Selective “naked-eye” sensing of acetate ion based on conformational flexible amide-pyridinium receptor

A simple pincer-shape anion receptor L1 containing amide-pyridinium as binding unit was synthesized and its anion binding properties were investigated by UV–Vis, NMR titration spectra and molecular simulation. L1 displayed better affinity toward AcO^? ion with visible color change compared with other investigated anions, including F^?, H₂PO₄ ^?, Cl^?, Br^?, I^?, NO₃ ^? and HSO₄ ^? ions. The selectivity was ascribed to the synergistic effects arising from hydrogen bonding, electrostatic interaction and induced-fit process.     

New coumarin-urea based receptor for anions: a selective off–on fluorescence response to fluoride

A novel fluorosensor for anions, 1,11-bis(4-methylcoumarin-7-yl)-6-methyl-1,3,6,9,11-pentaazaundeca-2,10-dione (L), which contains two coumarin–urea units spaced by a flexible diethylenetriamine fragment, was easily prepared in 65% yield by a one-pot two-step procedure. The binding ability of L toward several anions (G) was evaluated by ¹H NMR, UV–vis, and fluorescence titration. It was found that L forms stable [LG] and [LG₂] species in both DMSO and CH₃CN solvents. Furthermore, the fluorescence emission of L in the visible range (400 nm) is affected by the presence of anions; it is quenched by acetate, chloride, and pyrophosphate while it is enhanced by fluoride. Thus, this novel fluorosensor provides a selective off–on response to the presence of fluoride in solution.     

Hydrogen peroxide sensor based on glassy carbon electrode modified with ��-manganese dioxide nanorods

A solid bar microextraction (SBME) method containing sorbent materials 2?mg in the lumen of a porous hollow fiber membrane 2.5?cm for the extraction of carbamazepine, diclofenac and ibuprofen from river water samples is described. The desorbed analytes were analyzed using reversed-phase high performance liquid chromatography with ultraviolet detection. In order to achieve optimum performance, several extraction parameters were optimized. Of the sorbents evaluated, LiChrosorb RP-8 was the most promising. Under the optimized conditions, limits of detection from 0.7 to 0.9???g?L^?1, precisions from 5.5 to 6.4% and a correlation coefficient of 0.999 were obtained for the target drugs over a concentration range of 1?C200???g?L^?1. In comparison with the solid phase extraction, the SBME system offers distinct advantages due to its higher enrichment factors, lower consumption of organic solvents and time saving.

Amperometric glucose sensor based on platinum–iridium nanomaterials

This communication reports on a novel amperometric glucose sensor based on nanoporous Pt–Ir catalysts. Pt–Ir nanostructures with different contents of iridium were directly grown on Ti substrates using a one-step facile hydrothermal method and were characterized using scanning electron microscopy and energy dispersive X-ray spectroscopy. Our electrochemical study has shown that the nanoporous Pt–Ir(38%) electrode exhibits very strong and sensitive amperometric responses to glucose even in the presence of a high concentration of Cl⁻ and other common interfering species such as ascorbic acid, acetamidophenol and uric acid, promising for nonenzymatic glucose detection.     

Multiplex sensor for detection of different metal ions based on on–off of fluorescent gold nanoclusters

