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Artificial enzymes with high stability, adjustable catalytic activity, controllable preparation, and good reproducibility have been widely studied. Noble metal nanozymes, particularly gold nanoparticles (Au NPs), exhibit good catalytic activity, but their stability is poor. In this study, zeolitic imidazolate framework-8 (ZIF-8) was used as a carrier for Au NPs, thus improving the utilization efficiency and conservation stability of the nanozymes. A ZIF-8/Au nanocomposite with peroxidase activity and a raspberry-shaped structure was synthesized. In the assay, ZIF-8/Au catalyzed the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to a blue product oxidized TMB (oxTMB). Glutathione (GSH) selectively inhibited this reaction, with a detection limit of 0.28 µM and linear range of 0.5-60 µM. Using the photo and chromaticity analysis functions, we developed a portable analysis method using a smartphone equipped with a camera module as a detection terminal for a wide range of rapid screening techniques for GSH. Preparation of raspberry-shaped ZIF-8/Au improved the catalytic activity of Au NPs and good results were demonstrated in serum, which suggests their promising application under physiological conditions., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.)

Heavy metal ions seriously threaten human health; even a trace of them can damage the renal, nervous, and immune systems irreversibly. Although established nanozyme-based colorimetric assays have been designed for the rapid detection of heavy metal ions, the general contained surface organic ligands of nanocatalysts and low absorptivity of metal ions on solid substrates might result in a weak effect on active sites and prevent the realization of their full detection potential. Here, we developed a nanozyme-based colorimetric sensor (CPM-Pt) made by pyrolysis of peat moss with preabsorbed traces of Pt ions to ultrasensitively detect Ag + . The calcination removes organic components and produces bare nanozymes that expose rich active sites. The strong protective effect from the porous carbon support enables the embedded Pt nanoparticles (Pt NPs) with a partially stable positive charge after pyrolysis (∼28% Pt 2+ species). By the d 8 - d 10 metal-metal interactions between Pt 2+ (4 f 14 5 d 8 ) and Ag + (4 d 10 ), the high proportion of Pt 2+ species on the surface of Pt NPs can readily capture/absorb Ag + . Subsequently, Ag + accepts electrons from the support to form Ag atoms, which rapidly cover the peroxidase-like active sites of bare Pt NPs, weakening the activation of H 2 O 2 to realize the response of Ag + . The colorimetric detection limit of Ag + reached an unprecedented 1.1 pM, and the corresponding naked-eye color recognition is ultrasensitive to extremely low levels (100 pM).

Exploiting low cost, water-soluble, and near-infrared (NIR) emissive electrochemiluminophores (ECLphores) is significantly important for biological applications. In this study, bright and NIR electrogenerated chemiluminescence (ECL) emissive copper nanoclusters (Cu NCs) were synthesized through a facile one-pot wet chemical reduction method. ECL properties of obtained Cu NCs were examined in the presence of potassium persulfate, resulting in maximum intensity at 735 nm, at least 135 nm red-shifted with respect to all other Cu NCs. Electrochemistry, photoluminescence (PL), and spooling ECL spectroscopies were used to track NIR ECL emission of Cu NCs ascribed to the monomeric excited states. Due to the abundant binding sites of bovine serum albumin (BSA) to anchor target biomolecules, a sandwich-type ECL immunosensor was thus fabricated using such BSA-templated Cu NCs as tags and alpha fetoprotein antigen (AFP) as a model protein for the first time. Without assisting any signal amplification strategies, the proposed NIR ECL biosensor exhibited a wide linear range (1-400 ng mL -1 ) and low detection limit (0.02 ng mL -1 ) as well as superior selectivity and reproducibility and was successfully applied in real human serum sample determination. This work sets the stage for the development of novel non-noble metal nanoclusters for large-scale and emerging nanotechnology applications.

