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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]

Chrysin and baicalein are the major flavonoids found in oroxylum indicum, an essential herb in traditional Chinese medicine (TCM). Owing to their similar characteristics and physiochemical property, it is a great challenge to detect both of them simultaneously. In this work, tantalum oxide (Ta 2 O 5 ) particles and chitosan modified carbon paste electrode (Ta 2 O 5 -CTS-CPE) was prepared and characterized by scanning electron microscope (SEM), X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV) and electrochemical impedance spectrum(EIS). Under the optimum conditions, the prepared Ta 2 O 5 -CTS-CPE exhibited excellent electrocatalytic activity toward the oxidation of chrysin and baicalein, and it could serve as the sensor for highly sensitive and simultaneous determination both of them. The linear range is 0.08–4.0 μM for both of them, and the detection limits were determined to be 0.03 and 0.05 μM (S/N=3) for chrysin and baicalein, respectively. Furthermore, the proposed electrochemical sensor displayed high sensitivity, excellent stability and got satisfactory results in oroxylum indicum samples analysis. [ABSTRACT FROM AUTHOR]

Based on data of number of fog and haze days in Baoji City from 1981 to 2013, the changing trends and mutation of number of fog and haze days in Baoji over the past 33 years were analyzed by using trend coefficient, tendency rate, linear regression analysis, anomaly percentage, Mann-Kendall mutation test and sliding t test. The results showed that during the 33 years, the number of fog and haze days in Baoji declined by 16.255 d/10 a, and there was a cyclical turbulence every 6, 15 or 28 years. The frequency of fog and haze weather was the highest in winter, followed by spring and autumn, while it was the lowest in summer. According to the anomaly percentage of the number of fog and haze days in 12 months during 1981 -2013, the anomaly percentage changed most greatly in July, followed by September, October, April, May, June, August, February and March, but it fluctuated less greatly in January. The number of fog and haze days from 1981 to 2013 had obvious mutation trends in a single year and a single season, and mutation types are different. [ABSTRACT FROM AUTHOR]

[Display omitted] • A dual-amplification strategy coupling ExoIII-assisted chain cycling with CHA reaction was used for TOB detection. • A Poly A structure was used to fix the probe and adjust the probe density on the electrode surface. • The biosensor has a regenerative characteristic. Based on ExoIII-assisted nucleic acid circulation and catalytic hairpin assembly (CHA) reaction, a dual-amplification electrochemical biosensors strategy for sensitive detection of tobramycin was presented. When the target was present, the trigger 1 (T1) was released to unfold hairpin DNA (H1), which allowed the ExoIII-assisted nucleic acid circulation to proceed smoothly and create a lot of trigger 2(T2). Following that, the CHA reaction between H2 and H3 proceeded under the catalysis of T2 and produced plenty of H2-H3 complex. Signal probe labeled with ferrocene was immobilized on the electrode ahead by adenine (PolyA). Finally, the H2-H3 complex combined with the probe and the DNA strand labeled with ferrocene (C2) fell off the electrode surface. The above process significantly reduced the electrochemical signal, so the biosensor has a low detection limit of 0.11 nM. Moreover, this biosensor has a satisfactory regenerability. [ABSTRACT FROM AUTHOR]

Abstract: The development of transfection enhancement of liposomes with attributes of high stability and easy handling in gene therapy is challenging. In this study, we report didodecyldimethylammonium bromide (DDAB, a cationic lipid) coated gold nanoparticles (DDAB-AuNPs), which can enhance the transfection efficiency generated by two kinds of commercially available cationic liposomes: Lipotap and DOTAP. It showed that DDAB-AuNPs at the optimal concentrations could produce more than 2 times increase when measuring the number of cells expressed green fluorescent protein and 48-fold increase for luciferase levels after transfection, respectively. The electrophoretic mobility shift assay (EMSA) and confocal laser scanning microscopy (CLSM) experiments showed that more DNA molecules binding to the lipoplexes after adding DDAB-AuNPs. In addition, the flow cytometry (FCM) results indicated that DDAB-AuNPs increased cellular uptake efficiency of DNA molecules, which might account for the enhancement of transfection efficiency. It has also been found that the DDAB-AuNPs could decrease the cytotoxicity of liposomes to the cells. [Copyright &y& Elsevier]

Abstract: DNA was efficiently bound to water-soluble positively charged CdTe quantum dots (QDs) through complementary electrostatic interaction. These QDs–DNA complexes were disrupted and DNA was released by glutathione (GSH) at intracellular concentrations. Interestingly, there was almost no detectable DNA released by extracellular concentration of GSH. The formation of QDs–DNA complexes and GSH-mediated DNA release from the complexes were confirmed by dye displacement assay, electrophoretic mobility shift assay (EMSA), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) experiments. The released DNA retained transcriptional activity and expressed enhanced green fluorescent protein (EGFP) after being transfected into HEK 293 cells. The transfection efficiency measured by flow cytometry (FCM) was comparable with the positive control. The obvious difference of GSH concentration in nature between the intra- and extracellular environments as well as the GSH concentration-dependent triggered release suggests potential applications of these positively QDs in selective unpacking of payload in living cells in a visible manner. [Copyright &y& Elsevier]

In this work, a novel "signal-on" electrochemical peptide biosensor based on peptide-conjugated hemin/G-quadruplex (DNAzyme-peptide) hybrid and rosebud-like MoSe 2 @reduced graphene oxide (MoSe 2 @rGO) nanocomposite, was developed for detection of prostate-specific antigen (PSA). Interestingly, the peptide not only served as recognition probe to detect PSA, but also acted as the enhancer to improve the enzyme activity of hemin/G4, which promoted the detection sensitivity. Up addition of PSA, Fe 3 O 4 -labeled DNAzyme-peptide probe was cleaved, followed by the magnetic separation. The cleaved DNAzyme-peptide was then captured onto the cysteine-modified electrode via the interaction between carboxyl groups of peptide and amino group of cysteine. A strong electrochemical signal was obtained from hemin and further was amplified by the enhanced electrocatalysis of DNAzyme-peptide. Compared to the original DNAzyme, DNAzyme-peptide exhibited more than 3-fold enhancement in signal amplification. And MoSe 2 @rGO amplified the electrochemical signal due to its good conductivity and large surface area. So the proposed strategy detected PSA down to 0.3 fg/mL, and it showed the advantages of simplicity, low cost by avoiding the use of expensive protein enzyme and additional electroactive species. Therefore, the proposed biosensor potentially provided a very effective tool for early diagnosis of cancer by the detection of PSA. Image 1 • A versatile DNAzyme-peptide hybrid with improved peroxidase activity was prepared for the first time. • DNAzyme-peptide acted as protein-recognition probe, signal reporter and electrocatalyst. • Rosebud-like MoSe 2 @rGO was employed as the ideal electrode substrate material. • High sensitivity was achieved by the enhanced electrocatalysis of DNAzyme-peptide and large surface area of MoSe 2 @rGO. [ABSTRACT FROM AUTHOR]

