Multienzymes activity of metals and metal oxide nanomaterials: applications from biotechnology to medicine and environmental engineering.

With the rapid advancement and progress of nanotechnology, nanomaterials with enzyme-like catalytic activity have fascinated the remarkable attention of researchers, due to their low cost, high operational stability, adjustable catalytic activity, and ease of recycling and reuse. Nanozymes can catalyze the same reactions as performed by enzymes in nature. In contrast the intrinsic shortcomings of natural enzymes such as high manufacturing cost, low operational stability, production complexity, harsh catalytic conditions and difficulties of recycling, did not limit their wide applications. The broad interest in enzymatic nanomaterial relies on their outstanding properties such as stability, high activity, and rigidity to harsh environments, long-term storage and easy preparation, which make them a convenient substitute instead of the native enzyme. These abilities make the nanozymes suitable for multiple applications in sensing and imaging, tissue engineering, environmental protection, satisfactory tumor diagnostic and therapeutic, because of distinguished properties compared with other artificial enzymes such as high biocompatibility, low toxicity, size dependent catalytic activities, large surface area for further bioconjugation or modification and also smart response to external stimuli. This review summarizes and highlights latest progress in applications of metal and metal oxide nanomaterials with enzyme/multienzyme mimicking activities. We cover the applications of sensing, cancer therapy, water treatment and anti-bacterial efficacy. We also put forward the current challenges and prospects in this research area, hoping to extension of this emerging field. In addition to therapeutic potential of nanozymes for disease prevention, their practical effects in diagnostics, to monitor the presence of SARS-CoV-2 and related biomarkers for future pandemics will be predicted.

CuO/Cu-MOF nanocomposite for highly sensitive detection of nitric oxide released from living cells using an electrochemical microfluidic device.

The integration of large surface area and high catalytic profiles of Cu-MOF and CuO nanoparticles is described toward electrochemical sensing of nitric oxide (NO) in a microfluidic platform. The CuO/Cu-MOF nanocomposite was prepared through hydrothermal method, and its formation was confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectroscopy (EDS). The CuO/Cu-MOF nanostructured modified Au electrodes enabled electrocatalytic NO oxidation at 0.6 V vs. reference electrode, demonstrating linear response over a broad concentration range of 0.03-1 µM and 1-500 µM with a detection limit of 7.8 nM. The interference effect of organic molecules and common ions was negligible, and the sensing system demonstrated excellent stability. Finally, an electrochemical microfluidic NO sensor was developed to detect of NO released from cancer cells, which were stimulated by L-arginine. Furthermore, in the presence of Fe3+, the stressed cells produced more NO. This work offers considerable potential for its practical applications in clinical diagnostics through determination of chemical symptoms in microliter-volume biological samples. Electrochemical microfluidic NO sensor was developed for detection of NO released from cancer cells. This miniaturized device consumes less materials and provides the basis for greener analytical chemistry.

A strategy for visual optical determination of glucose based on a smartphone device using fluorescent boron-doped carbon nanoparticles as a light-up probe.

Boronic acid-doped carbon nanoparticles were prepared and are shown to undergo aggregation induced emission (AIE). The nanoparticle composite is a viable fluorescent probe for glucose determination by using the RGB technique and a smartphone. The structure and the chemical composition of the doped carbon nanoparticles were confirmed by SEM, TEM, FTIR and UV-vis spectroscopy. The combination of 4-carboxyphenylboronic acid with o-phenylenediamine and rhodamine B endowed the hybrid with high fluorescence intensity (quantum yield 46%). Compared with conventional two-step preparation of boronic acid-based fluorescent probes for glucose, the present one step synthesis strategy is simpler and more effective. The addition of glucose causes the formation of covalent bonds between the cis-diols group of glucose molecules and boronic acid moiety. Fluorescent intensity can be quantified using dual wavelengths simultaneously, where both increases, as the target analytes bind to the bronic acid. These variations was monitored by the smartphone camera, and the green channel intensities of the colored images were processed by using the RGB option of a smartphone. The assay works in the 32 µM to 2 mM glucose concentration range and has an 8 µM detection limit. The method was successfully used for the assay of glucose in diluted human serum. Graphical abstractThe fluorometric method was developed for determination of glucose using boron doped carbon nanoparticles (BCNBs). The BCNPs aggregate after covalent binding between the cis-diols of glucose and boronic acid. The green channel of the images is recorded by a smartphone camera.

Ni-hemin metal-organic framework with highly efficient peroxidase catalytic activity: toward colorimetric cancer cell detection and targeted therapeutics.

