Zeolitic imidazole framework-derived rich-Zn-Co3O4/N-doped porous carbon with multiple enzyme-like activities for synergistic cancer therapy

Reactive oxygen species (ROS)-centered chemodynamic therapy (CDT) holds significant potential for tumor-specific treatment. However, insufficient endogenous H2O2 and extra glutathione within tumor microenvironment (TME) severely deteriorate the CDT's effectiveness. Herein, rich-Zn-Co3O4/N-doped porous carbon (Zn-Co3O4/NC) was fabricated by two-step pyrolysis, and applied to build high-efficiency nano-platform for synergistic cancer therapy upon combination with glucose oxidase (GOx), labeled Zn-Co3O4/NC-GOx for clarity. Specifically, the multiple enzyme-like activities of the Zn-Co3O4/NC were scrutinously investigated, including peroxidase-like activity to convert H2O2 to O2∙-, catalase-like activity to decompose H2O2 into O2, and oxidase-like activity to transform O2 to O2∙-, which achieved the CDT through the catalytic cascade reaction. Simultaneously, GOx reacted with intracellular glucose to produce gluconic acid and H2O2, realizing starvation therapy. In the acidic TME, the Zn-Co3O4/NC-GOx rapidly caused intracellular Zn2+ pool overload and disrupted cellular homeostasis for ion-intervention therapy. Additionally, the Zn-Co3O4/NC exhibited glutathione peroxidase-like activity, which consumed glutathione in tumor cells and reduced the ROS consumption for ferroptosis. The tumor treatments offer some constructive insights into the nanozyme-mediated catalytic medicine, coupled by avoiding the TME limitations.

Dendritic quinary PtRhMoCoFe high-entropy alloy as a robust immunosensing nanoplatform for ultrasensitive detection of biomarker

Recently, high-entropy alloys have superior physicochemical properties as compared to conventional alloys for their glamorous "cocktail effect". Nevertheless, they are scarcely applied to electrochemical immunoassays until now. Herein, uniform PtRhMoCoFe high-entropy alloyed nanodendrites (HEANDs) were synthesized by a wet-chemical co-reduction method, where glucose and oleylamine behaved as the co-reducing agents. Then, a series of characterizations were conducted to illustrate the synergistic effect among multiple metals and fascinating structural characteristics of PtRhMoCoFe HEANDs. The obtained high-entropy alloy was adopted to build a electrochemical label-free biosensor for ultrasensitive bioassay of biomarker cTnI. In the optimized analytical system, the resultant sensor exhibited a dynamic linear range of 0.0001-200 ng mL-1 and a low detection limit of 0.0095 pg mL-1 (S/N = 3). Eventually, this sensing platform was further explored in serum samples with satisfied recovery (102.0 %). This research renders some constructive insights for synthesis of high-entropy alloys and their expanded applications in bioassays and bio-devices.

Noble metal-free FeCoNiMnV high entropy alloy anchored on N-doped carbon nanotubes with prominent activity and durability for oxygen reduction and zinc-air batteries

Efficient and stable oxygen reduction reaction (ORR) catalysts are essential for constructing reliable energy conversion and storage devices. Herein, we prepared noble metal-free FeCoNiMnV high-entropy alloy supported on nitrogen-doped carbon nanotubes (FeCoNiMnV HEA/N-CNTs) by a one-step pyrolysis at 800 °C, as certificated by a set of characterizations. The graphitization degree of the N-CHTs was optimized by tuning the pyrolysis temperature in the control groups. The resultant catalyst greatly enhanced the ORR characteristics in the alkaline media, showing the positive onset potential (Eonset) of 0.99 V and half-wave potential (E1/2) of 0.85 V. More importantly, the above FeCoNiMnV HEA/N-CNTs assembled Zn-air battery exhibited a greater open-circuit voltage (1.482 V), larger power density (185.12 mW cm-2), and outstanding cycle stability (1698 cycles, 566 h). This study provides some valuable insights on developing sustainable ORR catalysts in Zn-air batteries.

Methanol-induced assembly and pyrolysis preparation of three-dimensional N-doped interconnected open carbon cages supported FeNb2O6 nanoparticles for boosting oxygen reduction reaction and Zn-air battery

Three-dimensional (3D) hollow carbon is one of advanced nanomaterials widely applied in oxygen reduction reaction (ORR). Herein, iron niobate (FeNb2O6) nanoparticles supported on metal-organic frameworks (MOFs)-derived 3D N-doped interconnected open carbon cages (FeNb2O6/NICC) were prepared by methanol induced assembly and pyrolysis strategy. During the fabrication process, the evaporation of methanol promoted the assembly and cross linkage of ZIF-8, rather than individual particles. The assembled ZIF-8 particles worked as in-situ sacrificial templates, in turn forming hierarchically interconnected open carbon cages after high-temperature pyrolysis. The as-made FeNb2O6/NICC showed a positive onset potential of 1.09 V and a half-wave potential of 0.88 V for the ORR, outperforming commercial Pt/C under the identical conditions. Later on, the as-built Zn-air battery with the FeNb2O6/NICC presented a greater power density of 100.6 mW cm-2 and durable long-cycle stability by operating for 200 h. For preparing 3D hollow carbon materials, this synthesis does not require a tedious removal process of template, which is more convenient than traditional method with silica and polystyrene spheres as templates. This work affords an exceptional example of developing 3D N-doped interconnected hollow carbon composites for energy conversion and storage devices.

MOF-derived sandwich-structured dual Z-Scheme Co9S8@ZnIn2S4/CdSe hollow nanocages heterojunction: Target-induced ultrasensitive photoelectrochemical sensing of chlorpyrifos

Exploring efficient photoactive material presents an intriguing opportunity to enhance the analytical performance of photoelectrochemical (PEC) sensor in the environmental analysis. In this work, a sandwich-structured multi-interface Co9S8@ZnIn2S4/CdSe QDs dual Z-Scheme heterojunction, derived from metal-organic framework (MOF), was synthesized as a sensing platform for chlorpyrifos detection, by integrating with enzyme-induced in situ insoluble precipitates strategy. The meticulously designed Co9S8@ZnIn2S4/CdSe QDs exhibited enhanced charge separation efficiency and was proved to be a highly effective sensing platform for the immobilization of biomolecules, attributing to the intrinsic dual Z-Scheme heterojunction and the distinctive hollow structure. The proposed PEC sensing platform combined with enzyme-induced in situ precipitate signal amplification strategy achieved superior performance for sensing of chlorpyrifos (CPF), showing in wide linear range (1.0 pg mL-1-100 ng mL-1), with a limit of detection (0.6 pg mL-1), excellent selectivity, and stability. This work offers valuable insights for the design of novel advanced photoactive materials aimed at detecting environmental pollutants with low level concentration.

Fluorescent metal nanoclusters: From luminescence mechanism to applications in enzyme activity assays

Metal nanoclusters (MNCs) have outstanding fluorescence property and biocompatibility, which show widespread applications in biological analysis. Particularly, evaluation of enzyme activity with the fluorescent MNCs has been developed rapidly within the past several years. In this review, we first introduced the fluorescent mechanism of mono- and bi-metallic nanoclusters, respectively, whose interesting luminescence properties are mainly resulted from electron transfer between the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels. Meanwhile, the charge migration within the structure occurs through ligand-metal charge transfer (LMCT) or ligand-metal-metal charge transfer (LMMCT). On such foundation, diverse enzyme activities were rigorously evaluated, including three transferases and nine hydrolases, in turn harvesting rapid research progresses within past 5 years. Finally, we summarized the design strategies for evaluating enzyme activity with the MNCs, presented the major issues and challenges remained in the relevant research, coupled by showing some improvement measures. This review will attract researchers dedicated to the studies of the MNCs and provide some constructive insights for their further applications in enzyme analysis.

