Bridged β-cyclodextrin-functionalized MWCNT with higher supramolecular recognition capability: The simultaneous electrochemical determination of three phenols

Triple microenvironment modulation of zeolite imidazolate framework (ZIF) nanocages for boosting dopamine electrocatalysis

Multiple microenvironmental modulation of zeolite imidazole framework-8 (ZIF-8) is expected to solve the long-term intractable problem of low sensitivity in electrochemical sensing. Herein, the metal phthalocyanines with different central ions (PcM, M = Fe, Co, Ni and Cu) were introduced into ZIF-8 by in-situ synthesis method. Then, the hollow composite nanomaterials, HZIF-8/PcFe and HZIF-8@PcFe (HZIF-8, i.e., hollow ZIF-8) with different TA (tannic acid) coating thicknesses (∼11 nm and ∼33 nm) were successfully fabricated by carefully designed polyphenol-mediated modulation (PMM) strategy. Next, the HZIF-8@PcFe electrochemical sensor was constructed for selective and sensitive analysis by selecting dopamine (DA) as the analyte. The TA coating (superhydrophilic state), PcFe (redox properties) and hollow MOF cavity (faster mass transfer) was used as the triple microenvironment modulation of ZIF-8 to enhance the electrocatalytic performance. Under the optimum conditions (pH = 8.0), the linear correlations of 0.3 to 200 μmol/L was obtained for the peak current response, with a detection limit of 0.1 μmol/L (S/N = 3, i.e., Signal/Noise = 3). Meanwhile, the HZIF-8@PcFe electrochemical sensor exhibited excellent interference selectivity, reproducibility and stability, which enabled it to detect low abundance DA in real samples. And the F-test (homogeneity test of variance) and t-test (student's t test) statistical analyses were employed to enhance the accuracy of the actual samples' detection. This work will enlighten researchers working in the field of porous framework composites and open up new paths for the development of hollow MOFs hybrid materials in electrochemical sensing.

Controllable assembly of hollow interpenetrated zeolite imidazole framework nanocomposite for dopamine charge collection

The synergistic armor-etching (SAE) approach was proposed using natural organic weak acid (tannic acid, i.e., TA) for the controllable assembly of hollow and interpenetrated HZIF-8@MWCNTs hybrid nanomaterial (ZIF-8, zeolitic imidazolate framework-8; MWCNTs, multi-walled carbon nanotubes), which exhibited highly ordered crystal structure and unique morphological characteristics. The SAE strategy not only can rapidly etch solid ZIF- material into a hollow structure (~ 10 min), but also form the TA shell (~ 33 nm) on its surface. Then, the HZIF-8@MWCNTs electrochemical sensor was constructed for selective and sensitive detection of the target molecule (dopamine, DA). A sequence of studies indicated that the fabricated TA coating was capable of promoting the spread of DA into the reactive centers of hollow MOF and MWCNTs, which exhibited outstanding electroanalytical characteristics through the synergistic effect. The DPV oxidation peak of DA was strongest at 50 mV vs. Ag/AgCl reference electrode. Under the optimal conditions, there are two linear dynamic ranges of current response of 0.01 ~ 10 and 10 ~ 550 µmol L- 1 with a detection limit of 0.003 µmol·L- 1 (S/N = 3). Simultaneously, the HZIF-8@MWCNTs electrochemical sensor could detect low levels of DA in real products. The recoveries of the actual sample tests were between 98.2% and 102%, and the relative standard deviation (R.S.D.) of all studies was less than 3.0%. The statistical analyses (F-test and t-test) were employed to demonstrate the accuracy of method developed. This work will enlighten researchers operating in the domain of MOFs composites, accelerating the advancement of electrochemical sensing on the basis of hollow MOFs materials.

MnO2-DNA nanomaterials toward the dual signal detection of P-aminophenol micropollutants

P-Aminophenol (PAP), a potentially toxic and mutagenic compound, is widely distributed in water and soil and has serious side effects on human health. This study presents a convenient, sensitive, and effective dual-signal assay for the detection of PAP in the environment. Two-dimensional manganese dioxide (MnO₂) nanosheets were used as the carrier and quencher for fluorophore-labelled DNA to form a dual-signal nanoprobe, MnO₂-DNA. Based on a specific redox reaction between the MnO₂ nanosheets and target PAP, the corresponding absorption intensity of the product and the fluorescence intensity were both "turn-on" and also exhibited excellent correlation with the concentration of PAP. This strategy not only remarkably simplifies the detection process but also improves the reliability of results due to the dual-signal response, which has promising applications in environmental, clinical, and industrial research fields.

