Synergistic combination of cyclodextrin edge-functionalized graphene and multiwall carbon nanotubes as conductive bridges toward enhanced sensing response of supramolecular recognition

Highly sensitive determination of paracetamol, uric acid, dopamine, and catechol based on flexible plastic electrochemical sensors

Flexible sensing is an alternative to traditional sensing and possesses good flexibility and wearability. Intrinsically conductive polymers, particularly poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS), have received significant attention due to their high mechanical flexibility and good biocompatibility. Here, we report the design of highly conductive and electrochemically active PEDOT:PSS-coated plastic substrate electrodes by combining N-doped graphene (NG) or S-doped graphene (SG) with methanesulfonic acid-treated PEDOT:PSS (denoted as NG-f-MSA-PEDOT:PSS/PET and SG-f-MSA-PEDOT:PSS/PET) by a simple drop-coating method. At room temperature, the NG-f-MSA-PEDOT:PSS/PET electrode demonstrated the lowest detection limits of 17.09, 33.84, 28.30, and 44.96 nM for paracetamol, uric acid, dopamine, and catechol (S/N = 3), respectively. The NG-f-MSA-PEDOT:PSS/PET electrode had good anti-interference ability and reproducibility without employing expensive noble metals and requiring much effort to polish the surface of traditional glass carbon electrodes. Most importantly, this film electrode could maintain a stable electrochemical response under different bending and crease states and had excellent mechanical stability and flexibility.

Green preparation of core-shell Cu@Pd nanoparticles with chitosan for glucose detection

Although core-shell structure is favored by many applications, preparing it with green way is rarely been reported. Herein, a core-shell structured Cu@Pd-CS nanocomposite is greenly fabricated utilizing a natural chitosan and applied to glucose detection. As-obtained Cu@Pd-CS nanoparticles were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and powder X-ray diffraction (XRD). When applied to glucose detection, the Cu@Pd-CS exhibits good stability, sensitivity and anti-interference. Moreover, it has a good linear relationship in glucose concentrations range of 0.1-1 mM with the sensitivity of 1.53 μA mM^-1 cm^-2 and 1-10 mM with the sensitivity of 23.00 μA mM^-1 cm^-2. This work proves the practicability of building metal-based core-shell structure nanoparticles with green resources and glucose detection application.

Core/Shell Piezoelectric Nanofibers with Spatial Self-Orientated β-Phase Nanocrystals for Real-Time Micropressure Monitoring of Cardiovascular Walls

Implantable pressure biosensors show great potential for assessment and diagnostics of pressure-related diseases. Here, we present a structural design strategy to fabricate core/shell polyvinylidene difluoride (PVDF)/hydroxylamine hydrochloride (HHE) organic piezoelectric nanofibers (OPNs) with well-controlled and self-orientated nanocrystals in the spatial uniaxial orientation (SUO) of β-phase-rich fibers, which significantly enhance piezoelectric performance, fatigue resistance, stability, and biocompatibility. Then PVDF/HHE OPNs soft sensors are developed and used to monitor subtle pressure changes in vivo. Upon implanting into pig, PVDF/HHE OPNs sensors demonstrate their ultrahigh detecting sensitivity and accuracy to capture micropressure changes at the outside of cardiovascular walls, and output piezoelectric signals can real-time and synchronously reflect and distinguish changes of cardiovascular elasticity and occurrence of atrioventricular heart-block and formation of thrombus. Such biological information can provide a diagnostic basis for early assessment and diagnosis of thrombosis and atherosclerosis, especially for postoperative recrudescence of thrombus deep within the human body.

Edge-Oxidation of Graphites by Hydrogen Peroxide

A simple and eco-friendly procedure of edge oxidation of high-surface area graphites, based on hydrogen peroxide treatments at 60 °C, is presented. Already, short-term treatments lead to O/C weight ratios higher than 0.1, leaving unaltered interlayer spacing and correlation length. This clearly indicates that all oxidized groups are located on exposed sites (mainly on lateral edges) of the graphitic layers. Short-term H₂O₂ treatments, as expected, increase hydrophilicity and reduce thermal stability with respect to the starting graphite. Long-term treatments, on the contrary, reduce hydrophilicity and increase thermal stability with respect to the starting graphite, mainly due to surface area reduction associated with the oxidation procedure. Exfoliation of a substantial fraction of the obtained edge-oxidized graphite can be achieved by simple procedures of dispersion and sonication in water.