Sensitive and selective analysis of low content nucleic acid sequences plays an important role in pathogen analysis, disease diagnosis and biomedicine. The electrochemical biosensor based on toehold-mediated strand displacement reaction (TMSD) is highly attractive in nucleic acid detection due to their improved sensitivity and rapid response. But the traditional TMSD carried out on the electrode always with low displacement efficiency and complicated electrode operation, resulting in compromised sensing performance. There is a great need to construct a novel TMSD based electrochemical detection strategy to overcome such challenges in nucleic acid detecting. Herein, a triple signal amplification electrochemical aptasensor was developed for ultrasensitive detection of CYFRA21-1 DNA. The dual-output toehold mediated strand displacement reaction (dTMSD) can convert one input to two strands output within one strand displacement cycle. So that it possesses a higher efficiency for improving the sensitivity in comparison with the single-output TMSD. And the fuel strand was configured with a tail to realize successive DNA circuits through self-propelling as a DNA walker. All the above processes were carried out on magnetic beads, which is conducive to achieving effective sample purification and minimizing the background signals. Besides, Exonuclease III was further amplified signal. As a result, through the cascade use of above three technologies, the proposed biosensing strategy realized sensitive detection of target DNA with a low detection limit of 0.35 fM (S/N = 3) and wide linear range (0.5 fM-500 pM). The proposed novel dTMSD combining multiple signal amplification strategies for electrochemical detection of CYFRA21-1 DNA with easy operation not only possesses excellent sensitivity and selectivity, but also has potential application value for monitoring DNA in serum. Meanwhile, the development of highly sensitive and specific CYFRA21-1 DNA detection methods is very important for the prevention and treatment of lung cancer. Schematic illustration of the electrochemical aptasensor based on cascade signal amplification strategy. [Display omitted] • Dual-output toehold mediated strand displacement reaction (dTMSD) effectively increased the output of messenger probe. • Fuel strand-powered DNA walker further catalyzed target DNA circuits. • The dTMSD was undergone on magnetic beads can effectively purify the sample, reduce the background interference. • Exo III realized the recycling of the messenger probe and further enlarged the signal responds. • Ultrasensitive detection for target DNA was achieved by cascade signal amplification strategy. [ABSTRACT FROM AUTHOR]

[Display omitted] • NiCoMnS/rGO was synthesized by one-step hydrothermal method. • NiCoMnS/rGO nanocomposite showed good peroxidase-like activity. • NiCoMnS/rGO/GCE can catalyze H 2 O 2 reduction and glucose oxidation. It is attractive to develop non-noble-metal nanomaterials with large surface area and good conductivity as a high-active catalyst electrode for molecular detection in electrochemical sensors. In this work, we successfully fabricated NiCoMnS/rGO by one-step hydrothermal method, which showed good peroxidase-like activity in an acidic environment. The NiCoMnS/rGO modified electrode exhibited excellent enzyme-free electrochemical catalysis performance for hydrogen peroxide (H 2 O 2) reduction in acidic solutions and glucose oxidation in alkaline solutions. For the detection of H 2 O 2 , this electrochemical sensor displayed a wide linear range from 10.0 μM to 7.5 mM with a low limit of detection of 1.1 μM. As for glucose, it also showed a wide linear range from 50.0 μM to 1.3 mM with a low limit of detection of 1.0 μM. Moreover, it had good stability and reproducibility. It was also used for the determination of H 2 O 2 and glucose in real samples. This nanomaterial held great promise as an enzyme-free sensing platform toward H 2 O 2 and glucose detection. [ABSTRACT FROM AUTHOR]

• Triplex DNA molecular switch recognize different targets and release the same probe molecular. • CuInS 2 /rGO was used to enhance the photocurrent signal. • A universal photoelectrochemical aptasensor was constructed for antibiotic highly selective and sensitive detection. In this work, a universal and convenient photoelectrochemical (PEC) biosensor was proposed to detect antibiotic on the basis of CuInS 2 /rGO and triplex DNA molecular switch. High performance photoactive structure was formed via p-type CuInS 2 nanosphere complexed with rGO, which was employed to enhance the cathode photocurrent. Capture probe (CP) was conjugated onto the photoactive interface through covalent bonding. In the absence of target, the triplex DNA (THMS) was in a closed state. After introducing a target, the interaction between the target and the specific ring part DNA fragment leaded to the dissociation of the THMS and thereby liberated the single strand DNA (SP). The above identification process was completed in the homogeneous solution. Then, SP was captured to the electrode by CP and hybridized to form dsDNA. The steric effect of dsDNA hindered the interfacial charge transfer, resulting in signal-off photocurrent output. By only altering the specific loop section sequence of THMS, different targets can release the same SP, and can be detected on the same sensing platform under the same testing conditions. As proof of principle, three kinds of antibiotics amoxicillin (AMOX), ampicillin (AMP) and tobramycin (TOB) was detected, achieving limit of detection values of 3.17 pM, 0.63 nM and 2.81 fM, respectively. This approach was also used to detect antibiotic residues in food and environmental samples, which provides a promising paradigm for developing universal, high-performance and convenient PEC biosensing platform. [ABSTRACT FROM AUTHOR]

Review: 118 refs. [ABSTRACT FROM AUTHOR]

In this work, we propose a strategy for the fluorescence assay of histidine (His) and cysteine (Cys) by using lanthanide coordination polymer nanoparticles (Ln-CPN) as a fluorescent probe. The Ln-CPN were prepared by self-assembly of adenosine monophosphate (AMP) with Tb3+, i.e. AMP-Tb. The nonluminescent AMP-Tb could be efficiently sensitized by 5-sulfosalicylic acid (SSA). The fluorescence of AMP-Tb-SSA can be remarkably quenched by Cu2+, and that of the resulting Cu/SSA/AMP-Tb can be significantly enhanced by His and Cys. Thus, a specific fluorescence “turn-on” assay for His and Cys was developed by using Cu/SSA/AMP-Tb as a sensing platform. The enhanced fluorescence intensity was proportional to the His and Cys concentration in the range from 0.2 to 150 μM and 0.5 to 200 μM, respectively, with the detection limits of 70 nM and 100 nM. Additionally, taking advantage of a masking agent for His, the differentiation of His from Cys was achieved in our system. Furthermore, the protocol can also work well for analyzing His and Cys in practical plasma samples with recovery in the range of 100.3–104.1%. [ABSTRACT FROM AUTHOR]

Palladium nanoparticles with diameter of around 5–10 nm supported on poly (diallyldimethylammonium chloride) (PDDA)-functionalized graphene composites were prepared by a simple chemical method. As-prepared nanocomposites were characterized by transmission electron microscopy (TEM), x-ray diffraction (XRD), ultraviolet-visible spectrophotometry (UV–vis) and electrochemical techniques, which were clearly demonstrated that palladium nanoparticles were uniformly dispersed on the graphene sheets. Based on the PDDA-Gr-Pd nanocomposites, a new voltammetric sensor was established and exhibited excellent electrocatalytic activity and fast electron transfer rate toward taxifolin. Under the optimal conditions, a lower detection limit of 1×10 −9 mol L −1 (S/N=3) and a wide linear detection range from 4×10 −8 to 1×10 −6 mol L −1 were achieved by square wave voltammetry (SWV). The proposed method was successfully applied for determination of taxifolin in fructus polygoni orientalis with well results. [ABSTRACT FROM AUTHOR]

