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Graphical abstract Highlights • A new MOF-5@PDDA-rGO-Ni nanostructure is successfully synthetized for the first time. • MOF-5@PDDA-rGO-Ni/GCE sensor exercises an extraordinary response towards echinacoside as the first detection. • The ratiometric electrochemical sensor devotes a higher accuracy and repeatability than MOF-5@PDDA-rGO-Ni/GCE that affords. • The reliability and stability of the recommendable assay are fairly validated in real sample sliced Cistanche analysis. Abstract In this work, a brand new nanocomplex (denoted as MOF-5@PDDA-rGO-Ni) is elaborately designed and successfully synthesized meaning the in-situ assembly of porous-morphology Zn-based MOFs (MOF-5) onto the as-prepared PDDA-rGO-Ni (PGN for short) nanocomposites. When this nanocomplex contributes to construct the electrochemical sensor (MOF-5@PGN/GCE), it presents a highly-sensitive response towards echinacoside, and the first measurement for echinacoside by electrochemistry accordingly evolves forward. The crystallization processes are investigated by FT-IR instrument and XRD analysis, as well as micro-morphology of modified materials is visible upon SEM and TEM. Adorably, a novel ratiometric sensor was progressively fabricated by encapsulating methylene blue (MB) molecules into cubic MOF-5 framewoks (MB encased MOF-5@PGN/GCE), and apart from assisting in establishing the analysis method with extreme accuracy and favorable practicality, it dose devote a wider linear scale and a lower detection limit than that MOF-5@PGN/GCE has given out. Drawn from the developed calibration curve using differential pulse voltammetry (DPV) technique, the peak intensity ratio (I Ech /I MB) varies linearly with increased echinacoside concentration in the range of 3.0 × 10−8– 1.0 × 10−6 mol L−1 with limit of detection (LOD) reaching 1.0 × 10−8 mol L−1 (S/N = 3). Additionally, the proposed assay method has been employed to detect echinacoside in real sample sliced cistanche with satisfactory results. [ABSTRACT FROM AUTHOR]

Herein, we developed a high-performance electrochemical aptasensor for the detection of carcinoembryonic antigen (CEA) using highly active peptide-conjugated hemin/G-quadruplex (hGQ-peptide) and porous Pd nanoparticles (PdNPs). Of note, the hGQ-peptide showed an enhanced catalytic activity as compared to the unmodified hGQ, and thus served as efficient electrocatalyst in this biosensor. Porous PdNPs acted as supported matrixes for high immobilization of hGQ-peptide hybrids, aptamer, redox-active toluidine blue (Tb) and alcohol dehydrogenase (ADH), resulting in the formation of ADH/Tb/hGQ-peptide/aptamer/PdNPs as the proposed bioprobes. Upon the sandwich-type specific reaction between aptamer and CEA, the bioprobe was presented on the sensing interface. Highly effective signal amplification could be then achieved by the bioprobe catalyzed cascade enzymatic reaction. Compared with the original hGQ, the hGQ-peptide yielded more than 2-fold improvement in signal amplification because of the peptide-enhanced catalysis. Therefore, the designed aptasensor displayed a wide linear range from 0.0001 to 100 ng mL −1 with a lower detection limit of 20 fg mL −1 for CEA determination, presenting the better analytical performance as compared to the relevant prior biosensors. This work further expanded the application of hGQ DNAzyme in biosensor. With the good anti-interference ability and selectivity, the proposed electrochemical aptasensor held great promise for ultrasensitive detection of other proteins in clinical diagnosis. [ABSTRACT FROM AUTHOR]

With the aid of polyaniline (PANI), multi-wall carbon nanotubes (MWCNTs) were vertically arrayed on electrode surface by Langmuir–Blodgett technology, which was a novel preparation strategy of vertically aligned MWCNTs modified electrode. The proposed method was applied to design a sensitive voltammetric sensor for the determination of daidzein. Compared to the randomly dispersed MWCNTs modified electrode, a lower detection limit (8 × 10 −8 mol L −1 ) and wider linear range (1.0 × 10 −7 –9.0 × 10 −6 mol L −1 ) were achieved by the proposed sensor. The results indicated that the aligned morphology of MWCNTs could effectively facilitate the transportation of electrons and electrolyte ions. [ABSTRACT FROM AUTHOR]

