Electrochemical sensing for naphthol isomers based on the in situ growth of zeolitic imidazole framework-67 on ultrathin CoAl layered double hydroxide nanosheets by a reaction-diffusion technique.

It is established that ultrathin layered double hydroxide nanosheets (LDHNS) and zeolitic imidazole frameworks (ZIF) are desirable electrochemical sensing modifiers owing to their large surface area and abundant catalytic sites. Integration of them is thus an effective solution to maximize their electrocatalytic activity. Herein, a novel reaction-diffusion framework (RDF) technique is applied for the in situ growth of ZIF-67 on ultrathin CoAl-LDHNS (CoAl-LDHNS@ZIF-67). In a confined space of the agar gel matrix of RDF, the coordination reaction between organic ligands and CoAl-LDHNS without an additional Co2+ source achieves the controllable growth of ZIF-67 crystals through a long vertical diffusion. The prepared composite comprises both CoAl-LDHNS and ZIF-67 components with a certain ratio and provides a large surface area and amply catalytic sites, thus realizing a rapid transfer of electron and mass. The CoAl-LDHNS@ZIF-67 modified electrode is employed for the simultaneous detection of naphthol isomers by differential pulse voltammetry. Naphthol isomers display anodic reactions with a wide peak potential difference, allowing their simultaneous detection feasible. Voltammetric responses of α-naphthol and ß-naphthol follow good linearity against the concentration in a wide range from 0.3 to 150 µM with limits of detection of 54 and 82 nM, respectively. The proposed sensor also demonstrates excellent selectivity, stability, reproducibility, and practicability for the simultaneous detection of naphthol isomers.

In situ growth of ZIF-67 on ultrathin CoAl layered double hydroxide nanosheets for electrochemical sensing toward naphthol isomers.

Zeolitic imidazole frameworks (ZIF) and ultrathin layered double hydroxide nanosheets (LDHNS) have drawn growing attention in the electrocatalysis field. Combining the merits and maximizing the electrocatalytic activity of each building block in the corresponding composite is imperative but challenging. This work thus proposes a simple strategy for the in situ growth of ZIF-67 on ultrathin CoAl-LDHNS (LDHNS@ZIF-67) without an additional Co2+ source. Thanks to the ultrathin nature, CoAl-LDHNS provide more Co reactive sites for the ordered growth of ZIF-67 nanocrystals on this 2D matrix via coordination interactions between Co2+ and 2-methylimidazole. The obtained LDHNS@ZIF-67 provides more convenient pathways to rapid electron transportation between the basal electrode and analytes. Hence, the modified electrode can be applied for the truly simultaneous detection of naphthol isomers by differential pulse voltammetry. α-naphthol and ß-naphthol exhibit irreversible oxidation peaks at 0.327 and 0.487 V vs. saturated calomel electrode, respectively, making their simultaneous detection feasible. The voltammetric responses of both isomers are linear in concentrations ranging from 0.3 to 150 µM with limits of detection of 62 and 94 nM, respectively. The sensor exhibits advantages including good reproducibility, stability, selectivity, and practicability for the simultaneous detection of naphthol isomers in real water samples.

An assay for Staphylococcus aureus based on a self-catalytic ampicillin-metal (Fe3+)-organic gels-H2O2 chemiluminescence system with near-zero background noise.

A self-catalytic ampicillin-metal (Fe3+)-organic gels (AMP-MOGs (Fe))-H2O2 CL system, which is not influenced by transition metal ions, was studied. A method for CL detection of Staphylococcus aureus (S. aureus) based on the AMP-MOGs (Fe)-H2O2 CL system was achieved. A superior detection limit of 31 CFU mL-1 toward S. aureus was obtained with near-zero background noise.

Versatile "on-off" biosensing of thrombin and miRNA based on Ag(i) ion-enhanced or Ag nanocluster-quenched electrochemiluminescence coupled with hybridization chain reaction amplification.

A novel biosensing platform based on the Ag(i) ion-enhanced or Ag nanocluster (NC)-quenched electrochemiluminescence (ECL) of CdSe quantum dots (QDs) was designed for versatile "on-off" assays of thrombin (TB) and miRNA, in which bipedal molecular machine (BMM)-triggered surface programmatic chain reaction (SPCR) coupled with mesoporous silica nanoparticle (MSN) multiple amplification is used to introduce plentiful QDs and Ag+ ions to significantly improve the ECL signal.