BACKGROUND: Given the great benefits of artificial enzymes, a simple approach is proposed via assembling of Ni2+ with hemin for synthesis of Ni-hemin metal-organic-frameworks (Ni-hemin MOFs) mimic enzyme. The formation of the Ni-hemin MOFs was verified by scanning electron microscopy, Transmission electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Energy-dispersive X-ray spectroscopy and UV-vis absorption spectroscopy. This novel nanocomposite exhibited surprising peroxidase like activity monitored by catalytic oxidation of a typical peroxidase substrate, 3,3,5,5'-tetramethylbenzidine, in the presence of H2O2. By using folic acid conjugated MOF nanocomposite as a recognition element, we develop a colorimetric assay for the direct detection of cancer cells. RESULTS: The proposed sensor presented high sensitivity and selectivity for the detection of human breast cancer cells (MCF-7) and Human Caucasian gastric adenocarcinoma. By measuring UV-vis absorbance response, a wide detection range from 50 to 105 cells/mL with a detection limit as low as 10 cells/mLwas reached for MCF-7 cells. We further discuss therapeutics efficiency of Ni-hemin MOFs in the presence of H2O2 and ascorbic acid. Peroxidase-mimic Ni-hemin MOFs as reactive oxygen species which could damage MCF-7 cancer cells, however for normal cells (human embryonic kidney HEK 293 cells) killing effect was negligible. CONCLUSIONS: Based on these behaviors, the developed method offers a fast, easy and cheap assay for the interest in future diagnostic and treatment application.

Electrochemical monitoring of hydrogen peroxide by a signal-amplified microfluidic chip coupled with colloidal VO2 nanostructures as a peroxidase enzyme mimic.

We present a novel electrochemical microfluidic device for the sensitive and selective detection of hydrogen peroxide (H2O2) through a VO2 nanostructure enzyme mimic. The low-cost ($0.50) microfluidic chip was fabricated using a simple and rapid prototyping technique via three syringe needles. Each needle played the role of an electrode (working, reference, and counter), and was connected by micro-hoses to a construction of the electrochemical microfluidic chip. The colloidal VO2 nanoflakes with peroxidase-like activity could be easily transferred on to the electrodes by a syringe, for development of a novel electrochemical platform to enable the detection of H2O2. The unique microfluidic electrochemical sensor delivered a wide linear dynamic range from 0.5 to 300 µM, with a limit of detection of 0.14 µM. The facile, rapid, sensitive, and selective as-fabricated H2O2 sensors were proven to be appropriate for the real-time monitoring of H2O2 released from PC12 cells. The integration of a microfluidic sensor with an enzyme mimic nanostructure is essentially a promising strategy for the low-cost and accurate monitoring of physiological processes.

The prevalence and concentration of ochratoxin A in meat and edible offal: A global systematic review and meta-analysis.

The prevalence of ochratoxin A (OTA) in meat, edible offal, and meat products (MOP) was assessed through systematic review and meta-analysis. Four electronic databases were used to gather data from 1975 to September 15, 2022. Seventy-five articles comprising 8585 samples were identified and analyzed. The studies included in the analysis were conducted at a global level, with a predominant focus on Europe [72% (54/75)], Asia [13.33% (10/75)], Africa [13.33% (10/75)], and North America [1.33% (1/75)]. The overall prevalence of OTA in MOP was 39%. The highest and lowest prevalence percentages were recorded in Iraq (77%) and the USA (3%), respectively. Concerning food type, OTA prevalence was highest in the poultry gizzard (66%) and lowest in the cow liver (2%). The overall concentration of OTA in the MOP was 1.789 µg/kg. Poultry kidneys had the highest concentration of OTA (0.880-22.984 µg/kg), while pork had the lowest concentration (0.127-0.824 µg/kg). Conspicuous amounts of OTA contamination have been reported in fermented sausages. The lowest OTA concentration was found in Belgium (0.220 µg/kg) and the highest in Denmark (60.527µg/kg). These results can help food authorities minimize and control OTA in the MOP.

Facile Synthesis of Fe-Doped Hydroxyapatite Nanoparticles from Waste Coal Ash: Fabrication of a Portable Sensor for the Sensitive and Selective Colorimetric Detection of Hydrogen Sulfide.

In this work, a new strategy has been reported for the portable detection of H2S based on Fe-doped hydroxyapatite nanoparticles (Fe-HA) using a colorimetric paper test strip integrated with a smartphone platform. Fe-HA NPs were fabricated successfully via recycling waste coal ash. The obtained probe response toward H2S was through a distinct visual color change. The sensing mechanism is based on the displacement reaction, in which PO4 3- is replaced by S2-. The prepared test strip shows high selectivity, and the other compounds containing thiol and sulfur anion have a negligible effect on the detection of H2S. The designed scheme is applied for H2S detection in the concentration range of 0.5-130 ppm with a limit of detection of 70 ppb. Furthermore, such a disposable sensor was used as a practical system for monitoring H2S in actual water samples, suggesting the promising potential of this platform for suitable analysis of H2S in an aqueous environment.

