The synthesis of amphiphilic pillar[5]arene functionalized reduced graphene oxide and its application as novel fluorescence sensing platform for the determination of acetaminophen

Applications of Supramolecular Polymers Generated from Pillar[n]arene-Based Molecules

Supramolecular chemistry enables the manipulation of functional components on a molecular scale, facilitating a "bottom-up" approach to govern the sizes and structures of supramolecular materials. Using dynamic non-covalent interactions, supramolecular polymers can create materials with reversible and degradable characteristics and the abilities to self-heal and respond to external stimuli. Pillar[n]arene represents a novel class of macrocyclic hosts, emerging after cyclodextrins, crown ethers, calixarenes, and cucurbiturils. Its significance lies in its distinctive structure, comparing an electron-rich cavity and two finely adjustable rims, which has sparked considerable interest. Furthermore, the straightforward synthesis, uncomplicated functionalization, and remarkable properties of pillar[n]arene based on supramolecular interactions make it an excellent candidate for material construction, particularly in generating interpenetrating supramolecular polymers. Polymers resulting from supramolecular interactions involving pillar[n]arene find potential in various applications, including fluorescence sensors, substance adsorption and separation, catalysis, light-harvesting systems, artificial nanochannels, and drug delivery. In this context, we provide an overview of these recent frontier research fields in the use of pillar[n]arene-based supramolecular polymers, which serves as a source of inspiration for the creation of innovative functional polymer materials derived from pillar[n]arene derivatives.

Host–guest sensing towards sodium cyclamate based on a cationic pillar[6]arene reduced graphene nano-composite

A competitive fluorescence sensing for the detection of sodium cyclamate based on a cationic water-soluble pillar[6]arene graphene nano-composite.

Water-soluble pillar[5]arene-modified graphdiyne functional material and its application towards ultrasensitive and robust electrochemical methylamphetamine determination

Schematic illustration of the application of the novel material WP5–GDY/GCE for the electrochemical sensing of methylamphetamine (MA).

Facile Surface Functionalization of MXene by Pillar[5]arene for Enhanced Electrochemical Performance

A simple strategy was used to prepare functional two-dimensional materials via combination of pillar[5]arene (P5) and MXene. Electrochemical results of MXene-P5 exhibits high supramolecular recognition, enrichment capability, and high electrochemical...

Simultaneous detection of acetaminophen, catechol and hydroquinone using a graphene-assisted electrochemical sensor

Simple, rapid and sensitive analysis of drug-derived pollutants is critically valuable for environmental monitoring. Here, taking acetaminophen, hydroquinone and catechol as a study example, a sensor based on an ITO/APTES/r-GO@Au electrode was developed for separate and simultaneous determination of phenolic pollutants. ITO electrodes that are modified with 3-aminopropyltriethoxysilane (APTES), graphene (GO) and Au nanoparticles (Au NPs) can significantly enhance the electronic transport of phenolic pollutants at the electrode surface. The redox mechanisms of phenolic pollutants include the electron transfer with the enhancement of r-GO@Au. The modified ITO electrode exhibits excellent electrical properties to phenolic pollutants and a good linear relationship between ECL intensity and the concentration of phenolic pollutants, with a limit of detection of 0.82, 1.41 and 1.95 μM, respectively. The separate and simultaneous determination of AP, CC and HQ is feasible with the ITO/APTES/r-GO@Au electrode. The sensor shows great promise as a low-lost, sensitive, and rapid method for simultaneous determination of drug-derived pollutants.

Simple, rapid and sensitive analysis of drug-derived pollutants is critically valuable for environmental monitoring.