Langmuir–Blodgett (LB) film of C-Undecylcalix[4]resorcinarene (CUCR) as molecular receptor and pretreated glassy carbon electrode (GCE) as enhancer of electron transfer are integrated in the electrochemical sensor system. The new electrochemical sensor possesses the properties of calixarene (high supramolecular recognition and enrichment capability) and pretreated GCE (large surface area and high active sites). At the resulting electrode, the peak current of dopamine (DA) and uric acid (UA) increased dramatically compared with that on the bare GCE and pretreated GCE which due to the synergetic effects of LB film of CUCR and pretreated GCE. Using differential pulse voltammetry, the resulting electrode was applied to develop a high sensitive electrochemical sensor for the simultaneous determination of DA and UA in the presence of ascorbic acid (AA) for the first time. Under the selected conditions, the linear response ranges for DA and UA are 8.0 × 10 −8 to 6.0 × 10 −6 mol L −1 and 4.0 × 10 −7 to 4.0 × 10 −5 mol L −1 , with the detection limits of 2.0 × 10 −8 mol L −1 and 8.0 × 10 −8 mol L −1 , respectively. Besides, the resulting electrode also showed an excellent selectivity, stability and reproducibility. [ABSTRACT FROM AUTHOR]

A new type of voltammetric sensor, Langmuir-Blodgett (LB) film of multi-walled carbon nanotubes (MWCNTs) perpendicularly modified glassy carbon electrode (GCE), was prepared and applied in determination of methylparaben. Based on the excellent electrochemical property of vertical MWCNTs on the GCE (MWCNTs-LB/GCE), a sensitive voltammetric method for determination of methylparaben was erected with liner range from 1 × 10 −6 mol L −1 to 8 × 10 −5 mol L −1 and detection limit of 4 × 10 −7 mol L −1 . The electrochemical characters of MWCNTs-LB/GCE were investigated in detail and the reaction mechanism of methylparaben was discussed. Meanwhile, cosmetic samples were analyzed using proposed method and the results obtained were well satisfactory. [ABSTRACT FROM AUTHOR]

The electrodeposition of reduced graphene oxide (ERGO) film with preferred vertical orientation was fabricated on a glassy carbon electrode by using pulse potential method in a graphene oxide colloidal solution. Using square wave adsorptive stripping voltammetry (SWASV), the ERGO film was applied for the first time, in developing a high-sensitive electrochemical sensor for detection of taxifolin. Compared with bare glassy carbon electrode (GCE), the resulting electrodes (ERGO/GCE) exhibited excellent response toward the redox of taxifolin by significantly enhancing the redox peak currents and decreasing the peak-to-peak separation. Under the selected conditions, the peak currents were linear relationship with taxifolin concentration in the range of 1.0 × 10 −8 –1.0 × 10 −6 mol L −1 , with detection limit of 2.0 × 10 −9 mol L −1 . Besides, the ERGO/GCE also exhibited an excellent selectivity, stability, reproducibility and repeatability. [ABSTRACT FROM AUTHOR]

Abstract: A new and sensitive sensor for morphine, based on electrochemically reduced MWNTs-doped graphene oxide (ER-MWNTs-doped-GO) composite film modified glassy carbon electrode, was reported. Electrochemical impedance spectroscopy and scanning electron microscopy were employed to study the characteristic of the ER-MWNTs-doped-GO film. The electrochemical behaviour of morphine on this sensor was investigated in pH 4.5 phosphate buffer solution by cyclic voltammetry and linear sweep voltammetry. Significant advantages were achieved by combining the excellent conductivity of MWNTs and ER-GO with the film forming properties of GO. And some merits for response towards morphine from this sensor were showed such as wide linear range, fine selectivity and sensitivity, low detect limit and easy surface renewing. The application of the proposed method in analysis of real sample was also evaluated with good performance. [Copyright &y& Elsevier]

A facile and highly sensitive electrochemical sensor for kaempferol was fabricated by doping polyvinyl pyrrolidone cladding quantum dots to the carbon paste electrode. The quantum dots were characterized with transmission electron microscopy, ultraviolet spectrum and infrared spectrum. The electrochemical behaviors and kinetic parameters of kaempferol were investigated on the sensor by cyclic voltammetry and chronocoulometry in NaAc–HAc (pH 4.4). The proposed sensor accelerated the redox processes of kaempferol obviously, and the oxidation currents were linearly relationship with kaempferol in two concentration intervals: one was 6.0×10−8–2×10−6 mol/L and the other was 5.0×10−6–2.5×10−5 mol/L. The quantification limit obtained by square wave voltammetry was 6.0×10−8 mol/L. Merits such as extreme simplicity, low cost, good sensitivity, high sensitivity, good stability and reproducibility made it an excellent electrochemical sensor for kaempferol. A new electroanalytical method for kaempferol was proposed and used for determination of kaempferol in tablets with satisfactory results. [ABSTRACT FROM AUTHOR]

A new electrochemical sensor for codeine was fabricated based on composite graphene and Nafion film modified glassy carbon electrode. It was found that the electrochemical response of this sensor was greatly improved and displayed excellent analytical performance for codeine detection, which could be attributed to the high codeine loading capacity on the electrode surface and the outstanding electric conductivity of graphene. Under the optimized conditions at pH 4.0, the peak currents were linear relationship with codeine concentrations in the range of 5×10−8 to 9×10−6 molL−1 and 9×10−6 to 3×10−5 molL−1, using square wave voltammetry with a detection limit of 1.5×10−8 molL−1. The proposed method was successfully applied to the determination of codeine in both urine samples and cough syrup. [ABSTRACT FROM AUTHOR]

