Magnetic-field-assisted assembly of layered double hydroxide/metal porphyrin ultrathin films and their application for glucose sensors

Nanostructured Polyoxometalate-Based Heterogeneous Electrode Materials for Electrochemical Sensing of Glucose

We exploited a tactic to obtain a low-cost, high-efficiency, pollution-free, and stable nonenzymatic polyoxometalate-based heterogeneous electrode material for electrochemical sensing of glucose. It is first followed by the countercation exchange of K2Na8[Cu4(H2O)2(PW9O34)2] (CuPOM) using cesium chloride to prepare an insoluble CuPOM (Cs-CuPOM), which exhibits a uniform and perfect claviform shape with smooth surface. Further, it was mixed with graphite powder to prepare Cs-CuPOM-modified carbon paste electrode (Cs-CuPOM/CPE) with the Cs-CuPOM content between 15% and 50% in weight. This obtained electrode material Cs-CuPOM shows a better electrochemical sensor activity than Cs-MnPOM, Cs-FePOM, and other reported POM-based electrode materials for glucose oxidation on account of their quicker electron transfer kinetics, which also exhibits conspicuous characteristics with a wide linear range of 5-1500 μM. It also possesses a high sensitivity of 16.3 A M-1 cm-2 and a low limit of detection (LOD) of 0.99 × 10-6 M at the signal-to-noise ratio of 3. The conspicuous sensing feature, low cost, and liable synthetic method can make Cs-CuPOM a promising candidate for the exploitation of a preeminent glucose sensor.

Tweaking the Non-Volatile Write-Once-Read-Many-Times (WORM) Memory using Donor-Acceptor Architecture with Isatin as Core Acceptor

Organic memory devices have attracted attention because they promise flexible electronics, low manufacturing costs, and compatibility with large-scale integration. A series of new D-A architectures were synthesized employing different donor groups and the isatin moiety as the acceptor through Suzuki-Miyaura coupling reactions. Strong intramolecular interactions were observed in the synthesized compounds, further corroborated by an optimal bandgap. The SEM investigation confirmed good molecular ordering and superior thin film surface coverage. All the compounds demonstrated notable binary Write-Once-Read-Many-Times (WORM) memory behaviour. The threshold switching voltage for these D-A systems ranged from -0.79 to -2.37 V, with the compound having isobutyl substituent showing the lowest threshold voltage and maximum ON/OFF ratio of 102, thus outperforming others. The combined effects of charge transfer and charge trapping are responsible for the resistive switching mechanism prevailing in these systems. The alterations in D-A molecules that affect molecular packing, thin film morphology, and, finally, the memory performance of the active layer are highlighted in this work.

Current advancements and prospects of enzymatic and non-enzymatic electrochemical glucose sensors

This review discusses the most current developments and future perspectives in enzymatic and non-enzymatic glucose sensors, which have notably evolved over the preceding quadrennial period. Furthermore, a thorough exploration encompassed the sensor's intricate fabrication processes, the diverse range of materials employed, the underlying principles of detection, and an in-depth assessment of the sensors' efficacy in detecting glucose levels within essential bodily fluids such as human blood serums, urine, saliva, and interstitial fluids. It is worth noting that the accurate quantification of glucose concentrations within human blood has been effectively achieved by utilizing classical enzymatic sensors harmoniously integrated with optical and electrochemical transduction mechanisms. Monitoring glucose levels in various mediums has attracted exceptional attention from industrial to academic researchers for diabetes management, food quality control, clinical medicine, and bioprocess inspection. There has been an enormous demand for the creation of novel glucose sensors over the past ten years. Research has primarily concentrated on succeeding biocompatible and enhanced sensing abilities related to the present technologies, offering innovative avenues for more effective glucose sensors. Recent developments in wearable optical and electrochemical sensors with low cost, high stability, point-of-care testing, and online tracking of glucose concentration levels in biological fluids can aid in managing and controlling diabetes globally. New nanomaterials and biomolecules that can be used in electrochemical sensor systems to identify glucose concentration levels are developed thanks to advances in nanoscience and nanotechnology. Both enzymatic and non-enzymatic glucose electrochemical sensors have garnered much interest recently and have made significant strides in detecting glucose levels. In this review, we summarise several categories of non-enzymatic glucose sensor materials, including composites, non-precious transition metals and their metal oxides, hydroxides, precious metals and their alloys, carbon-based materials, conducting polymers, metal-organic framework (MOF)-based electrocatalysts, and wearable device-based glucose sensors deeply.

