Paper-based colorimetric sensor using bimetallic Nickel-Cobalt selenides nanozyme with artificial neural network-assisted for detection of H2O2 on smartphone.

Paper-based analytical devices (PADs) integrated with smartphones have shown great potential in various fields, but they also face challenges such as single signal reading, complex data processing and significant environmental impacting. In this study, a colorimetric PAD platform has been proposed using bimetallic nickel-cobalt selenides as highly active peroxidase mimic, smartphone with 3D-printing dark-cavity as a portable detector and an artificial neural network (ANN) model as multi-signal processing tool. Notably, the optimized nickel-cobalt selenides (Ni0.75Co0.25Se with Ni to Co ratio of 3/1) exhibit excellent peoxidase-mimetic activities and are capable of catalyzing the oxidation of four chromogenic reagents in the presence of H2O2. Using a smartphone with image capture function as a friendly signal readout tool, the Ni0.75Co0.25Se based four channel colorimetric sensing paper is used for multi-signal quantitative analysis of H2O2 by determining the Grey, red (R), green (G) and blue (B) channel values of the captured pictures. An intelligent on-site detection method for H2O2 has been constructed by combining an ANN model and a self-programmed easy-to-use smartphone APP with a dynamic range of 5 µM to 2 M. Noteworthy, machine learning-assisted smartphone sensing devices based on nanozyme and 3D printing technology provide new insights and universal strategies for visual ultrasensitive detection in a variety of fields, including environments monitoring, biomedical diagnosis and safety screening.

Engineering Platelet Membrane-Coated Bimetallic MOFs as Biodegradable Nanozymes for Efficient Antibacterial Therapy.

Nanocatalytic-based wound therapeutics present a promising strategy for generating reactive oxygen species (ROS) to antipathogen to promote wound healing. However, the full clinical potential of these nanocatalysts is limited by their low reactivity, limited targeting ability, and poor biodegradability in the wound microenvironment. Herein, a bio-organic nanozyme is developed by encapsulating a FeZn-based bimetallic organic framework (MOF) (MIL-88B-Fe/Zn) in platelet membranes (PM@MIL-88B-Fe/Zn) for antimicrobial activity during wound healing. The introduction of Zn in MIL-88B-Fe/Zn modulates the electronic structure of Fe thus accelerating the catalytic kinetics of its peroxidase-like activity to catalytically generate powerful ROS. The platelet membrane coating of MOF innovatively enhanced the interaction between nanoparticles and the biological environment, further developing bacterial-targeted therapy with excellent antibacterial activity against both gram-positive and gram-negative bacteria. Furthermore, this nanozyme markedly suppressed the levels of inflammatory cytokines and promoted angiogenesis in vivo to effectively treat skin surface wounds and accelerate wound healing. PM@MIL-88B-Fe/Zn exhibited superior biodegradability, favourable metabolism and non-toxic accumulation, eliminating concerns regarding side effects from long-term exposure. The high catalytic reactivity, excellent targeting features, and biodegradability of these nanoenzymes developed in this study provide useful insights into the design and synthesis of nanocatalysts/nanozymes for practical biomedical applications.

Oxidase-like V2C MXene nanozyme with inherent antibacterial properties for colorimetric sensing.

The microbial environment greatly affects the performance of colourimetric sensors, especially the interference of bacteria in the sample detected. This paper reports the fabrication of an antibacterial colorimetric sensor based on V2C MXene synthesized via simple intercalation and stripping. The prepared V2C nanosheets can mimic oxidase activity towards 3,3',5,5'-tetramethylbenzidine (TMB) oxidation without exogenously adding H2O2. Further mechanistic studies showed that V2C nanosheets could effectively activate the oxygen adsorbed on their surface, which in turn causes an increase in the bond length and a decrease in the magnetic moment of oxygen through electron transfer from the nanosheet surface to O2. The V2C nanosheets also exhibited excellent broad-spectrum antibacterial activity through the outbreak of reactive oxygen species. Owing to its unique catalytic activity and the inherent antibacterial ability for mimicking oxidase, a colorimetric sensing platform was developed to effectively determine L-cysteine levels at a detection limit of 30.0 nM (S/N = 3). It is impressive that the detection results of L-cysteine in various complex microbial environments are also very satisfactory. This study broadens the biological use of MXene-based nanomaterials through their satisfactory enzymatic activity and provides a simple and efficient colorimetric strategy for detection techniques used in complex microbial environments.

