A fluorescent probe for detecting thiamine using the luminescence intensity of nanoparticles

Determination of molecules and biomolecules using nanoparticles is promising in the development of analytical techniques. Modified Eu-doped Y₂O₃ nanoparticles (Y₂O₃:Eu NPs) by captopril have been used as a probe for thiamine (vitamin B₁) determination. According to the fluorescence enhancement of modified Eu-doped Y₂O₃ nanoparticles caused by thiamine, a simple and sensitive method were proposed for its detection. The increase in modified Y₂O₃:Eu NPs fluorescence signal as a function of thiamine concentration was found to be linear in the concentration range of 0–44 μM. The limit of detection (LOD) of thiamine by this method was 0.144 μM. All the measurements were performed in natural pH, at the room temperature under ambient conditions. Possible interaction mechanism was discussed.     

Experimental extraction of stern-layer capacitance in biosensor detection using silicon nanowire field-effect transistors

Accurate diagnose of a disease in the early stage is critical to treat the disease properly. To this end, a multitude of biosensors with advanced technologies have been developed to detect the number of biomolecules precisely. In this work, we propose a method for extracting the Stern layer capacitance (C_stern) using the experimental data of silicon nanowire ion-sensitive field-effect transistors (ISFETs) to help improve the accurate detection of target molecules. The proposed method was applied to both pH and virus sensing scheme, and the C_stern value of pH and a virus were extracted as 32 and 26 μF/cm², respectively. These findings indicated that the extracted C_stern was affected by the size of the ion and protein, which also was verified by a computer-aided simulation. These insights would be useful in the development of charge-based ISFET biosensors.     

Surface functionalization of chitosan-coated magnetic nanoparticles for covalent immobilization of yeast alcohol dehydrogenase from Saccharomyces cerevisiae

A novel and efficient immobilization of yeast alcohol dehydrogenase (YADH, EC1.1.1.1) from Saccharomyces cerevisiae has been developed by using the surface functionalization of chitosan-coated magnetic nanoparticles (Fe₃O₄/KCTS) as support. The magnetic Fe₃O₄/KCTS nanoparticles were prepared by binding chitosan alpha-ketoglutaric acid (KCTS) onto the surface of magnetic Fe₃O₄ nanoparticles. Later, covalent immobilization of YADH was attempted onto the Fe₃O₄/KCTS nanoparticles. The effect of various preparation conditions on the immobilized YADH process such as immobilization time, enzyme concentration and pH was investigated. The influence of pH and temperature on the activity of the free and immobilized YADH using phenylglyoxylic acid as substrate has also been studied. The optimum reaction temperature and pH value for the enzymatic conversion catalyzed by the immobilized YADH were 30 °C and 7.4, respectively. Compared to the free enzyme, the immobilized YADH retained 65% of its original activity and exhibited significant thermal stability and good durability.     

Effect of nanostructured MoS2 morphology on the glucose sensing of electrochemical biosensors

In this study, the effects of the morphological characteristics of MoS₂ nanomaterials on the glucose sensing of electrochemical biosensors were explored. Nanostructured MoS₂ materials, including nanoparticles (NPs), nanoflowers (NFs), and nanoplatelets (NPLs), were prepared via a simple hydrothermal method. The structure and morphological characteristics of MoS₂ nanomaterials were examined through X-ray diffraction, field emission scanning electron microscopy, and Raman spectroscopy. Electrochemical properties were analyzed through cyclic voltammetry. Results showed that the obtained sensitivity was 64, 68.7, and 77.6 μAmM⁻¹ cm⁻² for MoS₂ NP-, MoS₂ NF-, and MoS₂ NPL-based biosensors, respectively. The limit of detection (LOD) of all MoS₂-based glucose biosensors was 0.081 mM. In addition, the pH, temperature, glucose oxidase (GOx) concentration, reproducibility, specificity, and stability of glucose biosensors with different MoS₂ morphologies were also investigated and indicated the oxidation current response of the MoS₂ NPL-based glucose biosensor was higher than that of MoS₂ NF- and NP-based biosensors.     

