Photoelectrochemical immunoassay of cardiac troponin I based on ZnTCPP/CdIn2S4 type-II heterojunction and co-catalyzed precipitation biolabeling.

CdIn2S4 and zinc tetrakis(4-carboxyphenyl)porphyrin (ZnTCPP) were synthesized by hydrothermal method, and an organic dye-sensitized inorganic semiconductor ZnTCPP/CdIn2S4 type II heterojunction was constructed on a fluorine-doped tin oxide (FTO) substrate electrode. A sandwich immunostructure for signal-attenuation photoelectrochemical (PEC) detection of cardiac troponin I (cTnI) was constructed using the ZnTCPP/CdIn2S4/FTO photoanode and a horseradish peroxidase (HRP)-ZnFe2O4-Ab2-bovine serum albumin (BSA) immunolabeling complex. The bioenzyme HRP and the HRP-like nanozyme ZnFe2O4 can co-catalyze the oxidation of 4-chloro-1-naphthol (4-CN) by H2O2 to produce an insoluble precipitate on the photoanode, thus notably reducing the anodic photocurrent for quantitative determination of cTnI. Under the optimal conditions, the photocurrent at 0 V vs. SCE in 0.1 M phosphate buffer solution (pH 7.40) containing 0.1 M ascorbic acid was linear with the logarithm of cTnI concentration from 500 fg mL-1 to 50.0 ng mL-1, and the limit of detection (LOD, S/N = 3) is 0.15 pg mL-1. Spiked recoveries were 95.1% ~ 104% for assay of cTnI in human serum samples.

Photocurrent Polarity Switchable Sensing of Hyaluronidase Activity by Regulating Electrostatic Interactions between Two Semiconductors.

Photocurrent polarity switchable photoelectrochemical (PEC) sensing has superior accuracy and anti-interference ability to conventional PEC sensing. The development of a novel strategy for photocurrent polarity switchable sensing is of great interest. Herein, a novel strategy for photocurrent polarity switchable sensing is reported by regulating electrostatic interactions between two semiconductor photoactive materials. Hyaluronic acid (HA)-modified CuO nanosheets show a negatively charged surface, which prevents the attachment of CuO nanosheets to negatively charged CdS nanodendrite-modified photoelectrodes because of the strong electrostatic repulsion. In the presence of hyaluronidase (HAase), the specific hydrolysis of HA on the surface of CuO by HAase can yield a positively charged surface, so CuO can be attached to a CdS-modified photoelectrode via electrostatic attraction, leading to photocurrent polarity switching. The photocurrent polarity switchable detection of HAase activity is achieved with an ultralow detection limit of 2 × 10-3 U mL-1 and a wide linear detection range between 0.01 and 100 U mL-1. This work provides a new and effective photocurrent polarity switching strategy for PEC sensing and a simple and efficient method for detecting HAase activity.

Photoelectrochemical immunoassay of squamous cell carcinoma antigen based on CuO/nitrogen-doped porous carbon-ZnO biolabeling and a type-II In2O3/AgBiS2 heterojunction.

AgBiS2 was hydrothermally synthesized, In2O3 was synthesized by hydrothermal method and calcination, and the type-II In2O3/AgBiS2 heterojunction material of an optimized composition ratio was cast-coated on a fluorine-doped tin oxide (FTO) slice to fabricate an In2O3/AgBiS2/FTO photoanode. The signal-attenuated photoelectrochemistry sandwich immunoassay of squamous cell carcinoma antigen (SCCA) was realized on this photoanode, on the basis of a bovine serum albumin/secondary antibody/CuO nanoparticles/nitrogen-doped porous carbon-ZnO bionanocomposite that can competitively absorb light and deplete the electron donor ascorbic acid as well as show the steric hindrance and p-n quenching effects. Under the optimized conditions (e.g., at a bias of 0 V vs. SCE), the photocurrent was linear with the common logarithm of SCCA concentration from 2.00 pg mL-1 to 50.0 ng mL-1, with a limit of detection (LOD) of 0.62 pg mL-1 (S/N = 3). The immunoassay of SCCA in human serum samples gave satisfactory recovery (92.0~103%) and relative standard deviation (5.1~7.8%) results.

