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We report a sandwich-structured surface-enhanced Raman scattering substrate by integrating gold nanoparticles and electron beam lithography-fabricated hexagon-shaped silver nanohole arrays separated by single layer graphene. In the sandwich configuration, the graphene interlayer plays multiple roles for promoting the surface-enhanced Raman scattering performances: (i) acting as a supporting layer to avoid the dropping of the top layer of gold nanoparticles; (ii) an intrinsic spacer to create nanometer-scale gaps between gold nanoparticles and hexagon-shaped silver nanohole arrays; (iii) serving as a protective layer to suppress the oxidation of the bottom metal silver; (iv) functioning as a molecule harvester for adsorbing the target analyte. By decreasing inter-hole distances of hexagon-shaped silver nanohole arrays, we have obtained sub-10 nm-wide gaps neighboring the adjacent silver holes. Finite element numerical simulations demonstrated that the gold nanoparticle-graphene-hexagon-shaped silver nanohole array hybrid system generates a substantial amount of hot spots with strong electric field enhancement. The well-designed and fabricated gold nanoparticle-monolayer graphene-hexagon-shaped silver nanohole array sandwich structure exhibits high sensitivity with the limit of detection at sub-picomolar level and good reproducibility with a standard deviation of 6.2% for crystal violet. The work endows great potentials to the rational design and fabrication of two-dimensional material-plasmonic hybrids for surface-enhanced Raman scattering applications. [ABSTRACT FROM AUTHOR]

This paper describes the detection of volatile organic compounds (VOCs) using an e-nose system based on a virtual sensor array (VSA). The VSA was realized by seven different resonant modes of a single piezotransduced silicon bulk acoustic wave resonator (PSBAR) which can greatly reduce the complexity of a conventional e-nose system. The PSBAR was designed and fabricated using standard CMOS compatible process. The resonant modes of the PSBAR and its capability of VOCs discrimination were theoretically explored through finite element analysis. The discrimination effect was enhanced by the non-uniform adsorption of gas molecules on the top, side and bottom regions of the resonator. Score plots and radar fingerprints obtained respectively from principal component analysis (PCA) and fitted coefficient of adsorption isotherms for each VOC compose sufficient information to successfully discriminate different VOCs. The proposed novel VSA shows great potential as a compact and promising e-nose system. [ABSTRACT FROM AUTHOR]

Copper is a highly toxic environmental pollutant in the environmental, biological and chemical fields. Therefore, sensitive, selective and visual detection of Cu 2+ is very important for human health and practical applications. Herein, a novel hybrid ratiometric fluorescent nanosensor was developed for rapid and on-site visualization of Cu 2+ on the basis of integrating benzothiazole fluorophore (MDBT) and red-emissive quantum dots (QDs) embedded in silica nanospheres. Such hybrid ratiometric fluorescent nanosensor exhibits dual emissions at 420 and 640 nm under a single excitation wavelength. Due to the ions promoted oxidation reaction of Cu 2+ towards MDBT, the fluorescence of MDBT can be selectively enhanced. Although the embedded QDs are insensitive to the analyte, variations of the dual emission intensity ratios display continuous colour changes from red to blue. The ratiometric fluorescent approach shows high sensitivity and selectivity towards Cu 2+ against other interfering metal ions. The detection limit of Cu 2+ for the hybrid ratiometric fluorescent nanosensor is determined to be 41.71 nM, which is much lower than the allowable level of Cu 2+ (∼20 μM) in drinking water set by U.S. Environmental Protection Agency. Furthermore, this kind of novel nanosensor can also be applied for Cu 2+ detection in actual water samples and exhibits excellent detection ability. This hybrid ratiometric fluorescent nanosensor is simple, fully self-contained and thus potentially attractive for visual identification without the need of elaborate equipments. [ABSTRACT FROM AUTHOR]

The hybrid system combining graphene with plasmonic metal nanoparticles (NPs) has been of great interest owing to its excellent sensing capacity to be used as surface-enhanced Raman scattering (SERS) substrate. Here, we report an efficient SERS substrate by sandwiching monolayer graphene (1LG) between Au NPs and electron beam lithography-fabricated Ag nanostar arrays (NSAs). The design has integrated the orderness and strong plasmonic effect of Ag NSAs, the atomic thickness, mechanical flexibility and biological compatibility of graphene, as well as the chemical stability of Au. Calculations of finite element numerical simulations revealed that the Au NP-graphene-Ag NSA hybrid system generated high-density hot spots with strong electric field enhancement through the multi-dimensional couplings of plasmonic metal NPs. The fabricated Au NP-1LG-Ag NSA hybrid structure Exhibits 137-fold enhancement of the Raman response of graphene, and the limit of detection is 0.1 pM for rhodamine 6G molecules, which can be attributed to the extremely strong electric field enhancement and chemical enhancement of graphene. Furthermore, the Au NP-1LG-Ag NSA SERS substrate has achieved the simultaneous detection of rhodamine 6G and methylene blue. This work opens up an avenue for the rational design and fabrication of graphene-plasmonic hybrids for SERS sensing applications. [ABSTRACT FROM AUTHOR]

