Synthesis of gold Nanoshells through Improved Seed-Mediated Growth Approach: Brust-like, in Situ Seed Formation

Noble Metals Functionalized on Graphene Oxide Obtained by Different Methods-New Catalytic Materials

In recent years, research has focused on developing materials exhibiting outstanding mechanical, electrical, thermal, catalytic, magnetic and optical properties such as graphene/polymer, graphene/metal nanoparticles and graphene/ceramic nanocomposites. Two-dimensional sp² hybridized graphene has become a material of choice in research due to the excellent properties it displays electrically, thermally, optically and mechanically. Noble nanomaterials also present special physical and chemical properties and, therefore, they provide model building blocks in modifying nanoscale structures for various applications, ranging from nanomedicine to catalysis and optics. The introduction of noble metal nanoparticles (NPs) (Au, Ag and Pd) into chemically derived graphene is important in opening new avenues for both materials in different fields where they can provide hybrid materials with exceptional performance due to the synergistical result of the specific properties of each of the materials. This review presents the different synthetic procedures for preparing Pt, Ag, Pd and Au NP/graphene oxide (GO) and reduced graphene oxide (rGO) composites.

Plasmonically Modulated Gold Nanostructures for Photothermal Ablation of Bacteria

With the wide utilization of antibiotics, antibiotic-resistant bacteria have been often developed more frequently to cause potential global catastrophic consequences. Emerging photothermal ablation has been attracting extensive research interest for quick/effective eradication of pathogenic bacteria from contaminated surroundings and infected body. In this field, anisotropic gold nanostructures with tunable size/morphologies have been demonstrated to exhibit their outstanding photothermal performance through strong plasmonic absorption of near-infrared (NIR) light, efficient light to heat conversion, and easy surface modification for targeting bacteria. To this end, this review first introduces thermal treatment of infectious diseases followed by photothermal therapy via heat generation on NIR-absorbing gold nanostructures. Then, the usual synthesis and spectral features of diversified gold nanostructures and composites are systematically overviewed with the emphasis on the importance of size, shape, and composition to achieve strong plasmonic absorption in NIR region. Further, the innovated photothermal applications of gold nanostructures are comprehensively demonstrated to combat against bacterial infections, and some constructive suggestions are also discussed to improve photothermal technologies for practical applications.

Smart Gold Nanostructures for Light Mediated Cancer Theranostics: Combining Optical Diagnostics with Photothermal Therapy

Nanotheranostics, which combines optical multiplexed disease detection with therapeutic monitoring in a single modality, has the potential to propel the field of nanomedicine toward genuine personalized medicine. Currently employed mainstream modalities using gold nanoparticles (AuNPs) in diagnosis and treatment are limited by a lack of specificity and potential issues associated with systemic toxicity. Light-mediated nanotheranostics offers a relatively non-invasive alternative for cancer diagnosis and treatment by using AuNPs of specific shapes and sizes that absorb near infrared (NIR) light, inducing plasmon resonance for enhanced tumor detection and generating localized heat for tumor ablation. Over the last decade, significant progress has been made in the field of nanotheranostics, however the main biological and translational barriers to nanotheranostics leading to a new paradigm in anti-cancer nanomedicine stem from the molecular complexities of cancer and an incomplete mechanistic understanding of utilization of Au-NPs in living systems. This work provides a comprehensive overview on the biological, physical and translational barriers facing the development of nanotheranostics. It will also summarise the recent advances in engineering specific AuNPs, their unique characteristics and, importantly, tunability to achieve the desired optical/photothermal properties.

Diagnostic prospects and preclinical development of optical technologies using gold nanostructure contrast agents to boost endogenous tissue contrast

Numerous developments in optical biomedical imaging research utilizing gold nanostructures as contrast agents have advanced beyond basic research towards demonstrating potential as diagnostic tools; some of which are translating into clinical applications. Recent advances in optics, lasers and detection instrumentation along with the extensive, yet developing, knowledge-base in tailoring the optical properties of gold nanostructures has significantly improved the prospect of near-infrared (NIR) optical detection technologies. Of particular interest are optical coherence tomography (OCT), photoacoustic imaging (PAI), multispectral optoacoustic tomography (MSOT), Raman spectroscopy (RS) and surface enhanced spatially offset Raman spectroscopy (SESORS), due to their respective advancements. Here we discuss recent technological developments, as well as provide a prediction of their potential to impact on clinical diagnostics. A brief summary of each techniques' capability to distinguish abnormal (disease sites) from normal tissues, using endogenous signals alone is presented. We then elaborate on the use of exogenous gold nanostructures as contrast agents providing enhanced performance in the above-mentioned techniques. Finally, we consider the potential of these approaches to further catalyse advances in pre-clinical and clinical optical diagnostic technologies.