In this study, a multiplex fluorescence sensor for successive detection of Fe³⁺, Cu²⁺ and Hg²⁺ ions based on “on–off” of fluorescence of a single type of gold nanoclusters (Au NCs) is described. Any of the Fe³⁺, Cu²⁺ and Hg²⁺ ions can cause quenching fluorescence of Au NCs, which established a sensitive sensor for detection of these ions respectively. With the introduction of ethylene diamine tetraacetic acid (EDTA) to the system of Au NCs and metal ions, a restoration of fluorescence may be found with the exception of Hg²⁺. A highly selective detection of Hg²⁺ ion is, thus, achieved by masking Fe³⁺ and Cu²⁺. On the other hand, the masking of Fe³⁺ and Cu²⁺ leads to the enhancement of fluorescence of Au NCs, which in turn provides an approach for successive determination of Fe³⁺ and Cu²⁺ based on “on–off” of fluorescence of Au NCs. Moreover, this assay was applied to the successful detection of Fe³⁺, Cu²⁺ and Hg²⁺ in fish, a good linear relationship was found between these metal ions and the degree of quenched fluorescent intensity. The dynamic ranges of Hg²⁺, Fe³⁺ and Cu²⁺ were 1.96 × 10⁻¹⁰–1.01 × 10⁻⁹, 1.28 × 10⁻⁷–1.27 × 10⁻⁶ and 1.2 × 10⁻⁷–1.2 × 10⁻⁶ M with high sensitivity (the limit of detection of Fe³⁺ 2.0 × 10⁻⁸ M, Cu²⁺ 1.9 × 10⁻⁸ M and Hg²⁺ 2 × 10⁻¹⁰ M). These results indicate that the assay is suitable for sensitive detection of these metal ions even under the coexistence, which can not only determine all three kinds of metal ions successively but also of detecting any or several kinds of metal ions.     

Metallacycle-based complexes based on a flexible pyridyl–benzimidazole derivative

Three new coordination complexes, {Cd(pbmb)(NO₃)₂} _n (1), {Ag(pbmb)(NO₃)(C₃H₆O)} _n (2), and {Hg₂(pbmb)₂Cl₄} _n (3), have been synthesized under solvothermal or solution reactions based on a flexible N-heterocyclic ligand 1-((2-(pyridin-4-yl)-1H-benzoimidazol-1-yl)methyl)-1H-benzotriazole (pbmb) and structurally characterized by single-crystal X-ray diffraction, IR spectrum, and elemental analyses. Both 1 and 2 display a 1-D chain structure with metallacycle unit while 3 shows a binuclear cycle motif. The aromatic rings are directing groups for π?···?π stacking interactions. The π?···?π interactions and hydrogen bonds extend the simple chain structure and binuclear structure to 3-D supramolecular architectures. Complexes 1 and 3 exhibit strong luminescence in the solid state at room temperature whereas 2 shows fluorescence quenching.     

PVC membrane sensor based on periodate—Cetylpyridinium ion pair for the potentiometric determination of periodate

A new plasticized membrane sensor has been proposed for the determination of periodate based on periodate-cetylpyridinium ion pair complex. The electrode shows a linear, reproducible and stable potentiometric response with anionic Nernstian slope of 58.1 ± 0.5 mV/decade over a wide range of concentrations 10⁻⁵–10⁻² M and a detection limit of 2.0 × 10⁻⁶ M of IO₄⁻. The membrane exhibits a fast response time of 30–40 s which is independent of pH in the range 2.0–9.0. The selectivity coefficients indicate excellent selectivity for periodate over a large number of anions, e.g. iodide, bromide, chloride, iodate, bromate, nitrate, sulfate, phosphate, thiocyanate, chromate, thiosulfate, sulfite, perchlorate, citrate, acetate, oxalate, and nitrate. The prepared sensor has been successfully used for the determination of periodate (IO₄⁻) and iodate (IO₃⁻) ions with an average recovery of 99.84 ± 0.34% and 98.22 ± 0.43%, respectively. It is also applied to the determination of hydrazine compounds and aminophenol derivatives with an average recovery of 98.66 ± 0.53% and 98.40 ± 0.56%, respectively. Also, the proposed sensor was used for the determination of potassium iodate in iodized table salt and hydrazine in steam boiler feed water and p-aminophenol. The results obtained are in good agreement with those obtained by standard methods.     

Bent‐core mesogens based on semi‐flexible dicyclohexylmethane spacers

New, bent‐core mesogens are described in which the core of the molecule is a semiflexible, di(4‐aminocyclohexyl)methane spacer. The compounds show nematic, columnar nematic and columnar phases as shown by a combination of X‐ray diffraction and optical microscopy. The potential of these new mesogens as biaxial nematic candidates is considered.     