Photoelectrochemical aptasensing of oxytetracycline based on a BiVO4-carboxylated graphene-WO3 Z-scheme heterojunction.

A new BiVO4-carboxylated graphene (cG)-WO3 Z-scheme heterojunction was constructed on a fluorine-doped tin oxide (FTO) substrate electrode by ultrasonic mixing and cast-coating for determination of oxytetracycline (OTC). Since cG can absorb visible light and well match with the energy levels of WO3 and BiVO4 to promote the charge separation and transfer, the photocurrent on the BiVO4-cG-WO3/FTO photoelectrode is 4.4 times that on the control BiVO4-WO3/FTO photoelectrode. An amino-functionalized OTC aptamer was fixed on the BiVO4-cG-WO3/FTO photoelectrode by the 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide mediated amide reaction, and then hexaammonium ruthenium(III) (Ru(NH3)63+) was attached to the OTC aptamer to increase the photocurrent response to the OTC binding. Under the optimized conditions, the photocurrent on the BiVO4-cG-WO3/FTO photoelectrode at 0 V vs SCE was linear with the common logarithm of OTC concentration from 0.01 nM to 500 nM, with a limit of detection of 3.1 pM (S/N = 3). Satisfactory recovery results were obtained in the analysis of real water samples.

Degradable Magnetic Nanoplatform with Hydroxide Ions Triggered Photoacoustic, MR Imaging, and Photothermal Conversion for Precise Cancer Theranostic.

Theranostic agents based on inorganic nanomaterials are still suffered from the nonbiodegradable substances with long-term retention in body and unavoidable biological toxicity, as well as nonspecificity biodistribution with potential damage toward normal tissues. Here, we develop magnetic ions (FeIII, FeII, GdIII, MnII, and MnIII) coordinated nanoplatform (MICN) with framework structure and modify them with PEG (MICN-PEG). Notably, MICN-PEG demonstrates hydroxide ions (OH-) triggered the structure collapse along with responsive near-infrared photoacoustic (PA) signal, magnetic resonance imaging (MRI), and photothermal therapy (PTT) performances. Thereby, MICN-PEG is able to remain stable in tumors and exert excellent PA/MRI and PTT effects for multimodal imaging-guided cancer treatment. In contrast, MICN-PEG is gradually collapsed in normal tissues, resulting in the significant improvement of imaging accuracy and treatment specificity. MICN-PEG is gradually cleared after administration, minimizing concerns about the long-term toxicity.

A Novel Signaling Strategy for an Ultrasensitive Photoelectrochemical Immunoassay Based on Electro-Fenton Degradation of Liposomes on a Photoelectrode.

A signaling strategy can directly determine the analytical performance and application scope of photoelectrochemical (PEC) immunoassays, so it is of great significance to develop an effective signaling strategy. The electro-Fenton reaction has been extensively used to degrade organic pollutants, but it has not been applied to PEC immunoassays. Herein, we report a novel signaling strategy for a PEC immunoassay based on electro-Fenton degradation of liposomes (Lip) on a photoelectrode. Lip vesicles are coated on Au@TiO2 core-shell photoactive material, which can prevent ascorbic acid (AA) from scavenging photogenerated holes. In the presence of a target, the immunomagnetic bead labels are converted to Fe3+ for electro-Fenton reaction, and hydroxyl radicals generated by the electro-Fenton reaction can degrade the Lip vesicles on the photoelectrode. Because of the degradation of Lip vesicles, photogenerated holes can be scavenged more effectively by AA, leading to an increase in photocurrent. Based on the electro-Fenton-regulated interface electron transfer, the sensitive "signal on" PEC immunoassay of a carcinoembryonic antigen is achieved, which features a dynamic range from 0.05 to 5 × 104 pg mL-1 and a detection limit of 0.01 pg mL-1. Our work provides a novel and efficient PEC immunoassay platform by introducing the electro-Fenton reaction into PEC analysis.

