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An instrument-free, user-friendly, and cost-effective PAD colorimetric sensor that can quantitative detection of H 2 O 2 has been realized by using bimetallic nickel–cobalt selenides as highly active peroxidase mimic and smartphone integrated with dark cavity as detector. Integrated with an ANN model and a self-compiled easy-to-use smartphone APP, the intelligent and on-site detection of H 2 O 2 was constructed, which exhibited an ultra-wide dynamic range. [Display omitted] • An effective paper-based colorimetric sensor was prepared based on nanozyme. • The optimized Ni 0.75 Co 0.25 Se exhibited excellent peoxidase-mimetic activities. • The on-site detection of H 2 O 2 was constructed by a self-compiled smartphone APP. • The machine learning-assisted sensor can detect H 2 O 2 over a wide dynamic range. Paper-based analytical devices (PADs) integrated with smartphones have shown great potential in various fields, but they also face challenges such as single signal reading, complex data processing and significant environmental impacting. In this study, a colorimetric PAD platform has been proposed using bimetallic nickel–cobalt selenides as highly active peroxidase mimic, smartphone with 3D-printing dark-cavity as a portable detector and an artificial neural network (ANN) model as multi-signal processing tool. Notably, the optimized nickel–cobalt selenides (Ni 0.75 Co 0.25 Se with Ni to Co ratio of 3/1) exhibit excellent peoxidase-mimetic activities and are capable of catalyzing the oxidation of four chromogenic reagents in the presence of H 2 O 2. Using a smartphone with image capture function as a friendly signal readout tool, the Ni 0.75 Co 0.25 Se based four channel colorimetric sensing paper is used for multi-signal quantitative analysis of H 2 O 2 by determining the Grey, red (R), green (G) and blue (B) channel values of the captured pictures. An intelligent on-site detection method for H 2 O 2 has been constructed by combining an ANN model and a self-programmed easy-to-use smartphone APP with a dynamic range of 5 μM to 2 M. Noteworthy, machine learning-assisted smartphone sensing devices based on nanozyme and 3D printing technology provide new insights and universal strategies for visual ultrasensitive detection in a variety of fields, including environments monitoring, biomedical diagnosis and safety screening. [ABSTRACT FROM AUTHOR]

The microbial environment greatly affects the performance of colourimetric sensors, especially the interference of bacteria in the sample detected. This paper reports the fabrication of an antibacterial colorimetric sensor based on V 2 C MXene synthesized via simple intercalation and stripping. The prepared V 2 C nanosheets can mimic oxidase activity towards 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation without exogenously adding H 2 O 2. Further mechanistic studies showed that V 2 C nanosheets could effectively activate the oxygen adsorbed on their surface, which in turn causes an increase in the bond length and a decrease in the magnetic moment of oxygen through electron transfer from the nanosheet surface to O 2. The V 2 C nanosheets also exhibited excellent broad-spectrum antibacterial activity through the outbreak of reactive oxygen species. Owing to its unique catalytic activity and the inherent antibacterial ability for mimicking oxidase, a colorimetric sensing platform was developed to effectively determine L-cysteine levels at a detection limit of 30.0 nM (S/N = 3). It is impressive that the detection results of L-cysteine in various complex microbial environments are also very satisfactory. This study broadens the biological use of MXene-based nanomaterials through their satisfactory enzymatic activity and provides a simple and efficient colorimetric strategy for detection techniques used in complex microbial environments. The V 2 C MXene nanosheets possessed specific oxidase-like activity towards 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation avoiding the use of H 2 O 2. The characterization and simulation indicated that V 2 C nanosheets can effectively activate the oxygen adsorbed on its surface, in turn, causes an increase in bond length and a decrease in magnetic moment of oxygen through electron transfer from nanosheets surface to O 2. Due to exceptional ROS production capability, V 2 C nanosheets also has the significant antibacterial effect on gram-positive bacteria and gram-negative bacteria. Therefore, an effective colorimetric sensing of L-cysteine sensing has been developed in complex media with high selectivity and sensitivity. [Display omitted] • An antibacterial colorimetric sensor based on V 2 C MXene was developed. • The V 2 C nanosheets have distinctive oxidase-like activity avoiding the use of H 2 O 2. • The V 2 C nanosheets exhibit excellent broad-spectrum antibacterial activity. • The role of V 2 C is to effectively activate O 2 through electron transfer. • The L-cysteine detection system have the excellent anti-interference ability. [ABSTRACT FROM AUTHOR]