This work establishes a highly sensitive and simple stripping voltammetric method for the direct determination of trace iodide. In the presence of abounding bromide and appropriate amount of cetylpyridine bromide (CPB), the iodine was accumulated on the glassy carbon electrode surface as ion association complex (CPBI 2 Br). After accumulation for a period of time, a linear sweep potential with negative scanning was applied and the I 2 in CPBI 2 Br was reduced again into the solution. Under the optimization conditions, the stripping signals (peak current) were linear relationship with iodide concentration in range of 3.81×10 −3 µg/mL to 0.114 μg/mL and 0.127 μg/mL to 2.54 μg/mL, with a detection limit of 1.02 ng/mL ( S / N =3) for a accumulation time of 180 s. Determination of trace iodine in pharmaceutical sample, kelp and table salt were performed with high accuracy and satisfactory recovery results. [ABSTRACT FROM AUTHOR]

• P-type CuInS 2 microflower recombined rGO modified ITO was used as photocathode. • Target was recognized by triple helix DNA switch in homogeneous solution. • Ferrocene labeled single stranded DNA was released as signal probe. • Energy level matching between ferrocene and CuInS 2 leaded an enhanced photocurrent. A sensitive signal-on photoelectrochemical aptasensor for antibiotic determination was constructed based on the energy level matching between ferrocene and CuInS 2. P-type CuInS 2 microflower was complexed with reduced graphene oxide (CuInS 2 /rGO) to get photocathode current with good photoelectric conversion efficiency and stability. Then, hairpin DNA (HP) was covalently bonded to the electrode surface. A triple helix DNA (THMS) was used as a molecular switch. After the specific recognition between target and THMS in homogeneous solution, ferrocene labeled probe (Fc-T2) was released. Finally, Fc-T2 was captured by the HP, which leaded the obvious increase of photocurrent for the energy level matching between ferrocene and CuInS 2. The increase of the photocurrent signal was proportional to the concentration of target amoxicillin (AMOX), the linear range was 100 fM-100 nM with detection limit of 19.57 fM. Meanwhile, the method has been successfully applied for milk and lake water samples analysis with satisfactory results. [ABSTRACT FROM AUTHOR]

Various nucleic acid molecular machines have emerged in recent years. However, when the nucleic acid tracks are fully depleted, these walkers are highly susceptible to premature release or stalling in regions where the tracks are locally exhausted. In this work, a molecular walking machine with a cleat domain preventing dissociation from the track was explored for ultrasensitive detection of miRNA. It has been verified that the cleat design can enhance the signal amplification efficiency of molecular walking machines for electrochemical miRNA-141 detection. Notably, the single-step electrochemical biosensing platform utilizing the cleat-equipped molecular walking machine (CMWM) is exceptionally straightforward and rapid, concluding the reaction within 90 min and achieving a remarkable low detection limit of 0.26 fM. The proposed molecular walking machine with this specific cleat structure was utilized for the identification of miRNA-141 in cellular lysates, exhibiting remarkable selectivity and consistent reproducibility, showcasing its effective utility in bioanalysis. Therefore, the cleat walker developed in this study introduces an innovative method for constructing a miRNA electrochemical biosensing platform, offering new perspectives for its application in biomolecule detection and clinical disease diagnosis. A rapid one-step electrochemical method based on cleat-equipped molecular walking machine. [Display omitted] • The cleat DNA walker was successfully designed for miRNA-141 detection. • The cleat design was first applied in nuclease-powered DNA walker. • The cleat strategy can enhance the signal amplification efficiency of DNA walkers. • The proposed one-step method takes only 90 min. [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]

[Display omitted] • The probes were prepared by integrating the dual-enzyme catalytic activity of CuO NPs and luminescent of Ln ICPs via facile self-assembly. • The self-cascade nanoenzyme activity of CuO nanoparticles was significantly enhanced upon encapsulated into Ln ICPs. • A versatile ratiometric platform for ultrahigh selective and sensitive detection of GSH was established. Tandem enzyme can catalyze some cascade reactions with high efficiency, and some few tandem enzyme-like mimics have been discovered recently. Further improving the catalytic efficiency of tandem nanoenzymes with facile method may undoubtedly promote and broaden their applications in various fields. In this work, cupric oxide nanoparticles (CuO NPs) with dual-functional enzyme mimics were synthesized using the rapid deposition method in advance, which simultaneously combined with lanthanide infinite coordination polymers (Ln ICPs) during the self-assemble of Tb3+, guanine-5′-triphosphate (GTP) and auxiliary ligand terephthalic acid (TA). Excitingly, the obtained Tb-GTP/TA@CuO ICPs, not only displayed obviously enhanced tandem catalytic activity compared with pure CuO NPs, but also provided a versatile ratiometric platform for ultrahigh selective and sensitive detection of glutathione (GSH) under single-wavelength excitation. A good linear relationship between the ratio signal and the GSH concentration was spanning from 0.001 to 20 μM with an impressive detection limit of 0.50 nM. This study opens a new and universal avenue for preparing integrated multifunctional probes by coupling of nanoenzyme catalytic activity with superior luminescent Ln ICPs through facile method. [ABSTRACT FROM AUTHOR]

Design and fabrication of integrated multifunctional probes with intrinsic catalytic and detection abilities is of great importance to simplify the operation in biosensing application with high sensitivity. Herein, dual-emitting lanthanide coordination polymers (Ln-CPs) were facilely prepared by self-assembly of guanine diphosphate (GDP), terephthalic acid (TA), Tb3+ and Cu2+ designated as Tb/Cu-GDP/TA CPs. The doped Cu2+ endowed CPs with obviously enhanced peroxidase mimicking activity compared with free Cu2+. In the presence of H2O2, the probe catalyzed the oxidation of TA generating a new blue fluorescent product, while the fluorescence of Tb3+ decreased simultaneously. Therefore, a new sensitive ratiometric fluorescent sensor for H2O2 has been developed with a good linear range from 0.01 to 300 μM and limit of 1.62 nM. Moreover, the proposed platform could be extended to GSH ratiometric assay in the presence of H2O2, and interestingly, the detection performance could be easily adjusted by adding different concentration of H2O2. This work will facilitate the development of luminescent nanoenzymes based on Ln-CPs to construct the simple ratiomatric sensing platform. [ABSTRACT FROM AUTHOR]

