Self-assembled ordered AuNRs-modified electrodes for simultaneous determination of dopamine and topotecan with improved data reproducibility.

Gold nanomaterials have been widely explored in electrochemical sensors due to their high catalytic property and good stability in multi-medium. In this paper, the reproducibility of the signal among batches of gold nanorods (AuNRs)-modified electrodes was investigated to improve the data stabilization and repeatability. Ordered and random self-assembled AuNRs-modified electrodes were used as electrochemical sensors for the simultaneous determination of dopamine (DA) and topotecan (TPC), with the aim of obtaining an improved signal stability in batches of electrodes and realizing the simultaneous determination of both substances. The morphology and structure of the assemblies were analyzed and characterized by UV-Vis spectra, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray powder diffraction (XRD). Electrochemical studies showed that the ordered AuNRs/ITO electrodes have excellent signal reproducibility among several individuals due to the homogeneous mass transfer in the ordered arrangement of the AuNRs. Under the optimized conditions, the simultaneous detection results of DA and TPC showed good linearity in the ranges 1.75-45 µM and 1.5-40 µM, and the detection limits of DA and TPC were 0.06 µM and 0.17 µM, respectively. The results showed that the prepared ordered AuNR/ITO electrode had high sensitivity, long-term stability, and reproducibility for the simultaneous determination of DA and TPC, and it was expected to be applicable for real sample testing.

Single-crystal ordered macroporous metal-organic framework as support for molecularly imprinted polymers and their integration in membrane formant for the specific recognition of zearalenone.

Zearalenone is a fungal contaminant that is widely present in grains. Here, a novel molecularly imprinted membrane based on SOM-ZIF-8 was developed for the rapid and highly selective identification of zearalenone in grain samples. The molecularly imprinted membrane was prepared using polyvinylidene fluoride, cyclododecyl 2,4-dihydroxybenzoate as a template and SOM-ZIF-8 as a carrier. The factors influencing the extraction of zearalenone using this membrane, including the solution pH, extraction time, elution solvent, elution time, and elution volume, were studied in detail. The optimized conditions were 5 mL of sample solution at pH 6, extraction time of 45 min, 4 mL of acetonitrile:methanol = 9:1 as elution solvent, and elution time of 20 min. This method displayed a good linear range of 12-120 ng/g (R2  = 0.998) with the limits of detection and quantification of this method are 1.7 and 5.5 ng/g, respectively. In addition, the membrane was used to selectively identify zearalenone in grain samples with percent recoveries ranging from 87.9 to 101.0% and relative standard deviation of less than 6.6%. Overall, this study presents a simple and effective chromatographic pretreatment method for detecting zearalenone in food samples.

Synthesis of MOF-199/CNTs Nanocomposite for Selective Adsorption and Determination of Nonsteroidal Anti-Inflammatory Drugs in Human Urine.

A hybrid nanocomposite containing a moisture-resistant surface based on MOF-199 and carbon nanotubes (CNTs) was synthesized. Characterization was undertaken using powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The adsorption behavior of the MOF-199/CNTs composite to ibuprofen was then investigated at room temperature. Experimentation revealed that the hybrid absorbent had excellent adsorption capacity for the nonsteroidal anti-inflammatory drug (NSAID), ibuprofen, with maximum adsorption up to 40.8 mg/g. The adsorbent was able to be recycled several times without deactivation. Finally, the MOF-199/CNTs composite was used as the extraction sorbents for selective extraction of ibuprofen, ketoprofen and naproxen in human urine. The results showed successful application of the nanocomposite to NSAID analysis in spiked human urine samples. Recoveries at three concentrations were 89.7-96.8%, 79.3-85.5% and 95.6-97.5% for ibuprofen, ketoprofen and naproxen, respectively. The relative standard deviations (RSDs) were within the range of 2.9-5.3%. The results demonstrated that the MOF-199/CNTs composite is an excellent adsorbent for determination of NSAIDs in spiked urine samples.

Correction to: Synergistic effect of a cobalt fluoroporphyrin and graphene oxide on the simultaneous voltammetric determination of catechol and hydroquinone.

The published version of this article, unfortunately, contains error. The author found out that Chart 1 image was wrongly incorporated in the online paper.