Novel colorimetric sensor for mercury (Ⅱ) based on layer-by-layer assembly of unmodified silver triangular nanoplates

A simple layer-by-layer deposition technique was used to fabricate the multilayer thin films of unmodified silver triangular nanoplates(AgTNPs).The multilayer of AgTNPs thin films were fabricated by alternate deposition of each anionic sodium citrate stabilized AgTNPs and cationic poly(diallyldimethylammonium chloride).All prepared AgTNPs multilayer thin films were exhibited a strong plasmon band at the wavelength of 667 nm,which confirmed the formation of AgTNPs onto the substrate.The characteristics of the multilayer thin films were investigated using contact angle measurement,UV-visible spectroscopy,X-ray diffraction analysis(XRD),atomic force microscope(AFM)and field emission scanning electron microscope(FESEM).As these films are to be used as a mercury(II)colorimetric sensor,the changes in optical properties of the films were evaluated for various mercury(Ⅱ)concentrations.AgTNPs assembled into thin films showed a strong color shift from blue to mauve and colorless when exposed to mercury(Ⅱ).The constructed multilayer thin films exhibited excellent color changes of mercury(II) with a linear range between 0.5 and 20 ppm.The limit of detection(LOD) and limit of quantitation(LOQ) were 0.45 ± 0.002 and 1.52 ± 0.002 ppm,respectively.The recovery values of AgTNPs multilayer thin films are satisfactory in the range of 100.1%-106.4%when applied to determining mercury(Ⅱ) in water samples.     

Colorimetric assay for T4 polynucleotide kinase activity based on the horseradish peroxidase-mimicking DNAzyme combined with λ exonuclease cleavage

T4 polynucleotide kinase (PNK) plays a critical role in various cellular events. Here, we describe a novel colorimetric strategy for estimating the activity of PNK and screening its inhibitors taking advantage of the efficient cleavage of λ exonuclease and the horseradish peroxidase-mimicking DNAzyme (HRPzyme) signal amplification. A label-free hairpin DNA with the sequence of HRPzyme was utilized in the assay. The 5′-hydroxyl terminal of the hairpin DNA was firstly phosphorylated in the presence of PNK and then digested by λ exonuclease. As a result, the blocked ‘HRPzyme’ sequence of the hairpin DNA was released due to the removal of its completely complementary sequence. Using this strategy, the assay for PNK activity was successfully translated into the detection of HRPzyme. Because of the completely blocking and efficiently releasing of HRPzyme, the colorimetric method exhibited an excellent performance in PNK analysis with a low detection limit of 0.06 U mL⁻¹ and a wide detection range from 0.06 to 100 U mL⁻¹. Additionally, the effects of different inhibitors on PNK activity were also evaluated. The proposed strategy holds great potential in the development of high-throughput phosphorylation investigation as well as in the screening of the related drugs.     

Flow injection chemiluminescence sensor based on core–shell magnetic molecularly imprinted nanoparticles for determination of sulfadiazine

A novel flow injection chemiluminescence (FI-CL) sensor for determination of sulfadiazine (SDZ) using core–shell magnetic molecularly imprinted polymers (MMIPs) as recognition element is developed. Briefly, a hydrophilic MMIPs layer was produced at the surface of Fe₃O₄@SiO₂ magnetic nanoparticles (MNPs) via combination of molecular imprinting and reversible stimuli responsive hydrogel. And it provided the MMIPs with excellent adsorption capacity and rapid adsorption rate due to the imprinted sites mostly situated on the surface of MMIPs. Then the prepared SDZ-MMIPs were packed into flow cell to establish a novel FI-CL sensor. The sensor provided a wide linear range for SDZ of 4.0 × 10⁻⁷ to 1.0 × 10⁻⁴ mol L⁻¹ with a detection limit of 1.54 × 10⁻⁷ mol L⁻¹. And the relative standard deviation (RSD) for the determination of 1.0 × 10⁻⁶ mol L⁻¹ SDZ was 2.56% (n = 11). The proposed method was applied to determine SDZ in urine samples and satisfactory results were obtained.     

