Ratiometric DNA sensing with a host-guest FRET pair

Supramolecular Host-Guest System That Realizes Adaptive Selection of the Guest through Ligand Regulation

In host-guest chemistry, preserving the original supramolecular topology while achieving the selective recognition and encapsulation of various guest molecules remains a key challenge. In this study, we successfully designed and synthesized a series of bifunctional pyridine ligands derived from 9,9'-bianthracene, which were then coupled with half-sandwiched Cp*Ir/Rh building blocks to form tetranuclear supramolecular metallacycles. Through precise tuning of the ligands' dimensions and the conjugation areas of the building blocks, we effectively directed the host-guest system within these supramolecular structures. We further explored the spatial conformational factors influencing guest molecule screening. The unique properties of the three bidentate pyridyl ligands significantly affected the intra/intermolecular π-π stacking, CH-π interactions, and hydrogen bonding, which in turn influenced the system's ability to recognize and tolerate different guest molecules. Self-sorting investigations revealed a selective preference for certain ligands and building blocks during macrocyclic formation with no interference from externally imposed guest molecules. These studies also demonstrated the remarkable topological stability of the ligated macrocycles, ensuring high-intensity conformational integrity. The specific structures and behaviors of these supramolecular metallacycles were confirmed by using single-crystal X-ray diffraction, nuclear magnetic resonance (NMR), and mass spectrometry techniques.

Fluorescence Turn-ON Displacement Assays with Cucurbit[7]uril-Thiophenylpyridinium Complexes as Host-Dye Reporter Pairs

The N-methyl-4-thiophenylpyridinium cation (ThioPy) is a high affinity (Kd ca. 5 nM), fast-exchanging fluorescent probe for cucurbit[7]uril (CB7). The CB7/ThioPy complex shows a unique fluorescence turn-ON response upon displacement by an analyte in sensing application. This enabled the development of a real-time fluorescence assay with the MRFA peptide for the protease thermolysin, which is also suitable for the cancer biomarker cathepsin B. Moreover, liposome encapsulation of CB7/ThioPy in large unilamellar vesicles (LUVs) provided mechanistic insight into intravesicular dye displacement reactions.

Single Molecular Nanomedicines Based on Macrocyclic Carrier-Drug Conjugates for Concentration-Independent Encapsulation and Precise Activation of Drugs

Nanomedicines often rely on noncovalent self-assembly and encapsulation for drug loading and delivery. However, challenges such as reproducibility issues due to the multicomponent nature, off-target activation caused by premature drug release, and complex pharmacokinetics arising from assembly dissociation have hindered their clinical translation. In this study, we introduce an innovative design concept termed single molecular nanomedicine (SMNM) based on macrocyclic carrier-drug conjugates. Through the covalent linkage of two chemotherapy drugs to a hypoxia-cleavable macrocyclic carrier, azocalix[4]arene, we obtained two self-included complexes to serve as SMNMs. The intramolecular inclusion feature of the SMNMs has not only demonstrated comprehensive shielding and protection for the drugs but also effectively prevented off-target drug leakage, thereby significantly reducing their side effects and enhancing their antitumor therapeutic efficacy. Additionally, the attributes of being a single component and molecularly dispersed confer advantages such as ease of preparation and good reproducibility for SMNMs, which is desirable for clinical applications.

Challenges and Opportunities of Functionalized Cucurbiturils for Biomedical Applications

Cucurbit[n]uril (CB[n]) macrocycles (especially CB[5] to CB[8]) have shown exceptional attributes since their discovery in 2000. Their stability, water solubility, responsiveness to several stimuli, and remarkable binding properties have enabled a growing number of biological applications. Yet, soon after their discovery, the challenge of their functionalization was set. Nevertheless, after more than two decades, a myriad of CB[n] derivatives has been described, many of them used in cells or in vivo for advanced applications. This perspective summarizes key advances of this burgeoning field and points to the next opportunities and remaining challenges to fully express the potential of these fascinating macrocycles in biology and biomedical sciences.