Dendrite-Free Composite Li Anode Assisted by Ag Nanoparticles in a Wood-Derived Carbon Frame.

Using lithium metal as anode in lithium batteries has attracted great attention due to its ultrahigh theoretical capacity of 3860 mA h g-1. However, the uneven deposition of lithium will cause dendrites, resulting in a poor cycling performance. Herein, a dendrite-free Li composite anode is developed by anchoring Ag nanoparticles in a wood-derived carbon (WDC) frame. The composite anode is integrally formed and has enough room for Li deposition due to the aligned open channels preserved from natural wood, which can decrease anode volume change greatly during cycling. The Ag nanoparticles, serving as seeds of lithium deposition, can help in the even deposition of lithium in the channels of carbon matrix due to their lithiophilicity and then avoid lithium dendrite formation. The composite anode exhibits excellent cyclic performance over 450 h at 1 mA cm-2 and over 300 h at 3 mA cm-2. The full cell of Ag-WDC@LFP also exhibits the smallest electrochemical polarization from 0.2 to 5 C, and a stable specific capacity and a high Coulombic efficiency at 1 C after a long time cycle. These results indicate that Ag nanoparticles play an important role in restraining dendrite formation during lithium plating/stripping. The wood-derived composite cathode can achieve no lithium dendrite formation and can be applied in other storage batteries.

Electrochemical Detection of Nitrite in Food Based on Poly (3,4-ethylenedioxythiophene) Doped with Fe3O4 Nanoparticles Loaded Carboxylated Nanocrystalline Cellulose.

Carboxylated nanocrystalline cellulose (CNCC) was prepared by oxidation degradation of microcrystalline cellulose (MCC) using ammonium peroxydisulfate and modified with Fe3O4 nanoparticles to form Fe3O4-CNCC nanocomposite via simple refluxing process. The Fe3O4-CNCC nanocomposite doped poly(3,4-ethylenedioxythiophene) (PEDOT) was successfully decorated on the glassy carbon electrode (GCE) by electrochemical deposition. The PEDOT/Fe3O4-CNCC modified GCE with enlarged real electrochemical surface area was used to determine nitrite with high selectivity, sensitivity and outstanding reproducibility. Using amperometric current-time (i-t) curve, the proposed sensor provided a wider linear range (0.5-2500 ∆M) and a lower detection limit (0.1 ∆M) towards nitrite compared with the method of differential pulse voltammetry (DPV). This analytical method gave good selectivity in the practical measurement of nitrite in pickles.

Aptamer induced multicoloured Au NCs-MoS2 "switch on" fluorescence resonance energy transfer biosensor for dual color simultaneous detection of multiple tumor markers by single wavelength excitation.

An aptamer induced "switch on" fluorescence resonance energy transfer (FRET) biosensor for the simultaneous detection of multiple tumor markers (e.g., AFP and CEA) combining molybdenum disulfide (MoS2) nanosheets with multicolored Au NCs by a single excitation was developed for the first time. Here, AFP aptamer functionalized green colored Au NCs (510 nm) and CEA aptamer functionalized red colored Au NCs (650 nm) are used as energy donors, while MoS2 is used as energy receptor. On the basis of recording the change of the recovered fluorescence intensity at 510 nm and 650 nm upon the addition of targets CEA and AFP, these two tumor markers can be simultaneously quantitatively detected, with detection limits of 0.16 and 0.21 ng mL-1 (3σ) for AFP and CEA, respectively. In addition, it is noteworthy that the developed biosensor can not only realize accurate quantitative determination of multiple tumor markers by fluorescent intensity, but also be applied in semi-quantitative determination through photo visualization. More importantly, confocal microscope experiments prove that serums from normal and hepatoma patients can also be visually and qualitatively discriminated by this FRET-based biosensor with a single excitation wavelength, indicating promising potential of this assay for clinical diagnosis.

Near infrared fluorescent dual ligand functionalized Au NCs based multidimensional sensor array for pattern recognition of multiple proteins and serum discrimination.