Optical biomedical imaging research utilising gold nanostructures as contrast agents has advanced beyond basic science, demonstrating potential in various optical diagnostic tools; some of which are currently translating into clinical applications.

Engineered Gold Nanoshells Killing Tumor Cells: New Perspectives

The current strategies to treat different kinds of cancer are mainly based on chemotherapy, surgery and radiation therapy. Unfortunately, these approaches are not specific and rather invasive as well. In this scenario, metal nano-shells, in particular gold-based nanoshells, offer interesting perspectives in the effort to counteract tumor cells, due to their unique ability to tune Surface Plasmon Resonance in different light-absorbing ranges. In particular, the Visible and Near Infrared Regions of the electromagnetic spectrum are able to penetrate through tissues. In this way, the light absorbed by the gold nanoshell at a specific wavelength is converted into heat, inducing photothermal ablation in treated cancer cells. Furthermore, inert gold shells can be easily functionalized with different types of molecules in order to bind cellular targets in a selective manner. This review summarizes the current state-of-art of nanosystems embodying gold shells, regarding methods of synthesis, bio-conjugations, bio-distribution, imaging and photothermal effects (in vitro and in vivo), providing new insights for the development of multifunctional antitumor drugs.

MSOT/CT/MR imaging-guided and hypoxia-maneuvered oxygen self-supply radiotherapy based on one-pot MnO2-mSiO2@Au nanoparticles

Radiotherapy (RT) is one of the most widely applied treatments for cancer therapy in clinics. Herein, we constructed innovative multifunctional nanotheranostic MnO2-mSiO2@Au-HA nanoparticles (MAHNPs) based on one-pot MnO2-mSiO2 nanohybrids (MNHs) and gold nanoparticles (AuNPs) for multispectral optoacoustic tomography (MSOT)/computed tomography (CT) and magnetic resonance (MR) imaging-guided hypoxia-maneuvered radiotherapy. The MNHs were prepared via a facile one-pot approach, which avoided the leakage of MnO2 nanoparticles and increased the synthetic efficiency. The Mn2+ ions triggered the breakdown of endogenous H2O2 to generate O2 to convert the hypoxic tumor micro-environment (TME), thus enhancing radiotherapy by self-supply oxygen. In addition, hyaluronic acid (HA) was employed to modify the surface of the MnO2-mSiO2@Au nanoparticles to improve their biocompatibility and cellular uptake. The well-designed nanoparticles could perform remarkable photothermal therapy (PTT) and hypoxia-maneuvered radiotherapy (RT) simultaneously and MSOT/CT/MR imaging. The in vivo studies showed that the MAHNPs achieved almost total suppression of tumor growth without observable recurrence, which raises new possibilities for clinical nanotheranostics with multimodal diagnostic and therapeutic coalescent design.

Nanocomposite of polypyrrol and silica rods-gold nanoparticles core-shell as an ammonia sensor

Ammonia is widely needed in the chemical industry as well as in fertilizers for agriculture. However, in small as well as large quantities, it is not only hazardous for human health but also for our ecosystem. Therefore, ammonia sensing at low concentration with high sensitivity, selectivity and low response time as well as recovery time is important. Here, various nanosensors are fabricated using gold nanoparticles (∼15 nm), silica-gold nanoparticles coreshell particles and coreshell particles embedded in polypyrrol. Comparisons with bare polypyrrol and coreshell particles are also made. In fact, two types of coreshell particles with rod (∼300 nm × 2 μm) shape and spheres (200 nm) of silica were used to anchor gold nanoparticles on them. A comparison showed that silica-gold core-shell particle with silica rods had the highest sensitivity (∼166% @ 130 ppm) amongst all. The sensor is simple to operate (only resistance change is measured), requires no heater as the sensing occurs at room temperature, and showed no response, except for ammonia, to other gases or humidity. It also has a low response time (4 s) and recovery time (10 s) at the lowest (10 ppm) ammonia concentration measured here. Thus, a simple, economical ammonia sensor has been demonstrated here.