Cell Membrane and V2C MXene-Based Electrochemical Immunosensor with Enhanced Antifouling Capability for Detection of CD44.

The inactive adsorption and interference of biomolecules in electrochemical biosensors is a topic of intense interest. Directly utilizing native cell membranes to endow electrochemical surfaces with antifouling and biocompatible features is a promising strategy, rather than attempting to synthetically replicate complex biological interface properties. In this study, we present a facial and sensitive sandwich-type antifouling immunoassay through platelet membrane/Au nanoparticle/delaminated V2C nanosheet (PM/AuNPs/d-V2C)-modified electrode as the substrate of sensing interface and methylene blue/aminated metal organic framework (MB@NH2-Fe-MOF-Zn) as an electrochemical signal probe. The biosensor perfectly integrates the high conductivity of AuNPs-loaded V2C MXene with the excellent loading property of NH2-Fe-MOF-Zn to improve the electrochemical sensing performance. In addition, the excellent antifouling properties of the homogeneous cell membrane can effectively prevent the non-specific adsorption of model proteins. The obtained antifouling biosensor possesses the capability of ultrasensitive detection of CD44 and CD44-positive cancer cell in complex liquids and exhibits good analytical performance for the analysis of CD44 with a linear range from 0.5 ng/mL to 500 ng/mL. This strategy of developing cell membrane-based biosensing systems with enhanced antifouling capability can be easily expanded to the construction of other complex biosensors, and the advanced biological probes and analytical methods provide a favorable means to accurately quantify biomarkers associated with tumor progression.

Nitrogen and sulfur co-doping strategy to trigger the peroxidase-like and electrochemical activity of Ti3C2 nanosheets for sensitive uric acid detection.

The development of functional nanomaterials based on the unique structure and morphology of MXene for biosensing has aroused great interest. In this work, using thiourea as the doping source, a new structure composed of nitrogen and sulfur co-doped on the surface of Ti3C2 nanosheets was synthesized through a simple one-step synthesis method. Fortunately, the obtained nitrogen and sulfur co-doped Ti3C2 nanosheets (NS-Ti3C2 NSs) showed excellent peroxidase-like activity and electrochemical activity. The catalytic mechanism of modified Ti3C2 nanosheets was explored. It is revealed that the catalytic mechanism of NS-Ti3C2 NSs is composed of two important parts: the dissociation and adsorption of H2O2 and the protonation of TMB. In addition, the fabricated NS-Ti3C2 NSs-based electrochemical biosensor is superior to the counterpart from Ti3C2 nanosheets, indicating that the doping of nitrogen and sulfur elements provides more active sites and promotes electron transport efficiency. Combining the unique advantages of colorimetry and electrochemical technology, we have developed a fast, accurate, intuitive and efficient UA detection method for uric acid in the range of 2 µM-400 µM with a detection limit (LOD) of 0.19 µM. The established sensing platform in this study prove the possibility of the doping method for the development of MXene-based biosensors with high sensitivity and high performance, and pave the way for the future development of biosensors for biomedical fields.

Cell membrane-coated nanoparticles as peroxidase mimetics for cancer cell targeted detection and therapy.

The development of novel and efficient recognition molecules that can be easily modified by nanomaterials to achieve ultra-sensitive and specific cancer cell analysis is of great significance for its early diagnosis and timely prognosis. Herin, a new nanostructured hybrid based on cell membrane-coated Au cores- ultrathin Pt skins composite nanoparticles (Au@Pt@CM NPs) were developed for in vitro detection and treatment of cancer cells. In this strategy, the Au@Pt NPs acted as the signal transducer, and the cell membrane were used as the cancer-cell recognition tool. The synthesized Au@Pt@CM NPs could catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of the hydrogen peroxide and were demonstrated to have excellent peroxidase-like activity. Coated with the source cancer cell membrane, the nanoparticles achieved highly specific self-recognition to the source cell. Therefore, the colorimetric method based on Au@Pt@CM NPs could detect the cancer cells in the linear range from 50 to 100000 cells/mL with a limit of detection of 5 cells/mL, which is much lower than other colorimetric detection methods. Afterwards, the nanoparticles as a mimetic enzyme were used for therapeutics of cancer cells through the ROS-mediated oxidative damage. Due to the change of the redox state in the cells by the Au@Pt@CM NPs, the hybrid can achieve the growth inhibitory effect and the selective killing effect on cancer cells. It can be expected that this novel hybrid membrane coating method will bring new insight into developing targeted nanomaterials for tumor treatment and detection.