Electrochemical sensing of H2O2 using cobalt oxide modified TiO2 nanotubes

Cobalt oxide (Co₃O₄) modified anatase titanium dioxide nanotubes (ATNTs) have been investigated for the electrochemical sensing of hydrogen peroxide (H₂O₂). ATNTs have been synthesized by a two-step anodization process. ATNTs were then modified with Co₃O₄ employing chemical bath deposition method. The structure and morphology of ATNTs and their modification with Co₃O₄ has been confirmed by X-ray diffraction by scanning electron microscopy. H₂O₂ sensing has been studied in 0.1 M PBS solution, by cyclic voltammetry and amperometry. Variation in the peak positions and current densities was observed with addition of H₂O₂ for Co₃O₄ modified ATNTs. Sensitivity and limit of detection improved with modification of ATNTs with Co₃O₄ with precursor concentration up to 0.8 M. However, at higher precursor concentrations sensitivity and limit of detection toward H₂O₂ deteriorated. Co₃O₄ Modified ATNTS using 0.8 M precursor concentration are comparatively more suitable for H₂O₂ sensing applications due to the optimum formation of Co₃O₄/ATNTs heterojunctions.     

Structural Insight into Stabilization of Pickering Emulsions with Fe3O4@SiO2 Nanoparticles for Enzyme Catalysis in Organic Media

Encapsulation of enzymes with enhanced activity and recyclability in water‐in‐oil Pickering emulsions is a simple and efficient method for their immobilization; however, the effect produced by the structure of colloidal particles on the stabilization of the Pickering emulsion for enzyme catalysis has not been investigated in detail. In this study, four types of hydrophobic Fe₃O₄@SiO₂ nanoparticles (NPs) with similar chemical compositions, particle diameters, but different surface characteristics have been prepared and utilized for enzyme encapsulation in various water‐in‐oil magnetic Pickering emulsions, after which the relationship between NPs structure, size of emulsions droplets, and enzyme activity is examined. The obtained results indicate that (i) the more hydrophobic Fe₃O₄@SiO₂ NPs cause the higher enzyme activity; (ii) the higher hydrophobicity of oil phase also increases the enzyme activity, especially for Fe₃O₄@w‐SiO₂ NPs which form in the solvent of water. The results are mainly attributed to the higher specific surface area of emulsion droplets and interfacial mass transfer of substrates through the interfaces of droplets. The reported data provide new insights into the mechanism of stabilization of Pickering emulsions for enhancing enzyme activity and demonstrate efficient theoretical references for enzyme immobilization and synthesis of stable and active biocatalysts with high recyclability.     

NO Fluorescence Sensing by Europium Tetracyclines Complexes in the Presence of H2O2

The effect on the fluorescence of the europium:tetracycline (Eu:Tc), europium:oxytetracycline (Eu:OxyTc) and europium:chlortetracycline (Eu:ClTc) complexes in approximately 2:1 ratio of nitric oxide (NO), peroxynitrite (ONOO^?), hydrogen peroxide (H₂O₂) and superoxide (O₂ ^·?) was assessed at three ROS/RNS concentrations levels, 30 °C and pH 6.00, 7.00 and 8.00. Except for the NO, an enhancement of fluorescence intensity was observed at pH 7.00 for all the europium tetracyclines complexes—the high enhancement was observed for H₂O₂. The quenching of the fluorescence of the Tc complexes, without and with the presence of other ROS/RNS species, provoked by NO constituted the bases for an analytical strategy for NO detection. The quantification capability was evaluated in a NO donor and in a standard solution. Good quantification results were obtained with the Eu:Tc (3:1) and Eu:OxyTc (4:1) complexes in the presence of H₂O₂ 200 μM with a detection limit of about 3 μM (Eu:OxyTc).     

Encapsulation of Co3O4 Nanoparticles Inside CeO2 Nanotubes: An Efficient Biocatalyst for the Ultrasensitive Detection of Ascorbic Acid

A quick and sensitive detection of ascorbic acid (AA) is essential in the fields of biosensing and disease diagnosis. In this work, an effective approach combined with electrospinning, chemical bath deposition, and calcination process is developed to encapsulate Co₃O₄ nanoparticle into CeO₂ nanotubes as efficient peroxidase mimics for the detection of AA. The peroxidase‐like catalytic activity of the as‐prepared Co₃O₄@CeO₂ nanotubes is much higher than that of individual Co₃O₄ nanofibers and CeO₂ nanotubes alone due to the synergistic effect between the two components. Owing to the superior catalytic efficiency of the prepared Co₃O₄@CeO₂ nanotubes, a colorimetric route for the rapid and accurate detection of AA with a detection limit of 0.73 × 10⁻⁹m with a wide linear range from 0 to 0.8 × 10⁻⁶m is demonstrated. This detection limit is much better than the previous reports based on the enzyme‐like catalytic systems. In addition, a good selectivity toward the detection of AA over amino acids, common ions, dopamine, and uric acid is achieved. This study offers a new approach for the fabrication of Co₃O₄@CeO₂ nanotubes as sensing platform toward the detection of AA, which presents promising potential applications in biosensing, environmental monitoring, and medical diagnostics.     