Preparation and In Vitro Validation of a Cucurbit[7]uril-Peptide Conjugate Targeting the LDL Receptor

Here we report the coupling of a cyclic peptide (VH4127) targeting the low density lipoprotein (LDL) receptor (LDLR) noncompetitively to cucurbit[7]uril (CB[7]) to develop a new kind of drug delivery system (DDS), namely, CB[7]-VH4127, with maintained binding affinity to the LDLR. To evaluate the uptake potential of this bismacrocyclic compound, another conjugate was prepared comprising a high-affinity group for CB[7] (adamantyl(Ada)-amine) coupled to the fluorescent tracker Alexa680 (A680). The resulting A680-Ada·CB[7]-VH4127 supramolecular complex demonstrated conserved LDLR-binding potential and improved LDLR-mediated endocytosis and intracellular accumulation potential in LDLR-expressing cells. The combination of two technologies, namely, monofunctionalized CB[7] and the VH4127 LDLR-targeting peptide, opens new avenues in terms of targeting and intracellular delivery to LDLR-expressing tissues or tumors. The versatile transport capacity of CB[7], known to bind a large spectrum of bioactive or functional compounds, makes this new DDS suitable for a wide range of therapeutic or imaging applications.

Phototransduction in a supramolecular cascade: a mimic for essential features of the vision process

The tailored design of a light-triggered supramolecular cascade results in an artificial machinery that assimilates the transduction of photons into chemical communication and the final release of a neurotransmitter. This is reminiscent of key steps in the natural vision process.

Chemiluminescent Cucurbit[n]uril-Based Chemosensor for the Detection of Drugs in Biofluids

Chemiluminescence-based detection methods offer a superior signal-to-noise ratio and are commonly adopted for biosensors. This work presents the design and implementation of a supramolecular assay based on a chemiluminescent chemosensor. Specifically, an indicator displacement assay (IDA) with the supramolecular host-guest complex of chemiluminescent phenoxy 1,2-dioxetane and cucurbit[8]uril enables the low-micromolar detection of drugs in human urine and human serum samples. Cucurbit[8]uril thereby acts as a non-surfactant chemiluminescence enhancer and a synthetic receptor. Additionally, we show that adding an equimolar amount of cucurbit[8]uril to a commercially available dioxetane used in standard enzymatic chemiluminescence immunoassays enhances the chemiluminescence by more than 15 times. Finally, we demonstrate that a chemiluminescence resonance energy transfer between a unimolecular macrocyclic cucurbit[7]uril-dye conjugate and a phenoxy 1,2-dioxetane can be utilized to detect the herbicide paraquat at a micromolar concentration in aqueous media.

Conformationally Confined Emissive Cationic Macrocycle with Photocontrolled Organelle-Specific Translocation

The optimization of molecular conformation and aggregation modes is of great significance in creation of new luminescent materials for biochemical research and medical diagnostics. Herein, a highly emissive macrocycle (1) is reported, which is constructed by the cyclization reaction of triphenylamine with benzyl bromide and exhibits very distinctive photophysical performance both in aqueous solution and the solid state. Structural analysis reveals that the 1 can form self-interpenetrated complex and emit bright yellow fluorescence in the crystal lattice. The distorted yet symmetrical structure can endow 1 with unique two-photon absorption property upon excitation by near-infrared light. Also, 1 can be utilized as an efficient photosensitizer to produce singlet oxygen (1 O2 ) both in inanimate milieu and under cellular environment. More intriguingly, due to the strong association of 1 with negatively charged biomacromolecules, organelle-specific migration is achieved from lysosome to nucleus during the 1 O2 -induced cell apoptosis process. To be envisaged, this conformationally confined cationic macrocycle with photocontrolled lysosome-to-nucleus translocation may provide a feasible approach for in situ identifying different biospecies and monitoring physiological events at subcellular level.