Template-Regulated Bimetallic Sulfide Nanozymes with High Specificity and Activity for Visual Colorimetric Detection of Cellular H2O2.

For the past several decades, most of the research studies on nanozymes have been aimed at improving their catalytic activity and diversity; however, developing nanozymes with strong catalytic activity and great specificity remains a challenge. Herein, a simple and efficient template synthesis method was used to synthesize bimetallic sulfide nanoparticles, NiCo2S4 NPs, and prove that they have excellent peroxidase-like activity with good specificity. By regulating polyvinyl pyrrolidone (PVP) and hexadecyl trimethyl ammonium bromide as the templating agent, we have obtained the NiCo2S4 (PVP) NPs with a high Ni/Co ratio, thus exhibiting superior peroxidase activity. In addition, the NiCo2S4 NPs selectively catalyzed and oxidized colorless 3,3,5,5-tetramethylbenzidine (TMB). On being treated with H2O2, TMB turns blue while other substrates did not undergo the oxidation reaction under the same conditions, such as 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium (ABTS) and dopamine. The high specificity of NiCo2S4 NPs is due to the strong electrostatic driving coordination between negatively charged NiCo2S4 NPs and positively charged TMB. Due to the peroxidase activity of the developed NiCo2S4 NPs, a simple, low-cost, and reliable colorimetric method was established. Simultaneously, this method for in situ quantitative monitoring of H2O2 produced by MDA-MB-231 cells was also achieved. This study has provided a theoretical basis for the improvement of the activity and specificity of bimetallic sulfide nanozymes and may offer guidance for the further reasonable design of related materials.

Single-particle fibrinogen detection using platelet membrane-coated fluorescent polystyrene nanoparticles.

Fibrinogen participates in many physiological processes and is a biomarker for a variety of diseases. On this account, the development of a sensitive method for fibrinogen assay is particularly important. Herein, we demonstrate a new color-coded single-particle detection (SPD) method for fibrinogen detection by using platelet membrane-coated fluorescent polystyrene nanoparticles (PNPs) as the probes. Due to the specific interactions between fibrinogen and integrin receptors on platelet membranes, PNPs can form aggregated structures in the presence of fibrinogen. Therefore, colocalization events between green and red PNPs and the corresponding Pearson's correlation coefficient vary with the concentrations of fibrinogen. The sensing ability shows a linear range of 30-300 µg mL-1 and a limit of detection (LOD) of 3.9 µg mL-1 (11.3 nM) for fibrinogen detection. Moreover, it has been validated that the proposed biosensor can selectively detect fibrinogen and shows a good performance in real sample applications.

Dicer1 promotes Aß clearance via blocking B2 RNA-mediated repression of apolipoprotein E.

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

Brain Dicer1 Is Down-Regulated in a Mouse Model of Alzheimer's Disease Via Aß42-Induced Repression of Nuclear Factor Erythroid 2-Related Factor 2.