Fe single atoms encapsulated in N, P-codoped carbon nanosheets with enhanced peroxidase-like activity for colorimetric detection of methimazole

Excessive use of antithyroid drug methimazole (MMI) in pharmaceutical samples can cause hypothyroidism and symptoms of metabolic decline. Hence, it is urgent to develop rapid, low cost and accurate colorimetric method with peroxidase-like nanozymes for determination of MMI in medical, nutrition and pharmaceutical studies. Herein, Fe single atoms were facilely encapsulated into N, P-codoped carbon nanosheets (Fe SAs/NP-CSs) by a simple pyrolysis strategy, as certified by a series of characterizations. UV-vis absorption spectroscopy was employed to illustrate the high peroxidase-mimicking activity of the resultant Fe SAs/NP-CSs nanozyme through the typical catalysis of 3,3',5,5'-tetramethylbenzidine (TMB) oxidation. The catalytic mechanism was scrutionously investigated by the fluorescence spectroscopy and electron paramagnetic resonance (EPR) tests. Additionally, the introduced MMI had the ability to reduce the oxidation of TMB (termed oxTMB) as a peroxidase inhibitor, coupled by fading the blue color. By virtue of the above findings, a visual colorimetric sensor was established for dual detection of methimazole (MMI) with a linear scope of 5-50 mM and a LOD of 1.57 mM, coupled by assay of H2O2 at a linear range of 3-50 mM. According to the irreversible oxidation of the drug, its screening with acceptable results was achieved on the sensing platform even in commercial tablets The Fe SAs/NP-CSs nanozyme holds great potential for clinical diagnosis and drug analysis.

The dual ECL signal enhancement strategy of Pd nanoparticles attached covalent organic frameworks and exonuclease cycling reaction for the ultrasensitive detection of progesterone

Nowadays, novel and efficient signal amplification strategy in electrochemiluminescence (ECL) platform is urgently needed to enhance the sensitivity of biosensor. In this work, the dual ECL signal enhancement strategy was constructed by the interactions of Pd nanoparticles attached covalent organic frameworks (Pd NPs@COFs) with tris (bipyridine) ruthenium (RuP) and Exonuclease III (Exo.III) cycle reaction. Within this strategy, the COFs composite was generated from the covalent reaction between 2-nitro-1,4-phenylenediamine (NPD) and trialdehyde phloroglucinol (Tp), and then animated by glutamate (Glu) to attach the Pd NPs. Next, the "signal on" ECL biosensor was constructed by the coordination assembly of thiolation capture DNA (cDNA) onto the Pd NPs@COFs modified electrode. After the aptamer recognition of progesterone (P4) with hairpin DNA 1 (HP1), the Exo. III cycle reaction was initiated with HP2 to generate free DNA, which hybridized with cDNA to form double-stranded DNA (dsDNA). For that, the RuP was embedded into the groove of dsDNA and achieved the ultrasensitive detection of P4 with a lower limit of detection (LOD) down to 0.45 pM, as well as the excellent selectivity and stability. This work expands the COFs-based materials application in ECL signal amplification and valuable DNA cyclic reaction in biochemical testing field.

Dual amplification for PEC ultrasensitive aptasensing of biomarker HER-2 based on Z-scheme UiO-66/CdIn2S4 heterojunction and flower-like PtPdCu nanozyme

As an important prognostic indicator in breast cancer, human epithelial growth factor receptor-2 (HER-2) is of importance for assessing prognosis of breast cancer patients, whose accurate and facile analysis are imperative in clinical diagnosis and treatment. Herein, photoactive Z-scheme UiO-66/CdIn2S4 heterojunction was constructed by a hydrothermal method, whose optical property and photoactivity were critically investigated by a range of techniques, combined by elucidating the interfacial charge transfer mechanism. Meanwhile, PtPdCu nanoflowers (NFs) were fabricated by a simple aqueous wet-chemical method, whose peroxidase (POD)-mimicking catalytic activity was scrutinized by representative tetramethylbenzidine (TMB) oxidation in H2O2 system. Taken together, the UiO-66/CdIn2S4 based photoelectrochemical (PEC) aptasensor was established for quantitative analysis of HER-2, where the detection signals were further magnified through catalytic precipitation reaction towards 4-chloro-1-naphthol (4-CN) oxidation (assisted by the PtPdCu NFs nanozyme). The PEC aptasensor presented a broader linear range within 0.1 pg mL-1-0.1 μg mL-1 and a lower limit of detection of 0.07 pg mL-1. This work developed a new PEC aptasensor for ultrasensitive determination of HER-2, holding substantial promise for clinical diagnostics.

Porous poly(bismaleimide-co-divinylbenzene) microspheres as dispersive solid-phase extraction adsorbent coupled to high-performance liquid chromatography for the determination of triazine herbicide residues in vegetable samples

In this work, monodisperse and nano-porous poly(bismaleimide-co-divinylbenzene) microspheres with large specific surface area (427.6 m2 /g) and rich pore structure were prepared by one-pot self-stable precipitation polymerization of 2,2'-bis[4-(4-maleimidophenoxy) phenyl] propane and divinylbenzene. The prepared poly(bismaleimide-co-divinylbenzene) microspheres were employed as dispersive solid-phase extraction (DSPE) adsorbent for the extraction of triazine herbicides. Under optimized conditions, good linearities were obtained between the peak area and the concentration of triazine herbicides in the range of 1-400 µg/L (R2 ≥ 0.9987) with the limits of detection of 0.12-0.31 µg/L. Triazine herbicides were detected using the described approach in vegetable samples (i.e., cucumber, tomato, and maize) with recoveries of 93.6%-117.3% and relative standard deviations of 0.4%-3.5%. In addition, the recoveries of triazine herbicides remained above 80.7% after being used for nine DSPE cycles, showing excellent reusability of poly(bismaleimide-co-divinylbenzene) microspheres. The adsorption of poly(bismaleimide-co-divinylbenzene) microspheres toward triazine herbicides was a monolayer and chemical adsorption. The adsorption mechanism between triazine herbicides and adsorbents might be a combination of hydrogen bonding, electrostatic interaction, and π-π conjugation. The results confirmed the potential use of the poly(bismaleimide-co-divinylbenzene) microspheres-based DSPE coupled to the high-performance liquid chromatography method for the detection of triazine herbicide residues in vegetable samples.

Target-regulated photoactivities of CdS/Ni-MOF heterojunction with [Ru(bpy)2dppz]2+ intercalator: a bisphenol A photoelectrochemical aptasensor

Bisphenol A (BPA), an important endocrine disrupting compound, has infiltrated human daily lives through electronic devices, food containers, and children's toys. Developing of novel BPA assay methods with high sensitivity holds tremendous importance in valuing the pollution state. Here, we constructed an ultrasensitive photoelectrochemical (PEC) aptasensor for BPA determination by regulating photoactivities of CdS/Ni-based metal-organic framework (CdS/Ni-MOF) with [Ru(bpy)2dppz]2+ sensitizer. CdS/Ni-MOF spheres exhibited excellent photocatalytic performance, serving as a potential sensing platform for the construction of target recognition process. [Ru(bpy)2dppz]2+ were embedded into DNA double-stranded structure, functioning as sensitizer for modulating the signal response of the developed PEC aptasensor. The proposed PEC sensor exhibited outstanding analytical performances, including a wide linear range (0.1 to 1000.0 nM), low detection limit (0.026 nM, at 3σ/m), excellent selectivity, and high stability. This work provides a perspective for the design of ideal photosensitive materials and signal amplification strategies and extends their application in environment analysis.