Diacylhydrazine-based fluorescent probes are designed for selective detection of copper(II) and sulphide with two modes. The probes can not only be decomposed into rhodamine B by Cu 2+ , but can also be tuned to construct Cu ensembles for selective detection of sulphide. [ABSTRACT FROM AUTHOR]

A quinoline-vinyl-dihydroxylphenyl linkage comprising a donor-π-bridge-acceptor structural motif, in which the quinoline serves as an electron-withdrawing core, has been synthesized and used as a fluorescent sensor ( 2 ) for the recognition of Al 3+ and F − by colorimetry/fluorescence. The sensor 2 exhibited little fluorescence due to excited-state intramolecular proton transfer from the hydroxyl oxygens to the nitrogen of the quinoline moiety. By contrast, on coordination of Al 3+ or F − , sensor 2 afforded strong fluorescence. A reversible “off–on” optical switching mode has been constructed by sequential inputs from Al 3+ and F − ions to the sensor 2 via different excitation and emission wavelengths. 1 H NMR and IR spectroscopic analysis revealed that the Al 3+ is coordinated to the quinoline nitrogen and phenolic oxygen atoms, whereas the F − center is only coordinated by two phenolic oxygen atoms. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) have recently attracted great interest due to their potential applications, including ultrasensitive chiral recognition. We anticipate that optically active chiral COFs could be utilized to recognize chiral molecules more conveniently and intuitively with high enantioselectivity and reactivity. Here, we prepared the chiral functionalized monomer CTp using chiral (+)-diacetyl- L -tartaric anhydride ((+)-Ac- L -Ta) and 1,3,5-triformylphloroglucinol (Tp) to form the chiral (+)-Ac- L -Ta-functionalized Tp. 3,6-diaminocarbazole was then condensed with CTp to obtain carbazole-conjugated chiral COFs (CC-COFs) by C N Schiff base reaction of aldehyde and amino groups in the Tp and carbazole. The prepared optically active chiral COFs show good optical efficiency and thermal stability with the characteristics of porous organic polymers, such as a large specific surface area, adjustable pore structure, and robust skeleton constructed with covalent bonds. CC-COFs exhibit good enantioselectivity and anti-interference ability and can normally recognize the phenylalanine (Phe) enantiomer in the presence of amino acid enantiomers and ions. Furthermore, the fabricated CC-COFs achieve high resolution for optosensing of l - and D -Phe in the linear range of 0.05–5 μmol/L, with detection limits of 0.037 μmol/L and 0.027 μmol/L, respectively. CC-COFs can be applied successfully in the chirality recognition of enantiomers of l - and D -Phe in samples with a recovery of 84.8–99.0%. This strategy of optically active chiral COFs opens up new approaches for enantiomer recognition. [Display omitted] • A supersensitive fluorescence sensing platform for chiral recognition. • A one-pot polymerization strategy to fabricate optically active chiral COFs. • Carbazole-conjugated chiral COFs was prepared. • It exhibited good optical efficiency, thermal stability, good enantioselectivity. • It applied successfully in the chirality recognition of enantiomers of l - and D -Phe in samples. [ABSTRACT FROM AUTHOR]

The electrocatalytic oxidation of cysteine at carbon nanotube (CNT) was studied. It was found that the electrochemical behaviors of cysteine were greatly improved at CNTs, indicating that the anodic oxidation could be catalyzed at CNTs. The kinetics parameters of this process were calculated, the heterogeneous electron transfer rate constant k was 0.0042 cm s−1, (1−α)nα was 0.30. The carbon nanotube powder microelectrodes (CNTPMEs) were also found with higher sensitivity for cysteine detection than other common electrodes, and 2 μM sample could be determined easily, indicating that it could be used as cysteine sensors. [Copyright &y& Elsevier]

HRP was found with a direct electrochemistry at carbon nanotube microelectrode. The adsorbing HRP could transfer electron directly at CNT compared with common carbon electrode material. It was calculated that the transfer coefficient α was 0.57, and heterogeneous electron transfer rate constant was 2.48±0.03 s−1. It was found that the adsorbing HRP still keeps its catalytic activity to H2O2. [Copyright &y& Elsevier]