Here, a multidimensional sensor array capable of analyzing various proteins and discriminating between serums from different stages of breast cancer patients were developed based on six kinds of near infrared fluorescent dual ligand functionalized Au NCs (functionalized with different amino acids) as sensing receptors. These six kinds of different amino acids functionalized Au NCs were synthesized for the first time within 2h due to the direct donation of delocalized electrons of electron-rich atoms or groups of the ligands to the Au core. Based on this, ten proteins could be simultaneously and effectively discriminated by this "chemical nose/tongue" sensor array. Linear discrimination analysis (LDA) of the response patterns showed successful differentiation of the analytes at concentrations as low as 10nM with high identification accuracy. Isothermal titration calorimetry (ITC) experiment illustrates that Au NCs interacted with proteins mainly by hydrogen bonding and van der Waals forces. Furthermore, the greatest highlight of this sensor array is demonstrated by successfully discriminating between serums from different stages of breast cancer patients (early, middle and late) and healthy people, suggesting great potential for auxiliary diagnosis.

A novel dual-functional biosensor for fluorometric detection of inorganic pyrophosphate and pyrophosphatase activity based on globulin stabilized gold nanoclusters.

A novel ultrasensitive dual-functional biosensor for highly sensitive detection of inorganic pyrophosphate (PPi) and pyrophosphatase (PPase) activity was developed based on the fluorescent variation of globulin protected gold nanoclusters (Glo@Au NCs) with the assistance of Cu2+. Glo@Au NCs and PPi were used as the fluorescent indicator and substrate for PPase activity evaluation, respectively. In the presence of Cu2+, the fluorescence of the Glo@Au NCs will be quenched owing to the formation of Cu2+-Glo@Au NCs complex, while PPi can restore the fluorescence of the Cu2+-Glo@Au NCs complex because of its higher binding affinity with Cu2+. As PPase can catalyze the hydrolysis of PPi, it will lead to the release of Cu2+ and re-quench the fluorescence of the Glo@Au NCs. Based on this mechanism, quantitative evaluation of the PPi and PPase activity can be achieved ranging from 0.05 µM to 218.125 µM for PPi and from 0.1 to 8 mU for PPase, with detection limits of 0.02 µM and 0.04 mU, respectively, which is much lower than that of other PPi and PPase assay methods. More importantly, this ultrasensitive dual-functional biosensor can also be successfully applied to evaluate the PPase activity in human serum, showing great promise for practical diagnostic applications.

Label-free electrochemical aptasensor for adenosine detection based on cascade signal amplification strategy.

In this work, a simple and highly sensitive label-free electrochemical aptasensor for adenosine detection was developed based on target-aptamer binding triggered nicking endonuclease-assisted strand-replacement DNA polymerization and rolling circle amplification (RCA) strategy. The magnetic beads (MB) probe, which was attached the aptamer of adenosine and mDNA, was firstly fabricated. In the presence of adenosine, mDNA was released from MB upon recognition of the aptamer to target adenosine. The released mDNA as the primer activated autonomous DNA polymerization/nicking process and accompanied by the continuous release of replicated DNA fragments. Subsequently, numerous released DNA fragments were captured on the working electrode, and then as initiators to trigger the downstream RCA process leading to the formation of a long ssDNA concatemer for loading large amounts of Ru(NH3)63+. Therefore, a conspicuously amplified electrochemical signal through the developed dual-amplification strategy could be achieved. This method exhibited a high sensitivity toward adenosine with a detection limit of 0.032nM. Also, it exhibited high selectivity to different nucleoside families and good reproducibility. This design opens new horizons for integrating different disciplines, presenting a versatile tool for ultrasensitive detecting organic small molecules in medical research and clinical diagnosis.

Dual ligand co-functionalized fluorescent gold nanoclusters for the "turn on" sensing of glutathione in tumor cells.

In this work, we develop a facile one-step strategy for rapidly preparing dual ligand co-functionalized fluorescent gold nanoclusters (Au NCs) and establish a "turn on" approach for the rapid and selective sensing of glutathione (GSH) in aqueous solution and living cells. The as-prepared Au NCs exhibited orange red fluorescence (λem = 608 nm), a long lifetime (5.62 µs), a large stokes shift (>300 nm), and considerable stability and were systematically characterized by using fluorescence spectroscopy, high-resolution transmission electron microscopy (HRTEM), dynamic light scattering (DLS), X-ray photoelectron spectroscopy (XPS), fluorescence lifetime, infrared (IR) spectroscopy and ultraviolet absorption spectroscopy. Based on the fluorescence recovery induced by competitive coordination with Cu2+ between Au NCs and GSH, the present "turn on" approach offers a high sensitivity and excellent selectivity toward GSH detection with a detection limit of 9.7 nM. More importantly, this "turn on" approach could also be successfully applied for visualizing and monitoring the changes in the intracellular GSH level in Hep G2 cells, providing available potential for diagnostic applications.