A new fluorescent chemosensor for iron(III) based on the β-aminobisulfonate receptor

A simple fluorescent sensor 1 has been developed for the determination of Fe(III) in 100% aqueous solution at pH 7.0. The sensor comprises a novel aminobisulfonate receptor joined to a naphthalene fluorophore via a methylene spacer in the fluorophore-spacer-receptor format of photoinduced electron transfer (PET) based sensors. The fluorescence emission of the sensor was quenched upon addition of Fe(III) ions, most likely due to electron/energy transfer between Fe(III) and the excited naphthalene. The sensor displayed good selectivity for Fe(III) over other physiologically relevant metal ions and can estimate Fe(III) concentration between 16 and 63 μM. Stern Volmer analysis showed the binding stoichiometry to be 1:1 (host-guest) with a binding constant, calculated using the Benesi-Hilderbrand equation, of (7.6 ± 0.6) × 10⁴ M⁻¹.     

A sensitive amperometric sensor for hydrazine based on Pt nanoparticles-reduced graphene oxide–multi-walled carbon nanotubes composite

The platinum nanoparticles-reduced graphene oxide-multi-walled carbon nanotubes composite (PtNPs-rGO-MWCNTs) has been synthesised by one-step chemical co-reduction strategy in ethylene glycol (EG) system using sodium citrate as reducing agent. The X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), as well as the electrochemical methods have been used for the characterisation of this composite. Benefiting from the large effective surface and good carrier function of rGO-MWCNTs, PtNPs in this nanocomposite have some excellent characteristics such as small particle size, good dispersion, as well as high electrocatalytic activity. Based on this, a new electrochemical sensor for hydrazine has been fabricated using dropping method. Under the optimum conditions, the linear range for the determination of hydrazine by amperometry at 0.20 V (vs. SCE) in phosphate buffer (pH 7.0) is from 2.0 × 10^?7 mol L^?1 to 2.3 × 10^?3 mol L^?1. The detection limit and sensitivity is 4.5 × 10^?8 mol L^?1 (S/N = 3) and 219.7 μA mM^?1, respectively. This sensor has some attractive analytical features such as low detection limit, wide linear range, high sensitivity, as well as good stability.     

Construction and application of an electrochemical sensor based on graphene-MXene nanocomposites for baicalin detectionEI北大核心CSCD

Redox graphene-MXene(rGO-MXene) nanocomposites were prepared by ion polymerization and used to construct a highly sensitive electrochemical sensor for baicalin(BA) detection. The synergistic effect of rGO and MXene increased the specific surface area and electron transport capacity of the electrode, and significantly enhanced the electrochemical response of BA. The cyclic voltammetry and differential pulse voltammetry were used to investigate the electrochemical behavior of BA on the sensor. Under the optimal conditions, the peak current exhibited a good linear relationship with BA concentration in the range of 0. 05-10 μmol / L, and the limit of detection was as low as 28 nmol / L. The method was applied to analyze traditional Chinese medicine preparations containing baicalin, such as Qingkailing Capsule and Sanhuang Tablets with good accuracy and spiked recovery. The results were highly consistent with those of high performance liquid chromatography, providing a technical means for the rapid and sensitive detection of traditional Chinese medicine preparations. © 2022, Youke Publishing Co.,Ltd. All rights reserved.     

A new “naked-eye” colorimetric and ratiometric fluorescent sensor for imaging Hg2+ in living cells

A new oligothiophene-based sensor 3 TH for monitoring Hg²⁺ has been designed and synthesized based on the intramolecular charge transfer (ICT) mechanism. The 3 TH shows the significant specificity toward Hg²⁺ through “naked-eye” colorimetric detection as well as via ratiometric fluorescence enhancement response with low detection limit of 62 nM. In addition, sensor 3 TH shows high selectivity and sensitivity for Hg²⁺ with fast response in a suitable pH range. Moreover, the 3 TH-based test strips was used to conveniently detect Hg²⁺ ions in water. Furthermore, considering its good ‘‘turn-on’’ fluorescent sensing behavior and low cell cytotoxicity, 3 TH was successfully applied to detect and image Hg²⁺ in real water samples and living cells, which shows great potentials for application in environmental and biological systems.     