Abstract: Nonviral vectors are safer than viral systems for gene therapy applications. However, the limited efficacy always prevents their being widely used in clinical practice. Aside from searching new gene nonviral vectors, many researchers focus on finding out new substances to improve the transfection efficiency of existent vectors. In this work, we found a transfection enhancer, nocodazole (NCZ), for dimethyldioctadecylammonium (DODAB, a cationic lipid) bilayer coated gold nanoparticles (AuNPs) mediated gene delivery. It was found that NCZ produces 3-fold transfection enhancement to HEK 293T cells assessed by flow cytometry (FCM). The result was further confirmed by luciferase assay, in which NCZ induced more than 5 times improvement in transfection efficiency after 48h of transfection. The results from the inductively coupled plasma mass spectrometry (ICP-MS) and FCM showed that NCZ did not affect the internalization of DODAB–AuNPs/DNA complexes. The trafficking of the complexes by transmission electron microscopy (TEM) indicated that the interrupted transportation of the complexes to the lysosomes contributed greatly to the transfection enhancement. Therefore, NCZ can be used as a transfection enhancer in DODAB–AuNPs mediated transfection system. This work also gave an insight to improving the efficiency of lipid-mediated transfection: modifying lipid on gold nanoparticles and pre-treating cells by NCZ before the transfection. [Copyright &y& Elsevier]

Complexing with adenosine-5′-monophosphate (AMP) was proven to be a facile way to enhance the oxidase-mimicking activity of Ce4+, and enabled nanoenzyme recovery and reuse. Additionally, the oxidase-mimicking activity of AMP-Ce4+ infinite coordination polymers (ICPs) could be specifically inhibited by Fe2+. Based on this finding, we developed a simple and highly selective colorimetric assay to detect Fe2+. [ABSTRACT FROM AUTHOR]

In this work, a facile ratiometric fluorescence sensor for GSH measurement was designed based on MnO 2 nanosheet (NS), carbon dots (CDs), as well as a simple substrate o-phenylenediamine (OPD). Herein, MnO 2 NS played triple essential roles in the sensing system. First, it could be reduced by GSH through a special reaction, and therefore served as GSH recognizer. Second, it played as a fluorescence nanoquencher to strongly quench the fluorescence of CDs. Third, it could directly oxidize OPD to yield a luminescent product 2, 3-diaminophenazine (DAP) via the intrinsic oxidase-like activity. It revealed that MnO 2 NS could be reduced to Mn2+ in the presence of GSH. Thus its oxidase-like activity and fluorescence quenching abilities were inhibited, which then restricted the generation of DAP and recovered the fluorescence of CDs. Based on this phenomenon, a novel ratiometric fluorescence sensor for GSH determination was fabricated by measuring the ratio of fluorescent intensity of DAP to that of CDs. Besides, the constructed ratiometric fluorescent sensor, which could be facilely operated with single-wavelength excitation, exhibited high sensitivity and selectivity with a wider linear range and a lower detection limit. Image 1 • A facile single-wavelength excitation ratiometric fluorescence sensor was constructed for GSH. • MnO 2 nanosheets can not only effectively quench the fluorescence of CDs but also oxidize OPD into luminescent DAP due to its intrinsic oxidase-like activity. • DAP could also quench the fluorescence of CDs through the inner filter effect. [ABSTRACT FROM AUTHOR]

[Display omitted] • CuO NSs@Au NFs was used to provide strong cathode current and binding site for aptamer. • Specific binding effect of aptamer and target improved selectivity of the sensor. • The sensor with a wide linear range of 5 pM-300 nM and a low detection limit of 49.9 fM. A signal off type photoelectrochemical (PEC) aptasensor was constructed for the sensitive detection of chloramphenicol based on CuO nanosheets (CuO NSs) and gold nanoflowers (Au NFs) modified indium tin oxide (ITO) electrode. CuO NSs was p-type photoactive semiconductor materials, which had narrow band gap and high absorption rate of visible light. After combining with Au NFs, the composite CuO NSs@Au NFs produced a strong cathodic photocurrent for the excellent electron conductivity, large specific surface area and Surface Plasmon Resonance effect (SPR) of Au NFs. At the same time, Au NFs provided a binding site for aptamer, which greatly improved the sensitivity of the constructed sensing platform. After the target chloramphenicol (CAP) was specifically captured by the aptamers on the electrode, the formed bioconjugates seriously hindered the transfer of electrons and the absorption of light and caused a reduced photocurrent. For the detection of CAP, this signal off type PEC aptasensor had a linear range of 5 pM-300 nM and a limit of detection of 49.9 fM (S/N = 3) with good stability, selectivity and reproducibility. Meanwhile, the method had satisfactory recovery results in the detection of CAP in real-life samples such as milk, tap water, honey and chloramphenicol eye drops. [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]

In this work, a dual amplified signal enhancement approach based on coupling deoxyribozyme (DNAzyme)-driven bipedal DNA walkers (BDW) and terminal deoxynucleotidyl transferase (TdT)-mediated DNA elongation signal amplifications has been developed for highly sensitive and label-free electrochemical detection of thrombin in human serums. In presence of thrombin, the BDW complex, which is comprised from the target thrombin and two DNAzyme-containing probes, can exhibit autonomous cleavage behavior on the surface of the substrate DNA (SD) modified electrode, and remove the cleaved DNA fragment from the electrode surface. Subsequently, the TdT can catalyze the elongation of the SD with free 3′-OH termini and formation of many G-quadruplex sequence replicates with the presence of 2′-deoxyaguanosine-5′-triphosphate (dGTP) and adenosine 5′-triphosphate (dATP) at a molar ratio of 6:4. These G-quadruplex sequences bind hemin and generate drastically amplified current response for sensitive detection of thrombin in a "signal-on" and completely label-free fashion. Under optimized conditions, the response peak current was linear with the concentration of thrombin in the range from 0.5 pM to 100000 pM with detection limit of 0.31 pM. This research provides us a sustainable idea for the hyphenated multiple amplification strategies and a stable and effective method for the detection of protein biomarkers. Image 1 • A new electrochemical biosensor was developed based on dual cascade amplification strategy of DNAzyme-driven bipedal DNA walkers. • The developed electrochemical biosensor was completely label-free in a "signal-on" fashion. • The work proves the possibility of the strategy based on DNA machine hyphenating diversified amplification methods. [ABSTRACT FROM AUTHOR]

Herein, a signal-on electrochemical aptasensor for highly sensitive detection of thrombin (TB) was constructed based on the DNAzyme-driven DNA walker strategy. We developed a new dual functional hairpin DNA (HP) containing a substrate sequence of the Mg2+-dependent DNAzyme (in the loop region) and the G-quadruplex forming segment (in the stem region). The DNA walker (TBA 2 -DWs), containing a TB aptamer and an enzymatic sequence, was introduced onto gold electrode (GE) by aptamers-target specific recognition, and thus initiated the enzymatic sequences to hybridize with the substrate sequence. Then, the DNA walker could repeatedly bind and cleave HP in the assistance of Mg2+, unlocking many active G-quadruplex forming sequences. Finally, hemin can further bind the G-quadruplex to form G-quadruplex/hemin complexes and generate enhanced current output. The aptasensor for TB assay showed a linear detection range from 1 pM to 60000 pM with a lower detection limit of 0.58 pM. And more, the proposed detection strategy was enzyme-free and label-free. Image 1 • A signal-on electrochemical aptasensor based on DNAzyme-driven DNA Walker strategy has been developed. • DNA walker is driven by DNAzyme and induced by dual recognition of target molecules. • A new dual functional hairpin DNA (HP) was developed and used in this electrochemical anpptsensor. • A signal-on electrochemical aptasensor is designed from enzyme-free and label-free. [ABSTRACT FROM AUTHOR]