Palladium nanospheres-embedded metal-organic frameworks to enhance the ECL efficiency of 2,6-dimethyl-8-(3-carboxyphenyl)4,4'-difluoroboradiazene in aqueous solution for ultrasensitive Cu2+ detection

Nowadays, organic emitters suffer from insufficient electrochemiluminescence (ECL) efficiency in aqueous solutions, and their practical applications are severely restricted in the bio-sensing field. In this work, palladium nanospheres-embedded metal-organic frameworks (Pd@MOFs) were exploited to enhance the ECL efficiency of 2,6-dimethyl-8-(3-carboxyphenyl)4,4'-difluoroboradiazene (BET) prepared by a one-pot method in aqueous environment. First, the Pd@MOFs were generated via in situ reduction of Pd nanospheres anchored onto the MOFs, and fabricated by orderly coordination of palladium chloride (PdCl2) with 1,2,4,5-benzenetetramine (BTA) tetrahydrochloride. Then, the influence of protons on the ECL response of BET was studied in detail to obtain stronger ECL emission using potassium persulfate (K2S2O8) as co-reactant in aqueous environment. As a result, a 1.47-fold ECL efficiency enlargement of BET/K2S2O8 was harvested at the Pd@MOFs/GCE, where Ru(bpy)32+ behaved as a standard. Based on the fact that the ECL signals of the BET-covered Pd@MOFs modified glassy carbon electrode (simplified as BET/Pd@MOFs/GCE) can be quenched by Cu2+, the as-built ECL sensor showed a wide linear range (1.0-100.0 pM) and a limit of detection (LOD) as low as 0.12 pM. Hence, such research offers huge potential to promote the development of organic emitters in ECL biosensors and environmental monitoring.

Investigating Escherichia coli habitat transition from sediments to water in tropical urban lakes

Background

Escherichia coli is a commonly used faecal indicator bacterium to assess the level of faecal contamination in aquatic habitats. However, extensive studies have reported that sediment acts as a natural reservoir of E. coli in the extraintestinal environment. E. coli can be released from the sediment, and this may lead to overestimating the level of faecal contamination during water quality surveillance. Thus, we aimed to investigate the effects of E. coli habitat transition from sediment to water on its abundance in the water column.

Methods

This study enumerated the abundance of E. coli in the water and sediment at five urban lakes in the Kuala Lumpur-Petaling Jaya area, state of Selangor, Malaysia. We developed a novel method for measuring habitat transition rate of sediment E. coli to the water column, and evaluated the effects of habitat transition on E. coli abundance in the water column after accounting for its decay in the water column.

Results

The abundance of E. coli in the sediment ranged from below detection to 12,000 cfu g-1, and was about one order higher than in the water column (1 to 2,300 cfu mL-1). The habitat transition rates ranged from 0.03 to 0.41 h-1. In contrast, the E. coli decay rates ranged from 0.02 to 0.16 h-1. In most cases (>80%), the habitat transition rates were higher than the decay rates in our study.

Discussion

Our study provided a possible explanation for the persistence of E. coli in tropical lakes. To the best of our knowledge, this is the first quantitative study on habitat transition of E. coli from sediments to water column.

Self-enhanced Electrochemiluminescence Luminophore Based on Pd Nanocluster-Anchored Metal Organic Frameworks via Ion Annihilation for Sensitive Cell Assay of Human Lung Cancer

Electrochemiluminescence (ECL) has attracted significant interest in the analysis of cancer cells, where the ruthenium(II)-based emitter demonstrates urgency and feasibility to improve the ECL efficiency. In this work, the self-enhanced ECL luminophore was prepared by covalent anchoring of Pd nanoclusters on aminated metal organic frameworks (Pd NCs@MOFs), followed by linkage with bis(2,2'-bipyridine)-5-amino-1,10-phenanthroline ruthenium(II) (RuP). The resultant luminophore showed 214-fold self-magnification in the ECL efficiency over RuP alone, combined by promoting the interfacial photoelectron transfer. The enhanced mechanism through ion annihilation was critically proved by controlled experiments and density functional theory (DFT) calculations. Based on the above, a "signal off" ECL biosensor was built by assembly of tyrosine kinase 7 (PTK-7) aptamer (Apt) on the established sensing platform for analysis of human lung cancer cells (A549). The built sensor showed a lower detection limit of 8 cells mL-1, achieving the single-cell detection. This work reported a self-enhanced strategy for synthesis of advanced ECL emitters, combined by exploring the ECL biosensing devices in the single-cell analysis of cancers.

Fe-Ni dual-single atoms nanozyme with high peroxidase-like activity for sensitive colorimetric and fluorometric dual-mode detection of cholesterol

Cholesterol is widely existed in nerve myelin sheath and various membrane structures, whose abnormal level would deteriorate human cells or even cause diseases. Herein, Fe-Ni dual-single-atom nanozyme was efficiently incorporated into N-doped carbon nanosheets (FeNi DSAs/N-CSs) by a simple calcination method. Its nanozyme activity and catalytic mechanism were investigated in details. The FeNi DSAs/N-CSs nanozyme showed superior peroxidase-like property, which was applied for the dual-mode determination of hydrogen peroxide (H2O2) and cholesterol. The colorimetric/fluorometric assays of H2O2 displayed the linear ranges of 1-50 mM and 5-40 mM with low limits of detection of 0.45 mM and 3.33 mM, respectively. In parallel, there exhibited the linear ranges of 0.5-5.0 mM and 0.25-5.0 mM for the colorimetric/fluorometric analysis of cholesterol, coupled with the limits of detection down to 0.19 mM and 0.044 mM, respectively. This work provided a rapid, cost-effectiveness and simple colorimetric/fluorometric method for sensitive dual-mode detection of cholesterol in human serum samples.

Antioxidant CeO2 doped with carbon dots enhance ammonia production by an electroactive Azospirillum humicireducens SgZ-5T

Microbial nitrogen fixation is a fundamental process in the nitrogen cycle, providing a continuous supply of biologically available nitrogen essential for life. In this study, we combined cerium oxide-doped carbon dots (CeO2/CDs) with electroactive nitrogen-fixing bacterium Azospirillum humicireducens SgZ-5T to enhance nitrogen fixation through ammonium production. Our research demonstrates that treatment of SgZ-5T cells with CeO2/CDs (0.2 mg mL-1) resulted in a 265.70% increase in ammonium production compared to SgZ-5T cells alone. CeO2/CDs facilitate electron transfer in the biocatalytic process, thereby enhancing nitrogenase activity. Additionally, CeO2/CDs reduce the concentration of reactive oxygen species in SgZ-5T cells, leading to increased ammonium production. The upregulation of nifD, nifH and nifK gene expression upon incorporation of CeO2/CDs (0.2 mg mL-1) into SgZ-5T cells supports this observation. Our findings not only provide an economical and environmentally friendly approach to enhance biological nitrogen fixation but also hold potential for alleviating nitrogen fertilizer scarcity.

Confined synthesis of ternary FeCoMn single-atom nanozyme in N-doped hollow mesoporous carbon nanospheres for synergistic chemotherapy and chemodynamic cancer therapy

Recently, nanozymes show increasing biological applications and promising possibilities for therapeutic intervention, while their mediated therapeutic outcomes are severely compromised due to their insufficient catalytic activity and specificity. Herein, ternary FeCoMn single atoms were incorporated into N-doped hollow mesoporous carbon nanospheres by in situ confinement pyrolysis at 800 °C as high-efficiency nanozyme. The confinement strategy endows the as-prepared nanozyme with the enhanced catalase- and oxidase-like activities. Specifically, the FeCoMn TSAs/N-HCSs nanozyme can decompose intracellular H2O2 to generate O2 and subsequently convert O2 to cytotoxic superoxide radicals (O2∙-), which can initiate cascade enzymatic reactions in tumor microenvironment (TME) for chemodynamic therapy (CDT). Moreover, the cancer therapy was largely enhanced by loading with doxorubicin (DOX). Impressively, the FeCoMn TSAs/N-HCSs nanozyme-mediated CDT and the DOX-induced chemotherapy endow the DOX@FeCoMn TSAs/N-HCSs with effective tumor inhibition, showing the superior therapeutic efficacy.