The exploration of new strategies for portable detection of mercury ions with high sensitivity and selectivity is of great value for biochemical and environmental analyses. Herein, a straightforward, convenient, label-free, and portable sensing platform based on a Au nanoparticle (NP)-decorated WO 3 hollow nanoflower was constructed for the sensitive and selective detection of Hg(II) with a pressure, temperature, and colorimetric triple-signal readout. The resulting Au/WO 3 hollow nanoflowers (Au/WO 3 HNFs) could efficaciously impede the aggregation of Au NPs, thus significantly improving their catalytic activity and stability. The sensing mechanism of this new strategy using pressure as a signal readout was based on the mercury-triggered catalase mimetic activity of Au/WO 3 HNFs. In the presence of the model analyte Hg(II), H 2 O 2 in the detection system was decomposed to O 2 fleetly, resulting in a detectable pressure signal. Accordingly, the quantification of Hg(II) was facilely realized based on the pressure changes, and the detection limit could reach as low as 0.224 nM. In addition, colorimetric and photothermal detection of Hg(II) using the Au/WO 3 HNFs based on their mercury-stimulated peroxidase mimetic activity was also investigated, and the detection limits were calculated to be 78 nM and 0.22 μM for colorimetric and photothermal methods, respectively. Hence, this nanosensor can even achieve multimode determination of Hg(II) with the concept of point-of-care testing (POCT). Furthermore, the proposed multimode sensing platform also displayed satisfactory sensing performance for the Hg(II) assay in actual water samples. This promising strategy may provide novel insights on the fabrication of a multimode POCT platform for sensitive, selective, and accurate detection of heavy metal ions.

The rapid and sensitive surface-enhanced Raman scattering (SERS) detection of molecular biomarkers from real samples is still a challenge because the intrinsically trace analytes may have a low molecular affinity for metal surfaces. Herein, we develop a smart signal conversion and amplification strategy based on silver-gold-silica core-satellite structure nanoparticles (Ag@Au@SiO 2 NPs) to sensitively detect low adsorptive vitamin E using SERS, which has been considered a biomarker of neuromuscular disorders when its abnormal content is measured in the serum of patients. Through the reducibility of vitamin E, Ag + ions are rapidly reduced to Ag atoms, resulting in the epitaxial growth of Ag nanocrystals on gold nanoparticles forming satellite particle-particle gap-narrowed Ag@Au@SiO 2 NPs. The generated strong plasmonic field dramatically enhances the Raman signal of the Raman reporter molecule 4-aminothiophenol (4-ATP) and the detected vitamin E molecules at an estimated level of 58.19 nmol L -1 . The sensitivity of this operational SERS strategy provides tremendous prospects for the screening of neuromuscular disorders.

Although some ions, due to their unique chemical properties, can regulate the enzyme-like activity of nanomaterials, it is still a huge challenge to explore the mechanism of regulation. Herein, we found that Cr 6+ (CrO 4 2- ) as a smart switch can significantly increase the peroxidase-like (POD-like) activity of silver nanoparticles (Ag NPs), which were anchored efficiently on carbon spheres (Cal-CS/PEG/Ag) using amino-modified poly(ethylene glycol) (PEG) as a bridge. Density functional theory (DFT) calculations demonstrated that the addition of Cr 6+ can not only adjust the surface electronic redistribution of Ag atoms but also improve the geometric structure of the adsorbed intermediate, which resulted in the optimization of free energy and change of bond lengths in the catalytic reaction process, increasing the POD-like activity of Cal-CS/PEG/Ag. Based on the Cr 6+ -increased POD-like activity of Cal-CS/PEG/Ag, we successfully constructed a visual sensor of Cr 6+ along with quantitative analysis by the UV spectrum. The sensor has good selectivity for other 29 interfering ions and molecules with a detection limit of 79 nM. In this work, the detailed mechanism of the Cr 6+ -increased POD-like activity of Ag NPs was studied and a new possibility for the rational design of ion visual sensors using nanomaterials was proposed.