Due to widespread application of chlorpyrifos for controlling pests in agriculture, the continuous accumulation of chlorpyrifos residue has caused serious environmental pollution.The detection of chlorpyrifos is of great significance for humans and environment because it can arise a series of diseases by inhibiting acetylcholinesterase (AChE) activity. Photoelectrochemical sensing, as an emerging sensing technology, has great potential in the detection of chlorpyrifos. It is urgent that find a suitable photoelectric sensing strategy to effectively monitor chlorpyrifos. Herein, an n-n heterojunction was constructed by uniformly immobilizing n-type 3DBiOI, which had loose porous structure composed of numerous small and thin nanosheets, on the surface of TiO 2 with anatase/rutile (AR-TiO 2) heterophase junction. Under light irradiation, the proposed BiOI/AR-TiO 2 n-n heterojunction exhibited excellent optical absorption characteristics and photoelectrochemical activity. Additionally, the photoelectrochemical sensing platform demonstrated excellent analytical performance in monitoring chlorpyrifos. Under optimized conditions, it showed a wide detection range of 1 pg mL−1- 200 ng mL−1 and a detection limit (S/N = 3) as low as 0.24 pg mL−1, with superior selectivity and stability. The ultra-sensitivity and great specificity for detection of chlorpyrifos can be ascribed to chelation between Bi (Ⅲ) and C=N and P=S bonds in chlorpyrifos, which had been confirmed in this work. Meanwhile, the PEC sensor also had potential application value for monitoring chlorpyrifos in water samples, lettuce and pitaya, which the recoveries of samples ranged from 96.9% to 104.7% with a relative standard deviation (RSD) of 1.11%–5.93%. This sensor provided a novel idea for constructing heterojunctions with high photoelectric conversion efficiency and had a high application prospect for the detection of chlorpyrifos and other structural analogues. [Display omitted] • A novel BiOI/AR-TiO 2 n-n heterojunction was proposed by two-step drop-coated method. • Both AR-TiO 2 and n-type 3DBiOI had superior photoelectric conversion efficiency. • Synergistic effect of AR-TiO 2 and BiOI ensured the excellent performance of sensor. • The chelation of Bi-chlorpyrifos complex gave the sensor excellent selectivity. • This PEC sensor had good recovery results in the analysis of real samples. [ABSTRACT FROM AUTHOR]

Abstract Herein, a label-free and double recognition–amplification (LDRA) strategy for carcinoembryonic antigen (CEA) detection was developed, based on a new designed dual-function messenger probe (DMP) coalescing with DNA tetrahedron probes (DTPs) and hybridization chain reaction (HCR). The DMP possess dual-function to replace CEA for specific interface hybridization and initiate hybridization chain reaction. The interfacial hybridization event was quantitatively converted to an electrochemical signal by using hemin/G-quadruplex (h-Gx) formed after the hybridization chain reaction. Self-assembled DNA tetrahedron probes, which were readily decorated on an electrode surface as a scaffold with rigid support and ordered orientation, enabled the highly efficient strands hybridization and greatly increased target accessibility as well as significantly decreased noise. The proposed assay integrated dual recognition processes and HCR signal amplification processes, achieving the identification of low concentration of CEA as detection limit of 18.2 fg mL−1 (S/N = 3) and wider linearity range of 0.0001 ng mL−1–50 ng mL−1. A new electrochemical sensing method was proposed for CEA detection and used in real clinical samples. The obtained results were good consistency with those of clinical diagnosis. Highlights • A new dual-function messenger probe (DMP) was designed for specific interface hybridization and initiate HCR. • The employment of DNA tetrahedron probes increased the probability of hybridization and reduced the background signal. • The synergetic combination of DMP and hybridization chain reaction (HCR) improved the sensitivity of the detection. • The proposed strategy was used to analysis CEA in real sample and achieved a detection limit as low as 18.2 fg/mL. [ABSTRACT FROM AUTHOR]

A novel type of sandwich MOF was successfully synthesized on reduced graphene oxide (denoted as M@Pt@M-rGO) by an in situ synthesis method. The obtained M@Pt@M-rGO possesses excellent electrochemical properties. The surface morphology and structure of M@Pt@M-rGO were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), etc. By using M@Pt@M-rGO, a novel electrochemical sensor was constructed and successfully used for the simultaneous and sensitive detection of three isomers: hydroquinone (HQ), catechol (CT) and resorcinol (RS), with wider linear ranges of concentrations of 0.05–200 μM, 0.1–160 μM and 0.4–300 μM and lower detection limits of 0.015 μM, 0.032 μM and 0.133 μM (S/N = 3) for HQ, CT and RS, respectively. Besides, the proposed electrochemical sensor showed excellent anti-interference capability, high stability, good reproducibility, and satisfactory recovery for determination of isomers in river and lake water. [ABSTRACT FROM AUTHOR]

Abstract In this work, we proposed a ratiomatric fluorescent strategy for sensing Fe2+ by using the carbon dots (CDs) doped lanthanide coordination polymers (Ln-CPs). Herein, the Ln-CPs were prepared by self-assemble of adenosine monophosphate (AMP) with Tb3+ (AMP-Tb) through coordination reaction, and CDs were encapsulated during the assembly process as guest materials. A cofactor, phenanthroline (Phen), could incorporate into the CDs@AMP-Tb, and strongly sensitized the luminescence of Tb3+ through energy transfer. Therefore, the obtained CDs@AMP/Phen-Tb could emit dual fluorescence signals. One is the characteristic emission of Tb3+, which could be specifically quenched by Fe2+ due to the high affinity between Phen and Fe2+. Another is originated from CDs encapsulated in Ln-CPs, which did not change in the presence of Fe2+. Subsequently, CDs@AMP/Phen-Tb was chosen as the ratiomatric fluorescent probe for sensing Fe2+, where the fluorescence of Tb3+ was quenched serving as the reporter, while that of CDs remained constant serving as the internal control for self-calibration. In addition, with the help of a reducing agent, which can reduce Fe3+ to Fe2+ efficiently, the proposed method can also be applied in selective detection Fe3+. By taking advantage of the unique property of Ln-CPs, the proposed strategy promises flexibility for designing of a series of ratiometric fluorescent sensors and expanded in practical applications. Graphical abstract fx1 [ABSTRACT FROM AUTHOR]

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]

The nanocomposite of ruthenium oxide (RuO 2 ) loaded on Poly-(dimethyldiallylammonium chloride) (PDDA) functionalized reduced graphene oxide (RuO 2 -PDDA-rGO) was synthesized based on a one-step method. Based on the RuO 2 -PDDA-rGO modified glassy carbon electrode (GCE), a new electrochemical sensor (RuO 2 -PDDA-rGO/GCE) was fabricated and used in detection of baicalein for the first time. Compared with other reported electrochemical sensors for the detection of baicalein, the prepared RuO 2 -PDDA-rGO/GCE had a wider linear range (2–400 nM) and lower detection limit (0.6 nM, S/N = 3). The other advantages were the excellent repeatability of proposed method and good stability of prepared sensor. [ABSTRACT FROM AUTHOR]