Further Dimensions for Sensing in Biofluids: Distinguishing Bioorganic Analytes by the Salt-Induced Adaptation of a Cucurbit[7]uril-Based Chemosensor

Insufficient binding selectivity of chemosensors often renders biorelevant metabolites indistinguishable by the widely used indicator displacement assay. Array-based chemosensing methods are a common workaround but require additional effort for synthesizing a chemosensor library and setting up a sensing array. Moreover, it can be very challenging to tune the inherent binding preference of macrocyclic systems such as cucurbit[n]urils (CBn) by synthetic means. Using a novel cucurbit[7]uril-dye conjugate that undergoes salt-induced adaptation, we now succeeded in distinguishing 14 bioorganic analytes from each other through the facile stepwise addition of salts. The salt-specific concentration-resolved emission provides additional information about the system at a low synthetic effort. We present a data-driven approach to translate the human-visible curve differences into intuitive pairwise difference measures. Ion mobility experiments combined with density functional theory calculations gave further insights into the binding mechanism and uncovered an unprecedented ternary complex geometry for CB7. TThis work introduces the non-selectively binding, salt-adaptive cucurbit[n]uril system for sensing applications in biofluids such as urine, saliva, and blood serum.

Molecular Probes, Chemosensors, and Nanosensors for Optical Detection of Biorelevant Molecules and Ions in Aqueous Media and Biofluids

Synthetic molecular probes, chemosensors, and nanosensors used in combination with innovative assay protocols hold great potential for the development of robust, low-cost, and fast-responding sensors that are applicable in biofluids (urine, blood, and saliva). Particularly, the development of sensors for metabolites, neurotransmitters, drugs, and inorganic ions is highly desirable due to a lack of suitable biosensors. In addition, the monitoring and analysis of metabolic and signaling networks in cells and organisms by optical probes and chemosensors is becoming increasingly important in molecular biology and medicine. Thus, new perspectives for personalized diagnostics, theranostics, and biochemical/medical research will be unlocked when standing limitations of artificial binders and receptors are overcome. In this review, we survey synthetic sensing systems that have promising (future) application potential for the detection of small molecules, cations, and anions in aqueous media and biofluids. Special attention was given to sensing systems that provide a readily measurable optical signal through dynamic covalent chemistry, supramolecular host-guest interactions, or nanoparticles featuring plasmonic effects. This review shall also enable the reader to evaluate the current performance of molecular probes, chemosensors, and nanosensors in terms of sensitivity and selectivity with respect to practical requirement, and thereby inspiring new ideas for the development of further advanced systems.

Protein-Mediated Fluorescence Resonance Energy Transfer (P-FRET) Probe: Fabrication and Hydroxyl Radical Detection

Fluorescent probes based on fluorescence resonance energy transfer (FRET) are highly promising for diverse bioapplications. The key to constructing FRET probes is to confine the donor and acceptor within a sufficiently close distance. However, the commonly used covalent linkage often requires elaborate design and complex organic synthesis, and sometimes causes changes in the fluorescence properties of the donor and acceptor. Inspired by the binding between small molecules and protein in nature, herein, we propose a protein-mediated strategy to fabricate FRET probe. In such protein-mediated FRET (P-FRET) probe, protein acts as a carrier to simultaneously confine donor and acceptor in its cavity. As a proof of concept, we use bovine serum albumin (BSA) as a model protein, coumarin derivative as a donor and hydroxyl radical (·OH)-responsive dye fluorescein as an acceptor. Through a series of investigations, including binding parameters, fluorescence properties and detection performance, we prove that the construction of P-FRET probe is simple and feasible and the detection is sensitive. Our P-FRET strategy will provide new insights for the design of FRET probes.

Bz-8HQ: a novel supramolecular fluorochrome exhibiting multiple stimuli-responsiveness

A novel multifunctional fluorescent molecule (Bz-8HQ) was synthesized from the linkage of benzimidazole (Bz) and 8-hydroxyquinoline (8HQ) molecules and its response to multiple stimuli was investigated spectroscopically.