5-Hydroxytryptamine (5-HT) is an important neurotransmitter, and its content in the human body is of great significance to human health. In this study, an l-cysteine-terminated triangular silver nanoplate loaded on a MXene (two-dimensional transition metal carbide or nitride) (Tri-AgNP/l-Cys/MXene) electrochemical sensor was used to detect 5-HT. As an electrically active amino acid with a sulfhydryl group, l-cysteine (l-Cys) forms a more stable Ag-S bond with silver nanoparticles, which can selectively substitute trisodium citrate (TSC) in TSC-capped triangular silver nanoplates (Tri-Ag-NP/TSC). Due to the good conductivity, biocompatibility, and large surface area, MXenes provide a good platform for loading Tri-AgNP/l-Cys. Under optimized conditions, the concentration range for detecting 5-HT with the sensor is 0.5-150 μM, and the limit of detection (LOD) is 0.08 μM (S/N = 3). For detecting 5-HT in actual serum samples, the sensor also showed a good recovery rate (95.38-102.3%), and the relative standard deviation was 2.2-3.4%.

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., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Luminol, as a classical luminophore, plays a crucial role in electrochemiluminescence (ECL). However, the traditional luminol-H 2 O 2 ECL system suffers from the self-decomposition of H 2 O 2 at ambient temperature, which hinders its further application in quantitative analysis. In this work, for the first time, we developed atomically gold-supported two-dimensional VO 2 nanobelts (Au/VO 2 ) as an advanced co-reaction promoter to speed up the reduction of dissolved oxygen to superoxide radicals (O 2 •- ), which react with the luminol anion radical and greatly promote the ECL emission. The ECL resonance energy transfer (ECL-RET) between the hollow manganese dioxide nanospheres and luminol results in a conspicuously decreased ECL signal response, and in the presence of glutathione (GSH), effective redox reaction between manganese dioxide and GSH restores the ECL signal. As a consequence, the designed sensor based on ECL-RET-assisted Au/VO 2 signal amplification showed outstanding performance for "signal-on" detection of GSH in the concentration range of 10 -3 to 10 -10 M, and the detection limit was as low as 0.03 nM. The ECL sensor displayed excellent specificity and was successfully utilized to target GSH in real human serum samples. Importantly, this work not only highlights a powerful avenue for constructing an ultrasensitive ECL sensor for GSH but also provides some inspiration for the further design of high-performance co-reaction accelerators using the ECL technique.

Based on electrochemiluminescence resonance energy transfer (ERET) from Ru(bpy) 3 2+ to graphene oxide (GO), a novel label-free solid-state ECL sensor for sensitive detection of DNA was proposed. First, Ru(bpy) 3 2+ /AuNPs was successfully prepared by using a simple and green method and characterized by transmission electron microscopy (TEM), Energy Dispersive X-ray (EDX), and UV-vis spectroscopy. Then, the Ru(bpy) 3 2+ /AuNPs colloid was assembled on the gold electrode surface for solid-state ECL film which also later could be used to immobilize thiol-derivatized, single-stranded DNA (HS-ssDNA) via Au-S interactions. The stepwise modification procedure was characterized by cyclic voltammetry(CV), electrochemical impedance spectroscopy (EIS), probe approach curves (PAC) and ECL, respectively. The resulting modified electrode was tested as ECL biosensor for DNA detection. Upon addition of GO, the strong noncovalent interaction between HS-ssDNA and GO led to ECL quenching because of ERET. When in the presence of target ssDNA (t-ssDNA), the distance between the HS-ssDNA and GO increased, which significantly hindered the ERET and, thus, resulted in the restoration of ECL. The ECL intensity of the biosensor increased linearly with t-ssDNA concentration in the range of 50-1000pM, and the detection limit is 20pM. To the best of our knowledge, this is the first application of solid-state ERET from Ru(bpy) 3 2+ to GO and opens new opportunities for sensitive detection of biorecognition events., (Copyright © 2020 Elsevier B.V. All rights reserved.)

A novel Hg 2+ -responsive thermometer system for translating mercury detection into temperature monitoring was developed based on an aggregation-activated oxidase-like activity of gold nanoparticles.