This work focused on the development of a novel ratiometric fluorescence sensor for detection of Hg 2+ by using dye-doped lanthanide infinite coordination polymer (Ln-ICP) particles. The dye-doped Ln-ICP used herein was prepared by self-assemble of adenosine monophosphate (AMP) with Ce 3+ and Tb 3+ (Ce/Tb-AMP) through self-adaptive chemistry, in which the fluorescent dye coumarin was encapsulated during the assembly process as a guest molecule. Under 310 nm irradiation, the obtained coumarin@Ce/Tb-AMP itself emitted characteristic green luminescence of Tb 3+ , accompanied with a weak fluorescence at 445 nm originated from coumarin encapsulated in the Ce/Tb-AMP networks. The fluorescence emission of coumarin became strong when it was released to the solution. In the presence of Hg 2+ , the coumarin@Ce/Tb-AMP was destroyed due to the specific coordination interaction between AMP and Hg 2+ , which leaded to the release of coumarin to the solution meanwhile. Consequently, the fluorescence of Ce/Tb-AMP was quenched, while that of coumarin enhanced. On the basis of this strategy, we developed a novel ratiometric fluorescent sensor for the detection of Hg 2+ by measuring the ratio of fluorescent intensity of the coumarin@Ce/Tb-AMP suspension, which showed a wide linear range from 0.08 to 1000 nM and detection limit of 0.03 nM with high selectivity and sensitivity. Furthermore, the constructed ratiometric fluorescent sensor was successfully applied in detecting Hg 2+ in drinking water and human blood serum (HBS) with satisfactory results. [ABSTRACT FROM AUTHOR]

This work designed an artificial substrate peptide to synthesize peptide-hemin/G-quadruplex (peptide-DNAzyme) conjugates. In addition to enhancing catalytic activity of hemin/G-quadruplex, the peptide could also be induced and cleaved by prostate specific antigen (PSA). It was the first report on peptide-DNAzyme conjugates in application of the peptide biosensor. The polyethyleneimine-reduced graphene oxide@hollow platinum nanotubes (PEI-rGO@PtNTs) nanocomposites were cast on the glassy carbon electrode in order to form the interface of biocompatibility and huge surface area for bioprobes immobilization. In absence of PSA, the peptide-DNAzyme conjugates retained intact on the surface of the electrode to produce a strong response signal. But in presence of PSA, the peptide-DNAzyme conjugates were destroyed to release electron mediators, resulting in dramatical decrease of the electrochemicl signal. Therefore, the method had high sensitivity and super selectivity with the limit of detection calculated as 2.0 fg/mL. Furthermore, the strategy would be promising to apply for other proteases by transforming the synthetic peptide module of target. [ABSTRACT FROM AUTHOR]

Baicalein and baicalin are the major flavonoids found in Scutellariae Radix, an essential herb which has had a presence in traditional Chinese medicine (TCMs) for more than two thousands of years. Owing to their similar characteristics and physiochemical properties, sensitive, it is a great challenge to detect both of them simultaneously. In this work, a novel, facile and sensitive electrochemical method was proposed based on tantalum oxide (Ta 2 O 5 ), niobium oxide (Nb 2 O 5 ) particles and antiseptic chitosan modified carbon paste electrode (Ta 2 O 5 -Nb 2 O 5 @CTS-CPE). Scanning electron microscope (SEM), X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV) and electrochemical impedance spectrum (EIS) were used to characterize the properties and investigate the electrochemical response of the sensor. The electrochemical behaviors and redox mechanisms of two analytes were investigated at the target electrode. Under the optimum conditions, the highly sensitive and simultaneous determination of baicalein and baicalin was successfully achieved with a linear response range of 0.08–8.0 μM for both of them. The obtained detection limits for baicalein and baicalin were of 0.05 and 0.03 μM (S/N=3), respectively. Furthermore, the proposed sensor displayed high sensitivity, excellent stability and satisfactory results in Scutellariae Radix samples analysis and hydrolysis process analysis of baicalin in vivo . [ABSTRACT FROM AUTHOR]

In this work, poly(sodium p-styrenesulfonate) (PSS)-functionalized graphene supported palladium nanoparticles (Pd) composites were fabricated with simple ultrasonic bath method. The morphology and structure of PSS-GR-Pd composites were characterized using UV–vis absorption spectra, X-ray diffraction and Transmission Electron Microscopy. By combining the merits of the PSS-GR and Pd NPs, a new electrochemical sensor was erected to detect amaranth based on the PSS-GR-Pd nanocomposites. The electrochemical behavior of amaranth was investigated systematically in 0.1 mol L −1 phosphate buffer solution (PBS 2.0). At the optimum parameter, I pa was found to be linearly dependent on the concentrations of amaranth (1×10 −7 –9×10 −6 mol L −1 ). The detection limit was 7 nM (S/N=3) and sensitivity was 5.85 μA μM −1 . Finally, this system was utilized for determining amaranth in soft drink using the standard addition method. [ABSTRACT FROM AUTHOR]

A novel electrochemically activated doped Ta2O5 particles modified carbon paste electrode (EA-Ta2O5-CPE) was prepared and applied for selective and sensitive determination of chrysin. X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) techniques and cyclic voltammetry (CV) were used to characterize the Ta2O5 particles and investigate the electrochemical response of the sensor. Compared with bare CPE, the doped Ta2O5 modified electrode got much more porous by electrochemical treatment and exhibited larger effective surface area, more reactive site and excellent electrochemical catalytic activity toward the oxidation of chrysin. Under optimum conditions by LSV, the oxidation peak currents responded to chrysin linearly over a concentration range from 5.0×10−8 to 7.0×10−6 mol L−1 with a detection limit of 2.0×10−8 mol L−1 (5.08 ng mL−1). The fabricated sensor showed anti-interference ability against the biological common interferents (i.e. baicalein, baicalin) and provided to be reliable for the determination of chrysin in Chinese medicinal herb Oroxylum indicum and chrysin capsules samples with satisfactory results. [ABSTRACT FROM AUTHOR]

A new graphene nanocomposite, CeO 2 -poly(diallyldimethylammonium chloride)-graphene (CeO 2 -PDDA-GR), was prepared by an easy and low-cost hydrothermal method. The images of transmission electron microscopy (TEM) showed that well-shaped CeO 2 nanoparticles distributed more uniformly on the GR sheets. Based on the CeO 2 -PDDA-GR composites modified glassy carbon electrode, the electrochemical properties of eriocitrin were investigated in detail and a sensitive determination method was established synchronously. Differential pulse voltammetry (DPV) measurement revealed that the oxidation peak current increased linearly with eriocitrin concentrations in range of 1.0 × 10 − 8 mol L − 1 –1.0 × 10 − 6 mol L − 1 with detection limit of 7.0 × 10 − 10 mol L − 1 (S/N = 3). Moreover, the proposed method was used in determination of eriocitrin in lemon sample with accurate results. [ABSTRACT FROM AUTHOR]

