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.

Recent advances in nanoscience and nanotechnology radically changed the way we diagnose, treat, and prevent various diseases in all aspects of human life. Silver nanoparticles (AgNPs) are one of the most vital and fascinating nanomaterials among several metallic nanoparticles that are involved in biomedical applications. AgNPs play an important role in nanoscience and nanotechnology, particularly in nanomedicine. Although several noble metals have been used for various purposes, AgNPs have been focused on potential applications in cancer diagnosis and therapy. In this review, we discuss the synthesis of AgNPs using physical, chemical, and biological methods. We also discuss the properties of AgNPs and methods for their characterization. More importantly, we extensively discuss the multifunctional bio-applications of AgNPs; for example, as antibacterial, antifungal, antiviral, anti-inflammatory, anti-angiogenic, and anti-cancer agents, and the mechanism of the anti-cancer activity of AgNPs. In addition, we discuss therapeutic approaches and challenges for cancer therapy using AgNPs. Finally, we conclude by discussing the future perspective of AgNPs.

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Silver Nanoparticles: Synthesis, Characterization, Properties, Applications, and Therapeutic Approaches

Silver nanoparticles with different sizes (7, 29, and 89 nm mean values) were synthesized using gallic acid in an aqueous chemical reduction method. The nanoparticles were characterized using transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray diffraction (XRD), and ultraviolet–visible (UV–Vis) absorption spectroscopy; the antibacterial activity was assessed using the standard microdilution method, determining the minimum inhibitory concentration (MIC) according to the National Committee for Clinical Laboratory Standards. From the microscopies studies (TEM) we observed that silver nanoparticles have spherical (7 and 29 nm) and pseudospherical shape (89 nm) with a narrow size distribution. The sizes of the silver nanoparticles were controlled by varying some experimental conditions. It was found that the antibacterial activity of the nanoparticles varies when their size diminishes.

Synthesis and antibacterial activity of silver nanoparticles with different sizes

It has been almost 4 decades since the “war on cancer” was declared. It is now generally believed that personalized medicine is the future for cancer patient management. Possessing unprecedented potential for early detection, accurate diagnosis, and personalized treatment of cancer, nanoparticles have been extensively studied over the last decade. In this review, we will summarize the current state-of-the-art of gold nanoparticles in biomedical applications targeting cancer. Gold nanospheres, nanorods, nanoshells, nanocages, and surface enhanced Raman scattering nanoparticles will be discussed in detail regarding their uses in in vitro assays, ex vivo and in vivo imaging, cancer therapy, and drug delivery. Multifunctionality is the key feature of nanoparticle-based agents. Targeting ligands, imaging labels, therapeutic drugs, and other functionalities can all be integrated to allow for targeted molecular imaging and molecular therapy of cancer. Big strides have been made and many proof-of-principle studies have been successfully performed. The future looks brighter than ever yet many hurdles remain to be conquered. A multifunctional platform based on gold nanoparticles, with multiple receptor targeting, multimodality imaging, and multiple therapeutic entities, holds the promise for a “magic gold bullet” against cancer.

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Applications of gold nanoparticles in cancer nanotechnology.

Gold nanoparticles were prepared in the presence of poly(amidoamine) (PAMAM) dendrimers (generations 3.0 and 5.0) or poly(propyleneimine) (PPI) dendrimers (generations 3.0 and 4.0) with surface amino groups by laser irradiation. UV−visible absorption, dynamic light scattering, and transmission electron microscopy have been used to study the formation and structure of the nanocomposites. The reduction of Au3+ ions proceeded with an increase of the irradiation time, and the average diameters of the gold nanoparticles obtained tended to decrease with an increase of the dendrimer concentration. It is suggested that the dendrimers are adsorbed on the nanoparticles as a monolayer. Studies of the reduction reaction of 4-nitrophenol by the gold nanoparticles with NaBH4 reveal that the rate constants for PPI dendrimers are higher than those for PAMAM dendrimers, whereas the size of the PPI dendrimer of the same generation is considerably smaller than that of the PAMAM dendrimer.

Preparation of Gold−Dendrimer Nanocomposites by Laser Irradiation and Their Catalytic Reduction of 4-Nitrophenol

The synthesis of silver and gold metal nanospherical particles stabilized by the fourth-generation poly(amido amine) (G4 PAMAM) dendrimer is reported. The reduction of silver nitrate and sodium tetrachloroaurate in the presence of the PAMAM dendrimer having terminal amine groups results in the formation of stable, water-soluble nanoparticles. The formation and size of the particles have been determined from the UV−vis plasmon absorption band and transmission electron microscopic (TEM) analyses. The average particle sizes are (6.2 ± 1.7)−(12.2 ± 2.9) nm for silver and are (3.2 ± 0.7)−(7.3 ± 1.5) nm for gold, depending on the metal ion-to-dendrimer terminal amine ratio (M:D) used. Thus, dendrimer-protected silver particles are substantially larger than the gold particles synthesized in similar systems. Nanoparticles prepared at 0.25:1 and lower M:D ratios are stable for a long period of time. A TEM study of the morphology also shows a short-ranged hexagonal arrangement of particles in a monolayer onto the c...

Synthesis of Dendrimer-Passivated Noble Metal Nanoparticles in a Polar Medium: Comparison of Size between Silver and Gold Particles

Dodecanethiol-capped nanospherical gold metal particles have been synthesized using a biphasic Winsor II type microemulsion of diethyl ether/aerosol-OT/water. The reduction of gold(III) chloride in the presence of dodecanethiol results in the formation of stable, organically soluble nanoparticles of 4±0.6 nm average diameter. The UV–vis plasmon absorption band and transmission electron microscopic (TEM) analysis confirmed the formation and size of the particles. TEM morphology shows a two-dimensional array of these particles with an average spacing between gold cores of about 1.8 nm onto hydrophobic carbon surfaces. Elemental analysis results and the similarity of the Fourier transform infrared (FT-IR) spectrum of free dodecanethiol to that of composite material reveal the encapsulation of gold particles by dodecanethiol. The detailed analysis of FT-IR spectra of our composite material and its comparison with literature reports disclose that a Winsor II type system is superior for the synthesis of nanoparticles bounded by a three-dimensional self-assembled monolayer of alkanethiol with a close-packed all trans zigzag conformation. 1H NMR spectroscopic observations suggest the absence of free thiols. X-ray photoelectron spectroscopic analysis supports that the oxidation state of gold is zero (Au0). Thermogravimetric and differential thermal analysis indicates an interaction between thiol group and gold surfaces and thiol molecule per nearly three gold atoms in the composite particles.

Synthesis of Gold Nanoparticles in a Winsor II Type Microemulsion and Their Characterization

Gold nanoparticles surface-confined by hybrid self-assembled monolayers (SAMs) were synthesized by replacement of dendrimer-passivated nanoparticles by dodecanethiol. Transmission electron microscopy, small-angle X-ray scattering (SAXS), infrared absorption spectroscopy, 1H NMR and elemental analysis were performed to characterize hybrid-layer-passivated nanoparticles. The hybrid particles were separated into domains of small and large spheres. This indicates that the replacement may be dependent on the particle size.

Abhijit Manna

Papers

Synthesis of Dendrimer-Passivated Noble Metal Nanoparticles in a Polar Medium: Comparison of Size between Silver and Gold Particles

Synthesis of Gold Nanoparticles in a Winsor II Type Microemulsion and Their Characterization

Gold Nanoparticles Surface-confined by Hybrid Self-Assembled Monolayers of Dendrimer and Dodecanethiol