• Electrochemical ratiometric sensor is proposed for the detection of PSA. • Electroactive Ag nanodots are leached through resorcinol-formaldehyde surface. • Electroactive Cu 2 O NPs were designed to grow on rGO/Fe 3 O 4 NSs. • Electroactive Ag NPs and Cu 2 O NPs are detection and reference tags. • Electrochemical sensor achieves the accurate detection of PSA. Early detection of prostate specific antigen (PSA) could reduce the mortality from prostate cancer. Electroactive nanostructures have attracted much attention due to their excellent electronic conductivity and favorable biological microenvironment. In particular, electroactive Cu 2 O nanoparticles (NPs) and Ag NPs exhibited unique oxidation signals at around -0.1 V and +0.2 V. The separated and non-interfere oxidation signals enabled them to be alternative electrochemical beacons for the establishment of ratiometric electrochemical sensor for PSA detection. Electroactive Cu 2 O NPs were designed to grow on the surface of reduced graphene oxide/Fe 3 O 4 nanosheets (rGO/Fe 3 O 4 NSs) and served as reference tags due to the stable differential pulse voltammetry (DPV) signals of Cu 2 O NPs, magnetic properties for the absorption on electrode and the accelerated electron transfer ability of rGO. In order to improve the sensitivity of detection, a large number of small electroactive Ag nanodots were dispersed on the surface of Ag@resorcinol-formaldehyde (RF) NPs and served as detection tags. Electroactive Ag@RF-Ag NPs were assembled with rGO/Fe 3 O 4 /Cu 2 O NSs for the fabrication of ratiometric electrochemical aptasensor. With the addition of PSA, aptamers modified Ag@RF-Ag NPs disassembled from electrode surface, resulting in the decrease of DPV signals near +0.2 V and unchanged DPV signals at -0.1 V. This developed ratiometric electrochemical aptasensor achieved sensitive and accurate PSA detection. This proposed ratiometric electrochemical aptasensor has the advantages of easy preparation, simple structure and wide detection ranges. [ABSTRACT FROM AUTHOR]

A facile and efficient method was developed for the preparation of iridium nanoparticles (Ir NPs) with superior peroxidase-like activity. Under the catalytic action of the Ir NPs, the peroxidase substrate 3,3,5,5-tetramathylbenzidine (TMB) can be oxidized by H 2 O 2 to form a blue-colored production oxTMB. Kinetic analysis indicated that the catalytic behavior was in accordance with the typical Michaelis-Menten kinetics and the catalytic reaction followed the ping-pang mechanism. Electron Spin Resonance (ESR) experiment showed that no hydroxyl radical formed in the reaction process. Peroxide substrates with different electron withdrawing ability (benzoyl peroxide, H 2 O 2 and artemisinin) were used to study the catalytic reactions and results indicated that H 2 O 2 can oxidize TMB with much faster rate than artemisinin and slower rate than benzoyl peroxide. These results suggest an electron transfer mechanism was involved in the system of TMB-H 2 O 2 -Ir NPs. By using TMB as the colorimetric substrate, H 2 O 2 can be rapidly determined and the method was extended for the determination of xanthine based on its production of H 2 O 2 in the presence of xanthine oxidase. The prepared Ir NPs exhibit good stability in wide range of pH and temperature. The Ir NPs retained at least 90% of their initial catalytic activity after stored at ambient temperature for three months. The high specificity for H 2 O 2 and the excellent stability of the peroxidase-like Ir NPs showed the great application potential in biotechnology field. [ABSTRACT FROM AUTHOR]

Low cost and rapid detection of glutathione (GSH) has important clinical reference value for the diagnosis and treatment of related diseases. In this study, a one-step method for rapid detection of GSH is developed based on the characteristics of low cost, simple operation and rapid color development of pregnancy test strip. In this method, magnetic Fe 3 O 4 -doped MnO 2 nanosheet is first synthesized, and colloidal gold probe modified with hCG and ssDNA is absorbed on the surface of the nanosheet. Based on the oxidase-like properties of MnO 2 nanosheet, in the presence of GSH, a redox reaction between GSH with MnO 2 occurs to release hCG signal probe into the solution. The supernatant solution is loaded on pregnancy test strip after magnetic separation, and the test line develops color. Then the smartphone App developed in our lab is used to quantitatively detect GSH. The results show that under the optimal conditions, the GSH in the range of 40–800 μM has a good linear relationship with the color intensity of the test line on pregnancy test strip and the detection limit for GSH is 40 μM. So, this method can realize the detection of GSH with low cost, simple, rapid and sensitive, and it can meet the requirements of GSH detection in actual samples. • Fe 3 O 4 can quickly separate and purify hCG coupled signal probe from the solution. • Colloidal gold of the hCG signal probe has a color deepening effect. • Commercial pregnancy test strip and smartphone App are used to quantitative detection. [ABSTRACT FROM AUTHOR]