Synergistic effect of a cobalt fluoroporphyrin and graphene oxide on the simultaneous voltammetric determination of catechol and hydroquinone.

Graphene oxide (GO) was modified with the cobalt(II) and zinc(II) complexes (CoTFPP and ZnTFPP) of 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin in order to improve the electrocatalytic activity of GO towards catechol (CC) and hydroquinone (HQ). It is found that the CoTFPP-modified GO on a glassy carbon electrode (GCE) displays the highest electrocatalytic activity. The response to CC (at 0.14 V vs. SCE) is linear in the 1-220 µM concentration range. The response to HQ (at 0.04 V vs. SCE) extends from 1 µM to 200 µM. The sensitivity and detection limits are 10.40 µA∙µM-1∙cm-2 and 0.17 µM for CC, and 8.40 µA∙µM-1∙cm-2 and 0.21 µM for HQ. Experimental results indicate that the Co(II) and Zn(II) ions in the porphyrins positively affect the electron transfer rate in the hybrid materials. The GCE modified with CoTFPP/GO was successfully applied to the simultaneous determination of CC and HQ in spiked samples of tap and lake water. Graphical abstract Schematic presentation of a voltammetric method for simultaneous determination of catechol (CC) and hydroquinone (HQ). It is based on the use of a cobalt (II) fluoroporphyrin (CoTFPP) functionalized graphene oxide (GO) hybrid.

Preparation of a molecularly imprinted sensor based on quartz crystal microbalance for specific recognition of sialic acid in human urine.

A novel molecularly imprinted quartz crystal microbalance (QCM) sensor was successfully prepared for selective determination of sialic acid (SA) in human urine samples. To obtain the QCM sensor, we first modified the gold surface of the QCM chip by self-assembling of allylmercaptane to introduce polymerizable double bonds on the chip surface. Then, SA molecularly imprinted polymer (MIP) nanofilm was attached to the modified QCM chip surface. For comparison, we have also characterized the nonmodified and improved surfaces of the QCM sensor by using atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy. We then tested the selectivity and detection limit of the imprinted QCM sensor via a series of adsorption experiments. The results show a linear response in the range of 0.025-0.50 µmol L-1 for sialic acid. Moreover, the limit of detection (LOD) of the prepared imprinted QCM sensor was found to be 1.0 nmol L-1 for sialic acid, and high recovery values range from 87.6 to 108.5% with RSD < 8.7 (n = 5) for the spiked urine sample obtained. Overall, this work presents how a novel QCM sensor was developed and used to detect sialic acid in human urine samples. Graphical abstract Specific recognition of sialic acid by the MIP-QCM sensor system.

Determination of Phenolic Compounds in Environmental Water by HPLC Combination with On-Line Solid-Phase Extraction Using Molecularly Imprinted Polymers.

A novel molecularly imprinted polymer (MIP) was synthesized using halloysite nanotubes (HNT) as matrix, ß-cyclodextrin (ß-CD) and methyl propyl acid (MAA) as functional monomers, and 2,4,6-TCP as template molecule by graft copolymerization. Infrared spectroscopy and transmission electron microscopy (TEM) were used to characterize the as-synthesized imprinted polymer. The selective recognizability of the MIP towards four phenolic analogs were determined and the recognition coefficients for 2,4,6-TCP, 2,6-DCP, 4-CP and phenol were found to be 2.17, 1.85, 2.02 and 1.36, respectively. Using as the packing material of solid-phase extraction, the imprinted polymer has been applied to on-line extraction of the four phenolic compounds in environmental water. The corresponding analytical methods to determine these four phenolic compounds have been developed. Good linear relationships were obtained over the range of 0.05-5.0 mg x L(-1). The average recoveries for spiked samples were in the range of 74.8-97.2%, and the detection limits for 2,4,6-TCP, 2,6-DCP, p-chlorophenol, phenol were 0.19, 0.20, 0.75, 0.73 mg x L(-1), respectively. The method is rapid, accurate and high selectivity. It was feasible for the determination of trace level phenolic compounds in environmental samples.

Progress of quartz crystal microbalance in chiral analysis.

