Electrochemical properties modulation of Zinc oxide nanoparticles

The influence of zinc salts precursors (nitrate, acetate, chloride) on the electroactivity of the synthesised Zinc oxide nanoparticles (ZnONPs) was investigated using Glassy carbon ZnONPs modified electrode (ZnONPs films). The precipitation synthesised ZnONPs ‘s optical, morphological, size and Structural properties were assessed by usual spectroscopical technique. The XRD data confirmed synthesis of The ZnONPs which were predominately Zincite except for the nitrate product (zincite, ZHNH). All the NPs were of smaller size with the highest diameter size of 0.25 μM and lowest 0.066 μM for nitrate and chloride NPs respectively. All had good electroactivity, with rate constants (k_s) above 1 × 10⁻² indicating fast reversible reactions, values ranged from 0.6152 to 0.7515 for Zn(NO₃) and Zn(CH₃COO)₂ respectively. Excellent opto-electric properties were observed with the nitrate product that had the highest band gaps (∼3.7 eV), DPV current(,7.57 × 10⁻⁷ A) ΔE_p, diffusion coefficient (D_e) (3.120 × 10⁻¹(cm^2/s (Ariyanta et al., 2022) [5]) and rate constant (0.62 S^-1). In addition it had the lowest resistance as indicated by the R_s value (1.13 kΩ) below the bare electrode value lowest R_ct (444.77 kΩ) and CPE (3.00 × 10⁻⁶ F). For fabrication of sensors and batteries where low resistance and conductivity are essential, ZnONPs using Nitrate is ideal.     

Covalent decoration of graphene oxide with dendrimer-encapsulated nanoparticles for universal attachment of multiple nanoparticles on chemically converted graphene

We report a method for universal assembly of multiple nanoparticles with different sizes and compositions on a single chemically converted graphene sheet with good control over particle sizes in the range of 1 to 2 nm through the covalent immobilization of dendrimer-encapsulated nanoparticles.     

Interfacing colloidal graphene oxide sheets with gold nanoparticles

Aqueous solutions of graphene oxide (GO) and citrate-stabilised gold nanoparticles (AuNPs) are two classic, negatively charged colloids. Using the surface plasmon resonance spectra of AuNPs as a probe, we illustrate how the two like-charged colloids interact with each other and in so doing, reveal the unique solution behaviour of GO. We demonstrate that the electrical double layer of the GO sheets in water plays a key role in controlling the interaction between GO and AuNPs, which displays a one-way gate effect. It is shown that GO can capture and disperse AuNPs in water in a controllable fashion, without the need for additional chemical linkers. This discovery allows the successful synthesis of uncapped, yet solution-dispersible metal-nanoparticle assemblies. Such metal nanostructures have long been pursued for nano-plasmonics and sensing applications, but have remained difficult to prepare using conventional polymer dispersants. This work also makes clear that the combination of the two-dimensional conformation of GO along with its large molecular size and self-contained functional groups allows it to act as a unique soluble nanocarrier/substrate (the thinnest, functionalised flat substrate possible in nature) for the synthesis of new, soluble functional materials.     

Enhanced enantioselective oxidation of olefins catalyzed by Mn-porphyrin immobilized on graphene oxide

An efficient enantioselective heterogeneous catalyst, GO-[Mn(TPyP)tart], was prepared by covalent attachment of Mn(III) complex of H₂TPyP via the propyl linkage to graphene oxide (GO) nanosheet and using chiral tartrate counter ion. The catalyst was characterized by Fourier transform infrared (FT-IR), diffuse reflectance ultraviolet–visible (DR UV–Vis) spectroscopy, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman and thermogravimetric analysis (TGA). The graphene-supported Mn-porphyrin showed higher activity for the enantioselective epoxidation of unfunctionalized olefins with molecular oxygen in the presence of isobutyraldehyde. It could be recovered easily and reused in asymmetric oxidation of styrene precursor in a five-step sequence without any considerable loss of its catalytic activity and selectivity. The obtained optically epoxide selectivities were achieved in 86% to 100%.     

Zinc oxide nanoparticles in the ethelenepropylenediene rubber matrix

Nanocomposites based on zinc oxide nanoparticles and ethylene-propylene-diene rubber were synthesized by the thermal decomposition of zinc(II) acetate. The average size of the ZnO nanoparticles was determined using transmission electron microscopy. The phase compositions of the samples synthesized were identified by X-ray diffraction analysis.     