Dual-mode detection nanotags with non-interference sensing signals had great potential to overcome the limitations of individual sensors, such as narrow monitoring range and inaccurate detection results. Herein, Au-Ag@MnO 2 nanoparticles (NPs) with inherent surface-enhanced Raman spectroscopy (SERS) activity and plasmon-enhanced electroreduction (ER) signals were first reported. 2-mercaptobenzoimidazole-5-carboxylic acid (MBIA) mainly modulated the growth of Ag component and also endowed Au-Ag NPs with intrinsic SERS signals, thereby eliminating the need for additional modifications with SERS reporters. The deposition of MnO 2 shell on Au-Ag NPs weakened the SERS signals but displayed two ER peaks at 0.5 V and 0.1 V, owing to the ER process of Mn4+ and Ag+, respectively. The peak at 0.5 V was amplified 1.23 times under light exciting, owing to the proposed plasmon-enhanced ER principle·H 2 O 2 triggered the conversion of MnO 2 to Mn2+ and exposed the Au-Ag NPs, resulting in "turn on" SERS signals and "turn off" ratiometric electrochemical responses. SERS-active and electroactive Au-Ag@MnO 2 NPs achieved dual-mode detection of uric acid with urate oxidase (UOX) as catalysts. Rationally designed plasmonic metal-semiconductor heterogeneous nanocomposites may generate multiple-mode optical and electrochemical signals for accurate and quantitative detection applications. • Au-Ag@MnO 2 NPs show label-free intrinsic SERS activity. • Au-Ag@MnO 2 NPs exhibit electroreduction peaks at 0.5 V and 0.1 V. • Plasmon-enhanced electroreduction principle of Au-Ag@MnO 2 NPs is proposed. • H 2 O 2 triggers the "turn on" SERS signals and "turn off" ratiometric electroreduction peaks. • Dual-mode sensors are proposed for uric acid detection. [ABSTRACT FROM AUTHOR]

In this paper, we proposed an amplified assay using DNase I for sensitively sensing prostate specific antigen (PSA) based on CdSe/ZnS quantum dot labelled PSA aptamer/graphene oxide (QD-aptamer/GO). In this sensing system, GO could strongly bind QD conjugated aptamer and quench the fluorescence of QD, furthermore, GO could protect DNA from nuclease cleavage. When binding target PSA, aptamer probe released from the surface of GO nanosheet, then the free aptamer could be cleaved by nuclease, thus the QD and PSA were liberated, after that, the released PSA would bind another aptamer on GO nanosheet and start a new cycle, which resulted in amplification of restoring signal. The probe possessed steady fluorescence signal and high specificity due to the anti photobleaching of QD and the high affinity of aptamer to PSA. Under the optimum experimental conditions, fluorescence intensity increased linearly with the PSA concentration between 0.1 fg mL −1 and 3 fg mL −1 with the limit of quantification of 0.05 fg mL −1 , which was three orders of magnitude lower than that without DNase I. Finally, the method was applied to quantification of PSA in human serum samples. [ABSTRACT FROM AUTHOR]

This study has developed a new membrane based visualization method for the detection of ultratrace lead and cadmium ions. The basic steps were mainly as follows. Dithizone (Dz) was adsorbed on cellulose acetate membrane (CAM) and formed Dz-Pb 2+ /Cd 2+ complexes in the presence of lead and cadmium ions. Then the complexes were converted into Dz-PbS/CdS composites after further processing with sulfide ions. While the new formed Dz-PbS/CdS composites could act as a catalyst in the subsequent silver stain reaction. With the silver nanoparticles depositing on CAM, the color of the membrane turned gray to black, which could be observed by naked eye. Semi-quantitative analysis of Pb 2+ /Cd 2+ was performed according to the ΔAverage gray value of CAM grayscale images. Results showed that under the optimal conditions, ΔAverage gray value had a good linear relation with the logarithm of the Pb 2+ /Cd 2+ concentration in the range from 1 nM to 100 nM, and the naked eye detection limit could reach 1 nM (∼0.0002 mg L −1 ). Besides, other common metal ions had no significant interference with the detection, indicating that the method had a good selectivity. Satisfactory results were obtained for the detection of Pb 2+ /Cd 2+ in real samples (lake water and soil samples). [ABSTRACT FROM AUTHOR]

A field-compatible technique involving the use of an electrochemical microbundle for real-time and simultaneous in vivo measurement of hydrogen peroxide, nitric oxide, and pH in plants was developed. The sensing electrodes of the microbundle included one Pt microelectrode for H 2 O 2 detection, one platinized Pt electrode for NO detection, and one iridium oxide electrodeposited Au electrode for pH detection. The microbundle showed a dynamic range up to 0.3 mM, with a low detection limit of 1.24 μM ( S / N = 3) and high sensitivity of 9.27 μA/M for H 2 O 2 ; and a dynamic range up to 0.26 mM, with a low detection limit of 1.38 μM ( S / N = 3) and high sensitivity of 27.1 μA/M for NO. Anodically grown iridium oxide films showed a near-Nernstian response with a slope of 51 ± 1.4 mV/pH and linear responses within the pH range of 2–10. The H 2 O 2 /NO/pH electrochemical microbundle was successfully employed for quantitative in vivo monitoring of H 2 O 2 , NO, and pH in oilseed rape for 45 h in the presence or absence of drought stress. This H 2 O 2 /NO/pH electrochemical microbundle can be a powerful tool for the in vivo simultaneous investigation of changes in H 2 O 2 , NO, and pH and hence can be used in phenotype screening. [ABSTRACT FROM AUTHOR]