Vapreotide-mediated hierarchical mineralized Ag/Au nanoshells for photothermal anti-tumor therapy

A new type of vapreotide-templated Ag/Au bimetallic nanoshells (Vap@Ag/AuNSs) were successfully designed and fabricated based on polypeptide-directed mineralization and hierarchical self-assembly mechanisms under mild synthetic conditions. The nanoparticles with polypeptides serving as a core and coated Ag/Au bimetallic nanoshells exhibit diverse advantages, such as excellent biocompatibility, tumor targeting and low-cost. The Vap@Ag/AuNSs share excellent dispersibility, uniform size (120 nm) and a positive zeta potential (36.74 ± 4.49 mV), hence they easily accumulate in negatively charged tumor tissue. The results of thermal imaging, temperature variation assays and photothermal conversion efficiency (41.6%) indicated that Vap@Ag/AuNSs have excellent photothermal conversion capability. Based on their photothermal response, as well as biocompatibility determined by MTT assay, the prominent anti-tumor effects of Vap@Ag/AuNSs have been verified by fluorescein diacetate staining. Therefore, Vap@Ag/AuNSs are novel and promising candidates for photothermal tumor therapy.

Synthesis of Au Nanoparticles Assisted by Linker-Modified TiO2 Nanoparticles

Plasmonic nanoparticles, especially gold ones, have been widely employed as photosensitizers in photoelectrovoltaic or photocatalytic systems. To improve the system's performance, a greater interaction of the nanoparticles with the semiconductor, generally TiO₂, is desired. Moreover, this performance is enhanced when an efficient covering of TiO₂ surface by the sensitizer is achieved. The Brust-Schiffrin-like methods are of the most employed approaches for nanoparticles synthesis. In a traditional approach, the reduction of the gold precursor is performed in the presence of a stabilizer (typically a thiol molecule) free in solution. A second step in which the obtained nanoparticles are anchored to the semiconductor surface is necessary in the case of photosensitive applications. Drawbacks like steric hindrance turn more difficult the covering of the semiconductor's surface by nanoparticles. In this paper, we report a variation of this methodology, where the linker is previously anchored to the TiO₂ nanoparticles surface. The resulting system is employed as the stabilizer in the gold reduction step. This strategy is carried out in aqueous media in two simple steps. A great covering of the titania surface by gold nanoparticles is achieved in all cases and the gold nanoparticles in the resulting nanoaggregate might be useful for photoelectrovoltaic or photocatalytic applications.

Piezoelectric Polyacrylonitrile Nanofiber Film-Based Dual-Function Self-Powered Flexible Sensor

To meet the growing demands in flexible and wearable electronics, various sensors have been designed for detecting and monitoring the physical quantity changes. However, most of these sensors can only detect one certain kind of physical quantity based on a single mechanism. In this paper, we have fabricated a multifunctional sensor made from carbonized electrospun polyacrylonitrile/barium titanate (PAN-C/BTO) nanofiber film. It can detect two physical quantities (pressure and curvature), independently and simultaneously, by integrating piezoresistive, piezoelectric, and triboelectric effects. For flex sensing with the impedance change of PAN-C/BTO nanofiber films during bending, it had a sensitivity of 1.12 deg^-1 from 58.9° to 120.2° and a working range of 28°-150°. For self-powered force sensing, it had a gauge factor of 1.44 V·N^-1 within the range of 0.15-25 N. The sensor had a long stability over 60 000 cycles at both sensing modes. The inclusion of barium titanate nanoparticles (BTO NPs) into the nanofiber film had an over 2.4 times enhancement of sensitivity for pressure sensing because of the synergy of piezoelectric and triboelectric effects. On the basis of multifunction and modularity, a series of potential applications of the sensor were demonstrated, including sensing human's swallowing, walking gaits, finger flexure, and finger-tapping. The self-powered flexible dual-mode sensor has great application potential in human-computer interactive and smart wearable sensing systems.

Shape-Controlled Synthesis of Au Nanostructures Using EDTA Tetrasodium Salt and Their Photothermal Therapy Applications

Tuning the optical properties of Au nanostructures is of paramount importance for scientific interest and has a wide variety of applications. Since the surface plasmon resonance properties of Au nanostructures can be readily adjusted by changing their shape, many approaches for preparing Au nanostructures with various shapes have been reported to date. However, complicated steps or the addition of several reagents would be required to achieve shape control of Au nanostructures. The present work describes a facile and effective shape-controlled synthesis of Au nanostructures and their photothermal therapy applications. The preparation procedure involved the reaction of HAuCl₄ and ethylenediaminetetraacetic acid (EDTA) tetrasodium salt, which acted as a reducing agent and ligand, at room temperature without the need for any toxic reagent or additives. The morphology control from spheres to branched forms and nanowire networks was easily achieved by varying the EDTA concentration. Detailed investigations revealed that the four carboxylic groups of the EDTA tetrasodium salt are essential for effective growth and stabilization. The produced Au nanowire networks exhibited a broad absorption band in the near-infrared (NIR) region, thereby showing efficient cancer therapeutic performance by inducing the selective photothermal destruction of cancerous glioblastoma cells (U87MG) under NIR irradiation.

