Food safety has received great attention due to its close connectivity with people's health and the harmonious development of national economy and society. Trace amount of toxic and harmful compounds in food and water are potentially harmful to human health. Excellent adsorbent and efficient extraction have received more and more attention in food safety detection. Metal-organic frameworks (MOFs) are an emerging class of porous functional materials with high porosity, large surface area, easy structural design, adjustable pore size, as well as acceptable chemical and thermal stability. In the past, the research on MOFs mainly focused on the structural design. Recently, more and more attention has been focused on applications of MOFs in food safety analysis. Meanwhile, their high porosity, tunable surface functionalities, various metal and ligands, as well as diverse coordination modes make MOFs promising as adsorption material for SPE. The merits of MOFs and their functional materials, in particular, are high enrichment, excellent matrix interference resistance, good selectivity, and environmentally-friendly development. Interesting research of MOFs and their functional materials in the pretreatment of food and water samples are summarized.

How to improve the accuracy of target detection substance in low-content and complex of real sample, which is still a major challenge in the analysis field. There is no doubt that the internal standard method is the best choice in the analysis methods. The internal standard method of ECL strategy can furnish more accurate detection results in the changeable complex environment, and it can dispel the primary vaguest interference in the system through the self-calibration of two emission spectra. Herein, we effectually explored a strong and stable bimodal ECL system based on graphitic carbon nitride quantum dots (g-CNQDs) as single luminophore in the presence of double coreactants potassium persulfate (K2S2O8) and tetrabutylammonium bromide (TBAB) under the optimized conditions. ECL-1 at 2.82 V and ECL-2 at 1.73 V were observed when the potential was scanned between -3 and 3 V at the scan rate of 0.2 V·s-1. The ECL-1 was responding to the analyte, that is, ascorbic acid (AA) and the ECL-2 was not for a certain concentration of AA; hence, the developed bimodal ECL system was used as internal standard method for quantitative AA in human serum due to the different sensitivity of the double-peak ECL signals to the target analytes. The linear relationships were obtained based on the ln I (ECL-1/ECL-2) against the concentration of AA in the concentration range of 3.5 to 330 nM, with a detection limit of 110 pM (S/N = 3).

A novel and highly sensitive photoelectrochemical biosensor for the detection of glucose based on ternary nanocomposites of Au/CuS/TiO2 (Au/CuS/TiO2) has been fabricated. Highly ordered TiO2 nanotube arrays (TiO2 NTs) were prepared by anodization of Ti foils, and CuS nanoparticles (NPs) and Au NPs were deposited on TiO2 NTs by the successive ionic layer adsorption and reaction (SILAR) method. The resultant Au/CuS/TiO2 exhibited excellent photoelectrochemical behavior as a glucose sensor under white light illumination due to the remarkable photocatalytic capabilities of TiO2 and CuS, and the surface plasmonic resonance (SPR) effect of Au NPs. The fabricated Au/CuS/TiO2 non-enzymatic photoelectrochemical sensor showed brilliant catalytic activity, favourable selectivity, good reproducibility and long-term stability for glucose detection under optimized conditions. The linear range was 0.1-3 μM (R = 0.9942) with a detection limit of 0.03 μM (S/N = 3). Moreover, the proposed sensor detected glucose in human serum samples. Thus, Au/CuS/TiO2 appears to be a promising photocatalyst for a non-enzymatic glucose sensor.

An original electrochemiluminescent (ECL) luminophore porphyrin nanosphere-graphene oxide composite (TCPP NS-GO) was prepared. The TCPP NS-GO could produce greatly enhanced ECL in buffer with potassium peroxydisulfate (K2S2O8) as the co-reactant. The enhancement ECL mechanism of TCPP NSGO/K2S2O8 system was investigated in detail. Moreover, The TCPP NS-GO composite had an abundant surface functional group to expand its application, which exhibited high sensitivity and selectivity to Fe3+. The wide linear relationship between ECL intensity and Fe3+ concentration from 0.002 to 5.128 mu mol L-1 (R-2 = 0.998) was found with the detection limit as low as 1 nmol L-1. The ECL quenching mechanism of Fe3+ was proved by UV-vis absorption spectroscopy, Fluorescence emission spectroscopy (FL) and Fourier transform infrared spectroscopy (FT-IR) analysis technology. (c) 2017 Elsevier B.V. All rights reserved.