A Zero-Strain Insertion Cathode Material for Room-Temperature Fluoride-Ion Batteries

A fluoride-ion battery (FIB) is a novel type of energy storage system that has a higher volumetric energy density and low cost. However, the high working temperature (>150 °C) and unsatisfactory cycling performance of cathode materials are not favorable for their practical application. Herein, fluoride ion-intercalated CoFe layered double hydroxide (LDH) (CoFe-F LDH) was prepared by a facile co-precipitation approach combined with ion-exchange. The CoFe-F LDH shows a reversible capacity of ∼50 mAh g^-1 after 100 cycles at room temperature. Although there is still a big gap between FIBs and lithium-ion batteries, the CoFe-F LDH is superior to most cathode materials for FIBs. Another important advantage of CoFe-F LDH FIBs is that they can work at room temperature, which has been rarely achieved in previous reports. The superior performance stems from the unique topochemical transformation property and small volume change (∼0.82%) of LDH in electrochemical cycles. Such a tiny volume change makes LDH a zero-strain cathode material for FIBs. The 2D diffusion pathways and weak interaction between fluoride ions and host layers facilitate the de/intercalation of fluoride ions, accompanied by the chemical state changes of Co²⁺/Co³⁺ and Fe²⁺/Fe³⁺ couples. First-principles calculations also reveal a low F^- diffusion barrier during the cyclic process. These findings expand the application field of LDH materials and propose a novel avenue for the designs of cathode materials toward room-temperature FIBs.

Glucose sensing on screen-printed electrochemical electrodes based on porous graphene aerogel @prussian blue

As one of the three major chronic diseases, diabetes often causes many complications, which can affect various parts of the body and even threaten the life of the patients. At present, the situation of diabetes in the world is quite serious. Accurate detection of blood glucose is very important for the diagnosis, treatment and medication of diabetes as well as the self-management of diabetic patients. In this paper, an electrochemical glucose biosensor was developed based on screen-printed electrode (SPE) modified with composite material of graphene aerogel (GA) and Prussian blue (PB) (denoted as GA@PB), which was fabricated via chemical reduction using L-ascorbic acid as a reducing agent through a freeze-drying process. Glucose was specifically captured by glucose oxidase (GOx) which were immobilized into the GA@PB by chitosan. The structure and performance of the sensor were characterized by scanning electron microscopy (SEM), Raman spectroscopy measurements, Fourier transform infrared spectrometer (FTIR), cyclic voltammetry (CV) and amperometric detection. The sensor exhibited a linear range of 0.5-6.0 mmol·L^-1 with limit of detection (LOD) of 0.15 mmol·L^-1, indicating that the combination of graphene aerogel and Prussian blue possess well conductivity and catalytic performance.

A flexible Ni–Ag-coated nylon yarn as an electrode for non-enzymatic glucose sensing

SCNY@Ni was prepared by electrochemical deposition and exhibited excellent performance for glucose determination.