Nanozyme-assisted ratiometric photoelectrochemical aptasensor over Cu2O nanocubes mediated photocurrent-polarity-switching based on S-scheme FeCdS@FeIn2S4 heterostructure

The controllable modulation of the response mode is highly attractive for the construction of photoelectrochemical (PEC) sensors with improved sensitivity and anti-interference ability in complex real samples matrix. Here, we present a charming proof-of-concept ratiometric PEC aptasensor of enrofloxacin (ENR) analysis via the controllable signal transduction. Different with the traditional sensing mechanism, this ratiometric PEC aptasensor integrates the anodic PEC signal induced by PtCuCo nanozyme-catalyzed precipitation reaction and the polarity-switching cathodic PEC response mediated by Cu2O nanocubes on S-scheme FeCdS@FeIn2S4 heterostructure. Taking advantages of the photocurrent-polarity-switching signal response model and the superior performance of the photoactive substrate material, the proposed ratiometric PEC aptasensor displays a good detection linear range for ENR analysis from 0.01 pg mL-1 to 10 ng mL-1, with a detection limit of 3.3 fg mL-1. This study provides a general platform for detecting interested trace analytes in real samples and expands the diversity of sensing strategy design.

Self-checking dual-modal aptasensor based on hybrid Z-scheme heterostructure of Zn-defective CdS/ZnS for oxytetracycline detection

Electrochemical detection methods have been widely used for trace target detection with satisfactory results. However, most of the existing electrochemical sensors rely only on single signal output, which inevitably suffer from the interference of the complex matrix of real samples. Herein, we proposed a dual-modal aptasensor for oxytetracycline assay with self-checking function by integrating photoelectrochemical (PEC) and electrochemical (EC) signal outputs in one analysis system. Zn-defective CdS/ZnS heterostructure was synthesized and served as the photo-electroactive substrate for constructing the biorecognition process, while methylene blue (MB) was used as a dual-functional probe to enhance both PEC and EC signals. Due to the high activity of Zn-defective CdS/ZnS heterojunction and the unique dual-modal signal readout strategy, the biosensing platform exhibits superior analytical performance with the relatively wide linear range (0.01-50 ng mL^-1), lower detection limits of 1.86 pg mL^-1 (PEC mode) and 3.08 pg mL^-1 (EC mode), as well as good selectivity, stability and reproducibility. The proposed dual-model analytical system with self-checking function is envisioned to provide a new approach for sensitive and reliable biosensing.

Label-free "signal-off" PEC aptasensor for determination of kanamycin based on 3D nanoflower-like FeIn2S4/CdS Z-scheme heterostructures

Highly photoactive 3D nanoflower-like FeIn2S4/CdS heterostructures were synthesized by hydrothermal treatment and low-temperature cation exchange. The FeIn2S4/CdS displayed 14.5 times signal amplification in contrast to FeIn2S4 alone. It was applied as a photoactive substrate to construct a label-free photoelectrochemical (PEC) aptasensor for ultrasensitive determination of kanamycin (KAN). Under the optimal conditions, the constructed PEC aptasensor displayed a wide linear range (5.0 × 10-4 ~ 5.0 × 101 ng mL-1) and a low detection limit (S/N = 3) of 40.01 fg mL-1. This study provides some constructive insights for preparation of advanced photoactive materials and exhibits great potential for quantitative determination of antibiotics in foods and environmental samples.

One-pot wet-chemical fabrication of 3D urchin-like core-shell Au@PdCu nanocrystals for electrochemical breast cancer immunoassay

Carbohydrate antigen 15-3 (CA15-3) is an important biomarker for early diagnosis of breast cancer. Herein, a label-free electrochemical immunosensor was built based on three-dimensional (3D) urchin-like core-shell Au@PdCu nanocrystals (labeled Au@PdCu NCs) for highly sensitive detection of CA15-3, where K3[Fe(CN)6] behaved as an electroactive probe. The Au@PdCu NCs were synthesized by a simple one-pot wet-chemical approach and the morphology, structures, and electrocatalytic property were investigated by several techniques. The Au@PdCu NCs prepared worked as electrode material to anchor more antibodies and as signal magnification material by virtue of its exceptional catalytic property. The developed biosensor exhibited a wide linear detection range from 0.1 to 300 U mL-1 and a low limit of detection (0.011 U mL-1, S/N = 3) for determination of CA15-3 under the optimal conditions. The established biosensing platform exhibits some insights for detecting other tumor biomarkers in clinical assays and early diagnosis.

Magnetic-assisted exciton-plasmon interactions modulated Bi2S3 nanorods@MoS2 nanosheets heterojunction: towards a split-type photoelectrochemical sensing of profenofos

A split-type photoelectrochemical (PEC) sensor was designed for the detection of profenofos (PFF) depending on the magnetic-assisted exciton-plasmon interactions (EPI) between the semiconductor substrate and Au NPs. The core-shell Bi2S3 nanorods@MoS2 nanosheets (Bi2S3 NRs@MoS2 NSs) heterostructure nanomaterial with fascinating performance was synthesized and used as the photovoltaic conversion substrate and signal molecules absorption platform. The PEC sensor is operated by co-incubating with the released Au NPs-cDNA from the surface of magnetic beads, originating from the target-triggered DNA double-stranded structure opening event. Due to the strong EPI effects, the photocurrent of Bi2S3 NRs@MoS2 NSs decreased and varied with the PFF concentrations. The proposed PEC sensor exhibited outstanding analytical performances, including a wide linear range (1.0 pg mL-1~1.0 μg mL-1), low detection limitation (0.23 pg mL-1, at 3 σ/m), excellent specificity, high stability, and applicability. Overall, this work provides a new signal strategy for PEC biosensors and extends its application in environmental analysis.

Cu2+-regulated one-pot wet-chemical synthesis of uniform PdCu nanostars for electrocatalytic oxidation of ethylene glycol and glycerol

The fabrication of effective and stable electrocatalysts is crucial for practical applications of direct alcohol fuel cells (DAFCs). In this study, bimetallic PdCu nanostars (PdCu NSs) were fabricated by a Cu²⁺-modulated one-pot wet-chemical method, where cetyltrimethyl ammonium bromide (CTAB) worked as a structure-regulating reagent. The morphology, compositions, crystal structures and formation mechanism of the as-prepared PdCu NSs were investigated by a series of techniques. The unique architectures created abundant active sites, which resulted in a large electrochemical active surface area (9.5 m² g^-1). The PdCu NSs showed negative shifts in the onset potentials and large forward peak current densities by contrast with those of commercial Pd black for the catalytic ethylene glycol oxidation reaction (EGOR) and glycerol oxidation reaction (GOR). It revealed that the PdCu NSs outperformed Pd black in the similar surroundings. This work provides a constructive strategy for fabrication of high-efficiency electrocatalysts for alcohol fuel cells.

Hollow cage-like PtCu nanozyme-regulated photo-activity of porous CdIn2S4/SnO2 heterojunctions for ultrasensitive PEC sensing of streptomycin

Streptomycin (STR) is extensively employed for preventive and curative purposes in animals, which is accumulated in human body through food chain and induces serious health problems. Herein, highly photoactive type II heterojunctions of porous CdIn₂S₄/SnO₂ microspheres were initially prepared, which can effectively inhibit the recombination of the charge-hole pairs. Besides, the peroxidase-mimicking catalytic property of the hollow PtCu nanocages (PtCu NCs) was carefully investigated by UV-vis spectroscopy, where catalytic oxidation of tetramethylbenzidine behaved as the benchmarked reaction. On such basis, a highly selective photoelectrochemical (PEC) aptasensor was established with the CdIn₂S₄/SnO₂ heterojunctions for bioanalysis of streptomycin, coupled by the PtCu NCs nanozyme-catalyzed biocatalytic precipitation to achieve signal magnification. Specifically, the home-made nanozyme was applied for catalytic oxidation of 3,3'-diaminobenzidine to generate insulating precipitate in aqueous H₂O₂ system and thereby block the light harvesting on the photoanode, showing steeply declined PEC responses. The as-built aptasensor showed a broad linear range of 0.01-200 nM with a low limit of detection of 7.50 pM (S/N = 3) for such analysis, combined by exploring its practical detection in milk samples. This work shows excellent nanozyme-catalyzed signal amplification for fabrication of ultrasensitive PEC biosensors towards other antibiotics detection.