An ultrasensitive and stable “dual-potential” ratiometric electrochemiluminescence (ECL) sensor is reported for specific DNA, the femtomolar detection limit (0.12 fM, S/N = 3) and high selectivity insure its potential applications in cancer biomarkers searching or monitoring. The excellent performance of the sensor comes from simultaneously fabricated layer by layer structure “target DNA + Hemin / Au-Luminol NPs / DNA* / sl DNA / TGA / QDs / MWNTs / GCE” mode which was based on the enhancing effect of luminol by G-quadruplex / hemin and Au nanoparticles and the quenching effect of CdSe/ZnS by G-quadruplex / hemin. (i) DNA-SH could combine with Au-Luminol NPs via S-Au bond to solve the problem of poor solubility and weak ECL intensity of luminol in neutral medium. (ii) Target DNA and Hemin formed the G-quadruplex / hemin peroxidase mimicking DNAzyme could enhance the ECL of luminol and quench the ECL of CdSe/ZnS simultaneously. (iii) DNA* was employed to increase a certain distance between CdSe/ZnS and Au-Luminol for enhancing the CdSe/ZnS QDs initial ECL intensity. The dual-potential ratiometric mode lower the influence of background and side reaction of the ECL sensor which were the most important factors in trace sensing.

Three-dimensional NiCo2O4 is a kind of superior sensing material owing to its high electron transfer capability, large available surface area and numbers of active sites. In this work, NiCo2O4 of the three-dimensional chestnut-like structure were easily achieved through a one step hydrothermal process. Afterwards, the morphology and structure were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Based on the three-dimensional porous chestnut-like NiCo2O4, an electrochemical sensor for hydrazine (N2H4) detection is fabricated. This electrochemical platform can realize good selectivity, excellent stability, high sensitivity (∼2154.4 μA mM-1 cm-2), and low detection limit (0.3 μM), as well as a wide linear range from 1 μM to 1096 μM. The synergistic effect of nickel-cobalt in such mixed transition metal oxides which Co in Co3O4 is partially replaced by Ni are beneficial for enhancing sensing properties. This study proves that three-dimensional porous chestnut-like NiCo2O4 is electrochemically active for catalytic performance which is particular and promising material for good application in the practical detection of N2H4.

A nitrite electrochemical sensor based on electrodeposition of zirconium dioxide nanoparticles on reduced graphene oxide modified electrode was successfully constructed for the detection of nitrite. The electrochemical behavior of the modified electrode was investigated by cyclic voltammetry and amperometric i-t curve. Under the optimal conditions, the amperometric i-t curve response of the electrode showed a linear relationship with nitrite concentration in the range of 3. 0. 10(-7) - 1. 0 x 10(-6) mol/L and 1. 0 x 10(-6) - 6. 0 x 10(-6) mol/L, and the detection limit was 1. 0 x 10(-7) mol/L (S/N = 3). The fabricated sensor exhibited high sensitivity, good stability and high reproducibility. This sensor was applied for the detection of nitrite in sausage samples with favorable recoveries of 93. 7% - 110. 4% and relative standard deviation (RSD) of 1. 6% - 2. 1%.

Graphitic carbon nitride quantum dots (g-CNQDs) are rarely used in the field of electrochemiluminescence. In this paper, g-CNQDs have a strong and stable electrochemiluminescence (ECL) signal generated in the presence of co-reactant K2S2O8. The ECL signal of g-CNQDs was quenched by the mechanism of resonance energy transfer (RET) between donor g-CNQDs and receptor riboflavin (RF) that is proved by UV-vis absorption spectroscopy, electrochemiluminescence and fluorescence emission spectroscopy analysis technology. Therefore, we achieved detection of the riboflavin content in the drug tablets of vitamin B-2 using ECL and FL. The determination results of ECL showed that the riboflavin content of the drug vitamin B2 (VB2) tablets was consistent with the fluorescence (FL) analysis, with wider linear range of 0.02-11 mu M and lower minimum detection limit of 0.63 nM (S/N = 3) than FL. Hence, the riboflavin content in human serum was further detected using ECL. The relative standard deviation is less than 6.5%, with an acceptable recovery of 95.33%-104.22%, which means that this sensor has potential applications in the actual sample analysis. As a new ECL luminary, g-CNQDs have opened a new field for the development and application of ECL sensor. (C) 2017 Elsevier B.V. All rights reserved.