Pillararene-based molecular-scale porous materials

This review discusses the design and syntheses of molecular-scale pillar[n]arene-based porous materials with promising applications and summarises the development of using pillar[n]arenes as the building blocks of porous materials. From the perspective of "role of participation" in the syntheses of molecular-scale pillar[n]arene-based porous materials, the content can be divided into pillar[n]arenes serving as supramolecular nanovalves on surfaces and as ligands for metal-organic frameworks and covalent organic polymers. By integrating pillararenes, which possess rigid pillar-like structures, electron-rich cavities and desirable host-guest properties, with porous polymers of large surface areas and abundant active sites, applications of the resulting materials in drug release platforms, molecular recognition, sensing, detection, gas adsorption, removal of water pollution, organic photovoltaic materials and heterogeneous catalysis can be realised simultaneously and efficiently. Finally, in the conclusions and perspectives part, we put forward the challenges and viewpoints of the current research on pillar[n]arene-based porous materials. We hope this article can provide a timely and valuable reference for researchers interested in synthetic macrocycles and porous materials.

Recent Applications of Pillar[n]arene-Based Host-Guest Recognition in Chemosensing and Imaging

Pillar[n]arene is a novel kind of synthetic supramolecular macrocyclic host characterized by its particular pillar-shaped structure consisting of an electron-rich cavity and two finely adjustable rims. Benefiting from its rigid structure, facile synthesis, ease of functionalization, and outstanding host-guest chemistry, pillar[n]arene shows great potential for diverse applications. Significantly, the host-guest recognition of pillar[n]arene provides a novel approach for chemosensing and imaging. Herein, this Review critically and comprehensively reviews the applications of pillar[n]arene-based host-guest recognition in chemosensing and imaging. The sensing and imaging mechanisms as well as the unique roles and advantages of pillar[n]arene-based host-guest recognition are summarized. In addition, preparations of hybrid materials based on pillar[n]arene and inorganic materials are also introduced comprehensively in the light of chemosensing and imaging. Finally, current challenges and perspectives on pillar[n]arene-based host-guest recognition in chemosensing and imaging are outlined.

Harnessing selectivity in chemical sensing via supramolecular interactions: from functionalization of nanomaterials to device applications

Chemical sensing is a strategic field of science and technology ultimately aiming at improving the quality of our lives and the sustainability of our Planet. Sensors bear a direct societal impact on well-being, which includes the quality and composition of the air we breathe, the water we drink, and the food we eat. Pristine low-dimensional materials are widely exploited as highly sensitive elements in chemical sensors, although they suffer from lack of intrinsic selectivity towards specific analytes. Here, we showcase the most recent strategies on the use of (supra)molecular interactions to harness the selectivity of suitably functionalized 0D, 1D, and 2D low-dimensional materials for chemical sensing. We discuss how the design and selection of receptors via machine learning and artificial intelligence hold a disruptive potential in chemical sensing, where selectivity is achieved by the design and high-throughput screening of large libraries of molecules exhibiting a set of affinity parameters that dictates the analyte specificity. We also discuss the importance of achieving selectivity along with other relevant characteristics in chemical sensing, such as high sensitivity, response speed, and reversibility, as milestones for true practical applications. Finally, for each distinct class of low-dimensional material, we present the most suitable functionalization strategies for their incorporation into efficient transducers for chemical sensing.

A UiO-66-NH2/carbon nanotube nanocomposite for simultaneous sensing of dopamine and acetaminophen

Carbon nanomaterials are quite promising to be combined with metal-organic frameworks (MOFs) to enhance the sensing ability of both materials. In this work, a MOF nanoparticle of UiO-66-NH₂ is integrated with carbon nanotubes (CNTs) (UiO-66-NH₂/CNTs) with a facile solvothermal method. The morphology, surface area and properties of this UiO-66-NH₂/CNTs nanocomposite was investigated using electron microscopy, XRD, XPS, BET analysis and electrochemical techniques. Catalytic oxidation of dopamine (DA) and acetaminophen (AC) on this nanocomposite was achieved, owing to a 3D hybrid structure or a large electroactive surface area, excellent electrical conductivity, a large number of active sites of this nanocomposite. It was further utilized as a sensing platform to establish an electrochemical sensor for the monitoring of both DA and AC. The enhanced oxidation signals led to the voltametric sensing of DA and AC in a broad linear range from 0.03 to 2.0 μM and low detection limits (S/N = 3) of 15 and 9 nM for DA and AC, respectively. The proposed sensor also possessed good reproducibility, repeatability, long-term stability, selectivity, and satisfactory recovery in serum samples analysis. Therefore, it has the great potential for the accurate quantification of DA and AC in complex matrixes.

