A versatile CuCo@PDA nanozyme-based aptamer-mediated lateral flow assay for highly sensitive, on-site and dual-readout detection of Aflatoxin B1.

Mycotoxin contaminations in food and environment seriously harms human health. Constructing sensitive and point-of-test early-warning tools for mycotoxin determination is in high demand. In this study, a CuCo@PDA nanozyme-based aptamer-mediated lateral flow assay (Apt-LFA) has been elaborately designed for on-site and sensitive determination of mycotoxin Aflatoxin B1 (AFB1). Benefiting from the rich functional groups and excellent peroxidase-like activity, the CuCo@PDA with original dark color can be conjugated with the specific recognition probe (i.e., aptamer), generating colorimetric signal on the test lines of Apt-LFA via a competitive sensing strategy. The signal can further be amplified in-situ by catalytic chromogenic reaction. Therefore, a visual and dual-readout detection of AFB1 has been realized. The developed Apt-LFA provides a flexible detection mode for qualitative and quantitative analysis of AFB1 by naked-eyes observation or smartphone readout. The smartphone-based LFA platform shows a reliable and ultrasensitive determination of AFB1 with the limit of detection (LOD) of 2.2 pg/mL. The recoveries in the real samples are in the range of 95.11-113.77% with coefficients of variations less than 9.84%. This study provides a new approach to realize point-of-test and sensitive detection of mycotoxins in food and environment using nanozyme-based Apt-LFAs.

A highly selective self-powered sensor based on the upconversion nanoparticles/CdS nanospheres for chlorpyrifos detection.

Light sources are crucial for photoelectrochemical (PEC) self-powered sensing, where visible light is widely used. However, due to its high energy, it has some downsides as an irradiation source for overall system, so it is urgent to achieve effective near-infrared (NIR) light absorption because it makes up a significant portion of the solar spectrum. Herein, up-conversion nanoparticles (UCNPs) that could increase the energy of low-energy radiation were combined with semiconductor CdS as the photoactive material (UCNPs/CdS), which broadens the response range of solar spectrum. The NIR light-excited self-powered sensor could be produced via oxidizing H2O at photoanode and lowering dissolved oxygen at cathode under the NIR light without external voltage. Meanwhile, molecularly imprinted polymer (MIP) was added to photoanode as a recognition element to increase the sensor's selectivity. The open-circuit voltage of the self-powered sensor grew linearly as chlorpyrifos concentration climbed from 0.01 to 100 ng mL-1, showing good selectivity as well as reproducibility. This work provides valuable basis for the preparation of efficient and practical PEC sensor with NIR light response.

Recent Advances in Thallium Removal from Water Environment by Metal Oxide Material.

Thallium is widely used in industrial and agricultural development. However, there is still a lack of systematic understanding of its environmental hazards and related treatment methods or technologies. Here, we critically assess the environmental behavior of thallium in aqueous systems. In addition, we first discuss the benefits and limitations of the synthetic methods of metal oxide materials that may affect the practicality and scalability of TI removal from water. We then assess the feasibility of different metal oxide materials for TI removal from water by estimating the material properties and contaminant removal mechanisms of four metal oxides (Mn, Fe, Al, and Ti). Next, we discuss the environmental factors that may inhibit the practicality and scalability of Tl removal from water. We conclude by highlighting the materials and processes that could serve as more sustainable alternatives to TI removal with further research and development.

A novel g-C3N4/g-C3N4-x homojunction with efficient interfacial charge transfer for photocatalytic degradation of atrazine and tetracycline.

The abuse of pesticides and antibiotics and their harm to the environment are the disadvantages of modern agriculture and breeding industry. g-C3N4 has shown great potential in photocatalytic water pollution purification under visible light irradiation, however, the conventional g-C3N4 suffers from the disadvantage of limited optical absorption and serious charge recombination, resulting in inefficient light energy conversion and pollutant degradation. This study provides a strategy of combining defect engineering with a built-in electric field to prepare homojunction a photocatalyst with high optical absorption rate and charge separation efficiency. Experiments and DFT simulation revealed the mechanism of significant improvement in the photocatalytic performance of the prepared catalyst, and proposed the pollutant degradation pathway. In addition, the photocatalytic effects of the prepared catalysts on different natural water bodies, natural light, and various water conditions were investigated, revealing the applicability of the catalysts in the purification of pollutants in various water environments.