Simultaneous electrochemical determination of nitrophenol isomers based on macroporous carbon functionalized with amino-bridged covalent organic polycalix[4]arenes

A glassy carbon electrode (GCE) modified by a hybrid, macroporous carbon (MPC) functionalized with triazine bridged covalent organic polycalix[4]arenes (CalCOP) (CalCOP-MPC), has been fabricated and utilized for simultaneous detection of nitrophenols (NP). The obtained CalCOP-MPC were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS), which confirmed that MPC had functionalized with CalCOP successfully. Benefiting from the synergistic supramolecular effect of macrocyclic receptor of CalCOP and the excellent electrical properties of MPC, the anodic peaks of o-nitrophenol (o-NP), m-nitrophenol (m-NP), and p-nitrophenol (p-NP) in their mixture can be well separated by the prepared electrode. Differential pulse voltammetry (DPV) measurements at CalCOP-MPC/GCE revealed that the linear ranges of NP isomers were all 1-400 μM, and the detection limit limits were 0.383 μM, 0.122 μM, and 0.212 μM for o-NP, m-NP, and p-NP, respectively. Moreover, the prepared modified electrodes showed a relatively good selectivity and stability, implying the prospect for detecting NP in real environmental samples.

β-Cyclodextrin-functionalized graphene and metal–organic framework composites for ultrasensitive electrochemical detection of chloramphenicol

Novel β-CD@functionalized graphene /Cu-BTC composites were in situ prepared using β-CD functionalized graphene and Cu-BTC, and a new electrochemical sensor for sensitive detection of chloramphenicol was developed based on the composites.

Advances and Classification of Cyclodextrin-Based Polymers for Food-Related Issues

Cyclodextrins (CDs) are a good alternative to reduce or enhance different biomolecule characteristics and have demonstrated great results in food science. However, CDs present intrinsic limitations that can be solved by derivative synthesis. This review represents a survey of the state of the art of CD-based materials and their uses in food science. A deep review of the structure is carried out and different groups for ordination are suggested. After that, different applications such as cholesterol complexation or its use as sensors are reviewed. The derivatives show novel and promising activities for the industry. A critical perspective of the materials suggests that they might not present toxicity, although more studies are required. These points suggest that the research in this field will be increased in the following years.

Application of nanomaterials decorated with cyclodextrins as sensing elements for environment analysis

Environmental pollution has brought adverse socio-economic consequences. Organic pollutants and heavy metals are the main culprits of environmental pollution. It is of great importance to develop novel, simple, rapid, sensitive, and low-cost detection approaches for sensing trace pollutants in environmental samples. A lot of detection strategies which are based on varieties of nanomaterials have been developed for environmental analysis in past decades. In this review, we retrospect a variety of nanomaterials decorated with cyclodextrins (CDs), including carbon nanomaterials decorated with CDs, noble metal nanomaterials decorated with CDs and other nanomaterials decorated with CDs, and their application in environmental analysis. CDs is a type of ideal modifying molecules which could recognize targets, improve the solubility and dispersibility of corresponding functionalized materials, and enhance the detecting performance of designed sensors. CDs have been widely immobilized to carbon nanomaterials, noble metal nanomaterials, phosphorene (BP) nanocomposites, metal organic framework (MOF), and magnetic nanomaterials, and these nanocomposites have been utilized as the sensing elements for different target analytes. Immobilizing CDs on different nanomaterials could extremely expand the development of new sensing systems for environmental analysis based on these materials, greatly broaden the species of sensing targets, and apparently improve their sensing performance. Herein, the nanomaterials decorated with CDs, as sensing elements for environmental analysis, were reviewed including the types of nanomaterials decorated with CDs and their applications in various sensing strategies for environmental analysis. Finally, the perspectives of the nanomaterials decorated with CDs used as sensing elements were also discussed.

da Silva Alves D, Okeke C, Breslin CB. Cyclodextrins as Supramolecular Recognition Systems: Applications in the Fabrication of Electrochemical Sensors