Dicer1 is a microRNA-processing enzyme which plays critical roles in neuronal survival and neuritogenesis. Dicer1 deletion induces neurodegeneration or degeneration in retinal pigment epithelium, which is associated with oxidative stress. Oxidative stress is thought to be central in the pathogenesis of Alzheimer's disease (AD). Therefore, we hypothesize that Dicer1 may play roles in AD. Using immunoblotting and quantitative real-time PCR, Dicer1 protein and mRNA were reduced in the hippocampi of the AD mouse model APPswe/PSEN1dE9 compared with littermate controls. SiRNA-mediated Dicer1 knockdown induced oxidative stress and apoptosis and reduced mitochondrial membrane potential in cultured neurons. Chronic Aß42 exposure decreased Dicer1 and nuclear factor erythroid 2-related factor 2 (Nrf2) which were reversed by N-acetyl-cystein. Nrf2 overexpression increased Dicer1 mRNA and protein and reverted the Aß42-induced Dicer1 reduction. We further cloned Dicer1 promoter variants harboring the Nrf2-binding site, the antioxidant response elements (ARE), into a luciferase reporter and found that simultaneous transfection of Nrf2-expressing plasmid increased luciferase expression from these promoter constructs. ChIP assays indicated that Nrf2 directly interacted with the ARE motifs in the Dicer1 promoter. Furthermore, Dicer1 overexpression in cultured neurons reverted Aß42-induced neurite deficits. Notably, injection of Dicer1-expressing adenovirus into the hippocampus of the mice significantly improved spatial learning. Altogether, we found novel roles of Dicer1 in AD and a novel regulatory pathway for Dicer1. These results suggest that Dicer1 is a target in AD therapy, especially at the early stage of this disorder. In this study, we found that Dicer1 was reduced in the brain of AD mice which is the first report to examine Dicer1 in AD. We further found (i) that Aß42 exposure decreased Dicer1 via attenuating Nrf2-ARE signaling and (ii) injection of Dicer1-expressing adenovirus into the hippocampus of the AD mice significantly improved spatial learning. Altogether, we found novel roles of Dicer1 in AD and a novel regulatory pathway for Dicer1. This study may open new avenues for investigating potential pathognomonics and pathogenesis in AD.

Excellent humidity sensor based on ultrathin HKUST-1 nanosheets.

The copper-based MOF, HKUST-1 has been applied for humidity sensing owing to hydrophilic ligands and open metal sites which are suitable for sensitively detecting moisture. However, most of the research on the sensor HKUST-1 focuses on the role of the central metal. There are few reports on the morphology-activity relationship of HKUST-1. In this work, we synthesized two kinds of HKUST-1 including octahedral structures and ultrathin nanosheets, and systematically studied the performance of moisture sensing. Compared to HKUST-1 octahedra, HKUST-1 nanosheets showed lower and wider detectable humidity range, achieving a fast response. Starting from the exposed hydrophilic functional groups of HKUST-1 nanosheets, we have revealed that hydrophilic ligands play an important role in improving the adsorption capacity during the adsorption process. In addition, ultra-thin HKUST-1 nanosheets act as an excellent mass transfer medium, accelerating proton transfer and water molecule movement. To further improve the performance of the HKUST-1 humidity sensor, black phosphorus quantum dots (BPQDs) with a high surface reactivity were used to build a composite sensing platform. The excellent proton transfer capability of BPQDs leads to one order of magnitude improvement in the sensitivity of the BPQDs/HKUST-1 systems compared to HKUST-1 only.

Intravenous injection of l-aspartic acid ß-hydroxamate attenuates choroidal neovascularization via anti-VEGF and anti-inflammation.

Choroidal neovascularization (CNV) is a hallmark of exudative age-related macular degeneration (exAMD) and a major cause of visual loss in AMD. Despite the widespread use of anti-VEGF therapy, serious adverse effects arise from repeated intravitreal injection of anti-VEGF antibodies, which warrant alternative strategy. We report herein that in a CNV murine model created by krypton red laser, intravenous injection of a serine racemase inhibitor, l-Aspartic acid ß-hydroxamate (L-ABH), significantly reduced CNV at the dose 6 mg/kg on the first day before and followed by 3 mg/kg on the third day after laser injury. The CNV volumes were analyzed with isolectin GS-IB4 staining on choroidal/RPE flat mounts on the seventh day after laser injury. Injection of L-ABH did not produce negative effects on retinal function and visual behavior. To dissect the mechanism in vitro, pretreatment with L-ABH in primary RPE cultures significantly reduced production of vascular endothelial growth factor (VEGF) and macrophage chemotactic protein 1 (MCP-1) by TNFα-primed RPEs. Consistent with these observations, L-ABH pretreatment significantly attenuated macrophage migration mediated by TNFα-primed RPE. Collectively, intravenous injection of L-ABH significantly reduced CNV volumes via reducing production of VEGF and MCP-1 by inflammation-primed RPEs.

Self-Assembling Peptide Artificial Enzyme as an Efficient Detection Prober and Inhibitor for Cancer Cells.