Optical determination of glucose and hydrogen peroxide using a nanocomposite prepared from glucose oxidase and magnetite nanoparticles immobilized on graphene oxide

Fe₃O₄ nanoparticles were deposited on sheets of graphene oxide (GO) by a precipitation method, and glucose oxidase (GOx) was then immobilized on this material to produce a GOx/Fe₃O₄/GO magnetic nanocomposite containing crosslinked enzyme clusters. The 3-component composite functions as a binary enzyme that was employed in a photometric method for the determination of glucose and hydrogen peroxide where the GOx/Fe₃O₄/GO nanoparticles cause the generation of H₂O₂ which, in turn, oxidize the substrate N,N-diethyl-p-phenylenediamine to form a purple product with an absorption maximum at 550 nm. The absorbance at 550 nm can be correlated to the concentration of glucose and/or hydrogen peroxide. Under optimized conditions, the calibration plot is linear in the 0.5 to 600 μM glucose concentration range, and the detection limit is 0.2 μM. The respective plot for H₂O₂ ranges from 0.1 to 10 μM, and the detection limit is 0.04 μM. The method was successfully applied to the determination of glucose in human serum samples. The GOx/Fe₃O₄/GO nanoparticles are reusable.

Diffusion and drift of graphene flake on graphite surface

Diffusion and drift of a graphene flake on a graphite surface are analyzed. A potential energy relief of the graphene flake is computed using ab initio and empirical calculations. Based on the analysis of this relief, different mechanisms of diffusion and drift of the graphene flake on the graphite surface are considered. A new mechanism of diffusion and drift of the flake is proposed. According to the proposed mechanism, rotational transition of the flake from commensurate to incommensurate state takes place with subsequent simultaneous rotation and translational motion until a commensurate state is reached again, and so on. Analytic expressions for the diffusion coefficient and mobility of the flake corresponding to different mechanisms are derived in wide ranges of temperatures and sizes of the flake. The molecular dynamics simulations and estimates based on ab initio and empirical calculations demonstrate that the proposed mechanism can be dominant under certain conditions. The influence of structural defects on the diffusion of the flake is examined on the basis of calculations of the potential energy relief and molecular dynamics simulations. The methods of control over the diffusion and drift of graphene components in nanoelectromechanical systems are discussed. The possibility to experimentally determine the barriers to relative motion of graphene layers based on the study of diffusion of a graphene flake is considered. The results obtained can also be applied to polycyclic aromatic molecules on graphene and should be qualitatively valid for a set of commensurate adsorbate-adsorbent systems.     

Biomedical application and hidden toxicity of Zinc oxide nanoparticles

Zinc oxide nanoparticles (ZnO NPs) represent a novel type of metal oxide nanoparticles enabling a new horizon for biomedical applications spanning from diagnosis to treatment. ZnO NPs are extensively used in commercial products such as sunscreens and daily-care products. Apart from that, ZnO NPs are used in food packaging and ointments and as an antimicrobial and antifungal agent. They are extensively used for many biomedical applications noticeably in pharmaceutics and theranostics. Its exceptional optical, electrical, and physiochemical properties, notably its incredible surface chemistry, make ZnO NPs a reliable option for bioimaging, biosensors, antimicrobial action, and drug and gene delivery. The present review covers findings and developments in ZnO NPs research in relation to its application and toxicity mechanism. A special emphasis has been given to the neurotoxic potential of the ZnO NPs and glial cell toxicity. Various factors contributing to the toxic potential of ZnO NPs and cell signaling pathways concerning its toxicity are also discussed. Available data point toward the risk of uncontrollable use of zinc nanoformulation. With increasing use, ZnO NPs pose a severe threat both to the ecosystem and human beings. In a nutshell, the review outlines the current state of the art of ZnO NPs.     

Facile synthesis and excellent catalytic activity of gold nanoparticles on graphene oxide

For the first time,Au nanoparticles on graphene oxide（GO-AuNPs） were successfully fabricated without applying any additional reductants,just by the redox reaction between AuCl₄^-1 and GO.Their structure was characterized by transmission electron microscopy and X-ray powder diffraction.The results show that flower-like AuNPs were successfully dispersed on GO surface.Importantly,they showed a high catalytic activity for the Suzuki-Miyaura coupling reaction in an aqueous medium.     