Structural and magnetic properties of nano nickel-zinc ferrite synthesized by reverse micelle technique

Nanocrystalline nickel-zinc ferrites (Ni_0.58Zn_0.42Fe₂O₄) at different pH values (less than 9.6, 9.6, 10.96, and 11.40) for the alkali-precipitating reaction were synthesized by reverse micelle technique. X-ray diffraction reveals a well-defined nickel-zinc ferrite crystal phase at pH=9.6. Increase in pH value obstructs pure-phase formation and results in partial formation of α-Fe₂O₃. The magnetic behaviour of the samples was studied by superconducting quantum interference device. All the samples show superparamagnetic behaviour at room temperature (300 K) and negligible hysteresis at low temperature (5 K). The low value of saturation magnetization is explained on the basis of spin canting. The high-field irreversibility and shifting of the hysteresis loop detected in single-phase sample has been assigned to a spin-disordered phase, which has a spin-freezing temperature of approximately 42 K and other two samples have an antiferromagnetic phase (α-Fe₂O₃) coupled to the ferromagnetic phase.     

Combined treatment approaches based on ultrasound for removal of triazophos from wastewater

Pesticides have been the major contributors to the growth of agricultural productivity, but the wide spread use in the fields and discharge from the manufacturing industries have also contributed to environmental concerns. In the present work, degradation of triazophos (O,O-diethyl-O-(1-phenyl-1H-1,2,4-triazol-3-yl) phosphorothioate) as a model pollutant has been investigated using high volume continuous ultrasonic flow cell for the first time. Effect of power dissipation and initial pH on the extent of triazophos degradation using acoustic cavitation has been investigated initially. Under the optimized set of operating power dissipation and pH, effect of addition of hydrogen peroxide (ratio of C₁₂H₁₆N₃O₃PS (Triazophos):H₂O₂ over the range of 1:1–1:5), ozone (over the flow rate of 100–400 mg/h) and Fenton’s reagent (C₁₂H₁₆N₃O₃PS:FeSO₄:H₂O₂ ratio over the range of 1:1:1–1:4:4) has been investigated as possible process intensification strategy. Combined operation of US with H₂O₂ and Ozone resulted in 48.6% and 54.6% triazophos degradation respectively whereas combination of US and Fenton’s reagent resulted in maximum degradation as 92.2% and also resulted in maximum COD removal as 88.5%. The study also focused on identification of intermediate products formed during the degradation as well as establishing the kinetic rate constants and the synergistic index for different approaches. The study has established that cavitation can be effectively used for triazophos degradation with significant intensification benefits based on the use of combination approach.     

A Multifunctional Magnetic Composite Material as a Drug Delivery System and a Magnetic Resonance Contrast Agent

Magnetic iron oxide coated in hydrogenation silica (Fe₃O₄@HSiO₂) is constructed as both a tumor drug carrier and a magnetic resonance (MR) contrast agent. Colchicine (COLC) is loaded in Fe₃O₄@HSiO₂ with the highest amount of 28.3 wt% at pH 9. The release performance of COLC can be controlled by pH, as the porous HSiO₂ shell can partially shed at pH below 3.0 to facilitate the release of COLC. MR imaging (MRI) tests prove that Fe₃O₄@HSiO₂ at pH 3.0 (H⁺‐Fe₃O₄@HSiO₂) shows a stronger MR contrast enhancement than Fe₃O₄. Cytotoxicity experiment indicates that Fe₃O₄@HSiO₂ has excellent biocompatibility and magnetic targeting performance. Additionally, COLC‐loaded Fe₃O₄@HSiO₂ (Fe₃O₄@HSiO₂–COLC) displays a higher inhibition effect on tumor cells under a magnetic field than free COLC. The visibility upon MRI, high targeting, and pH‐controlled release characteristics of Fe₃O₄@HSiO₂–COLC are favorable to achieve the aim of reducing side effects to normal tissues, making Fe₃O₄@HSiO₂–COLC an attractive drug delivery system for nanomedicine.     