3D printed bionic self-powered sensing device based on fern-shaped nitrogen doped BiVO4 photoanode with enriched oxygen vacancies.

A portable three-dimensional (3D) printed bionic sensing device with enhanced photoelectric response was fabricated for sensitive detection of Bisphenol A (BPA). The proposed sensor is operated upon by using a highly reactive dual-electrode system to generate electrical output and provide the sensing signal under photoirradiation, without an external power source. The fern-shaped nitrogen doped BiVO4 photoanode with enriched oxygen vacancies (Ov) bismuth vanadate (N/Ov/BiVO4) photoanode was first synthesized and applied to construct a bionic sensing device. Density functional theoretical (DFT) calculation shows that the synergistic of nitrogen doping and Ov on the surface of photoanode leads to the emergence of impurity levels in BiVO4's electronic structure, promoting the effective separation of photogenerated electron-hole pairs. Impressively, the unique fern-shaped bionic structure enhances the mass transfer efficiency of the sensing system and provides abundant binding sites of aptamer, realizing signal amplification. Moreover, a portable sensing device for automatic sample injection and detection is developed by integrating the detection system into a micromodel based on micro-nano 3D printing technology. Benefit from this ingenious design, the proposed bionic aptasensor displayed excellent electricity output and achieved high sensitivity and selectivity of BPA detection with a low limit of detection (0.025 nM) and broad linear range from 0.1 nM to 100 µM, paving a new way for the development of portable and on-site sensing devices.

Hollow NiCo@C Nanozyme-Embedded Paper-Based Colorimetric Aptasensor for Highly Sensitive Antibiotic Detection on a Smartphone Platform.

Antibiotic residues in the environment and in foods pose a serious threat to ecosystems and human health. Developing sensitive and on-site detection methods is therefore in high demand. In this work, a portable paper-based colorimetric sensor with a smartphone platform with an ultrahigh sensitivity has been designed for on-site and quantitative analysis of antibiotic residues based on aptamer-regulated nanozyme activity. The developed excellent peroxidase-like nanozymes, carbon-protected NiCo bimetal oxides with a unique hollow nanocage structure (NiCo@C HCs), could effectively catalyze the oxidation of chromogenic substrates by H2O2. Once bound to a specific aptamer, the enzyme-mimicking activity of NiCo@C HCs is obviously inhibited as a result of the masking of active sites but could be restored via the target-aptamer recognition. Herein, the aptamer-modified NiCo@C HCs are embedded on paper pieces to construct paper-based biochips for visual detection. Meanwhile, a smartphone platform is integrated for the signal readout. Using enrofloxacin (ENR) as an analyte model, the proposed paper-based analysis platform shows a reliable and sensitive detection of ENR with an ultralow detection limit of 0.029 ng/mL. The platform also works well in various real samples. This analysis method is facile in design, showing a great application potential for on-site and mass screening of antibiotic residues in the environment and in foods.

Multifunctional MnCo@C yolk-shell nanozymes with smartphone platform for rapid colorimetric analysis of total antioxidant capacity and phenolic compounds.