Colorimetric sensor array–smartphone–remote server coupling system for rapid detection of saccharides in beverages

A kind of “colorimetric sensor array–smartphone–remote server” coupling system was constructed for rapid on-site testing of saccharides. First, the binding capacity between saccharides and boric acid compounds (boric acid, phenylboronic acid and 3-nitrophenylboronic acid) was studied. The binding capacity of 3-nitrophenylboronic acid was found to be the highest, followed by phenylboronic acid and boric acid. Then a small-scale colorimetric sensor array (2 × 2) of pH indicator based on affinity interaction between 3-nitrophenylboronic acid and saccharides was developed to detect 19 kinds of saccharides. A camera phone was used to acquire the array images before and after reaction, then the self-developed color discrimination software in smartphone was applied to process pictures in order to obtain the color difference image and data of analytes. The color difference data were analyzed by several methods, including principal component analysis, hierarchical cluster analysis and linear discriminant analysis. The analysis results showed that the sensor array (2 × 2) established in this paper has great discriminative capability for 19 kinds of saccharides, and the classification accuracy is as high as 100%. Nineteen different quantitative models of saccharides that showed high accuracy and precision were established based on partial least-square method. Finally, the smartphone was connected to a remote server on which the qualitative analysis and quantitative analysis models for analytes had been established. The color difference data obtained by the smartphone were uploaded to the remote server for the qualitative analysis and quantitative analysis of saccharides. The effectiveness of the “colorimetric sensor array–smartphone–remote server” coupling system in rapid on-site detection of saccharides was further verified by the spike and recovery experiments. The qualitative analysis results showed that this coupling system could distinguish all of the analytes without a mistake, and the quantitative analysis results showed that the predicted values for saccharides were close to the real values.     

CuS–MWCNT based electrochemical sensor for sensitive detection of bisphenol A

The rapid and simple detection of bisphenol A is very important for the safety and reproduction of organisms. Here, a sensitive and reliable electrochemical sensor was established for bisphenol A detection based on the high amplification effect of copper sulfide-multi-walled carbon nanotube (CuS–MWCNT) nanocomposites. The flower-like CuS–MWCNT were successfully synthesized by a simple hydrothermal method accompanied by polyvinylpyrrolidone (PVP). Compared with bare glassy carbon electrode (GCE), CuS–MWCNT modified GCE could amplify the electrochemical signals in about ten times, which was attributed to the synergistic effect of CuS and MWCNT. The MWCNT could increase the specific surface area of electrodes and improve the electrode activity. The integration of CuS could further enhance the electrode conductivity as well as accelerate the electron transfer rate. Raman spectra and transmission electron microscope (TEM) were used to characterize the successful fabrication of CuS–MWCNT nanocomposites and its uniform and monodispersed morphology. Under optimizing conditions, the oxidation currents of bisphenol A via the differential pulse voltammetric (DPV) showed a good linear relationship with its concentration in a wide range of 0.5–100 μM, with a detection limit of 50 nM. This electrochemical sensor of bisphenol A provided a convenient and economical platform with high sensitivity and reproducibility, which had great potential in environmental monitoring.     

Novel sensor based on carbon paste/Nafion? modified with gold nanoparticles for the determination of glutathione

Several problems for the direct electrochemical oxidation of reduced glutathione (GSH) challenge the usage of electroanalytical techniques for its determination. In this work, the electrochemical oxidation of GSH catalyzed by gold nanoparticles electrodeposited on Nafion modified carbon paste electrode in 0.04?mol?L^?1 universal buffer solution (pH?7.4) is proved successful. The effect of various experimental parameters including pH, scan rate and stability on the voltammetric response of GSH was investigated. At the optimum conditions, the concentration of GSH was determined using differential pulse voltammetry (DPV) in two concentration ranges: 0.1?×?10^?7 to 1.6?×?10^?5?mol?L^?1 and 2.0?×?10^?5 to 2.0?×?10^?4?mol?L^?1 with correlation coefficients 0.9988, 0.9949 and the limit of detections (LOD) are 3.9?×?10^?9?mol?L^?1 and 8.2?×?10^?8?mol?L^?1, respectively, which confirmed the sensitivity of the electrode. The high sensitivity, wide linear range, good stability and reproducibility, and the minimal surface fouling make this modified electrode useful for the determination of spiked GSH in urine samples and in tablet with excellent recovery results obtained.