Developing a rapid, low-cost, and multimode detection method for heavy metal ions remains a compelling goal for many applications, including food safety, environmental and biological analysis. This study investigated the influence of Hg 2+ on the peroxidase-like activity of gold nanoparticles (GNPs) decorated on carbon dots (CDs) from lysine (denoted as GNP@CDs). A new type of Hg 2+ -triggered peroxidase-like activity of GNP@CDs was discovered, which could catalyze the oxidation of the colorless 3,3',5,5'-tetramethylbenzidine (TMB) into blue TMB. Based on the regulation of the catalytically triggered activity, a sensitive colorimetric method for the detection of Hg 2+ was developed, with a linear range of 7-150 nM, providing a limit of detection as low as 3.7 nM. The sensor is simple and rapid, and was successfully applied to the detection of Hg 2+ enrichment in chlorella, suggesting a promising application in biological analysis.

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 Cu 2+ and form Cu 2+ -PPi complex. In the presence of hydrogen peroxide, target inorganic pyrophosphatase (PPase) can hydrolyze PPi into inorganic phosphate (Pi) and release free Cu 2+ simultaneously, resulting in a Cu 2+ -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 Cu 2+ /Cu + conversion in Cu 2+ /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., Competing Interests: Declaration of competing interest We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Herein, a simple strategy for constructing activity-controllable nanozymes is proposed based on the glutathione (GSH)-gated surface chemistry of citrate-capped Pt nanoparticles (PtNPs). PtNPs have been shown to have oxidase-like activity that can effectively catalyze the oxidation of 3,3',5,5'-tertamethylbenzidine (TMB) by O2, resulting in a typical color reaction from colorless to blue. We found that GSH can inhibit the oxidase-like activity of PtNPs as a molecule-gated surface chemistry element, resulting in a dramatic decrease of the oxidation of TMB. The addition of copper ions (Cu2+) could oxidize GSH into glutathione disulfide (GSSG), resulting in the distinct suppression of GSH-modulated PtNP surface chemistry and oxidase-like activity inhibition, which further results in a significant acceleration of TMB oxidation and the obvious recovery of intense blue color. Furthermore, the color-based detection signal associated with the redox of TMB indicator here was found to show good fluorescence and a photothermal effect and exhibit sensitive and selective response toward the proposed molecule-gated surface chemistry and Cu2+ target. On the basis of this phenomenon, we successfully constructed a three-in-one sensor for Cu2+ with a triple signal readout, colorimetric, photothermal (temperature), and fluorescence, depending on the proposed in situ modulation method for PtNP catalysis. The applicability of the three-in-one sensor was also demonstrated by measuring Cu2+ in human serum with a standard addition method, and the results are of satisfactory accuracy as confirmed by ICP-MS measurements.

Background: Iron oxide nanocomposites have received a great attention for their application in various fields like physics, medicine, biology, and material science etc., due to their unique properties, such as magnetism, electrical properties, small size, biocompatibility and low toxicity., Methods: Fe 3 O 4 /Ag 3 PO 4 @WO 3 nanocomposites with different weight percent of Ag 3 PO 4 were successfully prepared through fabricated Ag 3 PO 4 /Fe 3 O 4 with WO 3 via in situ fabrication method, electrospinning involved precursor solution preparation and spinning to enhance photocatalyst performance under simulated sunlight for the degradation of methylene blue (MB) and antibacterial activity against Staphylococcus aureus (S. aureus)., Results: The photocatalytic degradation of methylene blue (MB) under simulated light irradiation indicated that the nanocomposite with 0.25 mg of Ag 3 PO 4 has the best activity. An additional advantage of these photocatalysts is magnetic recoverability, using external magnetic field and photocatalytic stability of the nanocomposites was evaluated for three cycles. In addition, using different scavengers, holes (h + ) and superoxide radical (O 2 ·-) radicals and hydroxide radical ( · OH) were identified the main oxidative species in the degradation reaction of methylene blue., Conclusions: The results reveal that Fe 3 O 4 /Ag 3 PO 4 @WO 3 -0.25 nanocomposites have photocatalytic and antibacterial activity against S. aureus. The photocatalyst and mechanism based on the enhancement of electron transfer processes between Ag 3 PO 4 and WO 3 nanoparticles.