Accurate on-site analysis of food quality, environmental pollutants, and disease biomarkers is of great significance for safeguarding public health. In this work, based on the novel nanozymes, MnCo oxides@carbon yolk-shell nanocages (MnCo@C NCs), a portable colorimetric sensor with smartphone platform has been developed for rapid, on-site and quantitative analysis of total antioxidant capacity (TAC) and phenolic compounds. The MnCo@C NCs are synthesized via one-step calcination of polydopamine-coated MnCo Prussian blue analogs (MnCo-PBA@PDA). The PDA-derived carbon shell is found to be able to protect the nanocages from collapsing, thus increasing their specific surface areas and porosity. Benefiting from the unique structure and multivalent MnCo bimetallic oxides, the MnCo@C NCs perform outstanding catalytic performance and multiple enzyme-mimicking activities including oxidase, laccase and catalase. Hence, a multifunctional application platform integrated smartphone has been constructed for rapid and sensitive colorimetric detection of three model analytes (i.e., ascorbic acid (AA), 2,4-dichlorophenol (2,4-DP), and epinephrine) with extremely low detection limits of 0.29 µM, 0.76 µM, and 0.70 µM, respectively. This sensor device is successfully applied in TAC analysis in vegetables, fruits, and beverages, as well as epinephrine determination in human serum samples. This work provides new insights into designing multifunctional nanozymes to advance the instant detection technology in the field of food supervision, environment monitoring, and human health.

A flexible photoelectrochemical aptasensor using heterojunction architecture of α-Fe2O3/d-C3N4 for ultrasensitive detection of penbritin.

The performance of photoelectrochemical (PEC) analysis system relies closely on the properties of the photoelectric electrodes. It is of great significance to integrate photoactive materials with flexible substrates to construct ultra-sensitive PEC sensors for practical application. This work reports a novel photoelectrode developed by immobilizing α-Fe2O3 nanoparticles (NPs)/defect-rich carbon nitride (d-C3N4), an excellent Z-scheme heterojunction photoelectric material, onto three-dimensional (3D) flexible carbon fiber textile. Specifically, 3D hierarchical structure of flexible carbon fiber textile provides larger specific surface area and higher mechanical strength than traditional electrodes, resulting in more reaction sites and faster reaction kinetics to achieve signal amplification. Simultaneously, α-Fe2O3/d-C3N4 Z-scheme heterojunction exhibits enhanced light absorption capability and high redox ability, thus dramatically improving the PEC performance. This photoelectrode was used to construct a flexible PEC aptasensor for ultrasensitive detection of penbritin, demonstrating excellent performance in terms of wide linear range (0.5 pM-50 nM), low detection limit (0.0125 pM) and high stability. The design principle is applicable to the manufacture of other photoelectric sensing systems, which provides an avenue for the development of portable environmental analysis and field diagnostics equipment.

Self-Powered Photoelectrochemical Aptasensor for Oxytetracycline Cathodic Detection Based on a Dual Z-Scheme WO3/g-C3N4/MnO2 Photoanode.

With the high sensitivity and anti-interference provided by a dual Z-scheme structure photoanode and a two-electrode system, a high-performance self-powered photoelectrochemical (PEC) aptasensor for oxytetracycline (OTC) detection was established in this work. Graphitic carbon nitride (g-C3N4) with excellent photoelectric properties was used to be combined with WO3 and MnO2 to form a kind of dual Z-scheme heterojunction. The designed unique structure and the complementary performances of the three materials collectively guaranteed the highly stable photocurrent output of the photoanode due to the wide range of light absorption and the high separation rate of electron-hole pairs. The aptamer-based cathode modified with reduced graphene oxide (rGO) and Au nanoparticles (Au NPs) provided high conductivity and aptamer-binding sites, which brought excellent selective recognition of OTC as well as the self-powered capacity by receiving electrons from the photoanode. In the PEC sensing of OTC, the device presented a wide detection range from 1 pM to 150 nM and a low detection limit of 0.1 pM. Besides, the developed PEC aptasenor showed good selectivity, reproducibility, and stability, so as to be applied to real samples. The proposed PEC sensing method can be considered an effective and promising direction for the detection of antibiotics in the future.

Visible light-activated self-powered photoelectrochemical aptasensor for ultrasensitive chloramphenicol detection based on DFT-proved Z-scheme Ag2CrO4/g-C3N4/graphene oxide.