Dual-Emissive Tris-Heteroleptic Ruthenium Complexes: Tuning the DNA-Triggered Ratiometric Emission Response by Ancillary Ligands

Three tris-heteroleptic mononuclear Ru(II) complexes with dual fluorescence and phosphorescence-[Ru(dpma)(bpy)(phen)]²⁺ (1²⁺), [Ru(dpma)(bpy)(dppz)]²⁺ (2²⁺), and [Ru(dpma)(phen)(dppz)]²⁺ (3²⁺)-have been designed and used as ratiometric light-response probes for DNA, where dpma is di(pyrid-2-yl)(methyl)-amine, bpy is 2,2'-bipyridine, phen is 1,10-phenanthroline, and dppz is dipyridophenazine, respectively. Single crystals of complex 2(PF₆)₂ have been obtained and studied by X-ray analysis. The interactions of these complexes with different DNAs are investigated by means of spectroscopic methods, viscosity measurements, and molecular modeling. In the presence of calf thymus DNA, complexes 2(PF₆)₂ and 3(PF₆)₂ show the emergence of a new lower-energy phosphorescence emission band; meanwhile, the higher-energy fluorescence emission band is essentially unchanged, functioning as an intrinsic internal reference. These two complexes exhibit stronger preference for calf thymus DNA over single-strand DNA (d(A)₁₆ and d(C)₁₆). In contrast, no binding interaction between 1(PF₆)₂ and calf thymus DNA is observed. The intrinsic binding constants (K_b) of 2(PF₆)₂ and 3(PF₆)₂ with calf thymus DNA are determined to be (1.4 ± 0.4) × 10⁵ and (9.5 ± 0.15) × 10⁴ M^-1, respectively. In addition, these spectroscopic results are compared with those of the prototype complex [Ru(bpy)₂(dppz)]²⁺ (4²⁺), and density functional theory and time-dependent density functional theory calculations are employed to elucidate these experimental findings.

Evolution of Supramolecular Systems Towards Next-Generation Biosensors

Supramolecular materials, which rely on dynamic non-covalent interactions, present a promising approach to advance the capabilities of currently available biosensors. The weak interactions between supramolecular monomers allow for adaptivity and responsiveness of supramolecular or self-assembling systems to external stimuli. In many cases, these characteristics improve the performance of recognition units, reporters, or signal transducers of biosensors. The facile methods for preparing supramolecular materials also allow for straightforward ways to combine them with other functional materials and create multicomponent sensors. To date, biosensors with supramolecular components are capable of not only detecting target analytes based on known ligand affinity or specific host-guest interactions, but can also be used for more complex structural detection such as chiral sensing. In this Review, we discuss the advancements in the area of biosensors, with a particular highlight on the designs of supramolecular materials employed in analytical applications over the years. We will first describe how different types of supramolecular components are currently used as recognition or reporter units for biosensors. The working mechanisms of detection and signal transduction by supramolecular systems will be presented, as well as the important hierarchical characteristics from the monomers to assemblies that contribute to selectivity and sensitivity. We will then examine how supramolecular materials are currently integrated in different types of biosensing platforms. Emerging trends and perspectives will be outlined, specifically for exploring new design and platforms that may bring supramolecular sensors a step closer towards practical use for multiplexed or differential sensing, higher throughput operations, real-time monitoring, reporting of biological function, as well as for environmental studies.

Wash-Free Detection of Nucleic Acids with Photoswitch-Mediated Fluorescence Resonance Energy Transfer against Optical Background Interference

The optical background such as autofluorescence and light scattering poses a big challenge to quantify nucleic acids with conventional fluorescence-based methods. We report here high-contrast nucleic acid detection with photoswitch-mediated fluorescence resonance energy transfer (FRET), which strongly occurs between the open forms of the photoswitch (a naphthopyran) and the signal fluorophores brought to the surface of the nanoprobes (≲15 nm). The fluorescence change (ΔF) upon UV irradiation is highly sensitive and more robust to quantify the target DNAs than traditional intensity measurements. Therefore, the method works in samples with strong background fluorescence from the unbound fluorophores. The photoswitchable nanoprobes could be easily prepared and interrogated in capillaries for high-throughput measurements. The method was evaluated in both sandwich-like hybridization and DNA label-free detection with a nucleic stain SG. Without DNA amplification and sample pretreatment of blood serum, the photoswitchable nanoprobes provided a limit of detection of 0.5 nM, which is ∼6 to 20 times lower than conventional FRET.