A TetR family transcriptional regulator, SP_2854 can affect the butenyl-spinosyn biosynthesis by regulating glucose metabolism in Saccharopolyspora pogona.

BACKGROUND: Butenyl-spinosyn produced by Saccharopolyspora pogona exhibits strong insecticidal activity and a broad pesticidal spectrum. Currently, important functional genes involve in butenyl-spinosyn biosynthesis remain unknown, which leads to difficulty in efficiently understanding its regulatory mechanism, and improving its production by metabolic engineering. RESULTS: Here, we identified a TetR family transcriptional regulator, SP_2854, that can positively regulate butenyl-spinosyn biosynthesis and affect strain growth, glucose consumption, and mycelial morphology in S. pogona. Using targeted metabolomic analyses, we found that SP_2854 overexpression enhanced glucose metabolism, while SP_2854 deletion had the opposite effect. To decipher the overproduction mechanism in detail, comparative proteomic analysis was carried out in the SP-2854 overexpressing mutant and the original strain, and we found that SP_2854 overexpression promoted the expression of proteins involved in glucose metabolism. CONCLUSION: Our findings suggest that SP_2854 can affect strain growth and development and butenyl-spinosyn biosynthesis in S. pogona by controlling glucose metabolism. The strategy reported here will be valuable in paving the way for genetic engineering of regulatory elements in actinomycetes to improve important natural products production.

Photoelectrochemical sandwich immunoassay of CYFRA21-1 based on In2O3/WO3 type-II heterojunction and CdS quantum dots-polydopamine nanospheres labeling.

Using an In2O3/WO3 type-II heterojunction modified fluorine-doped tin oxide (FTO) electrode as the photoanode and CdS quantum dots (QDs)-polydopamine nanospheres (PDA NSs) as the secondary antibody (Ab2) label, the photoelectrochemistry (PEC) sandwich immunosensing of the lung cancer marker CYFRA21-1 was studied. WO3 nanoplates were prepared by a hydrothermal method, In2O3 nanoporous spheres were prepared by a hydrothermal method followed by calcination, and the In2O3/WO3 type-II heterojunction with high PEC activity was prepared by ultrasonic mixing and cast-coating. PDA NSs with a high surface area can be loaded with abundant Ab2 molecules and many CdS QDs with an energy level well matched with the heterojunction, so the photocurrent signal can be amplified by the formation of a sandwich immunostructure. Through the simulation experiments of photoelectrode-modified chitosan films of varying thickness, the effective transport distance of photogenerated charges is preliminarily discussed. Under the optimized conditions, the photocurrent was linear with the common logarithm of CYFRA21-1 concentration from 100 fg mL-1 to 50 ng mL-1, with a limit of detection of 56 fg mL-1 (S/N = 3). The immunoassay of CYFRA21-1 in human serum samples gave satisfactory recovery results.

Au nanoclusters-decorated WO3 nanorods for ultrasensitive photoelectrochemical sensing of Hg2.

Photosensitizers and enzyme mimics are extensively used in photoelectrochemical (PEC) sensing, but few materials can be used as both photosensitizers and enzyme mimics in PEC sensing. Herein, we report Au nanoclusters (AuNCs) as both photosensitizers and peroxidase mimics for sensitive PEC sensing of Hg2+. It is found that AuNCs can act as photosensitizers to improve the PEC activity of WO3 nanorods; so the WO3/AuNCs composite material can be used as an advanced photosensitive material for PEC detection. AuNCs can also catalyze precipitate formation on the photoelectrode because of their peroxidase mimetic activity, and the interface electron transfer is hindered by the formed precipitate. Thus, the photocurrent of the WO3/AuNCs-based photoelectrode is quenched. When Hg2+ is present, the AuNCs-catalyzed precipitate formation is inhibited by Hg2+ because of the binding of Hg2+ to AuNCs through Hg2+-Au+ interactions. The photocurrent of the WO3/AuNCs-based photoelectrode increases accordingly, enabling "signal on" PEC detection of Hg2+. A broad linear range for Hg2+ detection is achieved between 1.0 pM and 50 nM with a detection limit of 0.2 pM. We have developed an advanced photosensitive material and introduced a simple method for PEC detection of Hg2+.