A visible light self-powered photoelectrochemical (PEC) aptasensor based on silver chromate particles, graphitic carbon nitride nanosheets and graphene oxide sheets (Ag2CrO4/g-C3N4/GO) for the ultrasensitive detection of chloramphenicol (CAP) was reported in this work. g-C3N4 was considered to be the fundamental photoelectric material because of its great oxidation ability of photogenerated hole as well as excellent biocompatibility and low toxicity. However, the narrow light absorption range and rapid carrier recombination rate limit the application of pure g-C3N4. Herein, Ag2CrO4 and GO as photosensitizer were introduced to improve the photoelectric properties of g-C3N4. The photocurrent of the developed ternary composite was about 3 times higher than that of pristine g-C3N4, which proves it can be used as a suitable photoelectric active material. Moreover, the mechanism of Z-scheme electron transfer path was proved by density functional theory (DFT) calculation. The fabricated PEC aptasensor exhibited high sensitivity toward CAP with a wide liner response of 0.5 pM to 50 nM and a detection limit of 0.29 pM. The specific recognition mechanism and excellent sensing performance indicated this aptasensor could serve as a useful tool for selective and ultrasensitive CAP detection in practical analysis.

CuS QDs/Co3O4 Polyhedra-Driven Multiple Signal Amplifications Activated h-BN Photoeletrochemical Biosensing Platform.

Herein, we developed an unmodified hexagonal boron nitride (h-BN) photoelectrochemical (PEC) biosensing platform with a low background signal and high sensitivity based on CuS quantum dots (QDs)/Co3O4 polyhedra-driven multiple signal amplifications. The prepared porous h-BN nanosheets with large specific surface areas, as the photoelectric substrate material, can provide extensive active reaction sites. Meanwhile, the CuS QDs/Co3O4 polyhedra were synthesized by the zeolitic imidazolate framework (ZIF-67) and utilized as a multiple signal amplifier, which can not only drive the p-n semiconductor quenching effect to compete with the h-BN photoelectrode for the consumption of electron donors and exciting light but also trigger a mimetic enzymatic catalytic precipitation effect to inhibit electron transfer. The quenching ability and peroxidase-like activity of CuS QDs/Co3O4 polyhedra were evaluated to prove its superiority, and the possible mechanisms of electron transfer and enzymatic catalytic were further analyzed in detail. The developed PEC biosensing platform for the chlorpyrifos assay presented outstanding performance with a wide linear range from 1 × 10-1 to 1 × 107 ng mL-1 and a low detection limit of 0.34 pg mL-1 and exhibited excellent selectivity, reproducibility, and stability. In addition, the CuS QDs/Co3O4 polyhedra-activated h-BN PEC biosensing platform may exhibit universality for various analytes via replacing the corresponding target aptamer sequence. This work provides a remarkable inspiration and valuable reference for the development of the PEC biosensor, and the signal amplifier-enabled unmodified PEC biosensing platform strategy has a bright application in early safety warning, bioanalysis and clinical diagnosis.

Au/CeO2/g-C3N4 heterostructures: Designing a self-powered aptasensor for ultrasensitive detection of Microcystin-LR by density functional theory.

Quantum-sized cerium dioxide (CeO2) show high catalytic capability as well as strong light absorption ability owing to its redox couple Ce4+/Ce3+ and abundant oxygen vacancies, which making it a potential material for designing superior photoelectrochemical (PEC) sensors. However, it has scarcely been applied in the field of PEC sensing, because its wide band gap and aggregation effect can restrict the photoelectric conversion efficiency. Herein, we address these two obstacles by coupling CeO2 quantum dots (QDs) with graphitic carbon nitride (g-CN) and Au nanoparticles (NPs). The electron transfer path in this proposed heterojunction was proved by density functional theory (DFT) calculation for the first time, which provided theoretical support for the detection of MC-LR. The as-obtained PEC aptasensor exhibited excellent analytical performance with a wide liner response of 0.05-105 pM, and the detection limit was 0.01 pM. By designing appropriate sensing system and specific recognition mechanism, this work may pave a unique avenue for constructing ultrasensitive and selective analysis of MC-LR in complex environment without any external electric source.

Ultrathin PtNi nanozyme based self-powered photoelectrochemical aptasensor for ultrasensitive chloramphenicol detection.