Self-Assembling Systems Based on Pillar[5]arenes and Surfactants for Encapsulation of Diagnostic Dye DAPI

In this paper, we report the development of the novel self-assembling systems based on oppositely charged Pillar[5]arenes and surfactants for encapsulation of diagnostic dye DAPI. For this purpose, the aggregation behavior of synthesized macrocycles and surfactants in the presence of Pillar[5]arenes functionalized by carboxy and ammonium terminal groups was studied. It has been demonstrated that by varying the molar ratio in Pillar[5]arene-surfactant systems, it is possible to obtain various types of supramolecular systems: host-guest complexes at equimolar ratio of Pillar[5]arene-surfactant and interpolyelectrolyte complexes (IPECs) are self-assembled materials formed in aqueous medium by two oppositely charged polyelectrolytes (macrocycle and surfactant micelles). It has been suggested that interaction of Pillar[5]arenes with surfactants is predominantly driven by cooperative electrostatic interactions. Synthesized stoichiometric and non-stoichiometric IPECs specifically interact with DAPI. UV-vis, luminescent spectroscopy and molecular docking data show the structural feature of dye-loaded IPEC and key role of the electrostatic, π-π-stacking, cation-π interactions in their formation. Such a strategy for the design of supramolecular Pillar[5]arene-surfactant systems will lead to a synergistic interaction of the two components and will allow specific interaction with the third component (drug or fluorescent tag), which will certainly be in demand in pharmaceuticals and biomedical diagnostics.

Cucurbiturils in nucleic acids research

During the past ten years, the importance of cucurbiturils (CB[n]) as macrocyclic hosts in supramolecular assemblies with various types of natural and synthetic nucleic acids (NAs) has increased explosively. As a component of such systems, CB[n] macrocycles can play a wide spectrum of roles from drug and gene delivery vehicles to catalysts/inhibitors of biochemical reactions and even building blocks for NA-based materials. The aim of this highlight article is to describe the development of the CB[n] applications in nucleic acids research and to outline the current situation and perspectives of this fascinating synergistic combination of supramolecular chemistry of CB[n] and NAs.

Covalent cucurbit[7]uril-dye conjugates for sensing in aqueous saline media and biofluids

Non-covalent chemosensing ensembles of cucurbit[n]urils (CBn) have been widely used in proof-of-concept sensing applications, but they are prone to disintegrate in saline media, e.g. biological fluids. We show here that covalent cucurbit[7]uril-indicator dye conjugates are buffer- (10× PBS buffer) and saline-stable (up to 1.4 M NaCl) and allow for selective sensing of Parkinson's drug amantadine in human urine and saliva, where the analogous non-covalent CB7⊃dye complex is dysfunctional. The in-depth analysis of the covalent host-dye conjugates in the gas-phase, and deionized versus saline aqueous media revealed interesting structural, thermodynamic and kinetic effects that are of general interest for the design of CBn-based supramolecular chemosensors and systems. This work also introduces a novel high-affinity indicator dye for CB7 through which fundamental limitations of indicator displacement assays (IDA) were exposed, namely an impractical slow equilibration time. Unlike non-covalent CBn⊃dye reporter pairs, the conjugate chemosensors can also operate through a SN2-type guest-dye exchange mechanism, which shortens assay times and opens new avenues for tailoring analyte-selectivity.