Photoelectrochemical sandwich immunoassay of brain glycogen phosphorylase based on methyl orange-sensitized TiO2 nanorods.

The photoelectrochemical immunoassay of glycogen phosphorylase BB (GPBB) was studied. A methyl orange/TiO2 nanorod heterojunction was constructed on a fluorine-doped tin oxide electrode by hydrothermal synthesis, calcination, and chemical adsorption. A sandwich immune structure consisting of GPBB as the first antibody, GPBB, and a CdS@mesoporous silica-ascorbic acid (AA)-GPBB as secondary antibody composite was constructed on each of the selected well surfaces of a 96-well microplate. By adding mercaptoethylamine to structurally destroy the secondary antibody composite and release the electron donor AA, the amplification of photocurrent, and thus the "off-on" photoelectrochemical biosensing of GPBB were realized. The use of the 96-well microplate provides good reproducibility of the assembled immune structures and eliminates the possible effect of the photogenerated hole-induced protein oxidation on the photocurrent. The relevant electrodes and materials were characterized by electrochemistry, UV-vis diffuse reflectance spectra, Fourier transform infrared spectroscopy, X-ray diffractometer, scanning electron microscopy/energy dispersive spectroscopy, transmission electron microscopy and BET method. Under the optimal conditions, the photocurrent was linear with the logarithm of GPBB concentration from 0.005 to 200 ng mL-1 and with a limit of detection of 1.7 pg mL-1 (S/N = 3). Satisfactory results were obtained in the analysis of real serum samples. A sandwich immune structure consisting of GPBB first antibody, GPBB, and a CdS@mesoporous silica-ascorbic acid (AA)-GPBB secondary antibody composite was constructed on each of the selected well surfaces of a 96-well microplate. By adding mercaptoethylamine to structurally destroy the secondary antibody composite and release the electron donor AA, the amplification of photocurrent, and thus the "off-on" photoelectrochemical biosensing of GPBB were realized.

Preparation of novel HKUST-1-glucose oxidase composites and their application in biosensing.

Copper-based metal-organic frameworks (MOF) and multi-walled carbon nanotubes (HKUST-1-MWCNTs) composite were synthesized by one-step hydrothermal method, and PDA-enzyme-HKUST-1-MWCNTs composite was prepared by one-pot method for the construction of glucose biosensors, which realized the sensitive amperometric detection of glucose at 0.7 V (vs. SCE). The sensitivity of the sensor for glucose detection was 178 µA mM-1cm-2 in the wide linear range of 0.005 ~ 7.05 mM, the detection limit was 0.12 µM and the corresponding RSD was 3.8%. Its high performance is mainly benefitted from the high porosity and large specific surface area of HKUST-1, the good conductivity of MWCNTs, and the excellent adhesion and dispersion of PDA. The strategy of combining PDA and MWCNTs to improve the dispersion and conductivity of MOF is expected to achieve a wider application of MOF-based materials in the electrochemical biosensing field.

Tailoring the Photoelectrochemical Activity of Hexametaphosphate-Capped CdS Quantum Dots by Ca2+-Triggered Surface Charge Regulation: A New Signaling Strategy for Sensitive Immunoassay.

