Although gold is the subject of one of the most ancient themes of investigation in science, its renaissance now leads to an exponentially increasing number of publications, especially in the context of emerging nanoscience and nanotechnology with nanoparticles and self-assembled monolayers (SAMs). We will limit the present review to gold nanoparticles (AuNPs), also called gold colloids. AuNPs are the most stable metal nanoparticles, and they present fascinating aspects such as their assembly of multiple types involving materials science, the behavior of the individual particles, size-related electronic, magnetic and optical properties (quantum size effect), and their applications to catalysis and biology. Their promises are in these fields as well as in the bottom-up approach of nanotechnology, and they will be key materials and building block in the 21st century. Whereas the extraction of gold started in the 5th millennium B.C. near Varna (Bulgaria) and reached 10 tons per year in Egypt around 1200-1300 B.C. when the marvelous statue of Touthankamon was constructed, it is probable that “soluble” gold appeared around the 5th or 4th century B.C. in Egypt and China. In antiquity, materials were used in an ecological sense for both aesthetic and curative purposes. Colloidal gold was used to make ruby glass 293 Chem. Rev. 2004, 104, 293−346

Gold nanoparticles: assembly, supramolecular chemistry, quantum-size-related properties, and applications toward biology, catalysis, and nanotechnology.

This review focuses on the synthesis, protection, functionalization, and application of magnetic nanoparticles, as well as the magnetic properties of nanostructured systems. Substantial progress in the size and shape control of magnetic nanoparticles has been made by developing methods such as co-precipitation, thermal decomposition and/or reduction, micelle synthesis, and hydrothermal synthesis. A major challenge still is protection against corrosion, and therefore suitable protection strategies will be emphasized, for example, surfactant/polymer coating, silica coating and carbon coating of magnetic nanoparticles or embedding them in a matrix/support. Properly protected magnetic nanoparticles can be used as building blocks for the fabrication of various functional systems, and their application in catalysis and biotechnology will be briefly reviewed. Finally, some future trends and perspectives in these research areas will be outlined.

Magnetic nanoparticles: Synthesis, protection, functionalization, and application

1. Introduction 20642. Synthesis of Magnetic Nanoparticles 20662.1. Classical Synthesis by Coprecipitation 20662.2. Reactions in Constrained Environments 20682.3. Hydrothermal and High-TemperatureReactions20692.4. Sol-Gel Reactions 20702.5. Polyol Methods 20712.6. Flow Injection Syntheses 20712.7. Electrochemical Methods 20712.8. Aerosol/Vapor Methods 20712.9. Sonolysis 20723. Stabilization of Magnetic Particles 20723.1. Monomeric Stabilizers 20723.1.1. Carboxylates 20733.1.2. Phosphates 20733.2. Inorganic Materials 20733.2.1. Silica 20733.2.2. Gold 20743.3. Polymer Stabilizers 20743.3.1. Dextran 20743.3.2. Polyethylene Glycol (PEG) 20753.3.3. Polyvinyl Alcohol (PVA) 20753.3.4. Alginate 20753.3.5. Chitosan 20753.3.6. Other Polymers 20753.4. Other Strategies for Stabilization 20764. Methods of Vectorization of the Particles 20765. Structural and Physicochemical Characterization 20785.1. Size, Polydispersity, Shape, and SurfaceCharacterization20795.2. Structure of Ferro- or FerrimagneticNanoparticles20805.2.1. Ferro- and Ferrimagnetic Nanoparticles 20805.3. Use of Nanoparticles as Contrast Agents forMRI20825.3.1. High Anisotropy Model 20845.3.2. Small Crystal and Low Anisotropy EnergyLimit20855.3.3. Practical Interests of Magnetic NuclearRelaxation for the Characterization ofSuperparamagnetic Colloid20855.3.4. Relaxation of Agglomerated Systems 20856. Applications 20866.1. MRI: Cellular Labeling, Molecular Imaging(Inﬂammation, Apoptose, etc.)20866.2.

Magnetic Iron Oxide Nanoparticles: Synthesis, Stabilization, Vectorization, Physicochemical Characterizations, and Biological Applications

Nanomaterials, such as metal or semiconductor nanoparticles and nanorods, exhibit similar dimensions to those of biomolecules, such as proteins (enzymes, antigens, antibodies) or DNA. The integration of nanoparticles, which exhibit unique electronic, photonic, and catalytic properties, with biomaterials, which display unique recognition, catalytic, and inhibition properties, yields novel hybrid nanobiomaterials of synergetic properties and functions. This review describes recent advances in the synthesis of biomolecule-nanoparticle/nanorod hybrid systems and the application of such assemblies in the generation of 2D and 3D ordered structures in solutions and on surfaces. Particular emphasis is directed to the use of biomolecule-nanoparticle (metallic or semiconductive) assemblies for bioanalytical applications and for the fabrication of bioelectronic devices.

Integrated Nanoparticle–Biomolecule Hybrid Systems: Synthesis, Properties, and Applications

In this review, the progress made in the last ten years concerning the synthesis of porous carbon materials is summarized. Porous carbon materials with various pore sizes and pore structures have been synthesized using several different routes. Microporous activated carbons have been synthesized through the activation process. Ordered microporous carbon materials have been synthesized using zeolites as templates. Mesoporous carbons with a disordered pore structure have been synthesized using various methods, including catalytic activation using metal species, carbonization of polymer/polymer blends, carbonization of organic aerogels, and template synthesis using silica nanoparticles. Ordered mesoporous carbons with various pore structures have been synthesized using mesoporous silica materials such as MCM-48, HMS, SBA-15, MCF, and MSU-X as templates. Ordered mesoporous carbons with graphitic pore walls have been synthesized using soft-carbon sources that can be converted to highly ordered graphite at high temperature. Hierarchically ordered mesoporous carbon materials have been synthesized using various designed silica templates. Some of these mesoporous carbon materials have successfully been used as adsorbents for bulky pollutants, as electrodes for supercapacitors and fuel cells, and as hosts for enzyme immobilization. Ordered macroporous carbon materials have been synthesized using colloidal crystals as templates. One-dimensional carbon nanostructured materials have been fabricated using anodic aluminum oxide (AAO) as a template.