Facile One-Step Electrodeposition Preparation of Cationic Pillar[6]arene-Modified Graphene Films on Glassy Carbon Electrodes for Enhanced Electrochemical Performance

In the present work, we have developed a facile one-step route for preparing electrochemically reduced graphene oxide-cationic pillar[6]arene (ErGO-CP6) nanocomposite films on glassy carbon electrodes (GCEs) directly from graphene oxide-cationic pillar[6]arene (GO-CP6) colloidal solution by using a pulsed electrodeposition technique. The electrocatalytic activity of ErGO-CP6 was examined by studying the oxidations of five purine bases [adenine (A), guanine (G), xanthine (X), hypoxanthine (HX), and uric acid (UA)]. It enhanced the oxidation currents of A, G, X, HX, and UA when compared to unmodified ErGO films and bare GCE, which is considered to be the synergetic effects of the graphene (excellent electrical properties and large surface area) and CP6 molecules (high inclusion complexation and enrichment capability).

Multimode binding and stimuli responsive displacement of acridine orange dye complexed with p-sulfonatocalix[4/6]arene macrocycles

Interaction of acridine orange (AOH+) dye with water soluble anionic p-sulfonatocalix[n]arene (SCXn) hosts, SCX4 and SCX6, having different cavity dimensions, has been investigated using multispectroscopic techniques. Intriguing modulation in the photophysical properties of AOH+ upon interaction with SCXn hosts indicate the formation of different host-guest complexes at different regions of the host concentrations. At lower host concentrations, AOH+ undergoes SCXn assisted aggregation, causing a drastic reduction in fluorescence intensity. At higher host concentrations, aggregated-AOH+-SCXn complexes disintegrate and monomeric-AOH+-SCXn exo and inclusion complexes are eventually formed, leading to a huge fluorescence enhancement finally. Observed effects are more pronounced with SCX6 as compared to SCX4 host. Time-resolved fluorescence studies indicate that at very high host concentrations, there is also a diffusion-controlled dynamic quenching for both monomeric-AOH+-SCXn exo and inclusion complexes, caused by the free SCXn present in the solution, a phenomenon not reported before for such host-guest systems. The aggregated-AOH+-SCXn complexes at lower host concentration were employed to investigate displacement study using an antiviral drug, 1-adamantanamine (AD) and a neurotransmitter, acetylcholine (AcCh), as the competitive binders cum external stimuli, which resulted in a drastic recovery of the fluorescence reduced initially due to aggregation process. Though both the AOH+-SCXn systems act as efficient supramolecular assemblies in sensing AD and AcCh as the analytes through fluorescence "OFF-ON" mechanism, the effect is more pronounced for AOH+-SCX4 system as compared to AOH+-SCX6. SCXn induced interesting modulation in the photophysical properties of AOH+ and the stimulus responsive dye displacement observed for aggregated-AOH+-SCXn systems can expectedly find applications in fluorescence OFF-ON sensing, supramolecular functional materials and similar others.

Calix[n]arene/Pillar[n]arene-Functionalized Graphene Nanocomposites and Their Applications

Calix[n]arenes and pillar[n]arenes, which contain repeating units of phenol and methane, are class of synthetic cyclic supramolecules. Their rigid structure, tunable cavity size, flexible functionalization, and rich host-guest properties make them ideal surface modifiers to construct functional hybrid materials. Introduction of the calix[n]arene/pillar[n]arene species to the graphene may bring new interesting or enhanced physicochemical/biological properties by combining their individual characteristics. Reported methods for the surface modification of graphene with calix[n]arene/pillar[n]arene utilize either covalent or non-covalent approaches. This mini-review presents the recent advancements in the functionalization of graphene nanomaterials with calix[n]arene/pillar[n]arene and their applications. At the end, the future outlook and challenges for the continued research of calix[n]arene/pillar[n]arene-functionalized graphene nanohybrids in the development of applied nanoscience are thoroughly discussed.