In this work, we discover an effective domino-effect-based detection mechanism for the rapid, high-selectivity, and ultrasensitive naked-eye colorimetric ratio assay of chromium(III) ion (Cr 3+ ) in aqueous solutions. This naked-eye colorimetric ratio assay to Cr 3+ relies on changes in absorbance properties that are due to the stimuli response of Cr 3+ for the morphological transformation of silver nanoflakes. In the presence of Cr 3+ , large silver nanoflakes can be stimulated to transform to small nanoparticles (NPs), which promoted a color change in solution from bright yellow to wine red that was detected by the naked eye and spectroscopic absorption methods. The proposed naked-eye sensing strategy was coupled with an ultraviolet (UV)-spectroscopic chemosensor for the detection of trace Cr 3+ . The detection method showed an ultralow detection limit of 1.4 nM (nanomole) for Cr 3+ in ultrapure water and 11.5 nM in human serum sample, respectively. On the basis of colorimetry, the lowest concentration of ∼50 nM for Cr 3+ in ultrapure water and human serum can be detected by the naked eye. This naked-eye-based colorimetric ratio assay for accurate and selective identification and high sensitivity of Cr 3+ is expected to have large potential and wide applications such as pharmaceutical analysis, clinical diagnosis, and environmental monitoring.

In this work, a novel nanohybrid (AuPtNPs/S-NS-GR) of well-defined Au-Pt bimetallic nanoparticles (Au-PtNPs) decorated on sulfonated nitrogen sulfur co-doped graphene (S-NS-GR) was developed. Firstly, nitrogen sulfur co-doped graphene (NS-GR) was synthesized by one-step thermal annealing method. Secondly, phenyl SO 3 H- group was introduced onto the surface of NS-GR via diazotization reaction, which could provide more binding sites for the formation of metal nanoparticles. Finally, Au-Pt bimetallic nanoparticles were anchored on the surface of S-NS-GR by using electrochemical deposition. The prepared material was characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS), Raman spectroscopy and electrochemical impedance spectra (EIS). In addition, the electrocatalytic activity towards dopamine (DA) and uric acid (UA) was systematically studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. Under optimum conditions, the linear ranges for the detection of DA and UA were 1.0×10 -8 - 4.0×10 -4 M and 1.0×10 -6 - 1.0×10 -3 M with the limits of detection (LOD, S/N = 3) of 0.006μM and 0.038μM, respectively. Furthermore, the modified electrode was applied to real sample analysis., (Copyright © 2017 Elsevier B.V. All rights reserved.)

A novel non-enzymatic superoxide anion (O 2 • - ) sensor was fabricated based on Ag nanoparticles (NPs)/L-cysteine functioned carbon nanotubes (Cys-MWCNTs) nanocomposites and used to measure the release of O 2 • - from living cells. In this strategy, AgNPs could be uniformly electrodeposited on the MWCNTs surface with average diameter of about 20nm as exhibited by scanning electronmicroscopy (SEM). Electrochemical study demonstrated that the AgNPs/Cys-MWCNTs modified glassy carbon electrode exhibited excellent catalytic activity toward the reduction of O 2 • - with a super wide linear range from 7.00×10 -11 to 7.41×10 -5 M and a low detection limit (LOD) of 2.33×10 -11 M (S/N=3). Meanwhile, the mechanism for O 2 • - reduction was also proposed for the first time. Importantly, this novel non-enzymatic O 2 • - sensor can detect O 2 • - release from cancer cells under both the external stimulation and the normal condition, which has the great potential application in clinical diagnostics to assess oxidative stress of living cells., (Copyright © 2016 Elsevier B.V. All rights reserved.)