Recent Progress in the Synthesis of Porous Carbon Materials

Precipitation of an insoluble, insulating product on monolayer-functionalized electrodes enables the development of new electrochemical biosensors. Faradaic impedance spectroscopy and cyclic voltammetry are used to probe the electron-transfer resistance at the conductive support upon the accumulation of the insoluble product on the electrode surface. Similarly, microgravimetric quartz crystal microbalance, QCM, analyses were used to assay the formation of the precipitate on the electrode. A horseradish peroxidase, HRP, monolayer electrode is used to analyze H2O2 via the biocatalyzed oxidation of 4-chloro-1-naphthol (1) and the precipitation of the insoluble product (2). A bienzyme-layered electrode consisting of HRP and glucose oxidase, GOx, is used to sense glucose. Biocatalyzed oxidation of glucose by O2, in the presence of GOx, yields H2O2, and the generated hydrogen peroxide effects the formation of the insoluble product (2) in the presence of HRP. The insoluble product accumulated on the electrode, a...

Precipitation of an Insoluble Product on Enzyme Monolayer Electrodes for Biosensor Applications: Characterization by Faradaic Impedance Spectroscopy, Cyclic Voltammetry, and Microgravimetric Quartz Crystal Microbalance Analyses

Magneto-Switchable Bioelectrocatalysis

A m-acrylamidophenylboronic acid−acrylamide copolymer is assembled by electropolymerization on Au-surfaces (Au-electrodes, Au-quartz crystals or Au-glass slides). The electrolysis time controls the film thickness on the electrodes. Addition of glucose to the copolymer film leads to the ligation of the sugar to the boronic acid sites and results in the swelling of the polymer. Faradaic impedance spectroscopy, chronopotentiometry, surface plasmon resonance spectroscopy (SPR), and microgravimetric quartz-crystal-microbalance measurements (QCM) are employed to characterize the swelling of the polymer film upon the binding of glucose. The swelling rate constant, upon the association of glucose to the polymer film, is estimated to be ksw = 1.7 × 10-4 s-1, while the shrinking rate constant of the polymer film, upon depletion of glucose, is ksh = 2.3 × 10-5 s-1. By following the swelling degree of the polymer film at variable glucose concentrations, the polymer matrix is used as an active medium for the sensing o...

Characterization of the Swelling of Acrylamidophenylboronic Acid−Acrylamide Hydrogels upon Interaction with Glucose by Faradaic Impedance Spectroscopy, Chronopotentiometry, Quartz-Crystal Microbalance (QCM), and Surface Plasmon Resonance (SPR) Experiments

Impedance spectroscopy is used to characterize the structure of biomaterial layers on the gate surface of ISFET devices, and to elucidate antigen−antibody binding interactions on the gate interface. The method is based on the recording of the transfer function of the system as a function of frequency and on the extraction of the respective τ1 and τ2 values of the systems. From the experimental values, the film thicknesses of the respective protein layers are estimated. The method is applied to elucidate the structures of a glucose oxidase, GOx, multilayer assembly, and of a di-biotin-cross-linked avidin multilayer system. The method is also used to sense the dinitrophenyl antibody by following the formation of the antigen−antibody complex on the gate surface.

The Use of Impedance Spectroscopy for the Characterization of Protein-Modified ISFET Devices: Application of the Method for the Analysis of Biorecognition Processes

The study provides a model for the effect on electrochemical processes of a magnetic field that is directed perpendicular to a planar electrode surface. The analysis assumes the formation of a hydrodynamic boundary layer of the fluid motion that is generated above a semi-infinite electrode as a result of magnetic force action. For a uniform magnetic field, the model predicts the decrease of the diffusion boundary layer thickness upon increasing either the magnetic field strength, B, or the reagent bulk concentration, C, with the power dependence corresponding to C 4/3B 2/3. The limiting current density, iL, is formulated as iL ≈ 0.5χm1/3(μoρ)-1/3R5/3D5/9ν-2/9nFC 4/3B 2/3. This permits semiquantitative interpretation of the enhanced mass transfer at electrode surfaces for electrochemical reactions and predicts a magnetic field effect on mass transfer-limited heterogeneous reactions of magnetic species. The results imply that the perpendicular magnetic field will affect any mass transport limited transforma...

and Eugenii Katz

Papers

Precipitation of an Insoluble Product on Enzyme Monolayer Electrodes for Biosensor Applications: Characterization by Faradaic Impedance Spectroscopy, Cyclic Voltammetry, and Microgravimetric Quartz Crystal Microbalance Analyses

Magneto-Switchable Bioelectrocatalysis

Characterization of the Swelling of Acrylamidophenylboronic Acid−Acrylamide Hydrogels upon Interaction with Glucose by Faradaic Impedance Spectroscopy, Chronopotentiometry, Quartz-Crystal Microbalance (QCM), and Surface Plasmon Resonance (SPR) Experiments

The Use of Impedance Spectroscopy for the Characterization of Protein-Modified ISFET Devices: Application of the Method for the Analysis of Biorecognition Processes

Effects of Magnetic Field Directed Orthogonally to Surfaces on Electrochemical Processes