Supramolecular chemistry, although focused mainly on noncovalent intermolecular and intramolecular interactions, which are considerably weaker than covalent interactions, can be employed to fabricate sensors with a remarkable affinity for a target analyte. In this review the development of cyclodextrin-based electrochemical sensors is described and discussed. Following a short introduction to the general properties of cyclodextrins and their ability to form inclusion complexes, the cyclodextrin-based sensors are introduced. This includes the combination of cyclodextrins with reduced graphene oxide, carbon nanotubes, conducting polymers, enzymes and aptamers, and electropolymerized cyclodextrin films. The applications of these materials as chiral recognition agents and biosensors and in the electrochemical detection of environmental contaminants, biomolecules and amino acids, drugs and flavonoids are reviewed and compared. Based on the papers reviewed, it is clear that cyclodextrins are promising molecular recognition agents in the creation of electrochemical sensors, chiral sensors, and biosensors. Moreover, they have been combined with a host of materials to enhance the detection of the target analytes. Nevertheless, challenges remain, including the development of more robust methods for the integration of cyclodextrins into the sensing unit.

A Facile In-Situ Development of L-Valine Film onto the Surface of Carbon Paste Electrode Towards the Detection of Environmentally Hazardous 4-Amino Phenol

A small scale of environmentally hazardous 4-aminophenol can show significant impact on human health. Hence, in the present work, we have designed L-Valine film (Vf) modified carbon paste electrode (Vf/CPE) for the determination of 4-aminophenol. Herein, a facile in-situ L-Valine film was developed by electrochemical polymerization method onto the surface of bare carbon paste electrode (BCPE) with the help of cyclic voltammetry (CV) technique. A two-folds of electrochemical peak current enhancement was achieved at Vf/CPE in comparison with BCPE towards the determination of 4-aminophenol in optimum pH 7.0 of phosphate buffer solution (PBS). This was achieved due to the large surface area and conductive nature of Vf/CPE, which was concluded through the techniques of cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The effect of pH of buffer and scan rate studies were successfully studied. Morphological changes of BCPE and Vf/CPE was studied with the help of scanning electron microscopy (SEM). The formation of Vf on CPE was also analyzed by Fourier transform infrared (FTIR) spectra. Under the optimized conditions, the limit of detection (LOD) and limit of quantification (LOQ) values of 4-aminophenol were estimated with the aid of chronoamperometry (CA) technique and was found to be 9.8 μM and 32 μM, respectively. Finally the proposed method was found to have satisfactory repeatability, reproducibility and stability results with low relative standard deviation (RSD) values.

Cyclodextrin polymer networks decorated with subnanometer metal nanoparticles for high-performance low-temperature catalysis

The synthesis of support materials with suitable coordination sites and confined structures for the controlled growth of ultrasmall metal nanoparticles is of great importance in heterogeneous catalysis. Here, by rational design of a cross-linked β-cyclodextrin polymer network (CPN), various metal nanoparticles (palladium, silver, platinum, gold, and rhodium) of subnanometer size (<1 nm) and narrow size distribution are formed via a mild and facile procedure. The presence of the metal coordination sites and the network structure are key to the successful synthesis and stabilization of the ultrasmall metal nanoparticles. The as-prepared CPN, loaded with palladium nanoparticles, is used as a heterogeneous catalyst and shows outstanding catalytic performance in the hydrogenation of nitro compounds and Suzuki-Miyaura coupling reaction under mild conditions. The CPN support works synergistically with the metal nanoparticles, achieving high catalytic activity and selectivity. In addition, the catalytic activity of the formed catalyst is controllable.

A boron nitride electrode modified with a nanocomposite prepared from an ionic liquid and tungsten disulfide for voltammetric sensing of 4-aminophenol

Boron nitride (BN) was used as a support and covered with an ionic liquid (IL) and tungsten disulfide (WS₂) nanoparticles to obtain an electrode for the determination of 4-aminophenol (4-AP). BN was prepared using a "solvent cutting" method, and the BN-IL-WS₂ nanocomposite was obtained by an ultrasonic method. BN and its hybrids were characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. When the BN-IL-WS₂ composites were coated on the surface of the electrode, the response to 4-AP was strongly amplified due to the strong synergetic effect between the three materials. The voltammetric response of the modified sensor (with a maximum at 0.29 V vs. Ag/AgCl) in solutions with a pH of 6 is linear in the 0.01-50 μΜ 4-AP concentration range, and the limit of detection is 3 nM. A modified glassy carbon electrode was applied for the determination of 4-AP in seawater and dispersions containing paracetamol tablets. The results were consistent with those obtained by HPLC. Graphical abstract Schematic representation of the voltammetric determination process of 4-aminophenol (4-AP). The electrochemical sensor based on the glassy carbon electrode modified with boron nitride (BN), ionic liquid (IL) and tungsten disulfide (WS₂) nanomaterials. They, exhibit an excellent performance compared with other electrodes.