N-Doped Carbon Nanotubes Supported Fe-Mn Dual-Single-Atoms Nanozyme with Synergistically Enhanced Peroxidase Activity for Sensitive Colorimetric Detection of Acetylcholinesterase and Its Inhibitor

Monitoring acetylcholinesterase (AChE) and its inhibitors is of importance for early diagnosis and therapy of neurological diseases. Herein, N-doped carbon nanotubes supported Fe-Mn dual-single-atoms (FeMn DSAs/N-CNTs) were fabricated by a simple pyrolysis, as thoroughly figured out by a series of the characterization techniques. The peroxidase-like activity of FeMn DSAs/N-CNTs was investigated by catalytic oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to generate rich hydroxyl radicals (·OH) in the H₂O₂ system, which effectively catalyzed colorless TMB oxidation to blue oxidized TMB (ox-TMB). Besides, the peroxidase-like activity was greatly weakened by thiocholine (derived from AChE), accompanied by making blue ox-TMB fade. Impressively, the highly improved peroxidase-like property is further evidenced by density functional theory (DFT) calculations, where the dual-single atoms show a lower energy barrier (0.079 eV) and their interactions with the N-CNTs played critical roles for producing the oxygen radicals. By virtue of the nanozyme, a low-cost, specific, and sensitive colorimetric sensor was built for detection of AChE with a broader linear range of 0.1-30 U L^-1 and a lower limit of detection (LOD, 0.066 U L^-1), combined with its feasible analysis in human serum samples. Also, this platform was applied for measuring huperzine A inhibitor with a wide linear scope of 5-500 nM and a LOD down to 4.17 nM. This strategy provides a low-cost and convenient approach for early clinical diagnosis and drug development.

Mulberry-like porous-hollow AuPtAg nanorods for electrochemical immunosensing of biomarker myoglobin

Mulberry-like AuPtAg porous hollow nanorods (PHNR) were facilely synthesized for the first time via a wet chemical method, where Au nanorods (Au NR) behaved as sacrificed template. The anisotropic oriented growth and etching process are involved in this synthesis. Their structural and electronic characteristics were scrutinously examined by TEM, EDS, XPS, and electrochemical techniques. The AuPtAg PHNR provided a large specific surface area and exposed a large number of active sites, showing highly enhanced catalytic activity. On this foundation, a label-free electrochemical immunosensor was developed for myoglobin (Myo) assay based on the AuPtAg PHNR. Further, the built sensor exhibited fast and ultrasensitive responses in a linear range of 0.0001 ~ 1000 ng mL^-1 with a low limit of detection (LOD = 0.46 pg mL^-1, S/N = 3), and enabled efficient application to human serum samples with acceptable results. Consequently, the developed AuPtAg PHNR-based platform has a broad prospect in practically monitoring Myo and other biomarkers in clinics.

Lignin-derived iron carbide/Mn, N, S-codoped carbon nanotubes as a high-efficiency catalyst for synergistically enhanced oxygen reduction reaction and rechargeable zinc-air battery

Design of efficient and durable oxygen reduction reaction (ORR) electrocatalysts still remains challenge in sustainable energy storage and conversion devices. To achieve sustainable development, it is of importance to prepare high-quality carbon-derived ORR catalysts from biomass. Herein, Fe₅C₂ nanoparticles (NPs) were facilely entrapped in Mn, N, S-codoped carbon nanotubes (Fe₅C₂/Mn, N, S-CNTs) by a one-step pyrolysis of the mixed lignin, metal precursors and dicyandiamide. The resulting Fe₅C₂/Mn, N, S-CNTs had open and tubular structures, which exhibited positive shifts in the onset potential (E_onset = 1.04 V) and high half-wave potential (E_1/2 = 0.85 V), showing excellent ORR characteristics. Further, the typical catalyst-assembled Zn-air battery showed a high power density (153.19 mW cm^-2) and good cycling performance as well as obvious cost advantage. The research provides some valuable insights for rational construction of low-cost and environmentally sustainable ORR catalysts in clean energy field, coupled by offering some valuable insights for reusing biomass wastes.

In situ electrostatic assembly of porphyrin as enhanced PEC photosensitizer for bioassay of single HCT-116 cells via competitive reaction

Nowadays, synthesis of novel organic photosensitizer is imperative but challenging for photoelectrochemical (PEC) assay in analytical and biomedical fields. In this work, the PEC responses enhanced about 4.3 folds after in situ electrostatic assembly of 1-butyl-3-methylimidazole tetrafluoroborate ([BIm][BF₄]) on meso-tetra (4-carboxyphenyl) porphine (TP), which was first covalently linked with NH₂ modified indium tin oxide electrode ([BIm]⁺-^-TP-NH₂-ITO). Moreover, the [BIm]⁺-^-TP-NH₂-ITO showed a much larger photocurrent in a water/dimethyl sulfoxide (DMSO) binary solvent with a water fraction (f_w) of 90%, which displayed 6.7-fold increase over that in pure DMSO, coupled by discussing the PEC enhanced mechanism in detail. Then, the PEC signals were sharply quenched via a competitive reaction between magnetic bead linked dsDNA (i.e., initial hybridization of aptamer DNA with linking DNA) and HCT-116 cells (closely associated with CRC), where the liberated L-DNA stripped the [BIm]⁺ from [BIm]⁺-^-TP-NH₂-ITO. The PEC detection strategy exhibited a wider linear range (30 ∼ 3 × 10⁵ cells mL^-1) and a lower limit of detection (6 cells mL^-1), achieving single-cell bioanalysis even in diluted human serum sample. The in situ assembly strategy offers a valuable biosensing platform to amplify the PEC signals with advanced organic photosensitizer for early diagnosis of tumors.

Hollow SnO2/CdS QDs/CdCO3 heterostructured nanocubes coupled with hollow PtPd/MnCo-CeO2 nanozyme-mediated synergistic amplification for ultrasensitive PEC immunoanalysis of lung cancer biomarker

Nowadays, lung cancer is one of the most dangerous cancers threatening human life all over the world. As a crucial biomarker, cytokeratin 19 fragment 21-1 (CYFRA 21-1) is extraordinary important for diagnosis of non-small cell lung cancer (NSCLC). In this work, we synthesized hollow SnO₂/CdS QDs/CdCO₃ heterostructured nanocubes with high and stable photocurrents, which applied to construction of a sandwich-typed photoelectrochemical (PEC) immunosensor for detection of CYFRA 21-1, integrated by in-situ catalytic precipitation strategy with home-built PtPd alloy anchored MnCo-CeO₂ (PtPd/MnCo-CeO₂) nanozyme for synergistic amplification. The interfacial electron transfer mechanism upon visible-light irradiation was investigated in details. Further, the PEC responses were seriously quenched by the specific immunoreaction and precipitation catalyzed by the PtPd/MnCo-CeO₂ nanozyme. The established biosensor showed a wider linear range of 0.001-200 ng mL^-1 and a lower limit of detection (LOD = 0.2 pg mL^-1, S/N = 3), coupled by exploring such analysis even in diluted human serum sample. This work opens a constructive avenue to develop ultrasensitive PEC sensing platforms for detecting diverse cancer biomarkers in clinic.

Bimetallic AuPt alloy/rod-like CeO2 nanojunctions with high peroxidase-like activity for colorimetric sensing of organophosphorus pesticides

Organophosphorus pesticides (OP) have extensive applications in agriculture, while their overuse causes inevitable residues in food, soil, and water, ultimately being harmful to human health and even causing diverse dysfunctions. Herein, a novel colorimetric platform was established for quantitative determination of malathion based on peroxidase mimic AuPt alloy decorated on CeO₂ nanorods (CeO₂@AuPt NRs). The synthesized nanozyme oxidized colorless 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H₂O₂. Besides, the oxidized TMB was inversely reduced by ascorbic acid (AA), which were originated from hydrolysis of L-ascorbic acid-2-phosphate (AA2P) with the assistance of acid phosphatase (ACP). Based upon this observation ACP analysis was explored by colorimetry, showing a wid linear range of 0.2 ~ 3.5 U L^-1 and a low limit of detection (LOD = 0.085 U L^-1, S/N = 3). Furthermore, malathion present in the colorimetric system inhibited the activity of ACP and simultaneously affected the generation of AA, in turn promoting the recovery of the chromogenic reaction. Based on this, the LOD was decreased to 1.5 nM (S/N = 3) for the assay of malathion with a wide linear range of 6 ~ 100 nM. This simple colorimetric platform provides some informative guidelines for determination of other pesticides and disease markers.