A new hybrid nanoparticle (NP; fluorenylmethoxycarbonyl-arginine-glycine-aspartate and hemin, Fmoc-RGD/hemin NP) was developed for the simultaneous detection and inhibition of breast cancer cells. Hemin can regulate the reactive oxygen species (ROS), while Fmoc-RGD acts as a scaffold for hemin nanocrystallization. Fmoc groups interact with the porphyrin groups of hemin through hydrophobic and π-π interactions to form a hydrophobic core of the NPs. The hydrophilic RGD chains surround the core to maintain the stability of the nanoparticles in an aqueous medium. The RGD groups of Fmoc-RGD are also selective for tumor cells. This interaction can be exploited to enhance the selectivity of tumor detection. Based on enhanced peroxidase activity, Fmoc-RGD/hemin NPs were developed as signal transducers in a facile and fast point-of-care cancer diagnosis platform. This platform is sensitive to breast cancer cells and hydrogen peroxide (H2O2), a biomarker for breast cancer. In addition, these Fmoc-RGD/hemin NPs can be used as nanoscavengers for ROS and for regulating the redox status of cancer cells. They also exhibit a targeted inhibitory effect on the epithelial-mesenchymal transition (EMT). The peptide-tuned self-assembly of Fmoc-RGD/hemin NPs as functional artificial enzymes boasts simple preparation, biofriendliness, and the versatility required for on-demand therapeutics and diagnostics for metastatic cancer cells. These NPs can therefore be used as effective tools for potential applications in medicine and biotechnology.

Seamless Signal Transduction from Three-Dimensional Cultured Cells to a Superoxide Anions Biosensor via In Situ Self-Assembly of Dipeptide Hydrogel.

This study demonstrates a new strategy for the development of a three-dimensional (3D) cell culture model-based cellular biosensing system. Distinctly different from the previously reported layering or separating fabrication of cell culture and sensing devices, herein living cells and enzymes as sensing elements are immobilized into a dipeptide-derived hydrogel matrix through simple one-pot self-assembly. The cells are then 3D cultured in the functional hydrogel, and the releasing superoxide anion (O2•-) is detected in situ by a cascade superoxide dismutase and horseradish peroxidase-based electrochemical biosensor. This novel design provides considerable advantages, including the possibility of capturing molecular signals immediately after they are secreted from living cells, due to the close proximity of the enzymes and the O2•--producing cells. Furthermore, incorporating all components in a 3D matrix provides a confinement environment, that can lead to a concentrating effect of analysts. These properties allow the sensing device to achieve ultrahigh sensitivity and a precise response to a very low number of O2•- molecules. The proposed approach, based on the self-assembly of a small molecular hydrogel, also simplifies experimental procedures and increases protocol flexibility to cell culture methodology and sensing design. Consequently, this novel 3D culture model-based cellular biosensing system is envisaged to be useful for cellular function and pathology, drug discovery, and toxicity studies.

Self-Assembled Peptide Hydrogel as a Smart Biointerface for Enzyme-Based Electrochemical Biosensing and Cell Monitoring.

A self-assembled peptide nanofibrous hydrogel composed of N-fluorenylmethoxycarbonyl-diphenylalanine (Fmoc-FF) was used to construct a smart biointerface. This biointerface was then used for enzyme-based electrochemical biosensing and cell monitoring. The Fmoc-FF hydrogel had two functions. One was as a matrix to embed an enzyme model, horseradish peroxidase (HRP), during the self-assembly of Fmoc-FF peptides. The other was use as a robust substrate for cell adhesion. Experimental data demonstrated that HRP was immobilized in a stable manner within the peptide hydrogel, and that HRP retained its inherent bioactivity toward H2O2. The HRP also can realize direct electron transfer in the Fmoc-FF hydrogel. The resulting third-generation electrochemical H2O2 biosensor exhibited good analytical performance, including a low limit of detection of 18 nM, satisfactory reproducibility, and high stability and selectivity. HeLa cells were then adhered to the HRP/Fmoc-FF hydrogel-modified electrode. The sensitive in situ monitoring of H2O2 released from HeLa cells was realized. This biointerface based on the Fmoc-FF hydrogel was easily prepared, environmentally friendly, and also versatile for integration of other cells and recognized molecules for the monitoring of various cellular biomolecules. The smart biointerface has potential application in broad physiological and pathological investigations.