Electrochemical Behavior of Gold Nanoparticles Generated In Situ on 3‐(1‐Imidazolyl)propyl‐silsesquioxane

Gold nanoparticles of different morphologies have been synthesized on a silica‐based organic‐inorganic hybrid material for catalytic applications. The gold nanoparticles formations proceed through in situ chemical reduction of the AuCl₄^? anions previously adsorbed on 3‐(1‐imidazolyl)propyl‐silsesquioxane, which plays the role of substrate and stabilizer. Two distinct reducing agents, sodium citrate and sodium borohydride, were employed to generate gold nanoparticles of different sizes. UV‐vis diffuse reflectance as well as transmission electron microscopy were employed to evaluate the particle’s morphology. Modified carbon paste electrodes were prepared from these materials and their electrochemical behavior investigated using potassium ferrocyanide and 4‐nitrophenol as redox model compounds. Both AuNPs‐modified electrodes decreased the overpotential of 4‐nitrophenol reduction by around 90 mV compared to the unmodified electrode as evidenced by cyclic voltammetry experiment. However, the smaller diameter particles (borohydride‐reduced) produced more significant catalytic effect as a consequence of their large surface area. Regarding the sensing parameters, the sensitivity is higher for the borohydride‐reduced AuNPs while the values of limit of detection are of the same order of magnitude. Thus, the detection limit and sensitivity are 70.0±0.6 nM and 187 µA/mM for the citrate‐reduced AuNPs; and 75.0±2.2 nM and 238 µA/mM for the borohydride‐reduced AuNPs.     

Targeted Tumor Computed Tomography Imaging Using Low‐Generation Dendrimer‐Stabilized Gold Nanoparticles

We report a facile approach to fabricating low‐generation poly(amidoamine) (PAMAM) dendrimer‐stabilized gold nanoparticles (Au DSNPs) functionalized with folic acid (FA) for in vitro and in vivo targeted computed tomography (CT) imaging of cancer cells. In this study, amine‐terminated generation 2 PAMAM dendrimers were employed as stabilizers to form Au DSNPs without additional reducing agents. The formed Au DSNPs with an Au core size of 5.5 nm were covalently modified with the targeting ligand FA, followed by acetylation of the remaining dendrimer terminal amines to endow the particles with targeting specificity and improved biocompatibility. Our characterization data show that the formed FA‐modified Au DSNPs are stable at different pH values (5—8) and temperatures (4–50 °C), as well as in different aqueous media. MTT assay data along with cell morphology observations reveal that the FA‐modified Au DSNPs are noncytotoxic in the particle concentration range of 0–3000 nM . X‐ray attenuation coefficient measurements show that the CT value of FA‐modified Au DSNPs is much higher than that of Omnipaque (a clinically used CT contrast agent) at the same concentration of the radiodense elements (Au or iodine). Importantly, the FA‐modified Au DSNPs are able to specifically target a model cancer cell line (KB cells, a human epithelial carcinoma cell line) over‐expressing FA receptors and they enable targeted CT imaging of the cancer cells in vitro and the xenografted tumor model in vivo after intravenous administration of the particles. With the simple synthesis approach, easy modification, good cytocompatibility, and high X‐ray attenuation coefficient, the FA‐modified low‐generation Au DSNPs could be used as promising contrast agents for targeted CT imaging of different tumors over‐expressing FA receptors.     

Green Synthesis of Gold Nanoparticles Using Plant Extracts as Beneficial Prospect for Cancer Theranostics