In this paper, a simple, low cost, highly sensitive voltammetric method for determination of tetrahydropalmatine was described, which was based on a new electrochemical sensor, poly (L-glutamic acid) functionalized electrochemical reduction graphene oxide modified glassy carbon electrode. The electrochemical behavior of tetrahydropalmatine was investigated in detail and some dynamic parameters of electrode process were calculated for the first time. Due to large surface area and good conductivity of proposed sensor, a wider linear range (3.0×10 −7 –2.0×10 −5 mol L −1 ) and lower detection limit (1.0×10 −7 mol L −1 ) were achieved for determination of tetrahydropalmatine. Meanwhile, the proposed method was used in determination of tetrahydropalmatine in Rhizoma Corydalis with well results. [ABSTRACT FROM AUTHOR]

[Display omitted] • Modification of AuNPs improved the stability of p-type CuInS 2 electrodes and provided binding sites for aptamer. • Specific binding effect of aptamer and target allowed photocurrent signal to change with high selectivity. • The cathode PEC sensor can detect tobramycin accurately and efficiently. In this work, A "signal-off" photoelectrochemical aptasensor was proposed for the ultrasensitive detection of tobramycin. Different from other common n -type semiconductors, p-type semiconductor CuInS 2 was used as the photocathode material in this sensor construction, which had strong anti-interference ability and reduced the occurrence probability of the false signal. Moreover, the compound of gold nanoparticles and CuInS 2 increased the stability of the photocathode. In the presence of tobramycin, it can be well recognized by specific aptamers mounted on the electrode surface, which resulted in decrease of photocurrent. Under optimal conditions, the developed sensor demonstrated in the linear range of 1 pM–100 nM with a low detection limit of 0.59 pM. Furthermore, our strategy achieved high sensitivity, high selectivity, accurately and successfully detected tobramycin in milk and lake water, providing an accurate and effective method for its detection. [ABSTRACT FROM AUTHOR]

• A high-efficiency electrochemical biosensor was proposed based on dual-output toehold mediated strand displacement reaction (TMSDR). • The whole sensing process was completely enzyme-free. • The homogeneous approach improved the efficiency of TMSDR. Herein, a "signal-on" electrochemical aptasensor based on dual-output toehold mediated strand displacement reaction (TMSDR) was developed to detect cytokeratin fragment antigen 21–1 (CYFRA 21–1). First, the methylene blue (MB) labeled signal probe (SP) was combined with a long template strand (TS) to form the three-strands duplex, which was immobilized on magnetic beads. The sequence of TS was innovatively designed with two toehold zones. Thus, with the presence of target DNA and Fuel strand (F), double SP and target were released through TMSDR. Besides, the released target could participate in the next cycle, achieving the further amplification. The released SP was selected by magnetic separation, then added to the gold electrode (GE) to hybridize with the hairpin DNA. Ultimately, the target can be detected by recording the current response of the MB. Under optimized conditions, the response peak current was linear with the concentration of CYFRA 21–1 in range from 10 pM to 1 μM with detection limit of 8.079 pM. The proposed signal amplification strategy was enzyme-free in homogenous solution and the using of magnetic beads improved the recognition efficiency and simplified the experimental steps, which endowed the sensor with super-sensitivity. [ABSTRACT FROM AUTHOR]

Scheme 1. Schematic description of the preparation of GOx@Tb-ATA/GDP CPs and detection of glucose. [Display omitted] • The dual-emission multi-functional probes based on Ln CPs were facilely prepared by self-assembly. • The ratiometric fluorescence method based on double ligand Ln3+ coordination polymers for H 2 O 2 detection was realized. • By integrating GOx through the adaptive inclusion property of CPs in the self-assembly process, a simple, highly selective and sensitive one-pot retiometric glucose assay was developed. A dual-emission lanthanide coordination polymers (Ln CPs) were facilely prepared by self-assembly of guanine diphosphate (GDP) and 2-aminoterephthalic acid (ATA) with Tb3+, termed as Tb-ATA/GDP CPs. GDP played as the antenna ligand to sensitize the luminescence of Tb3+, and ATA served as a fluorescent auxiliary ligand for the ratiometric assay. The obtained Tb-ATA/GDP CPs exhibited both blue-emission of ATA at 430 nm and characteristic green-emission of Tb3+ under a single excitation wavelength. Upon addition of H 2 O 2 , the fluorescence of Tb3+ could be selectively quenched and that of ATA slightly enhanced. The fluorescence intensity ratio at 430 nm and 549 nm (I 430 /I 549) increased linearly with increasing the concentration of H 2 O 2 in the range of 0.005–20 μM and 120–500 μM, and the detection limit was 3.42 nM. Furthermore, by integrating the glucose oxidase (GOx) through the adaptive inclusion ability of Ln CPs, GOx@Tb-ATA/GDP CPs were facilely obtained. Based on their high affinity to oxidize glucose and the fluorescence response to the generated H 2 O 2 , a simple, highly selective and sensitive one-pot ratiometric glucose assay was developed. This work will facilitate the design and construct of multi-functional fluorescent probes based on the Ln CPs, and exploit their applications in bio-sensing and environmental analysis. [ABSTRACT FROM AUTHOR]

Arctigenin was determinated by an electrochemical method for the first time based on a novel voltammetric sensor, which was prepared by simple dipping-drying of SWCNTs on glassy carbon electrode (GCE) initially and then electrochemical deposition of Iodide. The resulting Iodide/SWCNTs/GCE displayed a significant voltammetric response to arctigenin due to the electrocatalytic ability of Iodide for arctigenin and a large specific surface area, excellent electric conductivity of SWCNTs. Meanwhile, the redox mechanism of arctigenin on Iodide/SWCNTs/GCE was also studied. The wide linear range of 3 × 10 − 8 mol L − 1 to 5 × 10 − 6 mol L − 1 and low detection limit of 1 × 10 − 8 mol L − 1 for the determination of arctigenin were achieved together with high sensitivity, selectivity, good stability. To examine the practical analytical utility of the proposed electrode, the real sample Fructus Arctii was examined and the result was found satisfactory. [ABSTRACT FROM AUTHOR]

A novel voltammetric sensor was constructed by simple dripping single-walled carbon nanotubes (SWCNTs) on to the glass carbon electrode (GCE) firstly and electro-polymerizing l -Citrulline film subsequently. The resulting poly( l -Citrulline)/SWCNTs/GCE showed a significant voltammetric response to picroside II due to the synergistic effect of SWCNTs and poly( l -Citrulline) film. The first electroanalytical method of picroside II was proposed with detection linear range from 8.0×10 −8 to 5.0×10 −6 mol L −1 and a detection limit of 3×10 −8 mol L −1 .The high sensitivity, selectivity and long-term stability made the sensor suitable for the determination of picroside II. Moreover, based on the systematically investigation and some kinetics parameters calculated in the experimentation, the reaction mechanism of picroside II at the poly( l -Citrulline)/SWCNTs modified GCE was obtained reliably. Lastly, the proposed sensor was used for the determination of picroside II in real sample with satisfactory results. This work promoted the potential applications of amino acid materials and SWCNTs in electro-chemical sensors. [ABSTRACT FROM AUTHOR]