Hemin/G-Quadruplex Horseradish Peroxidase-Mimicking DNAzyme: Principle and Biosensing Application.

Enzymes are macromolecular biological catalysts that accelerate chemical reactions. Enzyme labels are commonly used to obtain signal amplification in sensors and biosensors on the basis of reactions of some enzymes such as horseradish peroxidase (HRP). However, use of natural enzymes can encounter some challenges. Lately, nucleic acids that exhibit catalytic properties have attracted growing interest because they have certain advantages in comparison with traditional protein enzymes. DNAzymes are DNA-based catalysts, representing an important class of functional DNA, which have been widely used because of their excellent activity, programmability, signal amplification through catalytic turnover, high chemical stability, simple synthesis, and easy modification. Considering these remarkable properties, the hemin/G-quadruplex DNAzyme is extensively used in electrochemical, colorimetric, and chemiluminescence sensors and biosensors for detection of various targets.

Intrinsic Enzyme-like Activities of Cerium Oxide Nanocomposite and Its Application for Extracellular H2O2 Detection Using an Electrochemical Microfluidic Device.

Artificial enzyme mimics have gained considerable attention for use in sensing applications due to their high stability and outstanding catalytic activity. We show that cerium oxide nanosheets (NSs) exhibit triple-enzyme mimetic activity. The oxidase-, peroxidase-, and catalase-like activities of the proposed nanoparticles are demonstrated using both colorimetric and electron paramagnetic resonance (EPR) spectroscopy. On the basis of the excellent catalytic activity of cerium oxide NSs toward hydrogen peroxide, an electrochemical approach for the high-throughput detection of H2O2 in living cells was established. This report presents an analytical microfluidic chip integrated with a cerium oxide NS mimic enzyme for the fabrication of a simple, sensitive, and low-cost electrochemical sensor. Three Au microelectrodes were fabricated on a glass substrate using photolithography, and the working electrode was functionalized using cerium oxide NSs. The operation of this biosensor is based on cerium oxide NSs and presents a high sensitivity over a wide detection range, between 100 nM and 20 mM, with a low detection limit of 20 nM and a high sensitivity threshold of 226.4 µA·cm-2·µM-1. This microfluidic sensor shows a strong response to H2O2, suggesting potential applications in monitoring H2O2 directly secreted from living cells. This sensor chip provides a promising platform for applications in the field of diagnostics and sensing.

CuO nanorods as a laccase mimicking enzyme for highly sensitive colorimetric and electrochemical dual biosensor: Application in living cell epinephrine analysis.

A sensitive colorimetric and electrochemical sensor for measuring of epinephrine (EP) was developed based on CuO nanorods (NRs), and applicability of the sensor for detection of release epinephrine (EP) from living cells was evaluated. The CuO NRs was prepared using a facile and efficient method in low temperature and characterized by Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and Energy-dispersive X-ray spectroscopy (EDX). The CuO NRs exhibited laccase-like activity and could oxidize epinephrine (EP) to a colored product. No interference from the common interfering agents such as dopamine, ascorbic acid and uric acid was observed. Colorimetric sensor demonstrated a linear range of 0.6-18 µM with detection limit of 0.31 µM. Furthermore, the electrochemical study showed CuO NRs exhibited excellent electrocatalytic activity towards epinephrine oxidation. Differential pulse voltammetry signals increase with increasing of EP concentration in the range 0.04-14 µM, with a detection limit of 20 nM. Finally, the proposed sensor applied to perform real-time monitoring of epinephrine released by PC12 cells, indicating that CuO NRs provide a new platform for developing high-performance sensors in biological applications.

Polymer dots as a novel probe for fluorescence sensing of dopamine and imaging in single living cell using droplet microfluidic platform.

We report here simple synthetic method for preparing polymer dots (Pdots) via hydrothermal treatment of organic dye (neutral red), urea and trisodium citrate. The prepared Pdots with enhanced quantum yield (quantum yield: 30.2%) was used as a selective and sensitive probe for fluorescent sensing of dopamine (DA) with high selectivity and sensitivity. The as-synthesized Pdots exhibited strong fluorescence intensity at 435 nm, which DA can trigger remarkable fluorescence quenching of such luminescent Pdots on the basis of inner filter effect (IFE) and static quenching effect (SQE). A wide linearity range (0.001 µM-900 µM) for DA detection was obtained with lower DL (3 S/N) of 0.28 nM, and no interference from other molecules such as ascorbic acid, urine acid, glutathione, glucose, epinephrine, arginine, cysteine, proline, creatinine, serine; alanine, L-therionine, Hg2+, Mg2+, K+, Ca2+ and Na+. The designed sensor was successfully applied in the imaging of DA in single living PC12 cells using droplet microfluidic approach, indicating its acceptable practicability of the proposed assay for DA detection with ultrahigh sensitivity in biological samples.