A 3D porous graphene aerogel@GOx based microfluidic biosensor for electrochemical glucose detection

As a chronic disease, diabetes may result in serious complications that endanger the health and life of patients. Accurate and real-time detection of blood sugar levels is of great significance for the prevention and treatment of diabetes. In this paper, an enzymatic electrochemical microfluidic biosensor for glucose detection was developed based on a three-dimensional (3D) porous graphene aerogel and glucose oxidase (GOx). A graphene aerogel was prepared by freeze-drying a graphene hydrogel and has a high electrical conductivity, the 3D porous structure provided a good near-biological condition for GOx and the increased specific surface area allowed more GOx to be immobilized on the graphene aerogel. The microfluidic system greatly reduced the consumption of samples during tests. Amperometric measurements were carried out to test glucose concentrations, and the enzyme biosensor showed a linear range from 1 mM to 18 mM (R² = 0.991). The limit of detection (LOD) was 0.87 mM (S/N = 3) and the sensor showed excellent selectivity and stability. Finally, monitoring glucose in serum samples was achieved by the proposed sensor and good recoveries were obtained. Due to its excellent performance, the proposed biosensor has a favorable application prospect in the prevention and clinical diagnosis of diabetes. Furthermore, our method, which is used to prepare a graphene aerogel modified electrode in a microfluidic chip, can be widely used in various electrochemical sensors.

A novel dual-tasking hollow cube NiFe2O4-NiCo-LDH@rGO hierarchical material for high preformance supercapacitor and glucose sensor

Binary transition metal oxides as electroactive materials have continuously aroused grumous attention due to their high theoretical specific capacitance, high valtage window, and multiple oxidation states. However, the tiny specific surface area, poor conductivity and unsatisfactory cycle stability limit their practical application. Hence, a synthetic strategy is designed to fabricate a dual-tasking hollow cube nickel ferrite (NiFe₂O₄) - based composite (NiFe₂O₄-NiCo-LDH@rGO) with hierarchical structure. The composite is constructed by firstly preparing hollow NiFe₂O₄ from cube-like Ni - Fe bimetallic organic framework (NiFe-MOF), and then integrating nickel cobalt layered double hydroxide (NiCo-LDH) nanowires, together with reduced graphene oxide (rGO) via pyrolysis in conjuction with hydrothermal method. The NiFe₂O₄ possessing cubic hollow structure contributes to a huge accessible surface area, meanwhile alleviates large volume expansion/contraction effect, which facilitates suffcient permeation of the electrolyte and rapid ion/charge transport, and results in high cycling stability. The introduction of layered NiCo-LDH results in hierarchical structure and thus offers maximum contact areas with electrolyte, which heightens the specific capacitance of obtained composite and enhances the electro-catlytic activity towards oxidation of glucose. Furthermore, rGO layer greatly improves the electrical conductivity and ion diffusion/transport capability of composite. Benefiting from the unique structure and individual components of NiFe₂O₄-NiCo-LDH@rGO composite, the electrode delivers a high specific capacitance (750 C g^-1) and superb durability. Simultaneously, the asymmetrical device based on NiFe₂O₄-NiCo-LDH@rGO as positive electrode delivers remarkable energy density (50 Wh kg^-1). Moreover, NiFe₂O₄-NiCo-LDH@rGO exhibits good sensing performance with a sensitivity of 111.86 µA/µM cm^-2, the wide linear range of 3.500 × 10^-5 - 4.525 × 10^-3 M, and the detection limit of 12.94 × 10^-6 M with a signal to noise ratio of 3. Consequently, the NiFe₂O₄-NiCo-LDH@rGO could provide a prospective notion constructing bifunctional materials with hollow-cube hierarchical structure in the field of supercapacitors and electrochemical sensors.

High-Power Ultrasonic Synthesis and Magnetic-Field-Assisted Arrangement of Nanosized Crystallites of Cobalt-Containing Layered Double Hydroxides

High-quality stoichiometric Co2Al–NO3 and Co2Al–CO3 layered double hydroxides (LDHs) have been obtained by precipitation followed by anion exchange, both high-power-sonication assisted. Application of high-power ultrasound has been demonstrated to result in a considerable acceleration of the crystallization process and the anion-exchange reaction. Two independent approaches were used to form bulk and 2-D samples of Co2Al–NO3 with the oriented crystallites, namely uniaxial pressing of deposits from sonicated LDH slurries and magnetic field-assisted arrangement of LDH crystallites precipitating on glass substrates. A convenient way of preparation of semi-transparent compacts with relatively big blocks of oriented crystallites have been demonstrated. Thin dense transparent films of highly-ordered crystallites of Co2Al–NO3 LDH have been produced and characterized.