Simple pyrolysis of graphene-wrapped PtNi nanoparticles supported on hierarchically N-doped porous carbon for sensitive detection of carbendazim

A novel electrochemical sensor was established based on graphene-wrapped PtNi nanoparticles supported on three-dimensional (3D) N-doped porous carbon (G-PtNi/3D-NPC) for the highly sensitive and selective detection of carbendazim (CBZ). In this sensing system, the encapsulation of PtNi nanoparticles (NPs) by graphene can effectively prevent the aggregation tendency and enhance the structural stability. The hierarchically porous nanostructures have a large specific surface area to expose a large number of active sites and the resulting enhanced electrical conductivity ultimate improves the electrocatalytic activity towards CBZ. Under the optimal conditions, the prepared sensor showed excellent electrochemical responses for the determination of CBZ with a linear range of 0.5-30 μM and lower limit of detection (LOD) of 0.04 μM (S/N = 3). It also shows excellent anti-interference ability at a working potential of 0.74 V. The feasibility of the senor is demonstrated for its practical assays in diluted peach and vegetable samples with acceptable recovery (95.8-97.3 %, peach; 97.2-97.6 %, vegetable) and a relative standard deviation (RSD) below 2.3%.

Integration of CuS/ZnIn2S4 flower-like heterojunctions and (MnCo)Fe2O4 nanozyme for signal amplification and their application to ultrasensitive PEC aptasensing of cancer biomarker

Vascular endothelial growth factor 165 (VEGF₁₆₅) is a crucial regulator of angiogenesis and works as a major protein biomarker of cancer metastasis. Therefore, its quantitative detection is pivotal in clinic. In this work, CuS/ZnIn₂S₄ flower-like heterojunctions had strong and stable photocurrents, which behaved as photoactive material to construct a photoelectrochemical (PEC) aptasensor for detecting VEGF₁₆₅, combined by home-prepared (MnCo)Fe₂O₄ nanozyme-mediated signal amplification. The interfacial photo-induced electron transfer mechanism was chiefly discussed by UV-vis diffuse reflectance spectroscopy in details. Specifically, the (MnCo)Fe₂O₄ modified VEGF₁₆₅ aptamer was released from the PEC aptasensing platform for its highly specific affinity to target VEGF₁₆₅, which terminated the color precipitation reaction, ultimately recovering the PEC signals. The developed sensor displayed a wider linear range from 1 × 10^-2 to 1 × 10⁴ pg mL^-1 with a smaller limit of detection (LOD) of 0.1 fg mL^-1. This study provides some valuable insights for building other ultrasensitive aptasensors for clinical assays of cancer biomarkers in practice.

Caffeine derived graphene-wrapped Fe3C nanoparticles entrapped in hierarchically porous FeNC nanosheets for boosting oxygen reduction reaction

It is a vital requirement to explore high-efficiency and stable electrocatalysts for oxygen reduction reaction (ORR) to further relieve energy depletion. However, it is a critical challenge to develop low cost and high-quality carbon-based catalysts. Herein, a caffeine chelation-triggered pyrolysis approach was developed to construct graphene-wrapped Fe₃C nanoparticles incorporated in hierarchically porous FeNC nanosheets (G-Fe₃C/FeNC). The present Fe salt and its content as well as the pyrolysis temperature were carefully investigated in the control groups. The G-Fe₃C/FeNC catalyst showed a more positive onset potential (E_onset = 1.09 V) and half-wave potential (E_1/2 = 0.88 V) in a 0.1 M KOH solution, which outperformed commercial Pt/C (E_1/2 = 0.83 V, E_onset = 0.95 V), showing the excellent catalytic performance for the ORR activity, coupled with remarkable stability (only 0.18 mV negative shift in E_1/2 after 2000 cycles). This work provides some valuable insights for developing advanced electrocatalysts for energy storage and conversion related research.

Integration of phosphate functionalized Pt/TiO2 and Ru(bpy)32+ sensitization for ultrasensitive assay of adenosine deaminase activity on a novel split-typed PEC aptasensor

To date, it is still a challenge for high-performance photoelectrochemical (PEC) assay of low-abundance adenosine deaminase (ADA) in fundamental research and clinical diagnosis. Herein, phosphate-functionalized Pt/TiO₂ (termed PO₄^3-/Pt/TiO₂) was prepared as ideal photoactive material to develop a split-typed PEC aptasensor for detection of ADA activity, coupled by a Ru(bpy)₃²⁺ sensitization strategy. We critically studied the effects of the PO₄^3- and Ru(bpy)₃²⁺ on the detection signals, and discussed the signal-amplified mechanism. Specifically, hairpin-structured adenosine (AD) aptamer was splited into single chain via ADA-induced catalytic reaction, and subsequently hybridized with complementary DNA (cDNA, initially coating on magnetic beads). The in-situ formed double-stranded DNA (dsDNA) was further intercalated by more Ru(bpy)₃²⁺ to amplify the photocurrents. The resultant PEC biosensor showed a broader linear range of 0.05-100 U L^-1 and a lower limit of detection (0.019 U L^-1), which can fill the blank for analysis of ADA activity. This research would provide some valuable insights for building advanced PEC aptasensors in ADA-related research and clinical diagnosis.

Ultrasensitive PEC cytosensor for breast cancer cells detection and inhibitor screening based on plum-branched CdS/Bi2S3 heterostructures

Breast cancer is the most common malignant tumor in women, which seriously threatens the life and health of patients. Therefore, facile and sensitive detection of human breast cancer cells is crucial for cancer diagnosis. In this work, plum-branched CdS/Bi₂S₃ heterostructures (CdS/Bi₂S₃ HSs) were synthesized under hydrothermal condition, whose photoelectrochemical (PEC) property and biocompatibility were scrutinously investigated. In parallel, a signal amplification strategy was designed based on immune recognition between epidermal growth factor receptor (EGFR) overexpressed on membrane of breast cancer cells MDA-MB-231 and its aptamer. Integration of the above together, a highly sensitive PEC cytosensor was developed for analysis of target MDA-MB-231 cells, exhibiting a wider linear range of 1 × 10² ∼ 3 × 10⁵ cells mL^-1 with a limit of detection (LOD) down to 6 cells mL^-1 (S/N = 3). Further, the biosensor was explored for anticancer drug (e.g., dacomitinib) screening by monitoring the variations in the PEC signals of the expressed EGFR upon drug stimulation. The obtained CdS/Bi₂S₃ HSs are identified as promising and feasible photoactive material for determination of cancer cells and drug screening in clinic and related research.

High-Activity Fe3 C as pH-Universal Electrocatalyst for Boosting Oxygen Reduction Reaction and Zinc-Air Battery

Transition metal catalysts are regarded as one of promising alternatives to replace traditional Pt-based catalysts for oxygen reduction reaction (ORR). In this work, an efficient ORR catalyst is synthesized by confining Fe₃ C nanoparticles into N, S co-doped porous carbon nanosheets (Fe₃ C/N,S-CNS) via high-temperature pyrolysis, in which 5-sulfosalicylic acid (SSA) demonstrates as an ideal complexing agent for iron (ΙΙΙ) acetylacetonate while g-C₃ N₄ behaves as a nitrogen source. The influence of the pyrolysis temperature on the ORR performance is strictly examined in the controlled experiments. The obtained catalyst exhibits excellent ORR performance (E_1/2  = 0.86 V; E_onset  = 0.98 V) in alkaline electrolyte, coupled by exhibiting the superior catalytic activity and stability (E_1/2  = 0.83 V, E_onset  = 0.95 V) to Pt/C in acidic media. In parallel, its ORR mechanism is carefully illustrated by the density functional theory (DFT) calculations, especially the role of the incorporated Fe₃ C played in the catalytic process. The catalyst-assembled Zn-air battery also exhibits a much higher power density (163 mW cm^-2 ) and ultralong cyclic stability in the charge-discharge test for 750 h with a gap increase down to 20 mV. This study provides some constructive insights for preparation of advanced ORR catalysts in green energy conversion units correlated systems.