Chiral analysis is one of the most important/challenging analytical tasks due to the necessity for differentiation of very slight differences in the molecular configurations between chiral isomers. It consists of two processes, chiral recognition and signal transduction. Quartz crystal microbalance (QCM) holds a great promise for the next-generation sensors, due to its remarkable mass sensitivity, fast response, capable of online detection and low cost. It has been the focus of academic and practical research on chiral analysis during the last two decades. This review provides a detailed overview of recent advances made in chiral analysis based on QCM detection with regard to the recognition elements, which include synthetic macromolecules, molecular imprinting polymers (MIPs), proteins, amino acids and their derivatives, etc. The prospects of using QCM for chiral analysis are also put forward.

Limitations and Progresses in Carbon-Based Cesium Lead Halide Perovskite Solar Cells.

Inorganic cesium lead halide perovskites (CsPbIxBr3-x, 0≤x≤3) are promising alternatives with great thermal stability. Additionally, the choice of moisture-resistive and dopant-free carbon as the electrode material can simultaneously solve the problems of stability and cost. Therefore, carbon electrode-based inorganic PSCs (C-IPSCs) represent a promising candidate for commercialization, yet both the efficiencies and stability of related devices demand further progress. This article reviews the recent advancement of C-IPSCs and then unravels the distinctive merits and limitations in this field. Subsequently, our perspective on various modification strategies is analyzed on a methodological level. Finally, this article outlooks the promising research contents and the remaining unresolved issues in this field. We believe that understanding and analyzing the related problems in this field are instructive to stimulate the future development of C-IPSCs.

Synthesis of Tetrasubstituted Alkenes by Rhodium-Catalyzed Regioselective Cyano Transfer.

We describe herein a novel, general, and robust approach to structurally diversified alkenyl nitriles through a Rh-catalyzed cyano transfer reaction between alkynyl-malononitrile derivatives and aryl/alkenyl boronic acids. This reaction exhibits high chemo- and regioselectivity and a broad substrate scope. The tetrasubstituted alkenyl dinitriles (34 examples, average 58% yield) are obtained through substrate tuning and ligand control.

A simple paper-based nickel nanocluster-europium mixed ratio fluorescent probe for rapid visual sensing of tetracyclines.

In this work, a ratiometric fluorometric sensor based on nickel nanoclusters (NiNCs)-europium complex (NiNCs-Eu3+) was constructed for the highly selectivity detection of tetracyclines (TCs) in water samples. In the presence of TCs, the blue fluorescence of the sensor NiNCs-Eu3+ was quenched at 430 nm and the characteristic red fluorescence of Eu3+-TCs appeared at 620 nm because of the combined help of inner filter effect (IFE) and antenna effect. Under the optimized conditions (100 mM Eu3+ (100 µL); temperature (25℃); reaction time (10 min), HEPES buffer solution (pH = 7.0)), the sensor offered a wide detection range of tetracycline (TC) and oxytetracycline (OTC) from 0.1 to 50 µM with the detection limit (LOD) of 25 nM and 21 nM, respectively. Moreover, the sensor was able to detect of TC and OTC in tap and lake water with high recovery rate (89.10%-97.60%). In addition, the portable paper-based sensor was constructed using filter paper embedded with NiNCs-Eu3+. The distinct fluorescent color of the paper-based sensor varied from bright blue to red against different concentrations of TC and OTC. These above findings demonstrated the potential for wide application of as-prepared ratio metric fluorescence sensor for visual detection of TCs in water samples.

Self-assembly of L-cysteine for chiral recognition of mandelic acid in gas phase.

This study demonstrates a new approach for the selective recognition of chiral mandelic acid by quartz crystal microbalance (QCM) using L-cysteine as the selector. The modification of L-cysteine on the QCM sensor was identified using resonant frequency detection, the contact angle, cyclic voltammetry, and X-ray photoelectron spectroscopy measurements. The chiral recognizability of L- and D-MA on the L-cysteine-modified surface was examined using QCM detection integrated with a vapor diffused molecular assembly reaction technique. The present chiral recognition results suggest that the L-cysteine is a good resolving agent for detecting chiral mandelic acid.

A molecularly imprinted gel photonic crystal sensor for recognition of chiral amino acids.