Dependence of pH and surfactant effect in the synthesis of magnetite (Fe3O4) nanoparticles and its properties

Nanoparticles of Fe₃O₄ were synthesized by co-precipitation in an aqueous solution containing ferrous and ferric salts (1:2) at varying pH with ammonia as a base. It was found that the value of pH influences the reaction mechanism for the formation of Fe₃O₄. Furthermore, the addition of mercaptoethanol significantly reduced the crystalline size of Fe₃O₄ nanoparticles from 15.03 to 8.02 nm. X-ray diffraction (XRD) spectra revealed that the synthesized nanoparticles were ε-Fe₂O₃ or Fe₃O₄ phase. To further prove the composition of the product, as-prepared Fe₃O₄ were examined by X-ray photoelectron spectroscopy (XPS). Magnetic properties of the obtained particles were determined by vibrating sample magnetometer (VSM). Further analysis of the X-ray studies shows that while maintaining a pH value of 6 and 9 in a solution containing iron salts II and III ions produces ε-Fe₂O₃. Whereas a pH value of 11 produces magnetite (Fe₃O₄) phase. All of these results show that the pH has a major role in the observed phase formation of (Fe₃O₄) nanoparticles.     

Degradation of diclofenac sodium using combined processes based on hydrodynamic cavitation and heterogeneous photocatalysis

Diclofenac sodium, a widely detected pharmaceutical drug in wastewater samples, has been selected as a model pollutant for degradation using novel combined approach of hydrodynamic cavitation and heterogeneous photocatalysis. A slit venturi has been used as cavitating device in the hydrodynamic cavitation reactor. The effect of various operating parameters such as inlet fluid pressure (2–4 bar) and initial pH of the solution (4–7.5) on the extent of degradation have been studied. The maximum extent of degradation of diclofenac sodium was obtained at inlet fluid pressure of 3 bar and initial pH as 4 using hydrodynamic cavitation alone. The loadings of TiO₂ and H₂O₂ have been optimised to maximise the extent of degradation of diclofenac sodium. Kinetic study revealed that the degradation of diclofenac sodium fitted first order kinetics over the selected range of operating protocols. It has been observed that combination of hydrodynamic cavitation with UV, UV/TiO₂ and UV/TiO₂/H₂O₂ results in enhanced extents of degradation as compared to the individual schemes. The maximum extent of degradation as 95% with 76% reduction in TOC has been observed using hydrodynamic cavitation in conjunction with UV/TiO₂/H₂O₂ under the optimised operating conditions. The diclofenac sodium degradation byproducts have been identified using LC/MS analysis.     

Improving dosimetric properties of tellurite glasses

Thermoluminscence (TL) properties of quaternary tellurite glass in the form 80(TeO₂)–5(TiO₂)–(15−x)(WO₃)–(x)A_nO_m where A_nO_m=Nb₂O₅, Nd₂O₃, Er₂O₃ and x mol% have been measured. TL main dosimetry peak for each produced glass sample were investigated for ⁶⁰Co gamma rays. Dosimetric properties of the quaternary tellurite glasses have been measured as a function of different compositions of the glass system in different rare earth oxides concentration by using thermoluminescence (TL) detection technique.     

Dispersion behavior and thermal conductivity characteristics of Al2O3–H2O nanofluids

Nanofluid is a kind of new engineering material consisting of solid nanoparticles with sizes typically of 1–100 nm suspended in base fluids. In this study, Al₂O₃–H₂O nanofluids were synthesized, their dispersion behaviors and thermal conductivity in water were investigated under different pH values and different sodium dodecylbenzenesulfonate (SDBS) concentration. The sedimentation kinetics was determined by examining the absorbency of particle in solution. The zeta potential and particle size of the particles were measured and the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory was used to calculate attractive and repulsive potentials. The thermal conductivity was measured by a hot disk thermal constants analyser. The results showed that the stability and thermal conductivity enhancements of Al₂O₃–H₂O nanofluids are highly dependent on pH values and different SDBS dispersant concentration of nano-suspensions, with an optimal pH value and SDBS concentration for the best dispersion behavior and the highest thermal conductivity. The absolute value of zeta potential and the absorbency of nano-Al₂O₃ suspensions with SDBS dispersant are higher at pH 8.0. The calculated DLVO interparticle interaction potentials verified the experimental results of the pH effect on the stability behavior. The Al₂O₃–H₂O nanofluids with an ounce of Al₂O₃ have noticeably higher thermal conductivity than the base fluid without nanoparticles, for Al₂O₃ nanoparticles at a weight fraction of 0.0015 (0.15 wt%), thermal conductivity was enhanced by up to 10.1%.     

