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Abstract: We demonstrate that core–shell multi-component nanocomposites can be grown in situ at room temperature by a novel one-step approach without adding any reductant and stabilizer. We have presented a one-step method for the synthesis of multi-component nanocomposites in water solution, the multi-component nanocomposites could be produced directly and quickly in an in situ wet-chemical reaction. Here, Au–polypyrrole (PPy)/Prussian blue (PB) nanocomposites have been synthesized successfully under the same circumstance. With the addition of pyrrole monomers into mixture solutions, the autopolymerization of pyrrole into PPy and AuCl4 − was reduced to elemental Au instantaneously as well as simultaneously. At the same time, PB produced along with elemental Au serving as a catalyst. Furthermore, we investigated the performance of Au–PPy/PB nanocomposites as amperometric sensor toward the reduction of H2O2, which displayed high sensitivity, fast response and good stability. The peak current of H2O2 increased linearly with the concentration of H2O2 in the range from 2.5×10−9 to 1.2×10−6 M, and the low detection limit of 8.3×10−10 M (S/N=3) was obtained. Therefore, this work provides a new pathway to design and fabricate novel multi-component nanocomposites, which have unique characteristics and hold great applications in the fields of sensors, electrocatalysis and others. [Copyright &y& Elsevier]

Abstract: Scanning electrochemical microscopy (SECM) has been proven to be a valuable technique for the quantitative investigation and surface analysis of a wide range of processes that occur at interfaces. In particular, there is a great deal of interest in studying the kinetics of charge transfer characteristics at the solid/liquid and liquid/liquid interface. This overview outlines recent advances and applications of SECM to the investigation of charge transfer reactions at the solid/liquid interface and liquid/liquid interface. [Copyright &y& Elsevier]

Based on the continuous wavelet transform (CWT), three types frequency spectra, wavelet frequency spectrum (WFS), point frequency spectrum (PFS) and time frequency spectrum (TFS), were developed. Two data sets were simulated and treated with the proposed spectra, the results indicated that WFS could extract the frequency information, which was like Fourier analysis but more accurate, PFS could obtain the frequency at any moment, TFS could show frequency change with time. These abilities of PFS and TFS were impossible for Fourier analysis. An oscillating chemical signal was processed with WFS and TFS. From the processed results, two points could be learned about the oscillating chemical reaction: one was the oscillating chemical reaction was a mixture one including two or more complex kinetics processes, the velocity of the switch from the reduced state (RS) to the oxidized state (OS) was faster than the reverse switch (from OS to RS); the other was increase of KBrO3 could decrease the velocities of both switches, which led to the oscillating period became longer. [Copyright &y& Elsevier]

An effective ratiometric fluorescent probe based on silicon particles/gold nanoclusters (SiNPs/AuNCs) nanohybrid has been fabricated and applied to be a "on-off-on" switch sensing platform for detection of Hg2+ and cysteine. In this elaborated sensing platform, the SiNPs just acted as internal reference signal, providing a build-in correction for background interferences and environmental effects, to which the AuNCs as a signal report unit for Hg2+ response was covalently grafted by amidation reaction. The fluorescence intensity of SiNPs/AuNCs could be effectively quenched upon adding Hg2+, accompanied with an easily distinguishable fluorescent color change. The ratiometric fluorescence signal (F 649 /F 511) of the established nanoprobe was linearly proportional to the concentration of Hg2+ ranging from 0.02 to 24 μM with a low detection limit of 5.6 nM, which is below the guideline value of Hg2+ in drinking water set by the World Health Organization. Interestingly, upon addition of cysteine, the Hg2+-quenched fluorescence intensity was recovered gradually. Furthermore, the approach developed has also been utilized for Hg2+ detection in real complex biological samples with satisfactory results. More importantly, benefiting from the good water-solubility and excellent biocompatibility, this nanoprobe can monitor the intracellular Hg2+ and cysteine in living cells, indicating its potential applications in advanced biosensing and bioimaging. Herein, we reported an effective dual-emission ratiometric probe for "on-off-on" detection of Hg2+ and cysteine. Image 1 • An efficient dual-emission fluorescent probe for simultaneously and visual detecting Hg2+ and L-Cys was constructed. • The probe could simultaneously detection of Hg2+ in human serum and urine samples. • Due to the ratiometric fluorescence model, the background interference was extincted. • The developed probe was successfully used for the fluorescence bioimaging of Hg2+ and L-Cys in live cells. [ABSTRACT FROM AUTHOR]