A new type of photonic crystal gel molecularly imprinted sensor (MIPHs) was synthesized for the visible chiral recognition of amino acids. The color of MIPHs was changed from green to red when it exposured to various l-pyroglutamic acid concentration (0.05-1.0mmoL/L). Thanks to sensitive reflectance of photonic crystal and high selectivity of MIPs, the constructed MIPHs exhibited good performance towards l-pyroglutamic acid in terms of fast response time (3 min) and low detection limit (LOD) (2.4 µmol/L). Besides, MIPHs was found to have good selectivity toward l-pyroglutamic acid in the presence of interference group with similar structures such as d-pyroglutamic acid, l-tryptophan, l-phenylalanine, and l-proline. In light of these findings, the MIPHs can be used for highly selective recognition of l-pyroglutamic acid. It is expected that our work is able to provide a new roadmap for the chiral identification and separation of amino acids.

Direct preparation of solid carbon dots by pyrolysis of collagen waste and their applications in fluorescent sensing and imaging.

The fluorescent carbon dots (CDs) have found their extensive applications in sensing, bioimaging, and photoelectronic devices. In general terms, the synthesis of CDs is straight-forward, though their subsequent purification can be laborious. Therefore, there is a need for easier ways to generate solid CDs with a high conversion yield. Herein, we used collagen waste as a carbon source in producing solid CDs through a calcination procedure without additional chemical decomposition treatment of the raw material. Considering a mass of acid has destroyed the original protein macromolecules into the assembled structure with amino acids and peptide chains in the commercial extraction procedure of collagen product. The residual tissues were assembled with weak intermolecular interactions, which would easily undergo dehydration, polymerization, and carbonization during the heat treatment to produce solid CDs directly. The calcination parameters were surveyed to give the highest conversion yield at 78%, which occurred at 300°C for 2 h. N and S atomic doping CDs (N-CDs and S-CDs) were synthesized at a similar process except for immersion of the collagen waste in sulfuric acid or nitric acid in advance. Further experiments suggested the prepared CDs can serve as an excellent sensor platform for Fe3+ in an acid medium with high anti-interference. The cytotoxicity assays confirmed the biosafety and biocompatibility of the CDs, suggesting potential applications in bioimaging. This work provides a new avenue for preparing solid CDs with high conversion yield.

Chiral recognition of mandelic acid by L-MA derivative-modified sensor in liquid environment.

This study demonstrates a new approach for the highly selective molecular recognition of chiral mandelic acid using an L-mandelic acid derivative with an optically active hydroxyl group as the selector. The proposed method is based on quartz crystal microbalance (QCM) detection combined with functional multilayer film techniques in a liquid environment. The present chiral recognition results suggest that the L-mandelic acid derivative is an excellent resolving agent for detecting chiral mandelic acid.

Highly Selectivity Molecularly Imprinted Fluorescence Sensor Based on Carbon Quantum Dots for the Determination of Anthraquinones.

Due to the complexity of traditional Chinese medicines (TCMs), it is very important to develop a method that can recognize anthraquinones, the active ingredients in TCMs, with high selectivity. Here, a molecularly imprinted fluorescence sensor was coated on the surface of carbon quantum dots (CDs). Allobarbital was used as functional monomer for this application using theoretical calculations and was successfully synthesized and characterized. The template molecule chrysophanol was combined with the functional monomer allobarbital using a hydrogen bond array. Then, a series of adsorption experiments were performed to study the specific recognition of anthraquinones by the prepared sensors. The results showed that the prepared sensor had a good linear response to concentrations of chrysophanol in the concentration range 0.5 mg · L-1 to 8.0 mg · L-1, a low detection limit (5.0 µg · L-1), high stability, and a short response time (20 min). Additionally, the obtained fluorescence sensor was successfully applied to selectively recognize anthraquinones in TCMs with recoveries of 90.1% to 101.7%. The prepared sensor displays excellent sensitivity and high selectivity towards anthraquinones, mainly due to the specific hydrogen binding sites for the target molecules. Overall, this fluorescence sensor can selectively recognize anthraquinones in TCMs, and provide a method for quality monitoring and rational utilization of TCMs.

Synthesis of a Molecularly Imprinted Polymer on NH2-MIL-101(Cr) for Specific Recognition of Diclofenac Sodium.