DNA-based chemiluminescent nanoprobes for highly sensitive and selective detection of mercury(II) ion.

A simple and sensitive DNA-stablized gold nanoparticle (AuNP)-based chemiluminescent (CL) probe for detecting mercury ion (Hg(2+)) in aqueous solution has been developed. The CL strategy relies upon the catalytic activity of unmodified AuNPs on the luminol-H2 O2 CL reaction, and the interaction of unmodified AuNPs with DNA. The unmodified AuNPs can effectively differentiate unstructured and folded DNA. The DNA desorbs from AuNPs in the presence of Hg(2+), leading to the increase in CL signal. By rationally varying the number of thymine in single-strand oligonucleotides, the detection range could be tuned. Employing single-strand oligonucleotides with 14 thymine in the detecting system, a sensitive linear range for Hg(2+) ions from 5.0 × 10(-10) to 1.0 × 10(-7) mol/L and a detection limit of 2.1 × 10(-10) mol/L are obtained. Changing the number of thymine to 10 and 6, it leads to a narrow detection range but a high sensitivity. Besides, DNA-based CL nanoprobes exhibit a remarkable selectivity for Hg(2+) ions over a variety of competing metal ions.

[Determination and distribution patterns analysis of rare earth elements in sediments of Prydz Bay].

A sensitive quantificational method was developed for the analysis of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, etc. in sediments of Prydz Bay by inductively coupled plasma mass spectrometry, and then the REE distribution patterns were analyzed. The samples were digested by microwave using HNO3-H2O2-HF as oxidant. The results showed that the total contents of rare earth elements in eight sites ranged from 117.35 to 348.63 microg x g(-1) and the maximum value was 2.97 times of the minimum value. The REE distribution patterns of different sites in sediments were basically identical and there was an obvious fractionation between LREEs and HREEs. The linear correlation of the method was preferable (r=0.999 7 - 1.000 0). The RSDs (n=3) were no more than 5.0%, and the relative errors were no more than 10%. The detection limits of rare earth elements reached ng x L(-1) level except for Sc. This method was suitable for the analysis of REEs in sediments with the advantages of rapidness, simplicity, high precision and accuracy.

Mesoporous Fe2O3 microspheres: rapid and effective enrichment of phosphopeptides for MALDI-TOF MS analysis.

Mesoporous Fe(2)O(3) microspheres have been successfully synthesized by the polymerization (urea and formaldehyde)-induced ferric hydroxide colloid aggregation. The urea-formaldehyde resin was removed by calcination in air. The obtained mesoporous Fe(2)O(3) materials have spherical morphology with uniform particle size of approximately 3.0 microm and porous surface with large inter-particle pores of approximately 48.0 nm. The surface area is as large as approximately 33.3 m(2)/g and the pore volume is 0.31 cm(3)/g. The mesoporous Fe(2)O(3) microspheres were used for the enrichment of phosphopeptides for the first time, in which high sensitivity, selectivity and capacity of specifically enriched phosphopeptides were achieved under a mild condition in a relative short time. After enriched from tryptic digest products of beta-casein by the novel mesoporous Fe(2)O(3) microspheres, phosphopeptides can be selectively detected with high intensity in MALDI-TOF mass spectrometry. Elimination of "shadow effect" was observed by using mesoporous Fe(2)O(3) microspheres, and the detectable limitation is 5x10(-10) M. This material is also effective for enrichment of phosphopeptides from the complex tryptic digests of commercial phosphoprotein casein, with much more phosphorylated sites (26 in 27 of total) and higher signal/noise ratio in the MALDI-TOF mass spectrometry, compared to commercial Fe(2)O(3) nanoparticles. It shows a great potential application in the field of rapid and effective isolation of phosphopeptides.

Zeolite nanoparticles with immobilized metal ions: isolation and MALDI-TOF-MS/MS identification of phosphopeptides.

Metal-ion-immobilized zeolite nanoparticles have been applied for the first time to isolate phosphopeptides from tryptic beta-casein digest; the phosphopeptides enriched on the modified zeolite nanoparticles could be effectively identified by MALDI-TOF-MS/MS.