoic acid) (H2 OBA), as a dicarboxylate linker, have been used to develop a dihydrotetrazine-functionalized pillared metal-organic framework (MOF), [Zn(OBA)(H2 DPT)0.5 ]⋅DMF (TMU-34), as a functionally convertible stimuli-responsive MOF-based sensor. Sonochemically synthesized TMU-34 powder has been employed in the sensing of volatile organic compounds (VOCs). The results show that TMU-34 can act as a solid-state, naked-eye visual chemosensor for the detection of chloroform in the liquid and gas phases. TMU-34, as a chemo-switchable MOF with rapid response, undergoes a significant color change from yellow to pink through reversible dynamic conversion of dihydrotetrazine into tetrazine upon exposure to chloroform in the presence of other VOCs. Whereas other colorimetric MOF-based sensors show a wide range of color changes in the presence of different analytes, TMU-34 undergoes a color change only in the presence of chloroform. A mechanism for the observed color change is proposed on the basis of UV/Vis and 1 H NMR spectroscopic studies. These observations reveal that TMU-34 represents one of the most promising candidates for the highly selective and sensitive detection of chloroform.

An understanding of solid-state crystal dynamics or flexibility in metal–organic frameworks (MOFs) showing multiple structural changes is highly demanding for the design of materials with potential applications in sensing and recognition. However, entangled MOFs showing such flexible behavior pose a great challenge in terms of extracting information on their dynamics because of their poor single-crystallinity. In this article, detailed experimental studies on a twofold entangled MOF (f-MOF-1) are reported, which unveil its structural response toward external stimuli such as temperature, pressure, and guest molecules. The crystallographic study shows multiple structural changes in f-MOF-1, by which the 3 D net deforms and slides upon guest removal. Two distinct desolvated phases, that is, f-MOF-1 a and f-MOF-1 b, could be isolated; the former is a metastable one and transformable to the latter phase upon heating. The two phases show different gated CO2 adsorption profiles. DFT-based calculations provide an insight into the selective and gated adsorption behavior with CO2 of f-MOF-1 b. The gate-opening threshold pressure of CO2 adsorption can be tuned strategically by changing the chemical functionality of the linker from ethanylene (−CH2−CH2−) in f-MOF-1 to an azo (−N=N−) functionality in an analogous MOF, f-MOF-2. The modulation of functionality has an indirect influence on the gate-opening pressure owing to the difference in inter-net interaction. The framework of f-MOF-1 is highly responsive toward CO2 gas molecules, and these results are supported by DFT calculations.

Stimuli-responsive materials are of immense importance because of their ability to undergo alteration of their properties in response to their environment. The properties of such materials can be tuned by subtle adjustments in temperature, pH, light, and so forth. Among such smart materials, multi-stimuli-responsive polymeric materials are of pronounced significance as they offer a wide range of applications and their properties can be tuned through several mechanisms. Here, we aim to highlight some recent studies showcasing the multi-stimuli-responsive character of these polymers, which are still relatively little known compared to their single-stimuli-responsive counterpart.

The synthesis of discrete multirotaxanes with well-defined structures remains a great challenge. Herein, we present the successful construction of diverse discrete multirotaxanes with well-defined supramolecular metallacycles as cores by a modular approach. Moreover, these novel multirotaxanes featured a stimuli-responsive property that enabled the introduction and removal of the bromide anion by taking advantage of dynamic nature of the supramolecular metallacycle scaffold. Through the combination of rotaxane-containing prefunctionalized building blocks with the corresponding different organoplatinum(II) acceptor building blocks (60, 120, or 180°), diverse discrete multirotaxanes with well-defined metallacycles (rhomboid or hexagon) as cores as well as certain numbers of rotaxane units were successfully obtained quantitatively by means of coordination-driven self-assembly. Furthermore, owing to the existence of a dynamic metallacycle as the supramolecular cores, the resultant multirotaxanes showed anion-induced disassembly and reassembly properties, which allowed for the reversible transformation between multirotaxanes and the corresponding individual rotaxane-containing building blocks. Therefore, this research not only enriches the family of discrete multirotaxanes, but also provides a novel strategy for the construction of "smart" stimuli-responsive multirotaxane systems.

New stimuli-responsive nanomaterials, made up of host-guest lipidic cubic phases (LCPs) are presented. These biocompatible, stable, transparent and water-insolu- ble LCPs are composed of monoolein (MO) as a neutral host, and small amounts of one of three judiciously de- signed and synthesized designer lipids as guest that pre- serve the structure and stability of LCPs, but render them specific functionalities. Efficient pH- and light-induced binding, release and sequestration of hydrophilic dyes are demonstrated. Significantly, these processes can be per- formed sequentially, thereby achieving both temporal and dosage control, opening up the possibility of using such LCPs as effective carriers to be used in drug delivery appli- cations. Specifically, because of the inherent optical trans- parency and molecular isotropy of LCPs they can be envis- aged as light-induced drug carriers in ophthalmology. The results presented here demonstrate the potential of mo- lecular design in creating new functional materials with predicted operating mode.

We present a general strategy to nanoengineer protein-based colloidal spheres (biomimetic protocells) as versatile delivery carriers with stimuli responsiveness by the electrostatic assembly of binary components (proteins and polypeptides) in association with intermolecular disulfide cross-linking. The size of the colloidal spheres, ranging from nanoscale to microscale, is readily tuned through parameters like protein and polypeptide concentration, the ratio between both, pH, and so on. Moreover, such colloidal spheres show versatile encapsulation of various guest molecules including small organic molecules and biomacromolecules. The pH and redox dual-responsiveness facilitates the rapid release of the payload in an acidic and reductant-enriched ambient such as in lysosomes. Thus, nanoengineering of protein-based biomimetic protocells opens a new alternative avenue for developing delivery vehicles with multifunctional properties towards a range of therapeutic and diagnostic applications.

A new class of supramolecular organometallic gels with a discrete rhomboidal metallacycle as the main skeleton was fabricated through hierarchical self-assembly (see figure). More importantly, by taking advantage of the dynamic nature of metal-ligand bonds, the stimuli-responsive gel-sol transition of the obtained gels was realized by disassembly and reassembly of the rhomboidal scaffold as controlled by bromide anions.

We report here the noncovalent synthesis of thermosensitive dendrimers. Short oligoguanosine strands were linked to the focal point of a dendron by using "click chemistry", and quadruplex formation was used to drive the self-assembly process in the presence of metal ions. The dynamic nature of these noncovalent assemblies can be exploited to create combinatorial libraries of dendrimers as demonstrated by the co-assembly of two components. These supramolecular dendrimers showed thermoresponsive behavior that can be tuned by varying the templating cations or the number of guanines in the oligonucleotide strand.

A stimuli-responsive con- trolled-release delivery system based on carbon nanotubes is demonstrated. Through TEM, FTIR spectroscopic, and thermogravimetric analysis, func- tional groups have been successfully at- tached to the open ends of the tubes, thereby enabling functionalized silica spheres to preferentially attach to the ends. This, in essence, plugs the ends of the tube. Controlling release of encap- sulated materials within the tubes is il- lustrated by fluorescein-filled carbon nanotubes. The discharge process can be triggered by exposure to 1,4-dithio- threitol (DTT) or at elevated tempera- ture. Moreover, both triggering sys- tems, DTT and temperature, provide rate of release control through in- creased DTT concentration or temper- ature choice, respectively. This delivery system paves the way for the develop- ment of a new generation of site-selec- tive, controlled-release, drug-delivery systems, and interactive nanosensor de- vices.