The development of efficient signaling strategies is highly important for photoelectrochemical (PEC) immunoassay. We report here a new and efficient strategy for sensitive PEC immunoassay by tailoring the electrostatic interaction between the photoactive material and the electron donor. The photoelectric conversion of hexametaphosphate (HMP)-capped CdS quantum dots (QDs) in Na2SO3 solution is significantly boosted after Ca2+ incubation. The negative surface charges on CdS@HMP QDs decrease because of the complexation reaction between HMP and Ca2+, and the electrostatic repulsion between CdS@HMP QDs and electron donor (SO32-) becomes weak accordingly, leading to an improved electron-hole separation efficiency. Inspired by the PEC response of CdS@HMP QDs to Ca2+, a novel "signal-on" PEC immunoassay platform is established by employing CaCO3 nanoparticles as labels. By regulating the surface charge of CdS@HMP QDs with in situ-generated Ca2+ from CaCO3 labels, sensitive detection of the carcinoembryonic antigen (CEA) is achieved. The linear detection range is 0.005-50 ng mL-1 and the detection limit is 1 pg mL-1 for CEA detection. Our work not only provides a facile route to tailor the photoelectric conversion but also lays the foundation for sensitive PEC immunoassay by simply regulating the surface charge of photoactive materials.

Identification of a TetR family regulator and a polyketide synthase gene cluster involved in growth development and butenyl-spinosyn biosynthesis of Saccharopolyspora pogona.

Butenyl-spinosyn produced by Saccharopolyspora pogona exhibits strong insecticidal activity and broad pesticidal spectrum. However, its synthetic level was low in the wild-type strain. At present, important functional genes involved in butenyl-spinosyn biosynthesis remain unknown, which leads to difficulty in efficiently editing its genome to improve the butenyl-spinosyn yield. To accelerate the genetic modification of S. pogona, we conducted comparative proteomics analysis to screen differentially expressed proteins related to butenyl-spinosyn biosynthesis. A TetR family regulatory protein was selected from the 289 differentially expressed proteins, and its encoding gene (SP_1288) was successfully deleted by CRISPR/Cas9 system. We further deleted a 32-kb polyketide synthase gene cluster (cluster 28) to reduce the competition for precursors. Phenotypic analysis revealed that the deletion of the SP_1288 and cluster 28 resulted in a 3.10-fold increase and a 35.4% decrease in the butenyl-spinosyn levels compared with the wild-type strain, respectively. The deletion of cluster 28 affected the cell growth, glucose consumption, mycelium morphology, and sporulation by controlling the expression of ptsH, ptsI, amfC, and other genes related to sporulation, whereas SP_1288 did not. These findings confirmed not only that the CRISPR/Cas9 system can be applied to the S. pogona genome editing but also that SP_1288 and cluster 28 are closely related to the butenyl-spinosyn biosynthesis and growth development of S. pogona. The strategy reported here will be useful to reveal the regulatory mechanism of butenyl-spinosyn and improve antibiotic production in other actinomycetes. KEY POINTS: • SP_1288 deletion can significantly promote the butenyl-spinosyn biosynthesis. • Cluster 28 deletion showed pleiotropic effects on S. pogona. • SP_1288 and cluster 28 were deleted by CRISPR/Cas9 system in S. pogona.

NiCoO2@CeO2 Nanoboxes for Ultrasensitive Electrochemical Immunosensing Based on the Oxygen Evolution Reaction in a Neutral Medium: Application for Interleukin-6 Detection.

The development of highly active electrocatalytic labels is important for constructing sensitive electrochemical immunosensors. Great progress has been made in developing non-noble-metal nanocatalysts toward the oxygen evolution reaction (OER) in the past decade, but non-noble-metal OER nanocatalysts have not been explored as electrocatalytic labels for immunosensing. Herein, we report NiCoO2@CeO2 nanoboxes (NBs) as novel electrocatalytic labels for ultrasensitive immunosensing based on the excellent OER activity of NiCoO2@CeO2 NBs in a neutral solution. The synthesis of NiCoO2@CeO2 NBs involves Ni2+ exchange and heat treatment of ZIF-67 nanocubes to produce NiCoO2 NBs, followed by the growth of CeO2 nanoparticles on the surface of NiCoO2 NBs. The NiCoO2@CeO2 NBs offer superior OER activity to NiCoO2 NBs because of the synergetic effect between NiCoO2 NBs and CeO2 nanoparticles. The formation of ester-like bridging between CeO2 and the carboxylic groups of antibody enables direct immobilization of the antibody on the NiCoO2@CeO2 surface. A sandwich-type electrochemical immunosensor using NiCoO2@CeO2 NBs as electrocatalytic labels features a broad linear range for interleukin-6 detection from 2.5 × 10-5 to 10 ng mL-1, with a low detection limit of 7 fg mL-1. Our work lays the foundation for developing electrochemical immunosensors and aptasensors based on non-noble-metal OER electrocatalysts.