A viable and simple method for preparing porous graphene network using silver nanoparticles (AgNPs) etching was proposed, and a sensitive biosensor was constructed based on the porous graphene (PGN) and horseradish peroxidase (HRP) to measure the release of H 2 O 2 from living cells. Owing to the large surface area and versatile porous structure, the use of nanoporous materials can significantly improve the analysis performance of the biosensor by loading large amounts of enzyme and accelerating diffusion rate. Meanwhile, the constructed electrode exhibited excellent electrochemical performance toward H 2 O 2 with a determination limit as low as 0.0267nM and wide linear range of 7 orders of magnitude, which was superior to other H 2 O 2 electrochemical sensors. Thus, this novel biosensor can detect the H 2 O 2 release from living cells not only under normal physiological conditions (10 -8 -10 -7 M) but also in emergency state with the increased concentration (~10 -4 M). This work provides tremendous potential for real-time tracking of the secretion of H 2 O 2 in different types of physiological and pathological investigations., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Rapid detection of sarcosine is a key requirement for both diagnosis and treatment of disease. We report here a simple yet sensitive colorimetric nanocomposite platform for rapid detection of sarcosine in alkaline media. The approach exploited the benefits of a rapid color-producing reaction between an organic indicator, 1,2-naphthoquinone-4-sulphonic acid sodium salt (NQS), and the analyte of sarcosine species as well as the good catalytic ability of graphene oxide (GO) to the formation of highly colored products due to its good water dispersibility, extremely large surface area and facile surface modification. As a result, a NQS functionalized GO nanocomposite through π-π stacking has been demonstrated to be useful as a highly efficient catalyst system for the selective and sensitive colorimetric determination of sarcosine by providing a nanocomposite-amplified colorimetric response. Meanwhile, the strategy offered excellent selectivity toward sarcosine species against other amino acids as well as a satisfying detection limit of 0.73 μM. More importantly, by using an electrochemical method, a credible sensing mechanism of GO nanocomposite-based colorimetric platform for a special analyte determination can be easily verified and elucidated, which also provides an attractive alternative to conventional characterization strategies.

A very efficient, simple approach was developed to fabricate a high Pt nanoparticles-loading multiwall carbon nanotube (MWCNTs) amperometric sensor for hydrogen peroxide (H2O2) determination. In this strategy, MWCNTs were first functionalized with an anionic surfactant, sodium dodecyl sulfate (SDS); then the Pt nanoparticles (NPs) were loaded on MWCNTs-SDS by electrodepositing. The large amounts of Pt nanoparticles could be well deposited on the surface of the MWCNTs-SDS modified electrode, as revealed by scanning electron microscopy (SEM). In addition, the PtNPs/MWCNTs-SDS composite was also characterized by electrochemical methods including cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The experimental results demonstrated that the constructed electrode exhibited good catalytic activity toward the hydrogen peroxide, and obtained a wide linear range from 5.8×10(-9) to 1.1×10(-3) M with a limit of detection (LOD) of 1.9×10(-9) M, which was superior to that obtained with other H2O2 electrochemical sensors reported previously. Moreover, it can also be applied to real samples analysis. The excellent performance of hydrogen peroxide sensor was ascribed to the MWCNTs-SDS composites being used as effective load matrix for the deposition of PtNPs and the synergistic amplification effect of the two kinds of nanomaterials-PtNPs and MWCNTs., (Copyright © 2014 Elsevier B.V. All rights reserved.)

