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.

Ju Mei,†,‡,∥ Nelson L. C. Leung,†,‡,∥ Ryan T. K. Kwok,†,‡ Jacky W. Y. Lam,†,‡ and Ben Zhong Tang*,†,‡,§ †HKUST-Shenzhen Research Institute, Hi-Tech Park, Nanshan, Shenzhen 518057, China ‡Department of Chemistry, HKUST Jockey Club Institute for Advanced Study, Institute of Molecular Functional Materials, Division of Biomedical Engineering, State Key Laboratory of Molecular Neuroscience, Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China Guangdong Innovative Research Team, SCUT-HKUST Joint Research Laboratory, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China

Aggregation-Induced Emission: Together We Shine, United We Soar!

Detection of chemical and biological agents plays a fundamental role in biomedical, forensic and environmental sciences1–4 as well as in anti bioterrorism applications.5–7 The development of highly sensitive, cost effective, miniature sensors is therefore in high demand which requires advanced technology coupled with fundamental knowledge in chemistry, biology and material sciences.8–13

In general, sensors feature two functional components: a recognition element to provide selective/specific binding with the target analytes and a transducer component for signaling the binding event. An efficient sensor relies heavily on these two essential components for the recognition process in terms of response time, signal to noise (S/N) ratio, selectivity and limits of detection (LOD).14,15 Therefore, designing sensors with higher efficacy depends on the development of novel materials to improve both the recognition and transduction processes. Nanomaterials feature unique physicochemical properties that can be of great utility in creating new recognition and transduction processes for chemical and biological sensors15–27 as well as improving the S/N ratio by miniaturization of the sensor elements.28

Gold nanoparticles (AuNPs) possess distinct physical and chemical attributes that make them excellent scaffolds for the fabrication of novel chemical and biological sensors (Figure 1).29–36 First, AuNPs can be synthesized in a straightforward manner and can be made highly stable. Second, they possess unique optoelectronic properties. Third, they provide high surface-to-volume ratio with excellent biocompatibility using appropriate ligands.30 Fourth, these properties of AuNPs can be readily tuned varying their size, shape and the surrounding chemical environment. For example, the binding event between recognition element and the analyte can alter physicochemical properties of transducer AuNPs, such as plasmon resonance absorption, conductivity, redox behavior, etc. that in turn can generate a detectable response signal. Finally, AuNPs offer a suitable platform for multi-functionalization with a wide range of organic or biological ligands for the selective binding and detection of small molecules and biological targets.30–32,36 Each of these attributes of AuNPs has allowed researchers to develop novel sensing strategies with improved sensitivity, stability and selectivity. In the last decade of research, the advent of AuNP as a sensory element provided us a broad spectrum of innovative approaches for the detection of metal ions, small molecules, proteins, nucleic acids, malignant cells, etc. in a rapid and efficient manner.37



Figure 1

Physical properties of AuNPs and schematic illustration of an AuNP-based detection system.



In this current review, we have highlighted the several synthetic routes and properties of AuNPs that make them excellent probes for different sensing strategies. Furthermore, we will discuss various sensing strategies and major advances in the last two decades of research utilizing AuNPs in the detection of variety of target analytes including metal ions, organic molecules, proteins, nucleic acids, and microorganisms.

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Gold nanoparticles in chemical and biological sensing.

Polydopamine and Its Derivative Materials: Synthesis and Promising Applications in Energy, Environmental, and Biomedical Fields

Arsenic removal from water/wastewater using adsorbents—A critical review

The synthesis and processing of nanoparticles consisting of metallic nanocrystal cores and organic monolayer shells promise interesting technological applications. Here, we report the synthesis of gold nanoparticles modified with ionic liquids based on the imidazolium cation. Aggregation-induced color changes of the gold nanoparticles in an aqueous solution were used as an optical sensor for anions via anion exchange of ionic liquid moiety. We also demonstrated the phase transfer of the gold nanoparticles from aqueous media to ionic liquid.

Synthesis of gold nanoparticles modified with ionic liquid based on the imidazolium cation.

Crystallization of CaCO3 in the presence and the absence of half-generation poly(amidoamine) (Gn.5 PAMAM) dendrimers was carried out by a double jet method to prevent heterogeneous nucleation at glass walls. The solution was kept at 25 °C under N2 for 4 days with gentle stirring. We found that the crystallization of CaCO3 in the presence of the anionic dendrimers resulted in the formation of spherical vaterite crystals, whereas rhombohedral calcite crystals were formed in the absence of additives. As the generation number of the PAMAM dendrimer increased from G1.5 to G3.5, the particle size of vaterite was decreased from 5.5 ± 1.1 to 2.3 ± 0.7 μm under the constant concentration (0.26 mM) of −COONa unit of the PAMAM dendrimers. With further increase in the generation number to G4.5, the particle size was not changed. The relationship between concentration of the dendrimer and the particle size in the same generation numbers of the PAMAM dendrimer was also studied under the same condition. As concentration...

Effect of Anionic Starburst Dendrimers on the Crystallization of CaCO3 in Aqueous Solution: Size Control of Spherical Vaterite Particles

Formation of an IPN (interpenetrating polymer network) of organic polymer and silica gel in the form of polymer hybrids was accomplished by utilizing the Diels−Alder reaction between maleimide and furan. Maleimide and furan groups were introduced in the side chain of poly(2-methyl-2-oxazoline), respectively. Polymer hybrids were prepared by acid-catalyzed sol−gel reaction of tetramethoxysilane (TMOS) in the presence of these polymers. The progress of the Diels−Alder reaction between maleimide and furan was confirmed by UV and FT-IR spectroscopy. The solvent resistance of the polymer hybrids was improved by the formation of the IPN structure. Retro-Diels−Alder reaction takes place at an elevated temperature, and these reactions can be cycled.

Thermally Reversible IPN Organic−Inorganic Polymer Hybrids Utilizing the Diels−Alder Reaction

Preparation of a novel core–shell nanostructured gold colloid–silk fibroin bioconjugate by the protein in situ redox technique at room temperature

Novel π-conjugated polymer-protected metal (M = Pd, Au, Pt) nanoparticles of narrow size distribution and high dispersity were prepared via reduction of the metal ions by a π-conjugated poly(dithiafulvene) (PDF) having strong electron-donating properties. The oxidized polymer protected the metal nanoparticles as stable colloidal forms without any precipitation for more than a month at room temperature under air. Due to the effect of the positively charged PDF, the absorption spectrum of the protected gold nanoparticle assigned to the surface plasmon resonance was found to display a strong red shift. The absorption band of the oxidized PDF assigned to the π−π* transition also showed a strong red shift compared with that of the pure PDF due to the effective expansion of π-conjugation of the oxidized PDF by charge transfer. The influences of the reaction temperature and PDF concentration were investigated on the metal nanoparticle size with the Pt nanoparticle as an example. The protected metal nanoparticles...

Kensuke Naka

Papers

Synthesis of gold nanoparticles modified with ionic liquid based on the imidazolium cation.

Effect of Anionic Starburst Dendrimers on the Crystallization of CaCO3 in Aqueous Solution: Size Control of Spherical Vaterite Particles

Thermally Reversible IPN Organic−Inorganic Polymer Hybrids Utilizing the Diels−Alder Reaction

Preparation of a novel core–shell nanostructured gold colloid–silk fibroin bioconjugate by the protein in situ redox technique at room temperature

Synthesis of Novel Stable Nanometer-Sized Metal (M = Pd, Au, Pt) Colloids Protected by a π-Conjugated Polymer