CuO/WO3 nanoparticles decorated graphene oxide nanosheets with enhanced peroxidase-like activity for electrochemical cancer cell detection and targeted therapeutics.

The novel method was developed for electrochemical cancer cell detection using CuO/WO3 nanoparticle decorated graphene oxide nanosheet (CuO/WO3-GO) with enhanced peroxidase like-activity, based on catalytic reaction of H2O2 with o-Phenylenediamine (OPD). The prepared nanocomposite conjugated with folic acid (FA), as a cancer cell-targeting ligand, and a miniaturized electrochemical cell for cancer cell detection was designed. In this strategy OPD could oxidize in the presence of H2O2 on the surface of working electrode, which produced an electrochemical signal. However, the redox response signal changed by interaction of cells with FA/CuO/WO3-GO. During interaction between cells and CuO/WO3-GO, some amount of H2O2-OPD system participated in chemical reaction and removed from the electrode, resulting in a decrease in the response signal. As a consequence, cancer cells detected in wide detection range of 50 to 105 cells/mL and a detection limit of 18 cells/mL. Furthermore, the nanocomposite shows therapeutic cancer treatment through superior peroxidase activity. This work unveils an effective method for simple, sensitive and selective monitoring of cancer cells and also has the potential for efficient cancer therapy, which will open an avenue of nanozymes toward biological applications.

Mimicking peroxidase activity of Co2(OH)2CO3-CeO2 nanocomposite for smartphone based detection of tumor marker using paper-based microfluidic immunodevice.

We present a paper-based microfluidic colorimetric immunosensor for the detection of carcinoembryonic antigen (CEA), using Co2(OH)2CO3-CeO2 nanocomposite with extraordinary intrinsic peroxidase like activity. The morphology and composition of the nanocomposite characterized with Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. The proposed immunosensor facilely fabricated by loading mixture of ionic liquid and chitosan functionalized primary antibodies (Ab1) on the surface of paper. Compared to traditional paper based immunodevice, when ionic liquid was used the nonspecific binding protein from the paper surface was more effectively removed. Secondary antibodies (Ab2) were stacked on the surface of the carboxylated Co2(OH)2CO3-CeO2 nanocomposite. The immunosensor response was obtained by a color change resulting from Co2(OH)2CO3-CeO2 nanocomposite catalyzing the oxidation of 3,3',5,5'-tetramethyl benzidine in the presence of H2O2. The colorimetric sensing was accomplished on the paper, using smartphone for taking a photo and then analyzing the colors with an installed application. Detection of CEA was performed by this method with a linear range from 0.002 to 75.0 ng mL-1 and a detection limit of 0.51 pg mL-1. In this paper we developed simple, cost-effective and portable design for sensitive immunoassay and point-of-care diagnostics of cancer marker.

A highly sensitive electrochemical immunosensor for hepatitis B virus surface antigen detection based on Hemin/G-quadruplex horseradish peroxidase-mimicking DNAzyme-signal amplification.

Here we prepared an electrochemical immunosensor employing Au sheet as working electrode, Fe3O4 magnetic nanoparticles (MNPs) as supporting matrix and hemin/G-quadruplex DNAzyme as signal amplifier for determination of hepatitis B virus surface antigen (HBsAg). First, the primary antibody of HBs (Ab1) was immobilized on the surface of the carboxyl-modified MNPs. Then, the assembly of antibody and alkylthiol/G-quadruplex DNA/hemin on gold nanoparticles was used as bio-bar-coded nanoparticle probe. Protein target was sandwiched between the primary antibody of HBs (Ab1) immobilized on the MNPs and hemin bio-bar-coded AuNPs probe labeled antibody (Ab2). Hemin/G-quadruplex structure as HRP mimicking-DNAzyme significantly improved the catalytic reduction of H2O2 by oxidation of methylene blue (MB). Square wave voltammetry signals of MB provided quantitative measurements of HBsAg with a linear concentration range of 0.3-1000 pgmL-1 and detection limit of 0.19 pgmL-1. Due to efficient catalytic activity of HRP mimicking-DNAzyme, the proposed immunosensor exhibited high sensitivity and it holds great promise for clinical application and provides a new platform for immunosensor development and fast disease diagnosis.