A novel method for glutathione (GSH) detection in real blood sample with a nickel hexacyanoferrate (NiHCF) film modified Pt ultramicroelectrode (UME) was proposed. The electrochemical properties of NiHCF film modified Pt UME were improved by introducing cetyltrimethylammonium bromide (CTAB) and Au nanoparticles (AuNPs) into NiHCF film. The novel hybrid films (NiHCF/CTAB/AuNPs) were prepared by electrodepositing NiHCF and AuNPs in the presence of CTAB on the surface of Pt UME. The results indicated that the prepared NiHCF/CTAB/AuNPs Pt UME had a sensitive respond toward the oxidation of GSH and could be used for its selective determination in the presence of other coexisting interferents in real blood samples. The calibration curve for GSH was found to be linear from 0.2-1 μM, and the limit of detection (S/N=3) was 0.08 μM. The strategy explored here might provide a new pathway to design NiHCF/CTAB/AuNPs film microsensor for in situ detecting GSH, which had unique characteristics and potential applications in the fields of sensor and medical diagnosis., (Copyright © 2013 Elsevier B.V. All rights reserved.)

A novel light "on-off" photoelectrochemical sensing for the sensitive determination of hydroquinone was developed based on the porphyrin-functionalized Au nanoparticles on graphene (porphyrin/AuNPs/graphene). Gold nanoparticles (AuNPs) were firstly modified onto graphene sheets using NaBH4 as reductant and the porphyrin/AuNPs/graphene nanocomposites were then synthesized by self-assembly decoration of sulfhydryl porphyrin on AuNPs modified graphene sheets by S-Au bond. The porphyrin/AuNPs/graphene nanocomposites were characterized by transmission electron microscopy, X-ray photoelectron, and ultraviolet-visible absorption spectroscopies. The nanocomposites showed good dispersion in water and on indium tin oxide (ITO) surface. The resulting porphyrin/AuNPs/graphene modified ITO electrode showed good photoelectrochemical behavior toward the oxidation of hydroquinone (HQ) at 0V under white light illumination. The proposed photoelectrochemical method could detect hydroquinone with a wide linear response ranging from 20 to 240nM (R=0.9914). The detection limit was 4.6nM for HQ (S/N=3). Thus, the nanocomposites would be expected to be a novel photoactive material for photoelectrochemical biosensing., (Copyright © 2013 Elsevier B.V. All rights reserved.)

A sensitive and selective imprinted electrochemical sensor for the determination of aflatoxin B (AFB) was constructed on a glassy carbon electrode by stepwise modification of functional multiwalled carbon nanotubes (MCNTs), Au/Pt bimetallic nanoparticles (Au/PtNPs), and a thin imprinted film. The fabrication of a homogeneous porous poly o-phenylenediamine (POPD)-grafted Au/Pt bimetallic multiwalled carbon nanotubes nanocomposite film was conducted by controllable electrodepositing technology. The sensitivity of the sensor was improved greatly because of the nanocomposite functional layer; the proposed sensor exhibited excellent selectivity toward AFB owing to the porous molecular imprinted polymer (MIP) film. The surface morphologies of the modified electrodes were characterized using a scanning electron microscope. The performance of the imprinted sensor was investigated by cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy in detail. A linear relationship between the sensor response signal and the logarithm of AFB concentrations ranging from 1 × 10 to 1 × 10 mol L was obtained with a detection limit of 0.03 nmol L. It was applied to detect AFB in hogwash oil successfully. [ABSTRACT FROM AUTHOR]

In this work, we report a novel Au-Pt bimetallic nanoparticles (Au-PtNPs) decorated on the surface of nitrogen-doped graphene (NG) functionalized with 1, 3, 6, 8-pyrene tetra sulfonic acid sodium salt (PyTS) by direct electrodeposition method. The results of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and electrochemical impendence spectrum (EIS) reveal that the Au-PtNPs were successfully anchored on the surface of NG sheets with a diameter of 20–40 nm. Further, the prepared Au-PtNPs/PyTS-NG nanocomposite exhibits superior catalytic activity for the oxidation of nitrite. Under optimal experimental conditions, an amperometric sensor with a linear range of 0.5–1621 μM and a detection limit of 0.19 μM (S/N=3) for the detection of nitrite was set up and applied to real samples. [ABSTRACT FROM AUTHOR]