Nanozymes have gained increasing attention in the field of biosensing. Rationally designed nanozymes with excellent catalytic activity are accessible to substitute natural enzymes. Herein, a novel self-powered photoelectrochemical (PEC) aptasensor was constructed for ultrasensitive detection of chloramphenicol (CAP) based on ultrathin PtNi nanowires (NWs) as nanozyme and benzene-ring doped g-C3N4 (BR-CN) as the photoactive material. The prepared 1-nm-thick PtNi nanozyme acted as a peroxidase, possessing higher catalytic activity than natural horseradish peroxidase (HRP) and other Pt-based mimic enzymes. Through the biotin-streptavidin specific interaction, streptavidin modified PtNi nanozyme was introduced into the dual-stranded DNA (dsDNA) formed by complementary DNA and biotinylated CAP aptamer. The PtNi nanozyme catalyzed 4-chloro-1-naphthol (4-CN) oxidation to generate insoluble precipitation on the electrode surface, resulting in an obvious photocurrent reduction. In the presence of CAP, the CAP aptamer was released from the electrode due to strong affinity with CAP, causing the decrease of catalytic precipitation and consequently the generation of a high photocurrent signal. On the basis of PtNi nanozyme signal amplification, the developed self-powered PEC aptasensor showed a wide linear range of 0.1 pM-100 nM with an ultralow detection limit of 26 fM for the determination of CAP. This work provides a feasible strategy for the design of high-activity nanozyme and self-powered PEC biosensor to achieve the ultrasensitive detection of target analyte.

Enhanced photoelectric conversion efficiency: A novel h-BN based self-powered photoelectrochemical aptasensor for ultrasensitive detection of diazinon.

This work presents a novel hexagonal boron nitride (h-BN) based self-powered photoelectrochemical (PEC) aptasensor for ultrasensitive detection of diazinon (DZN) with excellent photoelectric conversion efficiency. It was the first time that h-BN based materials were applied to PEC aptasensor, in which the construction of Z-scheme heterojunction of h-BN and graphitic carbon nitride (CN) via doping sulfur into h-BN was innovatively proposed. Meanwhile, Au nanoparticles (AuNPs) were utilized for the surface plasmon resonance (SPR) effect and the formation of new recombination centers. The charge transfer mechanism was expounded and verified by the electron spin resonance (ESR) spin-trap technique. The proposed PEC aptasensor for determination of DZN exhibited a wide linear range from 0.01 to 10000 nM and a low detection limit of 6.8 pM with superb selectivity and remarkable stability. Moreover, the constructed PEC aptasensor performed well with excellent recoveries in three different real samples. This work illustrated that PEC aptasensor is a promising alternative to conventional analytical technologies for the detection of DZN and other organophosphorus (OP) pesticides. The designing ideas of the proposed h-BN based material can provide a foothold for the innovative construction of photoactive materials for PEC bioanalysis.

Highly sensitive detection of microcystin-LR under visible light using a self-powered photoelectrochemical aptasensor based on a CoO/Au/g-C3N4 Z-scheme heterojunction.

Based on the unique photoelectrochemical properties of a CoO/Au/g-C3N4 Z-scheme heterojunction, a self-powered photoelectrochemical (PEC) aptasensor was constructed for the detection of microcystin-leucine arginine (MC-LR). Z-scheme heterojunctions can promote the separation of a photo-induced electron-hole pair, and the surface plasmonic resonance (SPR) of Au nanoparticles can significantly enhance the adsorption of visible light. Importantly, MC-LR molecules were captured by aptamers initially immobilized on the modified electrode due to their high affinity, and then oxidized by the photogenerated holes, which caused an amplified photocurrent signal, allowing the quantitative analysis of MC-LR by measuring the photocurrent intensity change. This PEC MC-LR aptasensor showed high sensitivity and selectivity within a wide linear response range from 0.1 pM to 10 nM and a detection limit of 0.01 pM. The application of this sensor in the analysis of lake water samples provided accurate results with a relative standard deviation (RSD) of 2.6%-4.2%.