Interaction of Cucurbit[7]uril With Protease Substrates: Application to Nanosecond Time-Resolved Fluorescence Assays

We report the use of the macrocyclic host cucurbit[7]uril (CB7) as a supramolecular additive in nanosecond time-resolved fluorescence (Nano-TRF) assays for proteases to enhance the discrimination of substrates and products and, thereby, the sensitivity. A peptide substrate was labeled with 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) as a long-lived (>300 ns) fluorescent probe and 3-nitrotyrosine was established as a non-fluorescent fluorescence resonance energy transfer (FRET) acceptor that acts as a “dark quencher.” The substrate was cleaved by the model proteases trypsin and chymotrypsin and the effects of the addition of CB7 to the enzyme assay mixture were investigated in detail using UV/VIS absorption as well as steady-state and time-resolved fluorescence spectroscopy. This also allowed us to identify the DBO and nitrotyrosine residues as preferential binding sites for CB7 and suggested a hairpin conformation of the peptide, in which the guanidinium side chain of an arginine residue is additionally bound to a vacant ureido rim of one of the CB7 hosts.

Förster resonance energy transfer (FRET)-based small-molecule sensors and imaging agents

In this tutorial review, we will explore recent advances in the construction and application of Förster resonance energy transfer (FRET)-based small-molecule fluorescent probes. The advantages of FRET-based fluorescent probes include: a large Stokes shift, ratiometric sensing and dual/multi-analyte responsive systems. We discuss the underlying energy donor-acceptor dye combinations and emphasise their applications for the detection or imaging of cations, anions, small neutral molecules, biomacromolecules, cellular microenvionments and dual/multi-analyte responsive systems.

Chemical signal cascading in a supramolecular network

A chemically-triggered signalling cascade between cucurbituril host-guest complexes by means of multi-step competitive displacement is demonstrated. The inter-complex communication of chemical information yields the release of bio-relevant cargo, reminiscent of cellular signalling pathways.

Cucurbit[7]uril-driven modulation of ligand-DNA interactions by ternary assembly

The design of small organic molecules with a predictable and desirable DNA-binding mechanism is a topical research task for biomedicine application. Herein, we demonstrate an attractive supramolecular strategy for controlling the non-covalent ligand-DNA interaction by binding with cucurbituril as a synthetic receptor. With a combination of UV/vis, CD and NMR experiments, we demonstrate that the bis-styryl dye with two suitable binding sites can involve double stranded DNA and cucurbituril in the formation of the supramolecular triad. The ternary assembly is formed as a result of the interaction of macrocyclic cucurbituril with one pyridinium fragment of the bis-styryl dye, while the second pyridinium fragment of the dye is effectively associated with DNA backbones, which leads to a change in the ligand-DNA binding mode from aggregation to a minor groove. This exciting outcome was supported by molecular docking studies that help to understand the molecular orientation of the supramolecular triad and elucidate the destruction of dye aggregates caused by cucurbituril. These studies provide valuable information on the mechanisms of DNA binding to small molecules and recognition processes in bioorganic supramolecular assemblies constructed from multiple non-covalent interactions.

Modelling haemoproteins: porphyrins and cyclodextrins as sources of inspiration

The association of hydrophobic cavities with porphyrin derivatives has been used to mimic haemoprotein structures. The most employed cavity in this field is β-cyclodextrin (β-CD), and scaffolds combining β-CDs and porphyrins are expected to inspire the combination of porphyrins and cucurbiturils in the near future. Aside from providing water solubility to various porphyrinic structures, the β-CD framework can also modulate and control the reactivity of the metal core of the porphyrin. After a general introduction of the challenges faced in the field of haemoprotein models and the binding behavior of β-CDs, this article will discuss covalent and non-covalent association of porphyrins with β-CDs. In each approach, the role of the CD differs according to the relative position of the concave CD host, either directly controlling the binding and transformation of a substrate on the metalloporphyrin or playing a dual role of controlling the water solubility and selecting the axial ligand of the metal core. The discussion will be of interest to the cucurbituril community as well as to the cavitand community, as the information provided should be useful for the design of haemoprotein mimics using cucurbiturils.