A new and sensitive voltammetric sensor for palmatine, based on an electrochemically reduced l-methionine functionalized graphene oxide modified glassy carbon electrode (l-Met-ERGO/GCE), is reported. The electrochemical characteristics of palmatine at the proposed sensor were studied systematically and some dynamic parameters were calculated for the first time. A reasonable reaction mechanism for palmatine on the l-Met-ERGO/GCE electrode was proposed and discussed, and this could be a reference for the pharmacological action of palmatine in clinical study. Under optimized conditions, the peak current had a linear relationship with palmatine concentration in the range of 1 × 10−7 to 5 × 10−5 mol L−1 with a detection limit of 6 × 10−8 mol L−1. Additionally, the proposed method was also used to detect palmatine in human urine samples, medicinal tablets and the Chinese herb Fibraurea recisa Pierre with satisfactory results. [ABSTRACT FROM AUTHOR]

A simple, inexpensive and highly sensitive voltammetric method for the determination of tectoridin was developed using a poly( l -Arginine) modified electrode. The redox character of tectoridin at proposed electrode was studied systematically and some dynamic parameters were calculated for the first time. A reasonable reaction mechanism of tectoridin on the poly( l -Arginine)/GCE was also dicussed and proposed, which could be a reference for the pharmacological action of tectoridin in clinical study. And the electroanalytical method for determination of tectoridin was established by differential pulse voltammograms (DPV). Under optimum conditions, the response peak currents were linear relationship with tectoridin concentrations in the range of 5.0×10 −8 –2.0×10 −6 mol L −1 with a detection limit of 4.0×10 −8 mol L −1 . Therefore, the high sensitivity for tectoridin sensing at the proposed electrode was achieved, and the proposed method could also be used to detect tectoridin in the Chinese medicinal herb Blackberrylily with satisfactory results. [ABSTRACT FROM AUTHOR]

An ultrasensitive photoelectrochemical (PEC) analysis method based on terminal deoxynucleotidyl transferase (TdT) amplification effect and G-quadruplex/hemin (G4/hemin) catalytic reaction assisted signal amplification was prepared for the determination of ampicillin. A novel Au NPs@SnIn 4 S 8 -graphene sensitized structure was used as photoactive material to attain an intense basic photocurrent. In the presence of the target, P1 obtained by strand displacement reaction was introduced into the electrode surface, and abundant G4/hemin was formed in the presence of TdT and hemin. Subsequently, G4/hemin with horseradish peroxidase-mimicking activity catalyzed the oxidation of 4-chloro-1-naphthol by H 2 O 2 to form benzo-4-chlorohexadienone precipitation on the modified electrode surface, which severely hindered the electron transfer and effectively inhibited the photocurrent output. The detection range of the PEC aptasensor for ampicillin was 10 fM-30 nM, and the limit of detection was 4.97 fM. The aptasensor had good stability and high sensitivity, and possessed a promising application in biological analysis and environmental monitoring. [Display omitted] • A label-free, highly sensitive photoelectrochemical aptasensor for ampicillin detection was proposed. • The introduction of the signal amplification strategy on TdT terminal extension and mimetic enzymatic catalytic precipitation achieved high sensitivity assay. • The aptasensor possesses a promising application in biological analysis and environmental monitoring. [ABSTRACT FROM AUTHOR]

A sensitive electrochemical method for determination of daphnetin at reduced graphene oxide (RGO) modified glassy carbon electrode (GCE) was developed. The graphene nanosheets were simply directly deposited onto a GCE surface through cyclic voltammetric reduction of graphene oxide colloidal solution. The redox character of daphnetin at ERGO/GCE was studied systematically and some dynamic parameters were calculated for the first time. The electroanalytical method for determination of daphnetin was established by differential pulse voltammograms (DPV). Under optimum conditions, the response peak currents were linear related with daphnetin concentrations in the range of 5.0 × 10 −8 to 2.0 × 10 −6 mol L −1 with a detection limit of 3.0 × 10 −8 mol L −1 . Therefore, the high sensitivity for daphnetin sensing at the proposed electrode was achieved, which was attributed to the introduced graphene films modified on GCE. Additionally, the proposed method could also be used to detect daphnetin in the medicinal capsules and Chinese medicinal herb Zushima with satisfactory results. [ABSTRACT FROM AUTHOR]

Schematic illustration of the principle of the fluorescence sensor for determination of CIP using AMP-Tb-luminol CPs. [Display omitted] • Lanthanide coordination polymers of AMP-Tb-luminol was synthesized via simple self-assembly process. • Due to the covalent bonds between central metal ions and luminescent ligand, Ln coordination polymers are favor for long-duration or complicated sample measurements particularly. • Dual-ligand coordinated AMP-Tb-luminol coordination polymers (CPs) for ratio-metric CIP assay. Herein, a facile self-assembly through adenosine monophosphate (AMP) and luminol with Tb3+ was employed to construct a dual-ligand coordinated AMP-Tb-luminol coordination polymers (CPs), which emitted the typical fluorescence of luminol. Based on the sensitization effect of ciprofloxacin (CIP) on the luminescence of Tb3+, a ratiometric sensor was fabricated using the fluorescence of luminol as an inert reference. The fluorescent intensity ratios of Tb3+ to that of luminol enhanced linearly with the CIP concentration in the range from 5 nM to 2.5 μM with a lower limit of detection of 2 nM. In addition, the proposed ratiometric fluorescent sensor exhibited high selectivity for CIP, which could also be used to detect CIP in human blood serum (HBS) with satisfactory results. To our knowledge, this is the first demonstration of using dual-ligand coordination lanthanide (Ln)-based CPs for ratio-metric CIP assay, and this straightforward strategy may open up a new platform for designing the ratio-metric sensors based on the Ln CPs. [ABSTRACT FROM AUTHOR]

Personal glucose meter (PGM) is one of the most commercially available POC (point-of-care) devices for monitoring the level of glucose reliably, yet its non-glucose quantification ability is limited since such strategy needs ingenious interface design and tedious enzyme conjugation. Herein, we constructed a portable and sensitive platform that can detect non-glucose target by combining enzyme-encapsulated zeolitic imidazole framework-90 (ZIF-90) with personal glucose meter. ZIF-90 is an ideal carrier and susceptor due to the extraordinary capability of packaging enzyme and stimuli-responsiveness. We selected adenosine-5′-triphosphate (ATP) as the target model of non-glucose analytes. Upon ATP-induced decomposition of MOF, the released enzyme (glucose oxidase or invertase) catalyzed substrate and gave rise to the change of the glucose concentration for PGM assay. This method determined ATP with a remarkably sensitivity of 233 nM and effective recovery in real serum samples. Our strategy provides a facile and practical approach for measuring the non-glucose target using PGM, and could potentially be applied in bimolecular detection in point-of-care diagnosis. [Display omitted] [ABSTRACT FROM AUTHOR]