Micro/nanomotors with extraordinary motion capability have shown great potential in biomedicine and environmental remediation to undertake cargo transport tasks. To realize efficient microscale cargo loading, it is critical to endow micro/nanomotors with a proper surface morphology, powerful propelling force, and great motion controllability. Herein, being inspired by pollination, a light-controlled micromotors with efficient motion and loading capacity based on sunflower pollen grain were successfully developed and investigated. Using focused laser irradiation, the convection generated by thermal Marangoni effect can effectively drive the micromotor underwater with great controllability. Moreover, the micromotor can exhibit two motion behaviors by adjusting the laser irradiation location, which can be employed for different application tasks. Furthermore, yeast cells, as a live cargo model, can be efficiently captured in the round-trip motion and transported in straight-line motion of the micromotor, while retaining high cell viability. These micromotors exhibit improved efficiency in capturing targets by introducing synergistic topographic interactions. Thus, these micromotors can be expected to largely extend the capabilities of micro/nanomotors in propulsion, motion control and cargo, thereby providing a way for the development of intelligent micromotors. [Display omitted] • Light-controlled micromotor was fabricated based on spiky pollen as bio-template. • The micromotor can perform underwater based on focused laser induced Marangoni effect. • Highly efficient capture and transport of living yeast cells could be achieved without any adverse effect on cell viability. [ABSTRACT FROM AUTHOR]

A new method is proposed for determination of carcino-embryonic antigen (CEA) based on quantum dot (QD)-modified aptamer probe by capillary electrophoresis-chemiluminescence (CE-CL) detection system. An oligonucleotide sequence A contains two parts, one is CEA aptamer and the other is bridging segment. Horseradish peroxidase (HRP) conjugates with sequence A (HRP-DNA A ) and then mixes with QD labeling complementary bridging segment (QD-DNA B ), forming HRP-DNA A-B -QD probe. When CEA exists, the specific combination of the aptamer in sequence A and CEA can form CEA/HRP-DNA A-B -QD complex. After separation of CEA/HRP-DNA A-B -QD complex and HRP-DNA A-B -QD probe by capillary electrophoresis (CE), the chemiluminescence (CL) catalyzed by CEA/HRP-DNA A-B -QD complex can be detected without any interference, and the content of CEA can be estimated by the CL intensity. It has been proved that the separation efficiency of HRP-DNA A-B -QD and CEA/HRP-DNA A-B -QD complex is improved greatly after QD modification, then the interference issue resulted from free HRP-DNA A-B -QD probe is solved well; and the specific combination of HRP-DNA A-B -QD and CEA leads to a closer distance of HRP and QD, then chemiluminescent resonance energy transfer (CRET) occurs, which confirms the validity of the strategy. Results show that the CL intensity has a linear relationship with the concentration of CEA in the range from 0.0654 to 6.54 ng/mL, and the limit of detection is approximately 8 pg/mL ( S / N = 3). This proposed method with high specificity has been applied for the accurate analysis of content of CEA in patient's serum. [ABSTRACT FROM AUTHOR]

It is important to design new ways with high specificity and sensitivity to detect lead (II). Here, ‘8–17’ DNAzyme was used as a Pb2+-dependent probe with high sensibility and selectivity based on chemiluminescence (CL). When Pb2+ was present, the substrate strand was cleaved and the active hemin/G-quadruplex DNAzyme structure was formed in the presence of another sequence which contained two parts, one could be complementary with part of the substrate strand and the other was a G rich subunit. The active hemin/G-quadruplex DNAzyme structure could catalyze luminol oxidation and quantitative analysis of Pb2+ was carried out according to the CL of luminol. Results showed that CL intensity of luminol at 452nm had a linear relation with the concentration of Pb2+ in the range from 5nM to 1μM, and the limit of detection was 0.79nM (S/N =3). This method was also used to detect the contents of Pb2+ in lake water and tobacco and the results (62.4±4.0nM and 15.2±2.2nM, respectively) were extremely closed to those of inductively coupled plasma-mass spectrometry (ICP-MS) (57.0±1.4nM and 14.5±0.91nM, respectively). [ABSTRACT FROM AUTHOR]