Gold nanoparticles (AuNPs) have been widely explored and are well-known for their medical applications. Chemical and physical synthesis methods are a way to make AuNPs. In any case, the hunt for other more ecologically friendly and cost-effective large-scale technologies, such as environmentally friendly biological processes known as green synthesis, has been gaining interest by worldwide researchers. The international focus on green nanotechnology research has resulted in various nanomaterials being used in environmentally and physiologically acceptable applications. Several advantages over conventional physical and chemical synthesis (simple, one-step approach to synthesize, cost-effectiveness, energy efficiency, and biocompatibility) have drawn scientists’ attention to exploring the green synthesis of AuNPs by exploiting plants’ secondary metabolites. Biogenic approaches, mainly the plant-based synthesis of metal nanoparticles, have been chosen as the ideal strategy due to their environmental and in vivo safety, as well as their ease of synthesis. In this review, we reviewed the use of green synthesized AuNPs in the treatment of cancer by utilizing phytochemicals found in plant extracts. This article reviews plant-based methods for producing AuNPs, characterization methods of synthesized AuNPs, and discusses their physiochemical properties. This study also discusses recent breakthroughs and achievements in using green synthesized AuNPs in cancer treatment and different mechanisms of action, such as reactive oxygen species (ROS), mediated mitochondrial dysfunction and caspase activation, leading to apoptosis, etc., for their anticancer and cytotoxic effects. Understanding the mechanisms underlying AuNPs therapeutic efficacy will aid in developing personalized medicines and treatments for cancer as a potential cancer therapeutic strategy.     

A New Enzyme Immobilization Technique Based on Thionine‐Bovine Serum Albumin Conjugate and Gold Colloidal Nanoparticles for Reagentless Amperometric Biosensor Applications

A novel enzyme immobilization technique based on thionine‐bovine serum albumin conjugate (Th‐BSA) and gold colloidal nanoparticles (nano‐Au) was developed. Thionine was covalently bound onto the BSA film with glutaraldehyde(GA) as cross‐linker to achieve Th‐BSA conjugate. The free amino groups of thionine were then used to attach nano‐Au for the immobilization of horseradish peroxidase (HRP). Such nano‐Au/Th‐BSA matrix shows a favorable microenvironment for retaining the native activity of the immobilized HRP and thionine immobilized in this way can effectively shuttle electrons between the electrode and the enzyme. The proposed biosensor displays excellent catalytic activity and rapid response for H₂O₂. The linear range for the determination of H₂O₂ is from 4.9×10^?7 to 1.6×10^?3 M with a detection limit of 2.1×10^?7 M at 3σ and a Michaelies‐Menten constant K value of 0.023 mM.     

Phenylboronic Acid‐Gold Nanoparticles for Potentiometric Detection of Saccharides

We propose a concept for the analytical application of gold nanoparticles modified by mercaptophenylboronic acid as a receptor of saccharides in a potentiometric sensor based on a conducting polymer.     

Liquid‐Crystalline Phases Made of Gold Nanoparticles

Spontaneous formation of smectic and columnar structures was observed when spherical gold nanoparticles were functionalized with mesogenic thiols (see layered structure and X‐ray pattern of a sample in smectic phase). The particle ordering is stimulated by softening of the interparticle potential and flexibility for deformation of the grafting layer.

     

Comparative Studies on the Quick Recognition of Melamine Using Unmodified Gold Nanoparticles and p‐Nitrobenzenesulfonic Grafted Silver Nanoparticles

Both unmodified gold nanoparticles (AuNPs) and p‐nitrobenzenesulfonic (p‐NBS) grafted silver nanoparticles (AgNPs) were prepared by chemical synthesis, respectively. They could be used for visual detection via the interaction with the twelve amide compounds including melamine. These color changes could be seen with the naked eye directly and monitored by ultraviolet visible (UV‐Vis) absorbance spectra. The recognition mechanism for both nanoparticles was comparatively investigated by the addition of glutathione (GSH) in the presence of melamine, respectively. The triple hydrogen bonding recognition and the attractive van der Waals interactions between melamine (0.5 mg/L) and AuNPs were responsible for the color change during its aggregation (red‐to‐purple or blue), whilst the electron donor‐acceptor interaction between melamine (0.2 mg/L) and p‐NBS modified on the surface of AgNPs resulted in the color changes (yellow‐to‐grey or dark green).     