Development of highly sensitive and accurate biosensors still faces a great challenge. Herein, glucose oxidase (GOx) is efficiently immobilized on the AuCu hydrogels owing to their porous structure and interfacial interaction, demonstrating enhanced catalytic activity, satisfactory stability and recyclability. Besides, by integration of AuCu@GOx and electrochromic material of Prussian blue, a sensitive and stable biosensing platform based on the excellent electrochromic property of Prussian blue and the enhanced enzyme activity of AuCu@GOx is developed, which enables the electrochemical and visual dual-mode detection of glucose. The as-constructed biosensing platform possesses a wide linear range, and good selectivity for glucose detection with a limit of detection of 0.82 μM in visual mode and 0.84 μM in electrochemical mode. This easy-to-operate biosensing platform opens a door for the practical application of the multi-mode strategy for glucose detection. [Display omitted] • AuCu hydrogels with porous structure can immobilize glucose oxidase with enhanced catalytic activity and stability. • A biosensing platform is developed based on the electrochromic property and enhanced enzyme activity • An electrochemical and visual detection strategy is used for glucose biosensing. [ABSTRACT FROM AUTHOR]

Advanced oxidation processes (AOPs) have recently proposed for advancing colorimetric sensing applications, owing to their excellent performance of sensitive color readout that generated from the oxidation of chromogenic substrates like 3,3′,5,5′-tetramethylbenzidine (TMB) by reactive oxygen species (ROS) of AOPs such as ·OH and ·O 2 − radicals. However, the efficiency of ROS generation and the related H 2 O 2 decomposition in most AOPs is quite low especially at neutral pH, which greatly hampered the practical sensing applications of the AOPs. We herein communicated that β -cyclodextrin (β -CD)-capped gold nanoparticles (β -CD@AuNPs) can promote catalysis at neutral pH for AOP as an excellent co-catalyst. In this strategy, inorganic pyrophosphate (PPi) ions was first used to coordinate with Cu2+ and form Cu2+-PPi complex. In the presence of hydrogen peroxide, target inorganic pyrophosphatase (PPase) can hydrolyze PPi into inorganic phosphate (Pi) and release free Cu2+ simultaneously, resulting in a Cu2+-triggered Fenton-like AOP reaction. The introduced β -CD@AuNPs acts as a co-catalyst, analogous to mediators in the most co-catalyzed system, to enhance the rate-limiting step of Cu2+/Cu+ conversion in Cu2+/H 2 O 2 Fenton-like AOP and resulting in an efficient generation of ·OH and ·O 2 − radicals, which further producing an intense blue color by oxidizing TMB into its oxidation product (TMBox) within a short time. Finally, this reaction system was used to simply detecting target PPase with the colorimetric and photothermal readout based on the in-situ generated TMBox indicator. More significantly, we successfully demonstrated nanozyme can serve as a co-catalyst to promote the AOP catalysis at neutral pH, and inspire other strategies to overcome the pH limitation in the AOP catalysis and expand its colorimetric and photothermometric application. Image 1 • Gold nanozyme as a co-catalyst was explored for promoting H 2 O 2 decomposition in a Fenton-like AOP reaction. • The pH limitation of traditional Fenton-like oxidation was broken successfully by using the co-catalysis system. • A colorimetric and photothermal PPase activity detection based on β -CD@AuNPs co-catalytic AOP system was developed. [ABSTRACT FROM AUTHOR]