Electrochemical detection of reduced graphene oxide nanoparticles in aqueous solution

We have demonstrated electrochemical detection of reduced graphene oxide (rGO) nanoparticles on an ultramicroelectrode (UME) in aqueous solution using rGO collision events. The collision phenomena are detected by monitoring a current–time transient. To attract the rGO to the UME surface, a positive electric field was developed near the UME using a redox reaction. As model systems, ferrocenemethanol and ferrocyanide oxidation reactions were adopted. Amperometric current measurements showed a staircase current response after attachment of rGO on the UME surface. The magnitude of the staircase current is given by the stepwise increase in current, which can provide insight into the size distribution of the rGO colliding with the UME. In the presence of higher concentrations of rGO, multiple collision events happened sequentially on the UME. In this case, an increasing current trend, rather than a single staircase current, was observed. The overall current increment for a given time is a measure of the concentration of rGO in solution. By using this method, charged conductive materials in an aqueous solution can be sensitively detected and/or accumulated.     

An electrochemical ascorbic acid sensor based on palladium nanoparticles supported on graphene oxide

In this study, an electrochemical ascorbic acid (AA) sensor was constructed based on a glassy carbon electrode modified with palladium nanoparticles supported on graphene oxide (PdNPs-GO). PdNPs with a mean diameter of 2.6 nm were homogeneously deposited on GO sheets by the redox reaction between PdCl₄²⁻ and GO. Cyclic voltammetry and amperometric methods were used to evaluate the electrocatalytic activity towards the oxidation of AA in neutral media. Compared to a bare GC or a Pd electrode, the anodic peak potential of AA (0.006 V) at PdNPs-GO modified electrode was shifted negatively, and the large anodic peak potential separation (0.172 V) of AA and dopamine (DA), which could contribute to the synergistic effect of GO and PdNPs, was investigated. A further amperometric experiment proved that the proposed sensor was capable of sensitive and selective sensing of AA even in the presence of DA and uric acid. The modified electrode exhibited a rapid response to AA within 5 s and the amperometric signal showed a good linear correlation to AA concentration in a broad range from 20 μM to 2.28 mM with a correlation coefficient of R = 0.9991. Moreover, the proposed sensor was applied to the determination of AA in vitamin C tablet samples. The satisfactory results obtained indicated that the proposed sensor was promising for the development of novel electrochemical sensing for AA determination.     

Photovoltaic properties of graphene oxide sheets beaded with ZnO nanoparticles

A hybrid material of graphene oxide (GO) sheets beaded with ZnO nanoparticles was prepared. The material extends over a few hundred square nanometers, in which the ZnO nanoparticles (average diameter (∼5 nm)) are dispersed evenly on the GO sheet. Both the surface photovoltage or surface photocurrent intensity for the material are much stronger than for pure ZnO nanoparticles, meaning that the free charge carriers can effectively be transferred from ZnO nanoparticles to GO sheets, which can serve as a probe to monitor the electron transfer from excited ZnO to GO. Anchoring ZnO nanoparticles on two dimensional carbon nanostructures such as GO can pave a way towards the design of ordered nanostructure assemblies that can harvest light energy efficiently.     

Cuprous oxide nanoparticles dispersed on reduced graphene oxide as an efficient electrocatalyst for oxygen reduction reaction

Cuprous oxide (Cu(2)O) nanoparticles dispersed on reduced graphene oxide (RGO) were prepared by reducing copper acetate supported on graphite oxide using diethylene glycol as both solvent and reducing agent. The Cu(2)O/RGO composite exhibits excellent catalytic activity and remarkable tolerance to methanol and CO in the oxygen reduction reaction.     

The use of palladium nanoparticles supported on graphene oxide in the Mizoroki-Heck reaction

We have developed a convenient single-step method for producing palladium nanoparticles on the surface of graphene oxide by reducing palladium chloride with NaBH₄. According to transmission electron microscopy data, palladium nanoparticles have a spheroidal shape; their sizes are 6–8 nm. The tests of immobilized palladium nanoparticles have shown that they exhibit high activity in the Mizoroki-Heck cross-coupling reaction.     