Parallel multiple detections of tumor markers is of significant for the efficient and accurate early monitoring of related cancers. Electrochemical aptasensors possess excellent selectivity and sensitive quantitative detection while maintaining multiple detection ability. The study of high and different electrochemical beacons is urgent to achieve multiple-level parallel detection. In this work, electroactive AgRu NPs and AgPt NPs were explored to exhibit electrooxidation peaks at 0.8 V and − 0.7 V, respectively. Plasmonic AgRu NPs and AgPt NPs harvested light energy and exhibited amplified electrooxidation activity under local surface plasmon resonance (LSPR) excitation. Plasmon-enhanced electrooxidation principle was proposed for AgM (M=Ru, Pt) NPs owing to the distinct imaginary part of dielectric constants between Ag and platinum group metals (PGM). The strong and non-interference electrooxidation peaks at 0.8 V and − 0.7 V enabled AgRu NPs and AgPt NPs to be different electroactive beacons for the sensitive and reliable quantitative dual detection of human epidermal growth factor receptor-2 (HER2) and epithelial cell adhesion molecule (EpCAM). The LODs were 0.3 pg mL−1 (7.5 amol mL−1) for EpCAM and 0.6 pg mL−1 (3.2 amol mL−1) for HER2. The proposed plasmon-promoted electrooxidation principle provides a novel route for the design of multiple electroactive plasmonic metal-PGM composite electrochemical beacons for simultaneous electroanalysis applications. [Display omitted] • AgRu NPs and AgPt NPs exhibit electro-oxidization peaks at 0.8 V and − 0.7 V. • Plasmonic AgM NPs show amplified electro-oxidization activity under LSPR excitation. • The proposed plasmon-promoted electro-oxidization principle is verified. • Two beacons are used for parallel multiple detection of tumor markers. [ABSTRACT FROM AUTHOR]

Abstract: Graphene (GR) can strongly interact with aptamers due to hydrophobic and π–π stacking interactions between nucleotide bases and GR, but hardly interact with aptamer–target complexes or rigid double-stranded DNA. The unique GR/aptamers interaction has been fascinatingly developed in fluorescent assay, colorimetric biosensing and mass spectrometric analysis. However, exploration of the unique GR/aptamers interaction in electrochemical biosensing is still at an early stage. In this regard, we reported herein a novel, sensitive and relatively cushy approach to construct electrochemical aptasensors by immobilizing GR/aptamers complex on the surface of poly(o-phenylenediamine) (PoPD) modified glassy carbon electrodes (GCE). Adenosine triphosphate (ATP) was chosen as a model analyte and a well-studied 27-mer single-stranded DNA aptamer was tailor-made to have methylene-blue (Mb) at both ends for use as an electrochemical probe. The Mb-dual-labeled aptamers/GR/PoPD/GCE exhibited a strong electrochemical signal due to the high electrons transfer and large surface area of GR and using double Mb labeled at two ends of aptamers. The presence of ATP triggers the structure switching of aptamer to form aptamer–ATP complex, causing the destruction of the interaction between aptamer and GR and thus the release of Mb-dual-labeled aptamer from the GR, resulting in a low electrochemical signal. Under optimal conditions, we have successfully detected ATP down to a detection limit of 0.3nM with a wide detection range of 10nM–2mM. And from the experiment of cancer cellular ATP assay, it is proved that the method may have great prospects in the field of biological analysis. [Copyright &y& Elsevier]

Various mycotoxins are widely present in crop products, which cause serious harm to human and animals. In this study, combining the specific recognition of aptamer with catalytic hairpin assembly (CHA) strategy, the pregnancy test strip is used to detect multiple mycotoxins. The signal amplification can be further achieved through following enzymatic reaction to increase sensitivity. In the experiment, there is no need to assemble test strip as well as prepare and purify antibody/hapten. It only requires to couple human chorionic gonadotropin (hCG) with DNA probe to realize the target determination via CHA process and enzymatic signal amplification on the test strip. Under optimal conditions, using the CHA based pregnancy test strip detection platform, the visual limits of detection for aflatoxin B 1 , ochratoxin and zearalenone can be obtained within 15 min, which are 20, 50 and 20 pg/mL, respectively. The detection results of the spiked samples show that the platform possesses satisfied accuracy, reproducibility and practicability. The method has facile scheme, low cost and good design versatility, and reveals potential application prospects in high sensitivity, low cost, and convenient detection of mycotoxins. [Display omitted] • Commercial test strip is used to detect mycotoxins with CHA strategy. • HCG is coupled with aptamer probe as signal and recognition element. • CHA and HRP based platform can realize dual signal amplification process. • The three mycotoxins are successfully determined in the spiked cereal samples. [ABSTRACT FROM AUTHOR]

Abstract: In this study, one-step electrochemical polymerized method for the fabrication of poly(o-aminophenol)/multi-walled carbon nanotubes (PoAP/MWCNTs) composite film was developed for the quantitative determination of levofloxacin. Scanning electron microscopy and electrochemical methods were used to characterize the PoAP/MWCNTs nanocomposite film. The sensor fabricated from the nanocomposite film showed good stability and enhanced electrocatalytic ability for the detection of levofloxacin. The large current response of levofloxacin on PoAP/MWCNTs composite film-modified electrode could be ascribed to the synergistic effect of the electrocatalytic property of PoAP and MWCNTs. The oxidative peak current increased linearly with the concentration of levofloxacin in the range of 3.0–200μM by differential pulse voltammetry, and the detection limit was 1.0μM (S/N=3). The proposed modified electrode also can be successfully applied to the determination of levofloxacin hydrochloride in pharmaceutical formulations. [Copyright &y& Elsevier]