Iron ions play a key role in many physiological processes, which can provide feedback for the evaluation of biological systems and environmental processes. New strategies for portable determination of Fe3+ therefore are still in urgent need. Here, through an in situ generation of prussian blue nanoparticles (PB NPs) in aqueous solution, we developed a bimodal method for photothermal and colorimetric detection of Fe3+. The sensing mechanism is based on the effective oxidation etching of Au–Cu core-shell nanocubes induced by Fe3+, accompanied by the in situ generation of PB NPs. It can be attributed to the specific reaction between ferrous ions (Fe2+) from the reduction of Fe3+ and potassium ferricyanide (K 3 [Fe(CN) 6 ]) in the reaction solution. The in situ produced PB NPs show distinct bare-eye-detectable readouts with highly sensitive colorimetric and photothermal responses and thus can be used for Fe3+ determination. Such colorimetric change signals of characteristic absorbance at 740 nm in the UV–vis spectra showed a sensitive response to Fe3+ with a LOD of 210 nM. Moreover, as a sensitive photothermal probe, PB NPs generated in our Fe3+-enabled reaction system also exhibited a sensitive response to Fe3+ with a LOD of 70 nM. In addition, the standard addition experiments demonstrate our photothermal and colorimetric probe has good applicability for Fe3+ detection in the river water sample. What's more, the proposed strategy opens a new horizon for affordable detection of metal ions using a common thermometer, and therefore has a great potential for analytical chemistry and some important applications such as environmental monitoring, disease diagnostics and food analysis. Photothermal and colorimetric dual mode detection of nanomolar ferric ions based on in situ generation of prussian blue nanoparticles. Image 1 • Photothermal and colorimetric dual mode iron ions sensor was explored. • Non-integration strategy of sensing elements was exploited for optical and thermal dual mode sensor. • Affordable detection of ferric ions was achieved by a common thermometer-based photothermal method. • A simple etching-based surface modulation of Au-Cu core-shell was successfully linked with metal ions detection event. [ABSTRACT FROM AUTHOR]

Three-dimensional NiCo 2 O 4 is a kind of superior sensing material owing to its high electron transfer capability, large available surface area and numbers of active sites. In this work, NiCo 2 O 4 of the three-dimensional chestnut-like structure were easily achieved through a one step hydrothermal process. Afterwards, the morphology and structure were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Based on the three-dimensional porous chestnut-like NiCo 2 O 4 , an electrochemical sensor for hydrazine (N 2 H 4 ) detection is fabricated. This electrochemical platform can realize good selectivity, excellent stability, high sensitivity (∼2154.4 μA mM -1  cm -2 ), and low detection limit (0.3 μM), as well as a wide linear range from 1 μM to 1096 μM. The synergistic effect of nickel-cobalt in such mixed transition metal oxides which Co in Co 3 O 4 is partially replaced by Ni are beneficial for enhancing sensing properties. This study proves that three-dimensional porous chestnut-like NiCo 2 O 4 is electrochemically active for catalytic performance which is particular and promising material for good application in the practical detection of N 2 H 4 . [ABSTRACT FROM AUTHOR]

Graphitic carbon nitride quantum dots (g-CNQDs) are rarely used in the field of electrochemiluminescence. In this paper, g-CNQDs have a strong and stable electrochemiluminescence (ECL) signal generated in the presence of co-reactant K 2 S 2 O 8 . The ECL signal of g-CNQDs was quenched by the mechanism of resonance energy transfer (RET) between donor g-CNQDs and receptor riboflavin (RF) that is proved by UV-vis absorption spectroscopy, electrochemiluminescence and fluorescence emission spectroscopy analysis technology. Therefore, we achieved detection of the riboflavin content in the drug tablets of vitamin B 2 using ECL and FL. The determination results of ECL showed that the riboflavin content of the drug vitamin B 2 (VB 2 ) tablets was consistent with the fluorescence (FL) analysis, with wider linear range of 0.02–11 μM and lower minimum detection limit of 0.63 nM (S/N = 3) than FL. Hence, the riboflavin content in human serum was further detected using ECL. The relative standard deviation is less than 6.5%, with an acceptable recovery of 95.33%–104.22%, which means that this sensor has potential applications in the actual sample analysis. As a new ECL luminary, g-CNQDs have opened a new field for the development and application of ECL sensor. [ABSTRACT FROM AUTHOR]