Pillararene-functionalised graphene nanomaterials

Pillararene-modified graphene materials integrate the advantages of both graphene and pillararenes; e.g., the cavity of pillararenes can recognise suitably sized electron-deficient and hydrophobic guest molecules via host–guest interactions, while the graphene composite is able to exhibit unique physiochemical properties including inertness, nanoscale, electrical and thermal structural properties. Those novel organic–inorganic hybrid composites can be efficiently prepared via both covalent and noncovalent bonds by classic organic reactions and supramolecular interactions, respectively. Pillararene-functionalised graphene materials have been used in various applications, such as electrochemical sensing guest molecules, performing as the platform for fluorescent probes, carrying out fluorescence quenching as the sensor, biosensing toxic molecules in cells, Raman and fluorescence bioimaging of cancer cells, photoacoustic and ultrasound imaging, as well as storage materials and reactors in energy fields.

The current research progress on diverse pillararene derivative functionalised graphene materials, including different synthesis strategies and various applications, is reviewed.

Direct electrodeposition of cationic pillar[6]arene-modified graphene oxide composite films and their host–guest inclusions for enhanced electrochemical performance

Cationic pillar[6]arene functionalized graphene films with enhanced host–guest electrochemical recognition performance were fabricated directly from GO-CP6 dispersions by a one-step pulsed electrodeposition technique.

Colorimetric sensing towards spermine based on supramolecular pillar[5]arene reduced and stabilized gold nanoparticles

We develop a novel and fast colorimetric sensing platform for spermine (Sp) by using macrocyclic host hydroxyl pillar[5]arene (P5) molecule reduced and stabilized Au nanoparticles via the supramolecular host-guest recognition interaction between P5 and Sp. The P5-modified Au nanoparticles (P5-Au) are easily obtained by redox reaction between hydroxyl groups in P5 and Au³⁺ in HAuCl₄, where hydroxyl groups are oxidized to carboxyl groups and Au³⁺ is reduced to Au⁰⁺ under alkali catalysis at room temperature without NaBH₄ or other reducing agent. A uniform diameter of about 5.0 nm and wine red color P5-Au nanoparticles can be synthesized by this green and rapid method. The mechanism of redox reaction between P5 and HAuCl₄ is studied by the XPS and ¹³C NMR, and the P5-Au is characterized by the TEM, XRD and XPS.

A novel fluorescence assay for resveratrol determination in red wine based on competitive host-guest recognition

A label-free fluorescence assay for resveratrol determination is presented for the first time. The approach was based on fluorescence resonance energy transfer (FRET), via competitive supramolecular recognition, between p-sulfonated calix[6]arene (CX6)-modified reduced graphene oxide (CX6@RGO) and a probe-resveratrol complex. The probe molecule (Rhodamine B or rhodamine 123) had a strong fluorescence signal, and its fluorescence was quenched by CX6@RGO, based on FRET. When the target molecule was added to CX6@RGO, the probe molecule was displaced by resveratrol, and a host-guest complex, CX6@RGO-resveratrol formed, turning-on the fluorescence signal. Fluorescence intensity of the CX6@RGO-probe complex increased linearly with increased resveratrol concentrations (2.0-40.0 μM). The proposed approach was used to determine resveratrol in red wine with satisfactory detection limits and recoveries. Compared with traditional determination methods, our procedure is advantageous because it saves time, is easy to operate, and does not require sample pretreatment.

Electrochemical determination of methyl parathion based on pillar[5]arene@AuNPs@reduced graphene oxide hybrid nanomaterials

The detection of pesticides has become a very important and critical research area because of the rapid development of agriculture and strict environmental protection regulations.