In this paper, an easy carbon radicals reaction procedure is put forward to functionalized graphene-supported Pt–Pd bimetallic nanoparticles (NPs). To begin with, graphene was functionalized with carboxylic sodium electro-catalyst through method of π–π interaction, which could provide more binding sites for Pt–Pd NPs. Then a fast method of in-situ electrochemical reduction was developed to synthesize highly dispersed Pt–Pd NPs on functionalized graphene. The prepared nanocomposite was characterized by Raman spectroscopy, thermogravimetric analysis (TGA), Fourier transformed infrared spectrometry (FT-IR), scanning electron microscopy (SEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and electrochemical technique. The obtained nanocomposite shows much high catalytic activity and long-term stability towards methanol oxidation than that of Pt or Pd black. It was suggesting the synergetic effects of bimetallic NPs. Moreover, it demonstrates that the incorporation of the carbon radical reaction with electrochemical reduction method is a novel approach to functionalize graphene. Our study may provide a new insight into electro-oxidation of methanol on bimetallic material. [ABSTRACT FROM AUTHOR]

• The synergy between surface geometry and surface electronic structure gives bimetallic nanoparticles unique properties. • The enhanced peroxidase mimetic activity by Hg–stimulated Cr@Ag NPs was used to construct a sensitive colorimetric sensor. • The developed colorimetric assay platform exhibits satisfying performances in real water samples. Metastable precious metal nanoparticles as precursors and self-templates with uniform atomic distribution provide unlimited possibilities for the construction of nano-secondary materials. Bimetallic nanomaterials with unexpected physical and chemical properties can be fabricated through a metal ion-mediated strategy. However, the interior functionalization of metastable precious metal nanoparticles so as to achieve synergistic interaction between precursors and external ions thus enhance the performance of bimetallic nanomaterials remains a challenge. Herein, the metal ion-mediated bimetallic nanomaterials such as Cr@Ag NPs, Ni@Ag NPs, Mn@Ag NPs, Cd@Ag NPs, and Pb@Ag NPs were precisely constructed on the basic of the seeds of silver nanoparticles (Ag NPs). More importantly, the integrated bimetallic nanomaterials Cr@Ag NPs could serve as the potential mimetic-peroxidase to sensitively and rapid identify Hg2+ in TMB-H 2 O 2 systems. Furthermore, the developed colorimetric assay platform exhibits satisfying performances in real water samples. The present study opens a new horizon for the design and construct novel nanomaterials with extraordinary opto-physical and chemical properties in colorimetric sensing. [ABSTRACT FROM AUTHOR]

• The evolution of noble metal nanoparticles colorimetric sensors was proposed. • The origins of noble metal nanoparticles colorimetric sensors are reviewed. • The advances of noble metal nanoparticles colorimetric sensors are summarized. Noble metal nanoparticles as color labels and signal generators have been widely accepted for the fabrication of colorimetric assays and sensors due to their simplicity and practicality. In the past, organic dye probes and interparticle distance-dependent nanocolorimetric sensors have witnessed great progress in chem/biosensing and recognition events. However, they often suffer from a low color resolution due to the inherent low extinction coefficients of organic dyes probes and the monocolor change-based signal readout. Currently, target-dependent in situ growth of noble metal nanoparticles provides a general means to follow naked-eye-detectable color readouts with high resolution, further allowing great advances in the development of monocolorimetric and multicolorimetric sensors for different target analytes in various detection areas, such as modern bioanalysis, environmental monitoring, food analysis and clinical diagnosis. However, reviews exploring the color readout classifications, signal generation and amplification mechanisms, as well as providing guidance on the progress of such noble metal nanoparticle growth-based colorimetric assays have rarely been reported. To highlight the significant advances in this newly-developing noble metal nanoparticle morphology/size-dependent colorimetric assays field, we herein exclusively summarise the sensing fundamentals, development evolution and cutting-edge applications of this emerging field. Finally, we provide general guidance on how to design such assays on the basis of their current challenges and future perspectives. [ABSTRACT FROM AUTHOR]