Self-powered photoelectrochemical aptasensor based on phosphorus doped porous ultrathin g-C3N4 nanosheets enhanced by surface plasmon resonance effect.

This work reports a facile and sensitive self-powered cathodic photoelectrochemical (PEC) aptasensor for the detection of oxytetracycline (OTC) based on Au nanoparticles-decorated phosphorus-doped porous ultrathin g-C3N4 nanosheets (Au/PCN-S). The prepared PCN-S possesses large specific surface area with abundant in-plane pores on its surface, ideal biocompatibility, and excellent visible light response. The in situ photo-reduced Au nanoparticles further enhanced the PEC performance owing to its unique surface plasmon resonance (SPR) effect. Under visible light irradiation, the photocurrent of Au/PCN-S composites was significantly enhanced, which was about 22 times higher than that of pure g-C3N4. In the self-powered PEC biosensing of OTC, the device exhibited high sensitivity toward the presence of dissolved oxygen in the electrolyte and presented a wide detection range from 0.5 to 200 nM and a detection limit of 0.34 nM, as well as certain selectivity, reproducibility and stability. The proposed Au/PCN-S nanocomposites would be considered as a promising visible light-responsive photoactive material for fabrication of PEC biosensors with high performance.

Effect of nonendocytic uptake of nanoparticles on human bronchial epithelial cells.

The toxicity of artificial nanoparticles is a major concern in industrial applications. Cellular uptake of hard nanoparticles could follow either endocytic or nonendocytic pathways, leading to different stimuli to the cells. Yet the cellular responses to nanoparticles following different pathways have not been compared due to the lack of an independent nonendocytic delivery method. We applied a unique delivery method, nanochannel electroporation (NEP), to produce predominantly nonendocytic uptakes of quantum dots (Q-dots) and multiwalled carbon nanotubes (MWCNTs) with different chemical modifications. NEP delivery bypassed endocytosis by electrophoretic injection of nanoparticles into human bronchial epithelial (BEAS-2B) cells at different dosages. Conventional exposure by direct nanoparticle suspending in cell culture medium was also performed as control. The dosage-dependent responses to nanoparticles under different uptake pathways were compared. Fluorescence colocalization demonstrated that nanoparticles followed both endocytic and nonendocytic pathways for cell entry in contact exposure, whereas NEP delivery of nanoparticles bypassed endocytosis. Nonendocytic entry resulted in much higher oxidation stress and, for MWCNTs, more cell death in BEAS-2B cells. Despite the observation that most nanoparticles were taken up by cells through endocytosis, the minor nonendocytic entry of nanoparticles seemed to dominate the overall cellular response in conventional contact exposure. Our finding suggests that prevention against nonendocytic uptake could help reduce the toxicity of hard nanoparticles.

Atomic carbide bonding leading to superior graphene networks.

A versatile method for achieving atomic carbide-bonded graphene networks on both metallic and non-metallic substrates is described. This consists of vacuum-assisted thermal exfoliation and floatation of functional graphenes at elevated temperatures, followed by deposition on substrates and in situ formation of carbide bonds. The cross-linked graphene networks with an interlayer distance of angstroms exhibits a unique combination of unprecedented properties.

High-performance nanopapers based on benzenesulfonic functionalized graphenes.

High-performance graphene nanopapers are prepared from an aqueous solution of functional graphenes with benzenesulfonic acid groups via covalent bonds. The formed hydrophobic graphene nanopapers showed the highest tensile strength of 360 MPa and Young's modulus of 102 GPa for samples with 13.7 wt % functional group and annealed at 150 °C. These samples showed a high electrical conductivity of 4.45 × 10(4) S/m after being annealed at 250 °C. The aforementioned properties of graphene nanopapers are much higher than any previously reported data. The properties of nanopapers depend on the degree of functionality on graphenes and the annealing temperatures, which are further evidenced by X-ray photoelectron spectroscopy, FTIR, and X-ray diffraction patterns. Such unique nanopapers can be easily bounded and sandwiched onto any solid surface to give rise to great potentials in many applications such as gas diffusion barriers, EMI shielding, thermal management, and anticorrosion.