A novel molecularly imprinted polymer material based on the metal-organic framework NH2-MIL-101(Cr) (MOF-MIP) was prepared. The synthesized MOF-MIP was characterized by IR, XRD, SEM and N2 absorption. The characterization results displayed that the MOF-MIP which exhibited an octahedral shape had good dispersibility, good thermal stability and a high surface area. Subsequently, the adsorption behavior of MOF-MIP to diclofenac sodium (DS) in aqueous solution was examined. A series of adsorption experiments demonstrated that the MOF-MIP had high transfer mass rates and high sensitivity and selectivity for DS. Then the MOF-MIP was used as the adsorbent of dispersive micro-solid phase extraction (DMSPE) for the detection of DS in urine. Under optimum conditions, the average recovery of DS ranged from 88.3 to 101.6% with RSD of 5.6%. The described method provides a rapid route for determination of DS in human urine.

Highly sensitive α-amanitin sensor based on molecularly imprinted photonic crystals.

α-amanitin is the most toxic amanita in mushrooms with lethal dose to humans around 0.1 mg. Kg-1. Hence, early identification of the poison would improve survival rates and prevent lethal poisoning cases. In this study, molecularly imprinted photonic crystal (MIPC) sensor was prepared by combining molecular imprinting with photonic crystal templates and tested towards the detection of α-amanitin. In this process, synthesized moiety of α-amanitin was utilized as template, dispersed SiO2 colloidal photonic crystal as carrier, methacrylic acid (MAA) as functional monomer, and ethylene glycol dimethacrylate (EDGMA) as crosslinker. The adsorption behavior of MIPC towards α-amanitin in ethanol solution showed shifts in diffraction peaks of MIPC upon binding with α-amanitin molecules. The reflection peak wavelength varied linearly with α-amanitin concentration according to the correlation formula: λ = 15.417c+489.17 (R2 = 0.9985). The recognition process was accompanied by gradual color change in MIPC film. The prepared MIPC sensor possessed wide linear range (10-9-10-3 mg L-1), change in visual color, low detection limit (10-10 mg L-1), short response time (2 min), and good reusability. The MIPC film was then tested towards the detection of α-amanitin in real biological samples (mushroom, urine, and serum) and showed reasonable shift in diffraction peaks and color change upon soaking in solutions spiked with α-amanitin at 10-6 mg L-1 and 10-3 mg L-1, suggesting the suitability of the film for the rapid identification of α-amanitin in complex sample matrices. Overall, the proposed sensor looks promising for the rapid identification of α-amanitin in clinical analysis and food poisoning.

Electrochemical sulfonylation of alkenes with sulfonyl hydrazides: a metal- and oxidant-free protocol for the synthesis of (E)-vinyl sulfones in water.

An efficient electrochemical transformation of a variety of alkenes and sulfonyl hydrazides into vinyl sulfones with a catalytic amount of tetrabutylammonium iodide in water is reported. The reaction proceeds smoothly to afford vinyl sulfones with good selectivities and yields at room temperature under air in an undivided cell. Cyclic voltammograms and control experiments have been performed to provide preliminary insight into the reaction mechanism. The key features of this reaction include using pure water as solvent, transition metal- and oxidant-free conditions, and being easily scaled up to gram-scale synthesis.

Chiral recognition of mandelic acid on quartz crystal microbalance by vapor diffused molecular assembly method.

This study presents a new approach for the highly selective recognition of chiral L/D-mandelic acid (MA) using a quartz crystal microbalance (QCM) with L-phenylalanine (L-Phe) as the selector. The immobilization of L-Phe on the gold surface of the QCM sensor was performed using a four steps layer-by-layer assembling procedure. The modification of the gold surface of the QCM sensor after each modification step was verified by the cyclic voltammetry, contact angle, FTIR, and QCM detection. The chiral recognition ability of L- and D-MA on the chiral surface was checked by sensing using the vapor diffused molecular assembly (VDMA) method with the QCM. The chiral discrimination factor between L- and D-MA, aplha(L-MA/D-MA), was found to be about 9. The L-Phe-modified QCM gold sensor also showed good stability and reusability. The high chiral discrimination ability of the modified surface might be the result of the different hydrogen bonding force between L- or D-MA and L-Phe.