A novel peptide nanotube and chitosan composite (PNT–CS) is prepared by self-assembly of dipeptide monomers in a CS aqueous solution. A scanning electron microscopy image showed that the composite had a three-dimensional (3D) network structure. Contact angle analysis indicated good hydrophilicity of the PNT–CS. X-ray diffraction patterns and FT-IR spectra revealed that the basical crystallinity properties and assembled manner of the PNTs in the composite could be maintained. Electrochemical characterization demonstrated that the PNT–CS had good conductivity and excellent stability during the electrochemical measurements. The composite combined the advantages of the two constituent materials and was further employed as an electrochemical cytosensor for the detection of cancer cells (K562). The linear range from 5 × 10 3 to 5 × 10 7 cells mL −1 with a detection limit of 630 cells mL −1 was obtained at the PNT–CS-modified electrodes using the electrochemical impedance method. These results are comparable with the previously reported cytosensors based on conventional nanomaterials. Nevertheless, the present method is very simple and suitable for down-up fabrication. The combination of the electrochemical properties, easy preparation, and excellent biocompatibility makes the PNT–CS a promising platform for next generation cytosensors. [ABSTRACT FROM AUTHOR]

An electrochemical sensor for hydrogen peroxide (HO) has been fabricated by electrodepositing gold nanoparticles (AuNPs) on an indium tin oxide (ITO) electrode modified with cobalt and manganese-layered double hydroxides (CoMn-LDHs). Scanning electron microscopy images reveal well-dispersed AuNPs with a typical size of 12 nm on the surface of the layered double hydroxides. Electrochemical characterizations show that the introduction of the LDH support significantly enhances the voltammetric response to HO. This is underpinned by a comparative study that uses single transition metal-LDHs (CoAl-LDHs or MgMn-LDHs) as supports. The results indicate that the presence of binary transition metals in the LDH layer may result in multiple interaction and interfacial effects between AuNPs and the support. At an optimal working voltage of +0.55 V (vs. Ag/AgCl), the sensor displays a wide linear range (0.1 μM to 1.27 mM), low detection limit (0.06 μM) and high sensitivity (125.0 μA∙mM∙cm), which are characteristics superior to those of most previously reported AuNP-based composite-modified electrodes. The sensor has good reproducibility and storage stability. In our view, this sensor represents a valuable tool for advanced sensing of HO. [ABSTRACT FROM AUTHOR]

The development of novel and efficient recognition molecules that can be easily modified by nanomaterials to achieve ultra-sensitive and specific cancer cell analysis is of great significance for its early diagnosis and timely prognosis. Herin, a new nanostructured hybrid based on cell membrane-coated Au cores− ultrathin Pt skins composite nanoparticles (Au@Pt@CM NPs) were developed for in vitro detection and treatment of cancer cells. In this strategy, the Au@Pt NPs acted as the signal transducer, and the cell membrane were used as the cancer-cell recognition tool. The synthesized Au@Pt@CM NPs could catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of the hydrogen peroxide and were demonstrated to have excellent peroxidase-like activity. Coated with the source cancer cell membrane, the nanoparticles achieved highly specific self-recognition to the source cell. Therefore, the colorimetric method based on Au@Pt@CM NPs could detect the cancer cells in the linear range from 50 to 100000 cells/mL with a limit of detection of 5 cells/mL, which is much lower than other colorimetric detection methods. Afterwards, the nanoparticles as a mimetic enzyme were used for therapeutics of cancer cells through the ROS-mediated oxidative damage. Due to the change of the redox state in the cells by the Au@Pt@CM NPs, the hybrid can achieve the growth inhibitory effect and the selective killing effect on cancer cells. It can be expected that this novel hybrid membrane coating method will bring new insight into developing targeted nanomaterials for tumor treatment and detection. A new nanostructured hybrid based on cell membrane-coated Au cores− ultrathin Pt skins composite nanoparticles (Au@Pt@CM NPs) were developed. Introduction of cell membrane as the identification element is an effective method for introducing multiple membrane antigens and surface functionalities that are desirable but hard to achieve using traditional synthetic techniques. The obtained nanoparticles can be used for in vitro detection and treatment of cancer cells. [Display omitted] • A new hybrid based on cell membrane-coated Au cores - ultrathin Pt skins nanoparticles was developed. • Au@Pt@CM NPs can simultaneously detect and treat breast cancer cells in vitro. • A sensitive and selective colorimetric sensing platform was obtained. • Au@Pt@CM NPs was used for therapeutics of cancer cells through the ROS-mediated oxidative damage. • This study provides a wide range of methods for medical diagnosis and biotechnology. [ABSTRACT FROM AUTHOR]