Bi-Underpotential/PtAu-bulk co-electrodeposition and subsequent Bi dissolution for the electrocatalytic oxidation and amperometric analysis of formaldehyde.

A PtAuBi-UPD composite electrocatalyst modified glassy carbon electrode (GCE) is prepared via the simultaneous underpotential deposition (UDP) of Bi and bulk deposition of Pt and Au, followed by stripping of the accessible Bi, and it shows high performance for the electrocatalytic oxidation and amperometric analysis of formaldehyde.

Three-dimensional macroporous gold electrodes superior to conventional gold disk electrodes in the construction of an electrochemical immunobiosensor for Staphylococcus aureus detection.

Herein, a three-dimensional macroporous gold (3DMG) electrode is demonstrated to be a better choice than a conventional gold disk electrode in the construction of an electrochemical immunobiosensor for Staphylococcus aureus (S. aureus) detection. The 3DMG electrode was prepared on a gold disk electrode by one-step electrodeposition using hydrogen bubbles as dynamic templates. The 3DMG electrode has a high electrochemically active surface area with pore sizes ranging from 20 to 50 µm, and these unique features are conducive to the immobilization of primary antibodies and the capture of S. aureus. Secondary antibodies (Ab2) and alkaline phosphatase (ALP) were immobilized on mesoporous silica nanospheres (MSNs), and the resulting ALP-MSNs-Ab2 composites were utilized as signal tags to construct a sandwich-type electrochemical immunobiosensor. S. aureus was measured based on alkaline phosphatase-catalyzed silver deposition and differential pulse voltammetric detection. The linear range is from 5 to 109 CFU mL-1, and the detection limit is 2 CFU mL-1 for S. aureus detection. Due to the signal amplification of the 3DMG electrode, the sensitivity of the immunobiosensor constructed on the 3DMG electrode is 9 times that of an immunobiosensor constructed on a gold disc electrode. The proposed biosensor was successfully applied for detecting S. aureus in milk samples.

miR-98-5p promotes apoptosis and inhibits migration and cell growth in papillary thyroid carcinoma through Bax/Caspase-3 by HMGA2.

BACKGROUND: The aims of this study were to investigate the function and mechanism of miRNA-98-5p in papillary thyroid carcinoma. METHODS: Quantitative real-time polymerase chain reaction (qRT-PCR) was used to measure the expression of miRNA-98-5p in papillary thyroid carcinoma. Western blotting and caspase-3/9 activity levels, flow cytometric analysis, cell migration assays, DAPI assay, cell proliferation assay, and LDH activity levels were used in this study. RESULTS: In patient with papillary thyroid carcinoma, miRNA-98-5p was reduced, and HMGA2 was increased. Downregulation of miRNA-98-5p promoted the cell growth, inhibited apoptosis, and induced HMGA2 protein expression in papillary thyroid carcinoma cell via activation of HMGA2. Overexpression of miRNA-98-5p inhibited the cell growth, induced apoptosis, and suppressed HMGA2 protein expression in papillary thyroid carcinoma cell through the suppression of HMGA2. Si-HMGA2 inhibited the effects of anti-miRNA-98-5p on cell growth of papillary thyroid carcinoma. CONCLUSION: Therefore, these results suggested the regulation of HMGA2 suppresses proliferation of papillary thyroid carcinoma through miRNA-98-5p.