β-cyclodextrin-functionalized magnetic graphene oxide for the efficient enrichment of bisphenols in milk and milk packaging

In this work, β-cyclodextrin-functionalized magnetic graphene oxide (NiFe₂O₄@GO@β-CD) was synthesized and employed as magnetic solid-phase extraction adsorbent for the extraction of bisphenols before high performance liquid chromatography analysis. The modification of β-cyclodextrin could enhance the adsorption performance of NiFe₂O₄@GO@β-CD towards bisphenols through the host-guest interaction and hydrogen-bond interaction. Under the optimal conditions, good linearities between peak area and concentration of bisphenols (1 - 300 μg L^-1, r ≥ 0.9989) were obtained with the limits of detection (S/N = 3) in the range of 0.050 - 0.10 μg L^-1. The recoveries of bisphenols in milk and milk packaging ranged from 78.0% to 101.6%. Moreover, NiFe₂O₄@GO@β-CD showed stable chemical properties and good reusability with the recoveries of bisphenols remained above 80.0% after 12 MSPE cycles. The adsorption characteristics of NiFe₂O₄@GO@β-CD towards bisphenols fitted well with the pseudo-second-order kinetic model and Langmuir model. The hydrogen-bond interaction, π-π interaction, host-guest interaction and electrostatic interaction between sorbent and bisphenols played important role during the adsorption process. The developed method showed potential applications for the analysis of trace bisphenols in milk and milk packaging.

Hydrogen Bond Organic Frameworks as Radical Reactors for Enhancement in ECL Efficiency and Their Ultrasensitive Biosensing

Nowadays, electrochemiluminescence (ECL) efficiency of an organic emitter is closely related with its potential applications in food safety and environmental monitoring fields. In this work, 2,4,6-tris(4-carboxyphenyl)-1,3,5-triazine (TATB) was self-assembled to form hydrogen bond organic frameworks (HOFs), which worked as ideal reactors to generate highly active oxygen-containing radicals, followed by linking with isoluminol (ILu) via amide bond (termed ILu-HOFs). After covalent assembly with aminated indium-tin oxide electrode (labeled NH₂-ITO), the ECL efficiency of the ILu-HOFs NH₂-ITO showed about a 23.4-time increase over that of ILu itself in the presence of H₂O₂. Meanwhile, the enhanced ECL mechanism was mainly studied by electron paramagnetic resonance, theoretical calculation, and electrochemistry. On the above foundation, an aptamer "sandwich" ECL biosensor was constructed for detecting isocarbophos (ICP) via in situ elimination of H₂O₂ with catalase-linked palladium nanocubes (CAT-Pd NCs). The as-built sensor showed a broad linear range (1 pM to 100 nM) and a low limit of detection (LOD) down to 0.4 pM, coupled with efficient assays of ICP in lake water and cucumber juice samples. This strategy provides an effective way for the synthesis of advanced ECL emitter, coupled by showing promising applications in environmental and food analysis.

Dual II-scheme nanosheet-like Bi2S3/Bi2O3/Ag2S heterostructures for ultrasensitive PEC aptasensing of aflatoxin B1 coupled with catalytic signal amplification by dendritic nanorod-like Au@Pd@Pt nanozyme

As one of the most toxic chemical substances, aflatoxin B1 (AFB1) has a strong carcinogenic effect even at a trace level in human and animal, which severely threatens human health and even causes cancers. Therefore, ultrasensitive detection of AFB1 is of significant importance. For such analysis, dual II-scheme sheet-like Bi₂S₃/Bi₂O₃/Ag₂S heterostructures were prepared by the in-situ growth method, which exhibited high separation efficiency for the electron-hole (e^--h⁺) pairs, prominent stability, and high photoactivity. Moreover, the dendritic nanorod-like Au@Pd@Pt (Au@Pd@Pt DNRs) nanozyme was homely synthesized, whose peroxidase-like activity was scrupulously investigated by catalytical oxidation of diaminobenzidine (DAB) in the presence of H₂O₂. Integration by the aptasensing strategy, a photoelectrochemical (PEC) "signal-on" aptasensor was prepared, which exhibited a broader linear range of 0.5 pg mL^-1-100 ng mL^-1 with a lower limit of detection (LOD = 0.09 pg mL^-1, S/N = 3). This work provides a feasible strategy to develop advanced PEC biosensors for actual analysis of environmental pollutants.

Z-scheme Cu2MoS4/CdS/In2S3 nanocages heterojunctions-based PEC aptasensor for ultrasensitive assay of fumonisin B1 via signal amplification with hollow PtPd–CoSnO3 nanozyme

Fumonisin B1 (FB1), the most prevalent and highest toxicity mycotoxins among fumonisins family, poses threats to human especially children and infants even at a trace level. Therefore, its facile and sensitive detection is of importance. Herein, Z-scheme Cu₂MoS₄/CdS/In₂S₃ nanocage-like heterojunctions (labeled Cu₂MoS₄/CdS/In₂S₃) were synthesized, whose photoelectrochemical (PEC) property and electron transfer mechanism were strictly investigated. The Cu₂MoS₄/CdS/In₂S₃ behaved as photoactive substrate for building a PEC sensing platform for detection of FB1, integrated with PtPd alloy modified hollow CoSnO₃ nanoboxes (labeled PtPd-CoSnO₃) nanozyme. By virtue of the stronger affinity between the target FB1 and its aptamer (FB1-Apt), the photocurrent was recovered by releasing the CoSnO₃-PtPd₃ modified FB1-Apt (FB1-Apt/PtPd-CoSnO₃) from the photoanode, which can terminate the catalytic precipitation reaction for its peroxidase-like property. The resultant PEC aptasensor exhibited a wider dynamic linear range from 1 × 10^-4 to 1 × 10² ng mL^-1 with a lower limit of detection (0.0723 pg mL^-1). Thus, this research provides a feasible PEC sensing platform for routine analysis of other mycotoxins in practice.

Tailoring enzymatic loading capacity on CdS nanorods@ZnIn2S4 nanosheets 1D/2D heterojunctions: Toward ultrasensitive photoelectrochemical bioassay of tobramycin

Despite advances in the development of photoelectrochemical (PEC) sensor, modulating the PEC response of assembled heterostructure interface is still a great challenge. Here, an ultrasensitive PEC aptasensor for tobramycin (TOB) assay was conducted based on one-dimensional/two-dimensional CdS nanorods@ZnIn₂S₄ nanosheets (1D/2D CdS NRs@ZnIn₂S₄ NSs) heterojunctions by tailoring enzymatic loading capacity. Firstly, alkaline phosphatase modified TOB aptamer (ALP-Apt) was linked via specific base complementary pairing, and insoluble precipitations were then produced through the ALP-triggered catalytic reaction with the aid of Ag⁺, which prevented the charge transfer and resulted in the decrement of photocurrent. In the presence of TOB, partial ALP-Apt detached from the electrode surface due to the strong affinity between TOB and its aptamer, leading to a reduction in the amount of ALP and insoluble precipitate, in turn the PEC response partially recovered. The photocurrents exhibited a wider linear range towards the TOB concentration of 1.0-5.0 × 10⁴ pg mL^-1, with a low detection limit of 0.96 pg mL^-1. The constructed PEC aptasensor gained satisfactory results for TOB assay in milk samples as well, which also offered significant promise for other pollutants in environmental analysis.