Abstract: Nitric oxide (NO) is a key signaling molecule in different physiological processes of plants. It is therefore very important to establish a simple, fast, sensitive and accurate detection method for NO detection. In this study, a novel amperometric biosensor based on immobilization of hemoglobin (Hb), chitosan (CS), graphene (GR) and the surfactant hexadecyltrimethylammonium bromide (CTAB) on a glassy carbon electrode was constructed to quantitatively measure NO. Atomic force microscopy, scanning electron microscopy and electrochemical methods were used to characterize the Hb–CS/GR–CTAB nanocomposite film. The biosensor fabricated from the nanocomposite film showed direct electrochemistry with a fast electron-transfer rate (60.3s−1) and high electrocatalytic activity towards the reduction of NO. Under optimal conditions, the resulting biosensor exhibited a high sensitivity of 615μAmM−1, a low detection limit of 6.75×10−9 M (S/N=3) and a small apparent Michaelis–Menten constant of 0.315μM. These results were superior to those for biosensors based on the graphite, GR/ionic liquid and carbon nanotubes. The biosensor was also used successfully for detection of additional NO in oilseed rape leaf homogenate samples. Furthermore, the biosensor had excellent long-term storage stability, as well as reproducibility and selectivity, and should have a potential application in monitoring NO in plant samples. [Copyright &y& Elsevier]

Abstract: In this paper, poly-o-phenylenediamine and Pt microparticle modified Pt electrode (POPD/Pt-MP/Pt) as microbiosensor has been developed to monitor in vivo oxidative burst induced by ultraviolet A (UV-A) and ultraviolet C (UV-C) radiation stress in oilseed rape (Brassica napus L.). Twice oxidative bursts were detected, appearing at 2 and 25h, respectively. According to the peak area of amperometry, the amount of H2O2 induced by UV stress was estimated to be 6.2×10−10 and 3.1×10−10 mol for such two oxidative bursts in detected leafstalk, respectively. This novel microbiosensor provides an effective tool for studying the defense reaction of the plant in the situation of UV stress and probing the antioxidative mechanism of the antioxidative enzyme. [Copyright &y& Elsevier]

Abstract: Horseradish peroxidase (HRP) and lipophilic quantum dots (QDs) were incorporated onto the surface of glassy carbon (GC) electrodes in various ways. It was found that HRP transfers electron directly onto the GC electrode only when the electrode was modified with QDs through vapor deposition. The response currents were linearly correlated with scan rate, indicating that the reaction is a surface controlled process. The average coverage of HRP on the electrode surface can be calculated as 2.29×10−11 molcm−2, and the heterogeneous electron transfer rate constant k was 5.80±0.70s−1. Absorption spectra and Fourier-transform infrared spectra showed that the conformation of HRP immobilized on the electrode has no obvious change. Further studies indicated that immobilized HRP retains excellent catalytic activity to H2O2. The apparent Michaelis–Menten constant was calculated as 0.152mM. It was also found that the modified electrode could be used as a sensor for H2O2, and the linear range of detection was 5.0×10−6 to 1.0×10−4 M, with a detection limit of 2.84×10−7 M. The sensor exhibited reproducibility, stability. [Copyright &y& Elsevier]

• Existing commercial test strip is used to detect various targets with facile design. • Human chorionic gonadotropin is coupled with aptamer/cDNA to recognize targets. • HCR based magnetic signal probe effectively improves the detection performance. • Smartphone App and portable device are applied to quantitative detection. • The four targets are successfully determined in the spiked human serum sample. Pregnancy test strip is currently one of the most mature and widely used biomedical test products. In this study, based on its simplicity and rapidity, the detecting target-human chorionic gonadotropin (hCG) is coupled with different hybridization probes, while the aptamer is linked with the initiator used for hybridization chain reaction (HCR), which can construct a signal amplification platform based on HCR. The method converts the detection of other biochemical molecules into the detection of hCG signal, and combines the magnetic separation technology to realize the detection of various targets with pregnancy test strip. The rapid quantitative detection can be achieved with smartphone App and portable detection device. Under the optimal experiment conditions, the method can realize rapid and sensitive detection of adenosine triphosphate, thrombin, carcinoembryonic antigen and DNA fragment in human serum, and the visual detection limits can reach 100 pM, 0.2 pM, 5 ng/mL and 5 pM, respectively. The design has low cost, simple operation, and good sensitivity and selectivity for target detection. Based on this design, the detection of multiple analytes can be implemented with different aptamer sequences, thereby broadening the application of commercial pregnancy test strip in the biomedical testing field. [ABSTRACT FROM AUTHOR]