Degradation of 2,4-dinitrophenol using a combination of hydrodynamic cavitation,chemical and advanced oxidation processes

In the present work, degradation of 2,4-dinitrophenol (DNP), a persistent organic contaminant with high toxicity and very low biodegradability has been investigated using combination of hydrodynamic cavitation (HC) and chemical/advanced oxidation. The cavitating conditions have been generated using orifice plate as a cavitating device. Initially, the optimization of basic operating parameters have been done by performing experiments over varying inlet pressure (over the range of 3–6 bar), temperature (30 °C, 35 °C and 40 °C) and solution pH (over the range of 3–11). Subsequently, combined treatment strategies have been investigated for process intensification of the degradation process. The effect of HC combined with chemical oxidation processes such as hydrogen peroxide (HC/H₂O₂), ferrous activated persulfate (HC/Na₂S₂O₈/FeSO₄) and HC coupled with advanced oxidation processes such as conventional Fenton (HC/FeSO₄/H₂O₂), advanced Fenton (HC/Fe/H₂O₂) and Fenton-like process (HC/CuO/H₂O₂) on the extent of degradation of DNP have also been investigated at optimized conditions of pH 4, temperature of 35 °C and inlet pressure of 4 bar. Kinetic study revealed that degradation of DNP fitted first order kinetics for all the approaches under investigation. Complete degradation with maximum rate of DNP degradation has been observed for the combined HC/Fenton process. The energy consumption analysis for hydrodynamic cavitation based process has been done on the basis of cavitational yield. Degradation intermediates have also been identified and quantified in the current work. The synergistic index calculated for all the combined processes indicates HC/Fenton process is more feasible than the combination of HC with other Fenton like processes.     

Ultrafast synthesis of Li1 + αV3O8 gel precursors for lithium battery applications

A versatile route has been developed to synthesize the Li_1 + αV₃O₈ gel precursor 50 times faster than the standard path without heating by using H₂O₂ and V₂O₅ and lithium salts as precursors. Upon heat treatment it leads to stoechiometric Li_1.1V₃O₈ with an electrochemical behavior similar to the one observed from the standard material. The role of the pH and the nature of the counter ion on the structural type and the morphology of the condensed Li_1 + αV₃O_8,nH₂O compound have been investigated. pH close to the zero charge point (≈ 2) lead to intercalated Li_xV₂O₅,nH₂O type gels whereas at pH 4 condensation drives to hewettite like structures.     

Microwave-assisted rapid synthesis of Ag nanoparticles/graphene nanosheet composites and their application for hydrogen peroxide detection

Abstract  

Ag nanoparticles/graphene nanosheet (AgNPs/GN) composites have been rapidly prepared by a one-pot microwave-assisted reduction method, carried out by microwave irradiation of a N,N-dimethylformamide (DMF) solution of graphene oxide (GO) and AgNO₃. Several analytical techniques including UV–vis spectroscopy, FT-IR spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) have been used to characterize the resulting AgNPs/GN composites. It suggests that such composites exhibit good catalytic activity toward reduction of hydrogen peroxide (H₂O₂), leading to a H₂O₂ sensor with a fast amperometric response time of less than 2 s. The linear detection range is estimated to be from 0.1 to 100 mM (r = 0.999), and the detection limit is estimated to be 0.5 μM at a signal-to-noise ratio of 3.     

Performance parameters and uncertainty of the method for assessment of Sr concentration in small powder samples using α-Al2O3:C beta detectors

Non-destructive detection of very low concentrations of ⁹⁰Sr (about 0.4 Bq g⁻¹) inside powdered samples with masses below 200 mg (such as tooth enamel prepared for EPR measurements) is not a trivial task. Most of the conventional measurement techniques require a special chemical treatment or an enrichment process. Thin-layer α-Al₂O₃:C passive luminescence beta detectors have been successfully used for measuring dose rates due to beta decay of ⁹⁰Sr inside small samples. In this paper, a new refinement is introduced for the assessment of ⁹⁰Sr concentration in dental tissue using thin-layer α-Al₂O₃:C passive luminescence beta detectors. The performance parameters of passive luminescence beta detection (such as detection and quantification limits) have been evaluated using statistical analysis of the experimental results. The sources of uncertainty have been analyzed and the total uncertainty calculated using Monte Carlo simulations. The results of TL passive beta detection for measurement of ⁹⁰Sr concentrations are shown to be in good agreement with those obtained using low-level beta counting.     

The structure and properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Al coatings deposited by microarc oxidation on graphite substrates

Protective α-Al₂O₃ coatings on the surface of a graphite article have been obtained by method of electric-arc metallization with aluminum and microarc oxidation (anodic spark process). Investigation of the obtained coating by scanning electron microscopy (SEM), X-ray diffraction (XRD), and proton elastic recoil detection analysis (ERDA) showed good quality of the Al and α-Al₂O₃ coatings on graphite. The proposed technology can be used for obtaining protective coatings in low-accessible sites of graphite articles.