Facile room temperature synthesis of a NiFe2O4-based magnetic covalent organic framework for the extraction of tetracycline residues in environmental water samples prior to HPLC

In this study, a functionalized magnetic covalent organic framework (NiFe₂O₄@TAPB-TPA) was fabricated with NiFe₂O₄ nanoparticles as the magnetic core, and 1,3,5-tris(4-aminophenyl)benzene (TAPB) and terephthalaldehyde (TPA) as building blocks by a facile room temperature strategy. Benefitting from the π-π stacking and hydrogen bond interaction, NiFe₂O₄@TAPB-TPA showed great potential as a magnetic adsorbent for the extraction of tetracyclines (TCs). Under optimal conditions, good linearities (R² > 0.9990) were obtained between the peak area and TC concentration in the range of 1-500 μg L^-1 with limits of detection ranging from 0.09 to 0.26 μg L^-1. The intra-day and inter-day relative standard deviations were less than 2.2% and 4.7%, respectively. The established method was successfully applied for the determination of TCs in diverse environmental water samples with satisfactory recoveries in the range of 91.6-102.7%. In addition, NiFe₂O₄@TAPB-TPA showed good reusability with the recoveries for TCs higher than 73.1% after nine recycles, indicating potential application of NiFe₂O₄@TAPB-TPA as an ideal adsorbent for the enrichment of TCs.

Covalent organic framework linked with amination luminol derivative as enhanced ECL luminophore for ultrasensitive analysis of cytochrome c

Cytochrome c (cyt c) plays a critical role in mitochondrial respiratory chain, whose absence is detrimental to electron transport and reduce adenosine triphosphate. For ultrasensitive detection of cyt c, sheet-like covalent organic frameworks (COFs) were prepared by orderly accumulation of 1,3,5-benzenetricarboxaldehyde (BTA) and p-phenylenediamine (PDA), and further grafted with N-(4-aminobutyl)-N-ethylisoluminol (ABEI) - an electrochemiluminescence (ECL) emitter. Specifically, the morphology and structure of the COFs-ABEI were mainly characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis, and X-ray photoelectron spectroscopy (XPS). In parallel, the optical properties of the emitter were certified by UV-vis absorbance spectroscopy, Fourier infrared spectroscopy (FTIR), fluorescence (FL), and ECL measurements, showing 2.25-time enhanced ECL efficiency over pure ABEI, coupled by illustrating the interfacial electron transport mechanism. On the above foundation, a label-free "signal off" ECL biosensor was constructed by virtue of the specific immune recognition between the aptamer of the target cyt c with its capture DNA (cDNA) anchored on the biosensing platform, exhibiting a wider linear range of 1.00 fg mL^-1-0.10 ng mL^-1 (R² = 0.998) and a lower limit of detection (LOD) down to 0.73 fg mL^-1. This work offers some constructive guidelines for sensitive bioassays of disease-related biomarkers in the clinical field.

Distribution of faecal indicator bacteria in tropical waters of Peninsular Malaysia and their decay rates in tropical seawater

We investigated the appropriateness of faecal indicator bacteria in tropical waters. We compared total coliform (undetectable to 7.2 × 10⁵ cfu 100 mL^-1), faecal coliform (undetectable to 6.1 × 10⁵ cfu 100 mL^-1) and enterococci (undetectable to 3.1 × 10⁴ cfu 100 mL^-1) distribution in Peninsular Malaysia. Faecal indicator bacteria was highest in freshwater, and lowest in seawater (q > 4.18, p < 0.01). We also measured the decay rates of Escherichia coli and Enterococcus faecium in microcosms. In seawater, average decay rate for E. coli was 0.084 ± 0.029 h^-1, and higher than E. faecium (0.048 ± 0.024 h^-1) (t = 2.527, p < 0.05). Grazing accounted for 54 % of both E. coli and E. faecium decay. E. coli decayed in the <0.02 μm seawater fraction (0.023 ± 0.012 h^-1) but E. faecium sometimes grew. Seawater warming further uncoupled the response from both E. coli and E. faecium as E. faecium grew and E. coli decayed with warming. Our results suggested that the prevalence of faecal indicator bacteria in tropical waters was not due to faecal pollution alone, and this will have serious implications towards the use of these faecal indicator bacteria.

Heterostructured BiVO4/CoPi nanoarrays as high-efficiency photoanode and AuPt nanodendrites as nanozyme for sensitive sensing of miRNA 141

MicroRNA (miRNA) is a new class of tumor biomarkers in human body for early diagnosis and therapy of cancers, whose detection has scientific significance and potential applications. Herein, a sensitive heterostructured BiVO₄/CoPi photoelectrochemical (PEC) biosensor was established for sensing miRNA 141 with assistance of home-synthesized AuPt nanodendrites (NDs) as nanozyme. Specifically, the BiVO₄/CoPi heterostructures displayed rough worm-like internetworks, as characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). In parallel, the PEC and UV-vis diffuse reflectance spectroscopy tests confirmed their excellent optical property, combined by discussing the interfacial electron transfer mechanism. Additionally, the AuPt NDs displayed superior peroxidase-like property in the presence of H₂O₂ as identified by benchmarked tetramethylbenzidine (TMB) oxidation, coupled by showing remarkable catalysis for 3-amino-9-ethylcarbazole (AEC) oxidation to form biocatalytic precipitation (BCP). Integrated by a cyclic enzyme strategy, the developed PEC biosensor exhibited a wider linear range of 5 fM ∼1 pM and a lower limit of detection (LOD) as low as 0.17 fM (S/N = 3). This work provides some valuable insights for sensitive analysis of tumor-associated miRNA in clinic.

Novel Ultrasensitive Photoelectrochemical Cytosensor Based on Hollow CdIn2S4/In2S3 Heterostructured Microspheres for HepG2 Cells Detection and Inhibitor Screening

Hepatocellular carcinoma is a life-threatening malignant tumor found around the world for its high morbidity and mortality. Therefore, it is of great importance for sensitive analysis of liver cancer cells (HepG2 cells) in clinical diagnosis and biomedical research. To fulfill this demand, hollow CdIn₂S₄/In₂S₃ heterostructured microspheres (termed CdIn₂S₄/In₂S₃ for clarity) were prepared by a two-step hydrothermal strategy and applied for building a novel photoelectrochemical (PEC) cytosensor for ultrasensitive and accurate detection of HepG2 cells through specific recognition of CD133 protein on the cell surface with the respective aptamer. The optical properties of CdIn₂S₄/In₂S₃ were investigated by UV-vis diffuse reflectance spectroscopy (DRS) and PEC technology. By virtue of their appealing PEC characteristics, the resultant PEC sensor exhibited a wider dynamic linear range from 1 × 10² to 2 × 10⁵ cells mL^-1 with a lower limit of detection (LOD, 23 cells mL^-1), combined by evaluating the expression level of CD133 protein stimulated by metformin as a benchmarked inhibitor. This work opens a valuable and feasible avenue for sensitive detection of diverse tumor cells, holding great potential in early clinical diagnosis and treatment coupled by screening inhibitors.

Bio-derived FeNi alloy confined in N-doped carbon nanosheets as efficient air electrodes for Zn-air battery

It is imperative to design and manufacture electrocatalysts towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) for popularization of rechargeable Zn-air batteries. Herein, FeNi alloy confined in N-doped carbon nanosheets (FeNi@NCSs) was harvested via a facile complexation-pyrolysis strategy from the mixture of guanine and metal chlorides. After strictly exploring the pyrolysis temperature and metal types, the resulted FeNi@NCSs showed greatly improved performances on both the ORR (onset potential of 0.93 V and half-wave potential of 0.84 V) and OER (overpotential of 318 mV at 10 mA cm^-2 and 379 mV at 100 mA cm^-2). Further, the FeNi@NCSs based Zn-air battery exhibited a higher open circuit voltage (1.496 V), a larger power density (128.8 mW cm^-2), and prominent durability (360 cycles, 120 h). This study provides an appealing approach to utilize biomass for synthesis of low-cost and high-efficiency electrocatalysts in energy associated systems.