Nitrogen and sulfur co-doped Nb 2 C MXene (NS-Nb 2 C) which successfully synthesized in a one-step treatment of Nb 2 C using thiourea as N,S resource is used as a stable and high-performance sensing material for highly sensitive detection of dopamine (DA) in gastric juice under acidic conditions. The NS-Nb 2 C is more electrochemically active than multilayered Nb 2 C nanosheets (ML-Nb 2 C) and delaminated Nb 2 C nanosheets (DL-Nb 2 C) under acidic conditions due to the provision of active sites, high surface area and enhanced conductivity caused by the heteroatom doping strategy. [Display omitted] • A novel electrochemical sensor based on nitrogen and sulfur co-doped Nb 2 C MXene is proposed for DA detection in gastric juice. • NS-Nb 2 C is more electrochemically active than multilayered Nb 2 C nanosheets and delaminated Nb 2 C nanosheets. • This work provides a new direction for the application of Nb-based MXene in the electrochemical sensing applications. • Nitrogen and sulfur co-doping is an effective method to improve the electrochemical performance of MXene. This work reports the synthesis and application of nitrogen and sulfur co-doped Nb 2 C MXene (NS-Nb 2 C) for the sensing of dopamine (DA) in gastric juice. NS-Nb 2 C MXene was successfully synthesized in a one-step treatment of Nb 2 C using thiourea as N,S resource. The heteroatom doping strategy enables introduction of N,S into MXene nanosheets and simultaneously induces the increased interlayer spacing, high surface area, and enhanced electrical conductivity. It was found that NS-Nb 2 C is more electrochemically active than multilayered Nb 2 C nanosheets (ML-Nb 2 C) and delaminated Nb 2 C nanosheets (DL-Nb 2 C). Based on this, the as-prepared NS-Nb 2 C/Nafion/GCE was used to study the electrochemical behavior of dopamine in pH = 3.0. The sensing interface not only utilizes the unique two-dimensional (2D) nanosheet morphology of Nb 2 C that has a larger surface area and conductive network, but also takes advantage of the more active sites provided by doping. This enables the sensor to achieve ultra-sensitive detection of dopamine (S/N = 3) with a low limit of detection (LOD) of 0.12 µM. In addition, the prepared sensor has good stability and selectivity, and the results of detecting DA in simulated gastric juice is satisfactory. The results indicated that the Nb-based MXenes provided a promising tool for acidic electrochemical sensing applications. [ABSTRACT FROM AUTHOR]