A Selective Cucurbit[8]uril-Peptide Beacon Ensemble for the Ratiometric Fluorescence Detection of Peptides

A convenient supramolecular strategy for constructing a ratiometric fluorescent chemosensing ensemble, consisting of a macrocyclic host (cucurbit[8]uril CB[8]), and a pyrene-tagged amphiphilic peptide beacon (AP 1), is reported. AP 1 unfolds upon encapsulation of the pyrene termini into the hydrophobic CB[8] cavity. This changes pyrene excimer to monomer emission. Substrates with higher affinity for the CB[8] cavity can displace AP 1 from the ensemble. The released AP 1 folds again to form a pyrene excimer, which allows for the ratiometric fluorescence monitoring of the substrate. In this report, the ensemble capacity for ratiometric fluorescence monitoring of biological substrates, such as amino acid derivatives, specific peptides, and proteins, in aqueous media is demonstrated.

Applications of Cucurbiturils in Medicinal Chemistry and Chemical Biology

The supramolecular chemistry of cucurbit[n]urils (CBn) has been rapidly developing to encompass diverse medicinal applications, including drug formulation and delivery, controlled drug release, and sensing for bioanalytical purposes. This is made possible by their unique recognition properties and very low cytotoxicity. In this review, we summarize the host-guest complexation of biologically important molecules with CBn, and highlight their implementation in medicinal chemistry and chemical biology.

DNA-supramolecule conjugates in theranostics

The elegant properties of deoxyribonucleic acid (DNA), such as accurate recognition, programmability and addressability, make it a well-defined and promising material to develop various molecular probes, drug delivery carriers and theranostic systems for cancer diagnosis and therapy. In addition, supramolecular chemistry, also termed "chemistry beyond the molecule", is a promising research field that aims to develop functional chemical systems by bringing discrete molecular components together in a manner that invokes noncovalent intermolecular forces, such as hydrophobic interaction, hydrogen bonding, metal coordination, and shape or size matching. Thus, DNA-supramolecule conjugates (DSCs) combine accurate recognition, programmability and addressability of DNA with the greater toolbox of supramolecular chemistry. This review discusses the applications of DSCs in sensing, protein activity regulation, cell behavior manipulation, and biomedicine.

Fabrication of a Luminescence-Silent System Based on a Post-Synthetic Modification Cd-MOFs: A Highly Selective and Sensitive Turn-on Luminescent Probe for Ascorbic Acid Detection

A unique three-dimensional luminescent metal-organic framework (Cd-MOFs), [Cd(tpbpc)₂]·2H₂O·DMF (Htpbpc = 4'-[4,2';6',4″]-terpyridin-4'-yl-biphenyl-4-carboxylic acid; DMF = dimethylformamide), was synthesized and structurally characterized; it exhibits excellent luminescent property and structural stability in aqueous solutions. Interestingly, an unparalleled luminescence-silent system CrO₄^2-@Cd-MOFs was successfully fabricated by postsynthetic modification of metal-organic frameworks. This luminescence-silent system represents a highly selective and sensitive turn-on luminescent responding to ascorbic acid. First, this advanced fluorescent sensor displays excellent performance for CrO₄^2- ions with a quenching of fluorescence intensity originating from fluorescence resonance energy transfer (FRET) mechanism. What's more, the fluorescent intensity of CrO₄^2-@Cd-MOFs system can be recovered (turn-on) for sensing ascorbic acid because of the elimination of FRET process. Such a novel fabrication strategy should offer the guidance to develop various MOFs-implicated luminescence-silent systems as "turn-on" sensors for detection of specific chemicals.

A colorimetric and fluorescent dual-modal displacement probe based on host-assisted modulation of intramolecular charge transfer and deaggregation

A new colorimetric and fluorescent dual-modal displacement probe based on a supramolecular host–guest complex involving macrocycle encapsulation that modulated intramolecular charge transfer and deaggregation.