Ultrathin NiS/Ni(OH)2 Nanosheets Filled within Ammonium Polyacrylate-Functionalized Polypyrrole Nanotubes as an Unique Nanoconfined System for Nonenzymatic Glucose Sensors

Ultrathin two-dimensional NiS/Ni(OH)₂ nanosheets (NiS/Ni(OH)₂ NSs) were successfully filled within the hollow interiors of ammonium polyacrylate-functionalized polypyrrole nanotubes (NH₄PA/PPyNTs) by a simple solvothermal method. This kind of novel hierarchical nanostructures with typical structural features of a nanoconfined system, denoted by NiS/Ni(OH)₂/NH₄PA/PPyNTs, were prepared by two main sections: polyacrylic acid (PAA) was first polymerized on PPyNTs containing vinyl groups, and the obtained PAA/PPyNTs exhibited a typical Janus structure, whose external surface was covered with carboxyl groups and the internal surface was still covered with PPy chains; second, Ni²⁺ ions as a precursor were facilely combined with -NH- segments in PPy chains by the coordination interaction under the solvothermal environment; therefore, NiS/Ni(OH)₂ NSs (<1 nm) were well distributed on the internal surface of NH₄PA/PPyNTs by the in situ growth. Because of the synergistic effects of ionizable NH₄PA, PPy with good conductivity, NiS and Ni(OH)₂ with electrocatalytical activity, as well as the nanoconfinement effect, the obtained NiS/Ni(OH)₂@NH₄PA/PPyNTs exhibited excellent electrocatalytic performance for detecting glucose. Sufficiently thin shells composed of ionizable NH₄PA and good conductive PPyNTs can not only promote the electronic transmission effectively during the electrochemical detection of glucose but also hardly limit the transport of glucose and products. In addition, ultrathin NiS/Ni(OH)₂ NSs may further enhance the electrocatalytic performance for glucose because of the more exposed active sites with the large surface area. Therefore, NiS/Ni(OH)₂@NH₄PA/PPyNTs can be applied as a good electrode material with stability and sensitivity for building a nonenzymatic glucose sensor.

A bifunctional nonenzymatic flexible glucose microsensor based on CoFe-Layered double hydroxide

A bifunctional flexible glucose microsensor has been successfully fabricated by directly growing a layered double hydroxide nanosheet array (LDH-NSA) on Ni wire. The as-obtained CoFe-LDH-NSA exhibits promising performances in electrochemical and colorimetric detection of glucose with high sensitivity and selectivity. This work demonstrates an effective strategy to fabricate multi-functional glucose nonenzyme sensors.

A review on electrochemical biosensing platform based on layered double hydroxides for small molecule biomarkers determination

The development of layered double hydroxides (LDHs), also known as anionic clays with uniform distribution of metal ions and facile exchangeability of intercalated anions, are now appealing an immense deal of attention in synthesis of multifunctional materials. In electrochemical biosensors, LDHs provide stable environment for immobilization of enzymes or other sensing materials and play crucial roles in development of clinical chemistry, point-of-care devices through analysis of various small molecule metabolites excreted by biological processes which in turn serve as molecular biomarkers for medical diagnostics. In this review, we summarize the recent development in fabrication of LDH based nanoarchitectures and their electrocatalytic applications in ultrasensitive in vitro determination of conventional biomarkers, i.e., H₂O₂, glucose, dopamine and other biomolecules. Moreover, detailed discussion has been compiled to differentiate electrochemical enzymatic and nonenzymatic biosensors, to evaluate useful concentration ranges of H₂O₂ and glucose for analytical circumstances and to distinguish tumorigenic and normal cells via quantifying the released H₂O₂ efflux from living cells. Here, we envision that electrochemical sensing platform based on structurally integrated LDH nanohybrids with highly conducting substrates will assist as diseases diagnostic probe further enhancing diagnosis as well as therapeutic window for chronic diseases. Finally, the perspective for fabrication and assembly of LDH electrode is proposed for the future innovation of electrochemical biosensors with high performance making them more reliable for in vitro diagnostics.