Ultrasensitive electrochemical detection of methyl parathion pesticide based on cationic water-soluble pillar[5]arene and reduced graphene nanocomposite

We report a rapid, sensitive and selective electrochemical sensor based on pillar[5]arene (CP5) reduced graphene (rGO) nanohybrid-modified glassy carbon electrode CP5-rGO/GCE for the trace detection of methyl parathion (MP) by differential pulse voltammetry (DPV) for the first time. Compared to beta-cyclodextrin (β-CD)-functionalized reduced graphene (rGO)-modified GCE β-CD-rGO/GCE, the proposed CP5-rGO/GCE sensor exhibits excellent electrochemical catalytic activity, rapid response, high sensitivity, good reproducibility and anti-interference ability towards MP. The recognition mechanism of β-CD/MP and CP5/MP was studied by ¹H NMR. The results indicate a higher supramolecular recognition capability between CP5 and MP compared to that between β-CD and MP. The β-CD-rGO and CP5-rGO nano-composites were prepared via a wet chemistry approach. The resulting nano-composites have been characterized by thermogravimetric analysis (TGA), fourier transform infrared spectrometry (FTIR), charge transfer resistance (R_ct) and zeta potential. The CP5-rGO/GCE combines the merits of CP5 and rGO, and is used for quantitative detection of MP. It has a low detection limit of 0.0003 μM (S/N = 3) and a linear response range of 0.001–150 μM for MP. This method has been used to detect MP in soil and waste water samples with satisfactory results. This study provides a promising electrochemical sensing platform and is a promising tool for the rapid, facile and sensitive analysis of MP.

A promising electrochemical sensing platform for the detection of methyl parathion based on cationic water-soluble pillar[5]arene reduced graphene nanocomposite.

A Fluorescence Sensing Determination of 2, 4, 6-Trinitrophenol Based on Cationic Water-Soluble Pillar[6]arene Graphene Nanocomposite

We describe a selective and sensitive fluorescence platform for the detection of trinitrophenol (TNP) based on competitive host–guest recognition between pyridine-functionalized pillar[6]arene (PCP6) and a probe (acridine orange, AO) that used PCP6-functionalized reduced graphene (PCP6-rGO) as the receptor. TNP is an electron-deficient and negative molecule, which is captured by PCP6 via electrostatic interactions and π–π interactions. Therefore, a selective and sensitive fluorescence probe for TNP detection is developed. It has a low detection limit of 0.0035 μM (S/N = 3) and a wider linear response of 0.01–5.0 and 5.0–125.0 for TNP. The sensing platform is also used to test TNP in two water and soil samples with satisfying results. This suggests that this approach has potential applications for the determination of TNP.

The synthesis of water-soluble phosphate pillar[5]arenes functionalized graphene as a fluorescent probe for sensitive detection of paraquat

We describe a selective and sensitive fluorescence platform for the detection of paraquat (PQ) based on competitive host-guest recognition between phosphate pillar[5]arenes (PWP5) and probe (Safranine T, ST) with using PWP5 functionalized reduced graphene (PWP5-rGO) as the receptor. PQ is a positive charge molecule that is captured by PWP5 via electrostatic interactions. The host-guest interaction between PWP5 and PQ is studied by ¹H NMR. Therefore, a selective and sensitive fluorescence sensing of detection PQ is developed. It has a linear response ranges of 0.01-2.0 and 2.0-50.0 μM and a low detection limit of 0.0035 μM (S/N = 3) for PQ. The sensing platform is also used to test PQ in two water samples with satisfying results. It suggests that this approach has potential applications for the determination of PQ.

Pillararene-based fluorescent chemosensors: recent advances and perspectives

This feature article summarizes recent research in the pillararene-based fluorescent chemosensor field in terms of ion sensing, small molecule recognition, biomolecule detection, fluorescent supramolecular aggregates, and biomedical imaging.