Metabolism of β-amyloid is critical for healthy brain. Decreased clearance of β-amyloid is associated with ensued accumulation of amyloid peptide, culminating in formation of senile plaques, a neuropathological hallmark of Alzheimer's disease(AD). Apolipoprotein E (APOE), a lipoprotein for phospholipid and cholesterol metabolism, is predominantly synthesized by glia in the central nervous system, controlling Aβ aggregation and metabolism. By use of stereotactic injection and a Morris water maze, we found that delivery of Dicer1-expressing adenovirus into the hippocampus of an animal model of AD mice APPswe/PSEN1deltaE9 significantly improved spatial memory. The effect was associated with reduced amyloid peptides in the hippocampus which were analyzed with immunofluorescence and enzyme-linked immunosorbent assay. With western blot, quantitative real-time PCR, fluorescence in situ hybridization, and northern blot,Dicer1 overexpression increased apolipoprotein E (APOE) and concomitantly decreased B2 RNA in the hippocampus of the AD mice and in astrocyte cultures whereas transfection of B2 Mm2 RNA decreased APOE mRNA and protein levels in astrocyte cultures. Further, human or mouse APOE mRNA was found containing Alu RNA or its equivalent, B2 Mm2 RNA, locating downstream of its 3′-untranslated region (UTR), respectively. The 3′-UTR or 3′-UTR in conjunction with the downstream Alu/B2 RNA were cloned into a luciferase reporter; with dual-luciferase assay, we found that simultaneous transfection of Dicer1 siRNA or Alu/B2 RNA decreased the corresponding luciferase activities which suggest that Alu RNA mediated APOE mRNA degradation. Altogether, Dicer1 expression mediated amyloid peptide clearance by increasing APOE via blocking B2 RNA-mediated APOE mRNA degradation. • Injection of Dicer1-expressing virus into the hippocampus of APP/PS1 mice improved spatial learning. • Dicer1 overexpression reduced the amount of amyloid plaque and gliosis in the APP/PS1 mice. • Dicer1 overexpression increased APOE mRNA and protein levels and reduced B2 Mm2 RNA in astrocyte cultures. • Dicer1 overexpression increased APOE by blocking the repressive effect of B2 Mm2 RNA on APOE mRNA. [ABSTRACT FROM AUTHOR]

Abstract Metal-organic frameworks (MOFs) as a type of potential matrix for enzyme immobilization have attracted much interest. However, the sensitivity of most MOF-enzymatic electrochemical biosensors has not been satisfactory so far due to the poor conductivity and low apparent affinity of MOFs. In this work, new strategies have been presented: (i) using MOFs that themselves possess catalytic properties for substrates, so the synergistic catalysis by combining the MOFs and immobilized enzymes can be reinforced; (ii) introducing hydrophilic carbon nanomaterials and preparing MOF/carbon composites, not only the conductivity of the matrix but also the apparent affinity of immobilized enzyme for hydrophilic substrate can be remarkably enhanced. Horseradish peroxidase (HRP) and zeolite imidazolate framework-67(Co)/multi-walled carbon nanotube composite (ZIF-67(Co)/MWCNT) were adopted as the model enzyme and the immobilized matrix to illustrate and examine the proposed strategies. Compared with single component (ZIF-67(Co) or MWCNTs) based HRP electrochemical biosensors, the composite electrochemical biosensor displayed increased apparent substrate affinity (Michaelis constant K m reduced by ~75%) and 1.3-fold increased sensitivity in the detection of H 2 O 2. The sensitivity (315 μA mM−1 cm−2) was also much larger than that of most previously reported MOF-HRP electrochemical biosensors. The proposed strategies are envisaged to be useful for other MOF-enzymes systems, which will be beneficial to the development of biocatalysis and biosensing. Graphical abstract Unlabelled Image Highlights • ZIF-67(Co)/MWCNT composite was prepared for enzymatic electrochemical biosensing. • The composite can immobilize HRP with high activity and substrate affinity. • Highly sensitive detection for H 2 O 2 was realized based on the composite. • The superior performance is attributed to the synergy of ZIF-67(Co) and MWCNTs. [ABSTRACT FROM AUTHOR]

Volatile organic compounds (VOCs) play an important role in atmospheric chemistry. Primary VOCs take part in chemical and photochemical reactions, contributing to ozone (O3) and secondary organic aerosol (SOA) formation, which may cause air pollution problems. High VOC concentrations might lead to dizziness, nausea, headaches, genotoxicity, reproductive weakness, and other diseases harmful to human health. Several studies have been performed to analyze the components, variations, or sources of VOCs at the ground level. In contrast, studies of the vertical distribution characteristics of VOCs are scarce, and the VOC potential for O3 formation in the boundary layer is not yet well understood. To better understand the VOC vertical variation regularities and related reasons in temporal and spatial dimensions, thus to deepen the understanding of their effects on O3 and SOA formation in the vertical direction and to identify the existing gaps in VOC vertical distributions, this study reviewed VOC sampling techniques, VOC vertical distribution characteristics, VOC diffusion models, and effects caused by VOCs. This work can be a valuable reference for decision making regarding environmental and health problems. [ABSTRACT FROM AUTHOR]