Ultrasensitive colorimetric detection of heparin based on self-assembly of gold nanoparticles on graphene oxide

A novel colorimetric method was developed for ultrasensitive detection of heparin based on self-assembly of gold nanoparticles (AuNPs) onto the surface of graphene oxide (GO). Polycationic protamine was used as a medium for inducing the self-assembly of citrate-capped AuNPs on GO through electrostatic interaction, resulting in a shift in the surface plasmon resonance (SPR) absorption of AuNPs and exhibiting a blue color. Addition of polyanionic heparin disturbed the self-assemble of AuNPs due to its strong affinity to protamine. With the increase of heparin concentration, the amounts of self-assembly AuNPs decreased and the color changed from blue to red in solution. Therefore, a "blue-to-red" colorimetric sensing strategy based on self-assembly of AuNPs could be established for heparin detection. Compared with the commonly reported aggregation-based methods ("red-to-blue"), the color change from blue to red was more eye-sensitive, especially in low concentration of target. Moreover, stronger interaction between protamine and heparin led to distinguish heparin from its analogues as well as various potentially coexistent physiological species. The strategy was simply achieved by the self-assembly nature of AuNPs and the application of two types of polyionic media, showing it to be label-free, simple, rapid and visual. This method could selectively detect heparin with a detection limit of 3.0 ng mL(-1) in standard aqueous solution and good linearity was obtained over the range 0.06-0.36 μg mL(-1) (R = 0.9936). It was successfully applied to determination of heparin in fetal bovine serum samples as low as 1.7 ng mL(-1) with a linear range of 0-0.8 μg mL(-1).     

Zinc oxide nanoparticles based microfluidic immunosensor applied in congenital hypothyroidism screening

In this article, we present an innovative approach for congenital hypothyroidism (CHT) screening. This pathology is the most common preventable cause of mental retardation, affecting newborns around the world. Its consequences could be avoided with an early diagnosis through the thyrotropin (TSH) level measurement. To accomplish the determination of TSH, synthesized zinc oxide (ZnO) nanobeads (NBs) covered by chitosan (CH), ZnO-CH NBs, were covalently attached to the central channel of the designed microfluidic device. These beads were employed as platform for anti-TSH monoclonal antibody immobilization to specifically recognize and capture TSH in neonatal samples without any special pretreatment. Afterwards, the amount of this trapped hormone was quantified by horseradish peroxidase (HRP)-conjugated anti-TSH antibody. HRP reacted with its enzymatic substrate in a redox process, which resulted in the appearance of a current whose magnitude was directly proportional to the level of TSH in the neonatal sample. The structure and morphology of synthesized ZnO-CH NBs were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The calculated detection limits for electrochemical detection and the enzyme-linked immunosorbent assay procedure were 0.00087 μUI mL^?1 and 0.015 μUI mL^?1, respectively, and the within- and between-assay coefficients of variation were below 6.31 % for the proposed method. According to the cut-off value for TSH neonatal screening, a reasonably good limit of detection was achieved. These above-mentioned features make the system advantageous for routine clinical analysis adaptation.     

Ni (II) schiff base complex immobilized on graphene oxide nano-sheets catalyzed epoxidation of alkenes

Ni (II) schiff base complex was synthesized by the reaction of nickel acetate tetrahydrate with N, N’-Bis(2,4-di-hydroxybenzaldehyde)-1,2-cyclohexanediamine and supported on modified grapheme oxide nano-sheets using 3-chloropropyltrimethoxysilane as a reactive surface modifier. The heterogeneous nano-catalyst was characterized by Fourier transform infrared spectra, X-ray diffraction, thermogravimetric analysis, transmission electron microscopy, nitrogen adsorption–desorption isotherms and atomic absorption spectroscopy. This catalyst was used for the epoxidation of alkenes using tert-butyl hydroperoxide as oxidant, giving excellent conversions and selectivity. The catalyst showed great reusability and selectivity without significant loss of activity in the epoxidation reactions.     

A glassy carbon electrode modified with graphene and tyrosinase immobilized on platinum nanoparticles for sensing organophosphorus pesticides

An amperometric biosensor is described for the detection of organophosphorus pesticides. It is based on the enzyme tyrosinase immobilized on platinum nanoparticles and the use of a glassy carbon electrode modified with graphene. Tyrosinase was immobilized on the electrode surface via electrostatic interaction between a monolayer of cysteamine and the enzyme. In the presence of catechol as a substrate, the pesticides chlorpyrifos, profenofos and malathion can be determined as a result of their inhibition of the enzyme which catalyzes the oxidation of catechol to o-quinone. Platinum nanoparticles and graphene effectively enhance the efficiency of the electrochemical reduction of o-quinone, thus improving sensitivity. Under optimum experimental conditions, the inhibition effect of the pesticides investigated is proportional to their concentrations in the lower ppb-range. The detection limits are 0.2, 0.8 and 3?ppb for chlorpyrifos, profenofos and malathion, respectively. The biosensor displays good repeatability and acceptable stability.