MoS2–Au@Pt nanohybrids as a sensing platform for electrochemical nonenzymatic glucose detection

A MoS₂–Au@Pt nanohybrid was used as a sensing platform for electrochemical nonenzymatic glucose detection with high sensitivity, selectivity and stability.

Nickel–cobalt double hydroxide nanosheets wrapped amorphous Ni(OH)2 nanoboxes: development of dopamine sensor with enhanced electrochemical properties

The Ni(OH)₂/NiCo-LDHs nanocomposites accelerated the electron transfer and successfully realized dopamine catalytic oxidation.

Porphyrinoids for Chemical Sensor Applications

Porphyrins and related macrocycles have been intensively exploited as sensing materials in chemical sensors, since in these devices they mimic most of their biological functions, such as reversible binding, catalytic activation, and optical changes. Such a magnificent bouquet of properties allows applying porphyrin derivatives to different transducers, ranging from nanogravimetric to optical devices, also enabling the realization of multifunctional chemical sensors, in which multiple transduction mechanisms are applied to the same sensing layer. Potential applications are further expanded through sensor arrays, where cross-selective sensing layers can be applied for the analysis of complex chemical matrices. The possibility of finely tuning the macrocycle properties by synthetic modification of the different components of the porphyrin ring, such as peripheral substituents, molecular skeleton, coordinated metal, allows creating a vast library of porphyrinoid-based sensing layers. From among these, one can select optimal arrays for a particular application. This feature is particularly suitable for sensor array applications, where cross-selective receptors are required. This Review briefly describes chemical sensor principles. The main part of the Review is divided into two sections, describing the porphyrin-based devices devoted to the detection of gaseous or liquid samples, according to the corresponding transduction mechanism. Although most devices are based on porphyrin derivatives, seminal examples of the application of corroles or other porphyrin analogues are evidenced in dedicated sections.

Molecular engineering of Ni-/Co-porphyrin multilayers on reduced graphene oxide sheets as bifunctional catalysts for oxygen evolution and oxygen reduction reactions

Ni- and Co-porphyrin multilayers on reduced graphene oxide (rGO) sheets are reported as novel bifunctional catalysts for the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR). After binding with organic porphyrin molecules, the catalytically-active Ni2+ and Co2+ ions are periodically constructed onto the rGO surfaces via the layer-by-layer (LBL) assembly technique. The resulting catalysts exhibit good performance towards both OER and ORR, which is achieved with accurate control of the composition and thickness of the multilayer structures. This work highlights the potential for the fabrication of efficient electrocatalysts via molecular design.

PdCuPt Nanocrystals with Multibranches for Enzyme-Free Glucose Detection

By carefully controlling the synthesis condition, branched PtCu bimetallic templates were synthesized in aqueous solution. After the galvanic replacement reaction between PtCu templates and the Pt precursors, PdCuPt trimetallic nanocrystals with branched structures were obtained. Owing to the open structure and the optimized composition, the electrochemical experimental results reveal that the PdCuPt trimetallic nanocrystals possess high electrocatalytic activity, selectivity and stability for the oxidation of glucose in alkaline solution. In detail, a detection limit of 1.29 μM and a sensitivity of 378 μA/mM/cm(2) are achieved. The good electrocatalytic performance should be attributed to the unique branched nanostructure as well as the synergistic effect among metals. The superior catalytic properties suggest that these nanocrystals are promising for enzyme-free detection of glucose.