An electrochemical sensor for the detection of p-nitrophenol based on a cyclodextrin-decorated gold nanoparticle–mesoporous carbon hybrid

A novel electrochemical sensor based on a cyclodextrin-decorated gold nanoparticle–mesoporous carbon hybrid was constructed for the detection of p-nitrophenol.

Recent developments in the synthesis and applications of graphene-family materials functionalized with cyclodextrins

The introduction of cyclodextrin species to graphene-family materials (GFMs) constitutes an important area of research, especially in terms of the development of applied nanoscience. The chemistry of cyclodextrins is the so-called host-guest chemistry, which has impacted on many fields of research, including catalysis, electrochemistry and nanomedicine. Cyclodextrins are water-soluble and biocompatible supramolecules, and therefore they may introduce new interesting properties to GFMs and may enhance the physicochemical/biological features of native GFMs. The reported methods for the conjugation of cyclodextrins to GFMs utilize either covalent or non-covalent approaches. The recent progress in the applications of GFMs functionalized with cyclodextrins, with the respect to the chemistry and features of these conjugates, is discussed. Special consideration is also given to the recent developments in (i) nanomedicine, (ii) electrochemistry, (iii) adsorption and (iv) catalysis. Examples of these materials are discussed in this work, together with the future outlook on the impact of GFM-cyclodextrin conjugates in the development of applied nanoscience.

A new strategy for the sensitive electrochemical determination of nitrophenol isomers using β-cyclodextrin derivative-functionalized silicon carbide

An illustration of simultaneous electrochemical determination of nitrophenol isomers using β-cyclodextrin derivative-functionalized silicon carbide.

Smart Combination of Cyclodextrin Polymer Host-Guest Recognition and Mg2+-Assistant Cyclic Cleavage Reaction for Sensitive Electrochemical Assay of Nucleic Acids

A novel enzyme-free electrochemical sensing strategy was proposed for sensitive monitoring of DNA and miRNA by smart combination of the cyclic cleavage reaction of Mg²⁺-dependent DNAzyme and the host-guest inclusion between ferrocene-labeled hairpin probe (H-1) and nitrogen-doped reduced graphene oxide/β-cyclodextrin polymer (NRGO/β-CDP) nanocomposites. The synthesized NRGO/β-CDP nanocomposites with high electrocatalytic activity and recognition capability were modified on the glassy carbon electrode to construct the sensing platform. Upon the hybridization reaction of subunit DNA in the loop region with target sequence, the active DNAzyme was liberated from the caged structure, which bound with H-1 to catalyze its cleavage in the presence of Mg²⁺ and triggered the target recycling amplification for the cleavage of a large number of H-1. Each cleaved H-1 was divided into two single-stranded oligonucleotides, leading to an obvious enhancement of peak current by the molecular recognition of β-CDP on the electrode. Thus, the constructed biosensor showed high sensitivity and selectivity for DNA and miRNA assays, with wide concentration ranges of 0.01-1000 and 0.05-500 pM and low detection limits of 3.2 and 18 fM, respectively. This developed sensing strategy may become a promising nucleic acid detection method in bioassays and clinical diagnosis.

Ultrasensitive electrochemical detection of Dicer1 3'UTR for the fast analysis of alternative cleavage and polyadenylation

Alternative cleavage and polyadenylation (APA) is involved in several important biological processes in animals, e.g. cell growth and development, and cancer progression. The increasing data show that cancer cells are inclined to produce mRNA isoforms with a shortened 3'UTR undergoing APA. For example, the Dicer1 isoform with a shorter 3'untranslated region (3'UTR) was found to be overexpressed in some cancer cells, which may be used as a potential novel prognostic biomarker for cancer. In the present work, a novel electrochemical biosensor for ultrasensitive determination of Dicer1 was designed by using gold nanoparticles and p-sulfonated calix[6]arene functionalized reduced graphene oxide (Au@SCX6-rGO) as nanocarriers. The results showed that the expressions of the shorter 3'UTR (Dicer1-S) both in BT474 and SKBR3 were obviously higher than those of the longer Dicer1 (Dicer1-L) by the constructed biosensor, which agreed well with the result analyzed by the RT-qPCR method. The detection ranges of Dicer1-S and Dicer1-L were 10^-14-10^-9 M and 10^-15-10^-10 M. The LODs were 3.5 and 0.53 fM. The specificity of the proposed biosensor was also very high. For the first time, the expressional analysis of different 3'UTRs caused by APA was studied by an electrochemical method. Moreover, the use of a macrocyclic host for constructing an electrochemical/biosensing platform has rarely been reported. The proposed electrochemical sensing strategy is thus expected to provide a new method for determination of novel biomarkers and a novel method for fast and cheap analysis of APA.