Self‐Assembled Fluorescent Organic Nanoparticles for Live‐Cell Imaging

Fluorescent, cell‐permeable, organic nanoparticles based on self‐assembled π‐conjugated oligomers with high absorption cross‐sections and high quantum yields have been developed. The nanoparticles are generated with a tuneable density of amino groups for charge‐mediated cellular uptake by a straightforward self‐assembly protocol, which allows for control over size and toxicity. The results show that a single amino group per ten oligomers is sufficient to achieve cellular uptake. The non‐toxic nanoparticles are suitable for both one‐ and two‐photon cellular imaging and flow cytometry, and undergo very efficient cellular uptake.     

Noninvasive Staging of Kidney Dysfunction Enabled by Renal‐Clearable Luminescent Gold Nanoparticles

As a “silent killer”, kidney disease is often hardly detected at an early stage but can cause lethal kidney failure later on. Thus, a preclinical imaging technique that can readily differentiate between the stages of kidney dysfunction is highly desired for improving our fundamental understanding of kidney disease progression. Herein, we report that in vivo fluorescence imaging, enabled by renal‐clearable near‐infrared‐emitting gold nanoparticles, can noninvasively detect kidney dysfunction, report on the dysfunctional stages, and even reveal adaptive function in a mouse model of unilateral obstructive nephropathy, which cannot be diagnosed with routine kidney function markers. These results demonstrate that low‐cost fluorescence kidney functional imaging is highly sensitive and useful for the longitudinal, noninvasive monitoring of kidney dysfunction progression in preclinical research.     

Crystallization of DNA‐Capped Gold Nanoparticles in High‐Concentration,Divalent Salt Environments

The multiparametric nature of nanoparticle self‐assembly makes it challenging to circumvent the instabilities that lead to aggregation and achieve crystallization under extreme conditions. By using non‐base‐pairing DNA as a model ligand instead of the typical base‐pairing design for programmability, long‐range 2D DNA–gold nanoparticle crystals can be obtained at extremely high salt concentrations and in a divalent salt environment. The interparticle spacings in these 2D nanoparticle crystals can be engineered and further tuned based on an empirical model incorporating the parameters of ligand length and ionic strength.     

Solvent‐Responsive Behavior of Polymer‐Brush‐Modified Amphiphilic Gold Nanoparticles

Amphiphilic polymer brushes grafted onto gold nanoparticles impart distinct solvent‐responsive behavior via the change to particle size and surface chemistry and, therefore, wide application prospects can be expected. Coarse‐grained simulations are performed for block and/or mixed polystyrene (PS)/poly(ethylene oxide) (PEO)‐modified amphiphilic gold nanoparticles (AuNP) to investigate their responsive behavior in five different solvents by analyzing their morphology, distribution density profiles, and gyration radii. Typical core–shell, Janus‐type, buckle‐like, ring‐like, jellyfish‐like, and octopus‐like morphologies are formed. Influence of block sequence, mixing mode, and several other effects are discussed. Responsive particle size and surface hydrophilicity can be successfully reproduced by altering solvents.

     

Ultra‐Low‐Field NMR Relaxation and Diffusion Measurements Using an Optical Magnetometer

Nuclear magnetic resonance (NMR) relaxometry and diffusometry are important tools for the characterization of heterogeneous materials and porous media, with applications including medical imaging, food characterization and oil‐well logging. These methods can be extremely effective in applications where high‐resolution NMR is either unnecessary, impractical, or both, as is the case in the emerging field of portable chemical characterization. Here, we present a proof‐of‐concept experiment demonstrating the use of high‐sensitivity optical magnetometers as detectors for ultra‐low‐field NMR relaxation and diffusion measurements.     

Grafting of Gold Nanoparticles onto Organogelator‐Templated Fibrous Mercaptosilica

Fibrous organosilicas functionalized with mercaptopropyl moieties (20 and 40 Mol‐% of –C₃H₆SH per Si) have been prepared through a smart, “one‐pot” sol‐gel route employing a phenazinic organogelator (DUOP) as a templating agent. The fibrous mercaptosilicas have been characterized morphologically (SEM observations) and chemically (Raman, ²⁹Si solid‐state NMR and chemical analysis), and the functionality of the final materials have been also confirmed by the efficient post‐grafting of Au nanoparticles. These fibrous gold‐mercaptosilica nanocomposite materials could be very useful for nanoelectronic or optoelectronic applications.