Abstract: A glassy carbon electrode (GCE) modified with a Langmuir–Blodgett (LB) film of p-tert-butylthiacalix[4]arene (TCA) has been investigated as a disposable sensor for measuring the trace levels of lead and cadmium. The possibility of determining lead and cadmium at trace levels was examined with differential pulse stripping voltammetry in the measurement step. The electrochemical response was characterized with respect to supporting electrolyte, pH of solution, accumulation time, accumulation potential, layers of the LB films, and possible interferences. Calibration plots were found to be linear in the range 2×10−7 to 5×10−5 moll−1 (Cd2+) and 1×10−7 to 2.5×10−5 moll−1 (Pb2+); the detection limits were 2×10−8 moll−1 (Cd2+) and 8×10−9 moll−1 (Pb2+). Possible recognition mechanism was also discussed. From the analysis of real samples (river, lake and tap water) it can be concluded that the method is sensitive and reproducible in determining of these elements and can be used in the analysis of natural water samples. [Copyright &y& Elsevier]

Abstract: A glassy carbon electrode (GCE) coated with Langmuir–Blodgett (LB) film of p-allylcalix[4]arene is described for simultaneous determination of traces of thallium and cadmium in environmental water. The LB film electrode in a 0.1M KH2PO4 solution shows a linear voltammetric response in the range of 5–250μgl−1 for thallium and 10–300μgl−1 for cadmium. The detection limits of thallium(I) and cadmium(II) are estimated to be 1.0μgl−1 (ca. 5.0×10−9 M) and 2.2μgl−1 (ca. 2.0×10−8 M), respectively. Above all, the indium does not respond to this LB film electrode. [Copyright &y& Elsevier]

• A novel structural of DNA nanotweezer is designed to construct electrochemical DNA biosensor. • Split G-rich sequences on the periphery of DNT is not only used as signal generator but also can reduce the background signal to improve sensitivity. • The preparation of this biosensor is convenient and inexpensive. • This DNA biosensor has high sensitivity, well stability and reproducibility for circulating tumor DNA detection. In this work, a label-free electrochemical biosensor for DNA assay was constructed based on a novel structural DNA nanotweezer (DNT) coupled with split G-quadruplex. The novel DNT consists of a long single strand with two hairpin structures in the middle as a recognition element and two short single strands with split G-rich sequences at outsides as a signal reporter. The target triggered two hairpin structures hybridized with each other, it caused the DNT transformation from "open" to "close". The "closed" DNT facilitated the split G-rich sequences combined together and provided electrochemical signals. Here, the hairpin structures were not only used for specific target identification but also avoided the false positive signals and improved the sensitivity. Additionally, the split G-rich sequences were put at outsides instead of insides, which significantly improved the signal-background ratio. Moreover, the construction of this biosensor was convenient and easy to control, which was beneficial to reduce the error generated by the operation process and improve stability and reproducibility. Under the optimal conditions, the proposed assay achieved a low detection limit (22 aM) and a wide linear range (1 fM to 1 nM) for circulating tumor DNA determination. This efficient and convenient DNT can be used as a template in electrochemical biosensors fabrication. [ABSTRACT FROM AUTHOR]

• A label-free and ultrasensitive DNA biosensor was constructed. • A novel simple multiple strand displacement reaction (MSDR) strategy was employed. • The MSDR was coupled with hybridization chain reaction for signal amplification. • The constructed biosensor achieved a low detection limit of 0.56 fM for Type b3a2 detection. Herein, a novel simple multiple strand displacement reaction (MSDR) coupled hybridization strand reaction (HCR) was proposed for label-free and ultrasensitive Type b3a2 assay. First, two kinds of messenger DNAs (mDNAs) were aligned on a long substrate strand DNA, which was immobilized on magnetic beads. Unlike traditional SDR, in the presence of target and a hairpin DNA, MSDR would be initiated and achieve target-recycling as well as the release of two mDNAs. Finally, one target input can convert into multiple mDNAs, which greatly increased the utility ratio of target. After magnetic separation, the released mDNAs can hybridize with the hairpin DNA immobilized on the electrode to trigger HCR and form a linear duplex-DNA structure. It can be used as an excellent template to in-situ grown silver nanoparticles (AgNPs) to generate electrochemical response directly. By taking advantage of MSDR as well as HCR, the electrochemical signal was amplified significantly. Under optimal conditions, this developed biosensor achieved a low detection limit of 0.56 fM (S/N = 3) and a wide linear range from 10 fM to 10 nM for sensitive detection of Type b3a2 with good selectivity and stability. [ABSTRACT FROM AUTHOR]