Polydopamine-based concentric nanoshells with programmable architectures and plasmonic properties

Nanoshells, classically comprising gold as the metallic component and silica as the dielectric material, are important for fundamental studies in nanoplasmonics. They also empower a myriad of applications, including sensing, energy harvesting, and cancer therapy. Yet, laborious preparation precludes the development of next-generation nanoshells with structural complexity, compositional diversity, and tailorable plasmonic behaviors. This work presents an efficient approach to the bottom-up assembly of concentric nanoshells. By employing polydopamine as the dielectric material and exploiting its intrinsic adhesiveness and pH-tunable surface charge, the growth of each shell only takes 3-4 hours at room temperature. A series of polydopamine-based concentric nanoshells with programmable nanogap thickness, elemental composition (gold and silver), and geometrical configuration (number of layers) is prepared, followed by extensive structural characterization. Four of the silver-containing nanostructures are newly reported. Systematic investigations into the plasmonic properties of concentric nanoshells as a function of their structural parameters further reveal multiple Fano resonances and local-field "hot spots", infrequently reported plasmonic features for individual nanostructures fabricated using bottom-up wet chemistry. These results establish materials design rules for engineering complex plasmon-based systems originating from the integration of multiple plasmonic elements into defined locations within a compact nanostructure.

NIR absorbing Au nanoparticle decorated layered double hydroxide nanohybrids for photothermal therapy and fluorescence imaging of cancer cells

Among inorganic nanomaterials, layered double hydroxides (LDHs) and gold nanoparticles (Au NPs) have received great attention in nanobiomedicine due to their unique properties. In this work, we have designed a nanohybrid of an LDH with Au NPs (LDH-Au) in order to use it for photothermal therapy, and optical and fluorescence imaging of cancer cells. The structural characteristics of the nanohybrid are investigated using X-ray diffraction, infrared spectroscopy, electron microscopy and elemental analyses. The extinction spectra of the nanohybrid exhibits broad absorption ranging from the visible to near infrared (NIR) region (500-1000 nm). The photothermal activity of the nanohybrid is explored using NIR laser irradiation. The electric field enhancement in the nanohybrid due to the interaction of Au NPs on the LDH is speculated through finite-difference time-domain (FDTD) calculations. The LDH-Au nanohybrid is found to be biocompatible with normal murine fibroblast (L929), human breast cancer (MCF-7) and cervical cancer (HeLa) cell lines up to a concentration of 1 mg mL^-1. The nanohybrid is explored for in vitro photothermal therapy of MCF-7 and HeLa cell lines. As a photothermal agent, the nanohybrid shows that 10 min exposure to an 808 nm laser (500 mW) is adequate to inhibit about 70% of cancer cells. Further, the nanohybrid is tagged with FITC to study both optical and fluorescence imaging with MCF-7 cell lines. The results demonstrate that the LDH-Au nanohybrid provides an innovative approach to photothermal therapy, and optical and fluorescence imaging of cancer cells.

In vivo self-assembly induced retention of gold nanoparticles for enhanced photothermal tumor treatment

A simple route to fabricate peptide modified spherical gold nanoparticles with enhanced retention performance in tumor sites for improved photothermal treatment.

Preparation of THPC-generated silver, platinum, and palladium nanoparticles and their use in the synthesis of Ag, Pt, Pd, and Pt/Ag nanoshells

Seed nanoparticles of Ag, Pt, and Pd (typically ≤4 nm in diameter) were synthesized using tetrakis(hydroxymethyl)phosphonium chloride (THPC) as reducing agent and utilized to prepare Ag, Pt, and Pd nanoshells, as well as hybrid Pt/Ag nanoshells, on silica cores.

Engineered gold nanoparticles for photothermal cancer therapy and bacteria killing

Gold nanoparticle mediated photothermal therapy in future medicine.