Cobalt oxide nanosheets wrapped onto nickel foam for non-enzymatic detection of glucose

Ultra-sensitive and highly selective detection of glucose is essential for the clinical diagnosis of diabetes. In this paper, an ultra-sensitive glucose sensor was successfully fabricated based on cobalt oxide (Co3O4) nanosheets directly grown on nickel foam through a simple hydrothermal method. Characterizations indicated that the Co3O4 nanosheets are completely and uniformly wrapped onto the surface of nickel foam to form a three-dimensional heterostructure. The resulting self-standing electrochemical electrode presents a high performance for the non-enzymatic detection of glucose, including short response time (<10 s), ultra-sensitivity (12.97 mA mM(-1) cm(-2)), excellent selectivity and low detection limit (0.058 μM, S/N = 3). These results indicate that Co3O4 nanosheets wrapped onto nickel foam are a low-cost, practical, and high performance electrochemical electrode for bio sensing.

A chitosan–Pt nanoparticles/carbon nanotubes-doped phosphomolybdate nanocomposite as a platform for the sensitive detection of nitrite in tap water

A polyoxometalate-based composite film decorated with CNTs and Pt–CHIT NPs was constructed on an electrode using the LBL self-assembly method. It acted as an electrochemical nitrite sensor with greatly enhanced electron transfer ability and sensing performance.

Porphyrin functionalized porous carbon derived from metal–organic framework as a biomimetic catalyst for electrochemical biosensing

A novel biomimetic catalyst was designed by the assembly of porphyrin on porous carbon derived from metal–organic frameworks for electrochemical biosensing.

Synthesis and assembly of nanomaterials under magnetic fields

Traditionally, magnetic field has long been regarded as an important means for studying the magnetic properties of materials. With the development of synthesis and assembly methods, magnetic field, similar to conventional reaction conditions such as temperature, pressure, and surfactant, has been developed as a new parameter for synthesizing and assembling special structures. To date, magnetic fields have been widely employed for materials synthesis and assembly of one-dimensional (1D), two-dimensional (2D) or three-dimensional (3D) aggregates. In this review, we aim to provide a summary on the applications of magnetic fields in this area. Overall, the objectives of this review are: (1) to theoretically discuss several factors that refer to magnetic field effects (MFEs); (2) to review the magnetic-field-induced synthesis of nanomaterials; the 1D structure of various nanomaterials, such as metal oxides/sulfide, metals, alloys, and carbon, will be described in detail. Moreover, the MFEs on spin states of ions, magnetic domain and product phase distribution will be also involved; (3) to review the alignment of carbon nanotubes, assembly of magnetic nanomaterials and photonic crystals with the help of magnetic fields; and (4) to sketch the future opportunities that magnetic fields can face in the area of materials synthesis and assembly.

Porphyrin-based sensor nanoarchitectonics in diverse physical detection modes

Porphyrins and related families of molecules are important organic modules as has been reflected in the award of the Nobel Prizes in Chemistry in 1915, 1930, 1961, 1962, 1965, and 1988 for work on porphyrin-related biological functionalities. The porphyrin core can be synthetically modified by introduction of various functional groups and other elements, allowing creation of numerous types of porphyrin derivatives. This feature makes porphyrins extremely useful molecules especially in combination with their other interesting photonic, electronic and magnetic properties, which in turn is reflected in their diverse signal input-output functionalities based on interactions with other molecules and external stimuli. Therefore, porphyrins and related macrocycles play a preeminent role in sensing applications involving chromophores. In this review, we discuss recent developments in porphyrin-based sensing applications in conjunction with the new advanced concept of nanoarchitectonics, which creates functional nanostructures based on a profound understanding of mutual interactions between the individual nanostructures and their arbitrary arrangements. Following a brief explanation of the basics of porphyrin chemistry and physics, recent examples in the corresponding fields are discussed according to a classification based on physical modes of detection including optical detection (absorption/photoluminescence spectroscopy and energy and electron transfer processes), other spectral modes (circular dichroism, plasmon and nuclear magnetic resonance), electronic and electrochemical modes, and other sensing modes.