A hierarchical multi-dimensional MGO-NS/CNT was presented as anode material for LIBs. The hierarchical multi-dimensional structure is beneficial to mass transfer of lithium ion/electrolyte/electron and alleviation of the volume expansion during the charge–discharge process. The MGO-NS/CNT exhibits a specific capacity of 800 mAh·g−1 at a large current density of 2000 mA g−1. After 150 charge/discharge cycles, the cycle retention rate is 84.51 %. [Display omitted] • A hierarchical multi-dimensional MGO-NS/CNT was presented as anode material for LIBs. • The hierarchical multi-dimensional structure is beneficial to mass transfer of lithium ion/electrolyte/electron. • The hierarchical multi-dimensional structure is beneficial to alleviation of the volume expansion. • The MGO-NS/CNT exhibits a specific capacity of 800 mAh·g−1 at a large current density of 2000 mA g−1. • After 150 charge/discharge cycles, the cycle retention rate is 84.51 %. The escalating demand for renewable and sustainable energy sources has led to a surge in the development of energy storage technologies. Lithium-ion batteries (LIBs), already a well-established technology, play a pivotal role in today's society. Nevertheless, the limited theoretical specific capacity of graphite-based anode materials currently utilized in LIBs restricts their widespread practical applications. Therefore, in this study, the Mn 2 GeO 4 based anode materials with different morphologies (such as one-dimensional nanowires, two-dimensional nanosheet and three-dimensional irregular nanoparticles) were successfully prepared through facile hydrothermal reaction or calcination. Notably, the experimental results revealed that the two-dimensional Mn 2 GeO 4 nanosheet (MGO-NS) sample exhibited superior electrochemical performance compared to the other two samples. Moreover, the MGO-NS was further modified by carbon nanotubes (CNTs) to form MGO-NS/CNT composite for enhanced stability. Upon conducting electrochemical tests, it was evident that the discharge specific capacity and cycling stability of the composite were significantly improved, holding promise for future energy storage applications. [ABSTRACT FROM AUTHOR]

The interface between Co 3 S 4 and Co(OH) 2 in Co 3 S 4 /Co(OH) 2 enhanced electron transfer, which might be responsible for the superior OER activity. [Display omitted] • Co(OH) 2 on Co 3 S 4 nanotubes (Co 3 S 4 /Co(OH) 2) as highly reactive and stable electrocatalysts for efficient OER. • The electron transfer between cobalt and sulfur and the pre-sculpted Co(OH) 2 promote the formation of rich hydroxide active species on the surface of Co 3 S 4 /Co(OH) 2. • Excellent electrocatalytic performance, including low overpotential, Tafel slope and high current density. Nanostructured transition metal sulfides (TMSs) have attracted great attention owing to their superior electric conductivity and easy redox reaction properties in oxygen evolution reaction (OER) catalysts. However, the strong metal-metalloid bonds (M−S) and metalloid-metalloid (S S) bonds in the crystal structure of TMSs are difficult to break, which might result in the insufficient formation of electrocatalytically active metal hydroxide species on the surface and prevent the realization of their full OER potential. Herein, we demonstrate an approach by sculpting Co(OH) 2 on Co 3 S 4 nanotubes (Co 3 S 4 /Co(OH) 2) as highly reactive and stable electrocatalysts for efficient OER. The electron transfer between cobalt and sulfur and the pre-sculpted Co(OH) 2 promote the formation of rich hydroxide active species on the surface of Co 3 S 4 /Co(OH) 2. The optimized Co 3 S 4 /Co(OH) 2 –0.8 catalyst possesses excellent electrocatalytic activity for OER in an alkaline medium, with a relatively low OER overpotential of 269 mV (at 10 mA cm−2) and a Tafel slope of 95.2 mV dec-1. This work provides a new sight of designing TMS electrocatalysts for practical application in efficient water splitting. [ABSTRACT FROM AUTHOR]