• HCR and microplate strategies improve the detection sensitivity of HBV-DNA on strip. • The detection limits of HCR and microplate strategies are enhanced 200 and 10-fold. • Recovery of HBV-DNA spiked in human serum is 97.2–102 %. Hepatitis B virus (HBV) can cause liver cancer, thus the detection of HBV-DNA is of great significance for liver cancer prevention. Since the concentration of HBV-DNA is often low, it is important to establish a highly sensitive detection method. In this study, microplate amplification and hybridization chain reaction (HCR) were used to improve the sensitive detection of HBV-DNA on dual strip biosensors. For the microplate-based amplification strategy on RS strip, the dual-DNA-AuNP probe could be immobilized on SA-Biotin-Anti-HBV-DNA-1 covered microplate through HBV-DNA. By adding dithiothreitol (DTT), a large amount of HS-RS-DNA on the dual-DNA-AuNP probe was dissociated. The indirect detection of HS-RS-DNA on RS strip could achieve the signal amplification of HBV-DNA. For the HCR-based strategy on HCR strip, HBV-DNA triggered the cascade reaction of H1-AuNP probe and H2-Biotin, a large amount of HCR product (AuNP-H1-H2-Biotin-AuNP-H1...) was produced. Thus, a lot of AuNP was fixed on the test zone of HCR strip to improve the HBV-DNA detection sensitivity. The detection limits by HCR strategy on HCR strip and microplate strategy on RS strip could reach to 5 pM and 0.1 nM, respectively, which were 200 and 10-fold higher than that of unamplified strategy, respectively. The recovery of HBV-DNA ranged from 97.2 to 102 % in the spiked human serum, presented a good accuracy for HBV-DNA detection in actual samples. [ABSTRACT FROM AUTHOR]

• Electrochemical chiral sensor is proposed for the detection of D-AAs. • D-amino acids oxidase can catalyze D-AAs to produce H 2 O 2. • Fe 3 O 4 @Au@Ag@Cu x O NPs are used as electroactive beacons. • Au and Ag double layers accelerate the electron transfer from Cu+ to Cu2+. • The limit of detection for D-Ala is as low as 52 pM. A simple and accurate magnetic electrochemical sensor is developed for the ultrasensitive chiral recognition of D-amino acids (D-AAs). Fe 3 O 4 @Au@Ag@Cu x O nanoparticles (NPs) (x = 1, 2) are controllable prepared and used as the electrochemical beacons. The controllable integration of plasmonic metal NPs, semiconductors and magnetic NPs enables multilayered Fe 3 O 4 @Au@Ag@Cu x O NPs to display a sharp copper stripping peak at -0.16 V, owning to the electron transfer from Cu+ to Cu2+ and the synergistic electron transfer of Au and Ag double layers. D-AAs can be catalyzed by D-amino acid oxidase (DAAO) to produce H 2 O 2. The autocatalytic oxidation reaction of Cu x O shell with the existence of H 2 O 2 induces the decrease of electrochemical signals of Fe 3 O 4 @Au@Ag@Cu x O NPs. Fe 3 O 4 @Au@Ag@Cu x O NPs served as electrochemical beacons achieve the sensitive and accurate enantioselective recognition of D-alanine (D-Ala) in the range from 100 pM to 10 μM. The limit of detection (LOD) is as low as 52 pM. This developed protocol can be extended to the fabrication of a large set of electroactive labels by the introduction of plasmonic metal NPs with high electron transfer efficiency, for the reliable enantioselective recognition with high sensitivity. [ABSTRACT FROM AUTHOR]

• Tumor susceptibility gene CYP1A1 and marker AFP was detected simultaneously by strip. • The biosensor detected tumor susceptibility gene and marker in real sample well. • Signal amplification was achieved by HRP catalyzing substrate at strip biosensor. • Double-labelled colloidal gold probe was used to detect SNP and AFP visually. Liver cancer is one of the most common cancers in the world. The gene CYP1A1 is closely related to the occurrence of cancer, and the tumor marker alpha-fetoprotein (AFP) is also one of the important indicators for liver cancer screening. Therefore, detection of these two substances is of great significance. In this paper, a test strip biosensor capable of simultaneously detecting cancer susceptibility gene CYP1A1 and AFP has been established. There were two detection lines in the strip biosensor, one was used for qualitative detection of susceptible gene by base complementary pairing, and the other was used for semi-quantitative detection of AFP by antigen-antibody reaction. Finally, signal amplification was achieved by horseradish peroxidase catalyzing substrate 3-amino-9-ethylcarbazole. Results showed that under the optimized conditions, the strip biosensor had a good linear relationship (R2 = 0.987) when AFP concentration was in the range of 20–250 ng/mL, and the other hundred times of proteins had no obvious interference to the detection, indicating that the method presented good selectivity. The detection of susceptibility gene CYP1A1 and AFP in real blood samples by the strip was in accordance the standard method, which showed that the method had good accuracy and could be used for qualitative judgment of SNP locus base type of susceptibility gene and semi-quantitative detection of tumor marker in real sample, so it had a good application potential. [ABSTRACT FROM AUTHOR]