Shape and size control of Cu nanoparticles by tailoring the surface morphologies of TiN-coated electrodes for biosensing applications

A method for controlling the shapes and sizes of Cu nanoparticles during electrodeposition has been developed by tailoring the surface morphologies of TiN-coated electrodes. Larger octahedral Cu NPs grew on a granular TiN film; smaller, irregular Cu NPs formed on a pyramidal TiN film. The surface morphology of the TiN film affected the accumulation of Cu(2+) and hexadecyltrimethylammonium (CTA(+)) ions, leading to the different shapes and sizes of the resulting Cu NPs. The significant steric effect of the CTA(+) ions was confirmed when using the film of pyramidal TiN as the electrode in the CTAB-containing electrolyte; it contributed to the growth of the smaller, irregular Cu NPs. The sensitivity of the smaller, irregular Cu NPs in the detection of glucose was better than that of the larger, octahedral Cu NPs because of the former's greater increase in the Cu(2+)-to-Cu(0) ratio.

Molecular rectifiers based on donor/acceptor assemblies: effect of orientation of the components' magnetic moments

In forming donor/acceptor assemblies that act as molecular rectifiers, we have introduced magnetic organic molecules as electron-donating and electron-accepting moieties. We have oriented the magnetic moment of the donor and acceptor components separately and immobilized them (and their moments) so that the molecular assemblies that act as rectifiers could be formed with moments mutually parallel or anti-parallel to each other. We have characterized the molecular assemblies formed on an electrode with a scanning tunneling microscope tip. Such donor/acceptor assemblies with a control over the orientation of moments of the components provided unique systems to study the effect of the nature of alignment on molecular rectifiers. We have observed that the rectification ratio increased in junctions with moments of the components being parallel to each other. The improvement in the rectification ratio has been explained in terms of an efficient electron-transfer process in a moment-aligned junction between the donor and acceptor moieties.

Magnetic moment assisted layer-by-layer film formation of a Prussian Blue analog

We formed magnetic moment assisted layer-by-layer (LbL) films of a Prussian Blue analogue (PB). We applied an external magnetic field to each monolayer of PB to orient the magnetic moment of the compound perpendicular to the substrate. Aligned moments or orientation of the magnetic compounds themselves were immobilized in each monolayer, so that the moments could augment formation of the subsequent monolayers of LbL adsorption process. We hence could form multilayered LbL films of PB molecules with their magnetic moments oriented perpendicular to the substrate. We also formed LbL films of the compound with their moments oriented parallel to the substrate and facing one particular direction. We have measured conductivity and dielectric constant of the two types of films and compared the parameters with that of conventional LbL films deposited without orienting magnetic moments of the molecules.

Layered-double-hydroxide-modified electrodes: electroanalytical applications

Two-dimensional inorganic solids, such as layered double hydroxides (LDHs), also defined as anionic clays, have open structures and unique anion-exchange properties which make them very appropriate materials for the immobilization of anions and biomolecules that often bear an overall negative charge. This review aims to describe the important aspects and new developments of electrochemical sensors and biosensors based on LDHs, evidencing the research from our own laboratory and other groups. It is intended to provide an overview of the various types of chemically modified electrodes that have been developed with these 2D layered materials, along with the significant advances made over the last several years. In particular, we report the main methods used for the deposition of LDH films on different substrates, the conductive properties of these materials, the possibility to use them in the development of membranes for potentiometric anion analysis, the early analytical applications of chemically modified electrodes based on the ability of LDHs to preconcentrate redox-active anions and finally the most recent applications exploiting their electrocatalytic properties. Another promising application field of LDHs, when they are employed as host structures for enzymes, is biosensing, which is described considering glucose as an example.