Choroidal neovascularization (CNV) is a hallmark of exudative age-related macular degeneration (exAMD) and a major cause of visual loss in AMD. Despite the widespread use of anti-VEGF therapy, serious adverse effects arise from repeated intravitreal injection of anti-VEGF antibodies, which warrant alternative strategy. We report herein that in a CNV murine model created by krypton red laser, intravenous injection of a serine racemase inhibitor, l-Aspartic acid β-hydroxamate (L-ABH), significantly reduced CNV at the dose 6 mg/kg on the first day before and followed by 3 mg/kg on the third day after laser injury. The CNV volumes were analyzed with isolectin GS-IB4 staining on choroidal/RPE flat mounts on the seventh day after laser injury. Injection of L-ABH did not produce negative effects on retinal function and visual behavior. To dissect the mechanism in vitro , pretreatment with L-ABH in primary RPE cultures significantly reduced production of vascular endothelial growth factor (VEGF) and macrophage chemotactic protein 1 (MCP-1) by TNFα-primed RPEs. Consistent with these observations, L-ABH pretreatment significantly attenuated macrophage migration mediated by TNFα-primed RPE. Collectively, intravenous injection of L-ABH significantly reduced CNV volumes via reducing production of VEGF and MCP-1 by inflammation-primed RPEs. We identify that intravenous injection of L-ABH significantly attenuates CNV by laser injury without negative effect on retinal function and visual behavior. The reducing effect on CNV is mediated via antagonizing VEGF and MCP-1 production by inflammation-primed RPEs. Image 1 • Intravenous injection of l-Aspartic acid β-hydroxamate (L-ABH) reduced choroidal neovascularization induced by laser injury. • Intravenous injection of L-ABH did not pose negative effect on retinal function and visual behavior. • Injection of L-ABH increased L-serine content and L/D-serine ratios in aqueous humor. • L-ABH inhibited production of MCP-1, VEGF by inflammation-primed RPEs. [ABSTRACT FROM AUTHOR]

The development of functional nanomaterials based on the unique structure and morphology of MXene for biosensing has aroused great interest. In this work, using thiourea as the doping source, a new structure composed of nitrogen and sulfur co-doped on the surface of Ti 3 C 2 nanosheets was synthesized through a simple one-step synthesis method. Fortunately, the obtained nitrogen and sulfur co-doped Ti 3 C 2 nanosheets (NS–Ti 3 C 2 NSs) showed excellent peroxidase-like activity and electrochemical activity. The catalytic mechanism of modified Ti 3 C 2 nanosheets was explored. It is revealed that the catalytic mechanism of NS-Ti 3 C 2 NSs is composed of two important parts: the dissociation and adsorption of H 2 O 2 and the protonation of TMB. In addition, the fabricated NS-Ti 3 C 2 NSs-based electrochemical biosensor is superior to the counterpart from Ti 3 C 2 nanosheets, indicating that the doping of nitrogen and sulfur elements provides more active sites and promotes electron transport efficiency. Combining the unique advantages of colorimetry and electrochemical technology, we have developed a fast, accurate, intuitive and efficient UA detection method for uric acid in the range of 2 μM–400 μM with a detection limit (LOD) of 0.19 μM. The established sensing platform in this study prove the possibility of the doping method for the development of MXene-based biosensors with high sensitivity and high performance, and pave the way for the future development of biosensors for biomedical fields. Using thiourea as the doping source, NS-Ti 3 C 2 NSs were synthesized via a simple one step for the non-enzymatic colorimetric and electrochemical uric acid (UA) detection. Compared with Ti 3 C 2 NSs, NS-Ti 3 C 2 NSs not only possessed peroxidase-mimicking activity, but also exhibited excellent electrochemical performance. Combining the unique advantages of colorimetry and electrochemical technology, we have developed a fast, accurate, intuitive and efficient UA detection method. [Display omitted] • One-step synthesis of nitrogen and sulfur co-doped Ti 3 C 2 nanosheets (NS–Ti 3 C 2 NSs). • A new colorimetric and electrochemical coupling sensing platform was established based on NS-Ti 3 C 2 NSs for sensing uric acid. • The developed sensing strategy shows excellent analytical performance. • Nitrogen and sulfur co-doping is an effective method to improve the peroxidase-like and electrochemical activity of MXene. [ABSTRACT FROM AUTHOR]