Development of a highly sensitive nanostructured electrochemical biosensor based on the integrated assembly of horseradish peroxidase (HRP) and single-walled carbon nanotubes (SWNTs) is described. In this study, we describe the use of a sodium cholate suspension-dialysis method to adsorb the horseradish peroxidase (HRP) onto single-walled carbon nanotubes (SWNTs). We demonstrate that HRP–SWNTs conjugates can be assembled into amperometric biosensors which l-cysteine were assembled on a gold electrode through the covalent bond of S–Au and was used as a substrate for the immobilization of enzymes. Direct electron transfer of HRP is realized at SWNTs, and both anodic and cathodic currents of the redox reaction at the l-cysteine–HRP–SWNTs-modified gold film upon electrocatalysis are amplified. Meanwhile, experimental results reveal that HRP is stably immobilized onto the SWNTs and maintains inherent enzymatic activity toward H2O2. The modified electrode shows high sensitivity toward H2O2. A linear response to hydrogen peroxide measurement is obtained over the range from 1.0 × 10−12 to 1.0 × 10−11 M and an amperometric detection limit of 2.1 × 10−13 M due to its bioelectrocatalytic reduction based on direct electron transfer between gold electrode and the active site of the HRP. The biosensor displays excellent operational, storage stability and highly sensitive. The excellent performance validates the integrated assembly as an attractive sensing element for the development of a new hydrogen peroxide amperometric biosensor.

The electrochemical properties of a Prussian blue (PB) electrode were improved by introducing cetyltrimethylammonium bromide (CTAB) and Au nanoparticles (AuNPs) into PB films. The novel hybrid films (PB/CTAB/AuNPs) were fabricated by electrodepositing PB and AuNPs in the presence of CTAB. The electrochemical behavior of the hybrid film in some supporting electrolyte (cations for the K+, Na+, or K+/Na+) was investigated in detail, and well-defined and reversible voltammetric responses were obtained in Na+-based electrolytes. The catalytic activity of the PB/CTAB/AuNPs electrode toward hydrogen peroxide (H2O2) reduction at a neutral pH was also investigated, and the results indicated that the electrochemical reduction of H2O2 in the presence of physiological levels of Na+ was superior to that of a PB-modified electrode. Moreover, the PB/CTAB/AuNPs electrode exhibited good performance, a low detection limit (0.1 mu M), and high stability at a wide range of concentrations (0.882-195 mu M). To determine the performance of PB nanocomposite electrodes in Na+-based phosphate buffers, an amperometric biosensor with a PB/CTAB/AuNPs electrocatalyst was developed. To fabricate this sensor, the enzyme was immobilized in sol-gel and was electrodeposited onto a PB nanocomposite film. The results indicated that the biosensor can be used at a wide range of concentrations (20-400 mu M) and possesses a low detection limit (7 mu M) for glucose. These characteristics demonstrate that PB nanocomposite film can be used as an electron mediator for biosensors in potassium-free phosphate buffers.

The detection of DNA damage is one of the most important topics in the DNA research fields. In this paper, an electrochemical method for the detection of DNA damage by combining the layer-by-layer assembly film with adriamycin (ADM) as an electrochemical probe was developed. Firstly, the layer-by-layer {dsDNA/PEI}n film was prepared by the alternate adsorption of polycationic polyethyleneimine (PEI) and negatively charged natural DNA onto glassy carbon electrode (GCE) surface. Its electrochemical behaviors were characterized by electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV), and the optimal value of n was determined to be 2. Secondly, the {dsDNA/PEI}2 film was immersed into the solution of ADM and the {dsDNA/PEI}2–ADM was obtained. While transferred into the blank solution, the {dsDNA/PEI}2–ADM would gradually release ADM, exhibiting the good reversibility of ADM incorporation. Finally, the DNA damage induced by styrene oxide (SO) was investigated and the promising results showed that the present method can be a useful tool for the detection of DNA damage.