We presented a new strategy for ultrasensitive detection of DNA sequences based on the novel detection probe which was labeled with Ag + using metallothionein (MT) as a bridge. The assay relied on a sandwich-type DNA hybridization in which the DNA targets were first hybridized to the captured oligonucleotide probes immobilized on Fe 3 O 4 @Au composite magnetic nanoparticles (MNPs), and then the Ag + -modified detection probes were used to monitor the presence of the specific DNA targets. After being anchored on the hybrids, Ag + was released down through acidic treatment and sensitively determined by a coupling flow injection–chemiluminescent reaction system (Ag + –Mn 2+ –K 2 S 2 O 8 –H 3 PO 4 –luminol) (FI–CL). The experiment results showed that the CL intensities increased linearly with the concentrations of DNA targets in the range from 10 to 500 pmol L −1 with a detection limit of 3.3 pmol L −1 . The high sensitivity in this work may be ascribed to the high molar ratio of Ag + –MT, the sensitive determination of Ag + by the coupling FI–CL reaction system and the perfect magnetic separation based on Fe 3 O 4 @Au composite MNPs. Moreover, the proposed strategy exhibited excellent selectivity against the mismatched DNA sequences and could be applied to real samples analysis. [ABSTRACT FROM AUTHOR]

The pharmacological research and detection of heavy metals of Chinese Herbal Medicines (CHMs) are important for environmental protection and human health. Here, a novel electrochemical sensor has been proposed for the detection of arsenic (As (Ⅲ)) in CHMs. The sensing system was constructed based on the octahedral GO/UiO-67@PtNPs composites, which had a porous structure with a large, unique surface area and was conducive to the adsorption and enrichment of As (Ⅲ). The oxygen-containing functional groups of GO immobilized As (Ⅲ) metal ions and its own electrical conductivity, and nanoparticles (PtNPs) have electrocatalytic effects on As (Ⅲ), which can accelerate electron transfer and increase the abundance of active sites. Under the optimized conditions, the homemade electrode showed excellent electrochemical properties, satisfactory linear range (2.7–40 nM), and a lower limit of detection (LOD, 0.42 nM). It might be low-cost, rapid, sensitive, and quantitatively identified of As (Ⅲ) in various environmental samples, especially in the medical field. A new GO/UiO-67@PtNPs composite with octahedral structure was synthesized for highly sensitive detection of arsenic (III) in Chinese herbal medicine by electrochemical method. [Display omitted] • A new GO/UiO-67@PtNPs composites with octahedral structure was synthesized successfully. • The composites was used as electrochemical sensor for the ultrasensitive recognition of As (Ⅲ) in Chinese Herbal Medicines. • The excellent property was ascribed to the electrical conductivity of GO and the electrocatalysis of PtNPs. • The proposed method provided a new, effective and low-cost method for rapid and superior capture As (Ⅲ). [ABSTRACT FROM AUTHOR]

Highlights: [•] Trp-GR was synthesized by utilizing a facile ultrasonic method. [•] The material as prepared had well dispersivity in water and better conductivity than pure GR. [•] Trp-GR/GCE showed excellent potential for the determination of AA, DA and UA. [•] The proposed method was applied for the analysis of AA, DA and UA in real samples. [Copyright &y& Elsevier]

Extracellular ATP (eATP) is an important biological signal transduction molecule. Although a variety of detection methods have been extensively used in ATP sensing and analysis, accurate detection of eATP remains difficult due to its extremely low concentration and spatiotemporal distribution. Here, an eATP measurement strategy based on tetrahedral DNA (T-DNA)-modified electrode sensing platform and hybridization chain reaction (HCR) combined with G-quadruplex/Hemin (G4/Hemin) DNAzyme dual signal amplification is proposed. In this strategy, ATP aptamer and RNA-cleaving DNAzyme were combined to form a split aptazyme. In the presence of ATP, this aptazyme hydrolyzes the cleaving substrate strand with high selectivity, releasing cleaved ssDNA, which are captured by the T-DNA assembled on the electrode surface, triggering an HCR on the electrode surface to form numerous linker sequences of the HCR dsDNA product. When G-quadruplex@AuNPs (G4) spherical nucleic acid enzymes (SNAzymes) with other linkers are used as nanocatalyst tags, they are captured by HCR dsDNA through sticky linkers present on the electrode surface. An amplified electrochemical redox current signal is generated through SNAzyme-mediated catalysis of H 2 O 2 , enabling easy detection of picomole amounts of ATP. Using this strategy, eATP levels released by tobacco suspension cells were accurately measured and the distribution and concentration of eATP released on the surface of an Arabidopsis leaf was determined. [Display omitted] • Novel T-DNA-based electrochemical aptazyme sensor for detecting ATP was designed. • Signal amplification was achieved by coupling aptazymes with HCR and SNAzymes. • The method showed high selectivity and detected extracellular ATP in plants. [ABSTRACT FROM AUTHOR]