Microwave-assisted synthesis of Pd3Ag nanocomposite via nature polysaccharide applied to glucose detection

In this work, a green strategy is performed to fabricate Pd₃Ag nanoparticles (NPs) using plant-extracted polysaccharide (Lilium brownie polysaccharide, LBP). As-obtained Pd₃Ag nanocomposite (Pd₃Ag-LBP/C) is surveyed including transmission election microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and powder X-ray diffraction (XRD). The result of glucose detection application shows that the Pd₃Ag-LBP/C glassy carbon electrode (GCE) exhibits good stability and sensitivity. It can completely cover the normal blood glucose concentration (3-8 mM) with high sensitivity of 77.20 μA mM^-1 cm^-2. This work undoubtedly has positive effects on green synthesis development. It not only proves the practicability of building nanomaterials by polysaccharide, but also offers an environmentally friendly way for fabricating other nanomaterials.

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.

Hierarchical Self-Assembly of Cyclodextrin and Dimethylamino-Substituted Arylene-Ethynylene on N-doped Graphene for Synergistically Enhanced Electrochemical Sensing of Dihydroxybenzene Isomers

An electrochemically active sensing nanomaterial (denoted as CD-MPEA-NG) has been successfully constructed by an hierarchical self-assembly of cyclodextrin (CD) and N,N-dimethyl-4-(phenylethynyl)aniline (MPEA) on N-doped graphene (NG) in a low-temperature hydrothermal process. The unique nanostructure of the high-performance CD-MPEA-NG was confirmed by utilizing Fourier transform infrared spectra, an X-ray diffractometer, and differential pulse voltammetry (DPV), etc. In particular, the method of density functional theory with dispersion energy (DFT-D) of wB97XD/LanL2DZ was employed to optimize and describe the face-to-face packing structure of heterodimers of NG and MPEA. The CD-MPEA-NG sensor exhibits highly sensitive performance toward dihydroxybenzene isomers, without relying on expensive noble metal or a complicated preparation process. The experimental results demonstrate that given the synergistic effect of NG and MPEA as a coupled sensing platform, CD as a supramolecular cavity can significantly enhance the electrochemical response. The detection limits (S/N = 3) for catechol (CT), resorcinol (RS), and hydroquinone (HQ) are 0.008, 0.018, and 0.011 μM by DPV, respectively. Besides, the CD-MPEA-NG sensor shows a superb anti-interference, reproducibility, and stability, and satisfactory recovery aimed at detecting isomers in Nanjing River water. The encouraging performance as well as simplified preparation approach strongly support the CD-MPEA-NG sensor is a fascinating electrode to develop as a seamless and sensitive electroanalytical technique.

Enhanced Electronic Communication and Electrochemical Sensitivity Benefiting from the Cooperation of Quadruple Hydrogen Bonding and π-π Interactions in Graphene/Multi-Walled Carbon Nanotube Hybrids

By designing a molecule labeled as UPPY with both ureidopyrimidinone (UP) and pyrene (PY) units, the supramolecular self-assembly of multiwalled carbon nanotube (MWNT) and reduced graphene oxide (rGO) was driven by the UP quadruple hydrogen-bonding and PY-based π-π interactions to form a novel hybrid of rGO-UPPY-MWNT in which the morphology of rGO-wrapped MWNT was found. Bridged by the two kinds of noncovalent bonding, enhanced electronic communication occurred in rGO-UPPY-MWNT. Also, under the cooperation of UP quadruple hydrogen-bonding and PY-based π-π interactions, higher electrical conductivity and better charge transfer were observed for rGO-UPPY-MWNT, compared with the rGO-MWNT composite without such noncovalent bonds, and that with just single PY-based π-π interaction (rGO-PY-MWNT) or UP quadruple hydrogen bond (rGO-UP-MWNT). Specifically, the electrical conductivity of rGO-PY-MWNT hybrids was increased approximately sevenfold, and the interfacial charge transfer resistance was nearly decreased by 1 order of magnitude compared with rGO-MWNT, rGO-UP-MWNT, and rGO-PY-MWNT. Resulting from its excellent electrical conductivity and charge transfer properties, the rGO-UPPY-MWNT modified electrode exhibited enhanced electrochemical activity toward dopamine with detection limit as low as 20 nM.

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.