Variable self-assembly and in situ host–guest reaction of beta-cyclodextrin-modified graphene oxide composite Langmuir films with azobenzene compounds

Different composite Langmuir films (GO–CD/N-Azo and GO–CD/PAA-Azo) are prepared via simple interfacial self-assembly process and host–guest reaction, demonstrating variable self-assembly for wide applications.

Synthesis of benzo[6]urils and their selective interactions with bipyridines

Benzo[6]urils bearing hydroxymethyl or methyl groups have been synthesized with a facile method, and their supramolecular interactions with bipyridine guests have been investigated.

Fabrication of 4-aminophenol sensor based on hydrothermally prepared ZnO/Yb2O3nanosheets

A facile hydrothermal process was used to prepare nanostructures of ZnO/Yb₂O₃in alkaline medium, which were applied for efficient chemical sensor development. The sensor fabricated with ZnO/Yb₂O₃nanostructures may be a promising sensitive chemical sensor for the effective detection of environmental effluents.

Highly-sensitive electrocatalytic determination for toxic phenols based on coupled cMWCNT/cyclodextrin edge-functionalized graphene composite

Highly-sensitive electrocatalytic determination of toxic phenol compounds is of significance in environmental monitoring due to their low degradation and high toxicity to the environment and humans. In this paper, a rapid and sensitive electrochemical sensor based on coupled carboxyl-multi-walled carbon nanotube (cMWCNT) and cyclodextrin (CD) edge-functionalized graphene composite was successfully employed towards trace detection of three typical phenols (4-aminophenol, 4-AP; 4-chlorophenol, 4-CP; 4-nitrophenol, 4-NP). The morphology studies from scanning electron microscope and transmission electron microscope analysis revealed that cMWCNTs as conductive bridges were successfully incorporated into CD edge-functionalized graphene layers. Further, The electrocatalytic detection performance of the 3D simultaneously reduced and self-assembled sensing architecture (GN-CD-cMWCNT) with trace amounts of CDs was evaluated. The electrochemical studies demonstrated that GN-CD-cMWCNT displays excellent electrocatalytic activity, high sensitivity and stability. Under optimal conditions, the current responses of 4-AP, 4-CP and 4-NP are linear to concentrations over two different ranges, with low detection limit of 0.019, 0.017 and 0.027μM (S/N=3), respectively. And, GN-CD-cMWCNT shows an excellent anti-interference ability against electroactive species and metal ions. In addition, validation of the applicability of the presented sensor was also performed for the determination of three phenols in tap water sample with satisfactory results.

β-CD Dimer-immobilized Ag Assembly Embedded Silica Nanoparticles for Sensitive Detection of Polycyclic Aromatic Hydrocarbons

We designed a β-CD dimer on silver nanoparticles embedded with silica nanoparticles (Ag@SiO₂ NPs) structure to detect polycyclic aromatic hydrocarbons (PAHs). Silica NPs were utilized as a template for embedding silver NPs to create hot spot structures and enhance the surface-enhanced Raman scattering (SERS) signal, and a thioether-bridged dimeric β-CD was immobilized on Ag NPs to capture PAHs. The assembled Ag NPs on silica NPs were confirmed by TEM and the presence of β-CD dimer on Ag@SiO₂ was confirmed by UV-vis and attenuated total reflection-Fourier transform infrared spectroscopy. The β-CD dimer@Ag@SiO₂ NPs were used as SERS substrate for detecting perylene, a PAH, directly and in a wide linearity range of 10⁻⁷ M to 10⁻² M with a low detection limit of 10⁻⁸ M. Also, the β-CD dimer@Ag@SiO₂ NPs exhibited 1000-fold greater sensitivity than Ag@SiO₂ NPs in terms of their perylene detection limit. Furthermore, we demonstrated the possibility of detecting various PAH compounds using the β-CD dimer@Ag@SiO₂ NPs as a multiplex detection tool. Various PAH compounds with the NPs exhibited their distinct SERS bands by the ratio of each PAHs. This approach of utilizing the assembled structure and the ligands to recognize target has potential for use in sensitive analytical sensors.