Sensitive photoelectrochemical immunoassay of Staphylococcus aureus based on one-pot electrodeposited ZnS/CdS heterojunction nanoparticles.

We report here a facile synthesis of ZnS/CdS heterojunction nanoparticles on an indium-tin oxide (ITO) electrode and their application in the ultrasensitive photoelectrochemical detection of Staphylococcus aureus (S. aureus). The ZnS/CdS/ITO electrode was prepared using one-pot electrodeposition in an acidic solution containing ZnCl2, CdCl2 and Na2S2O3. The optimal ZnS/CdS heterojunction nanoparticles with a Zn/Cd atomic ratio of 1 : 1 showed a high photoelectrochemical response to l-cysteine. l-Cysteine-encapsulated liposome (cysteine@liposome) immunonanocapsules were prepared and used as the labels for photoelectrochemical detection of S. aureus. By coupling cysteine@liposome immunonanocapsule labeling with immunomagnetic separation/enrichment and photoelectrochemical analysis using the ZnS/CdS/ITO electrode, sensitive photoelectrochemical detection of S. aureus was achieved. Under optimal conditions, the linear range for photoelectrochemical detection of S. aureus was from 1 to 4000 CFU mL-1. The proposed method was successfully used for photoelectrochemical detection of S. aureus in milk and juice samples.

Correction to: Magnetic-core@dual-functional-shell nanocomposites with peroxidase mimicking properties for use in colorimetric and electrochemical sensing of hydrogen peroxide.

A self-sacrificing catalytic method is described for the preparation of magnetic core/dual-functional-shell nanocomposites composed of magnetite, gold and Prussian blue (type Fe3O4@Au-PB). Two reaction pathways are integrated. The first involves chemical dissolution of Fe3O4 (the self-sacrificing step) by acid to release ferrous ions which then reacts with hexacyanoferrate(IV) to generate PB in the proximity of the magntic nanoparticles (MNPs). The second involves the reduction of tetrachloroaurate by hydroxylamine to generate gold under the catalytic effect of the MNPs. At the end, the MNP@Au-PB nanocomposite is formed. This method exploits both the chemical reactivity and catalytic effect of the MNPs in a single step. The multi-function material was applied (a) in an optical assay for H2O2; (b) in an amperometric assay for H2O2; (c) in an enzymatic choline assay using immobilized choline oxidase. The limit of electrochemical detection of H2O2 (at a potential as low as 50 mV) is 1.1 µM which is comparable or better than most analogous methods. The sensors display superior performance compared to the use of conventional core@single-shell (MNP@Au-PB) nanomaterials. Graphical abstract A self-sacrificing catalytic method is described to prepare magnetic core/dual-functional-shell nanocomposites composed of magnetic nanoparticle, gold and Prussian blue (type MNP@Au-PB). The nanocomposites worded well as candidates to develop colorimetric and electrochemical sensors of H2O2 with superior performance to analogues.

Au nanocluster-embedded chitosan nanocapsules as labels for the ultrasensitive fluorescence immunoassay of Escherichia coli O157:H7.

Herein, Au nanocluster (AuNC)-embedded chitosan (CS) nanocapsules were prepared and used as a novel signal amplification system for the sensitive fluorescence immunoassay of Escherichia coli O157:H7 (E. coli O157:H7). AuNCs were embedded in CS to form AuNCs@CS nanocapsules, where a large number of AuNCs were embedded in each nanocapsule. A rapid, ultrasensitive, and selective method for the fluorescence detection of E. coli O157:H7 was developed by coupling the nanocapsule-amplification strategy with immunological recognition and magnetic separation. Compared with a conventional immunoassay using AuNCs as labels, the fluorescence signals of the proposed immunoassay were greatly amplified, because much more fluorescent AuNCs are linked to each bacterial cell. As a result, a linear range was obtained from 3 to 700 CFU mL-1, with a detection limit of 1 CFU mL-1. This method was successfully used to detect E. coli O157:H7 in drinking water and milk samples.