Silica-coated Au Research Articles

NIR-Triggered Multifunctional NO Nanoplatform for Conquering Thermal Resistance in Biofilms.

Photothermal treatment (PTT) has emerged as a promising avenue for biofilm elimination, yet its potential drawbacks, such as local hyperpyrexia and bacterial heat resistance, have posed challenges. To address these concerns, an innovative nanoplatform (Au@mSiO2-arg/ICG) is devised that integrates phototherapeutic and gas therapeutic functionalities. This multifaceted nanoplatform is composed of mesoporous silica-coated Au nanorods (Au@mSiO2), supplemented with l-arginine (l-arg) and indocyanine green (ICG), and is engineered for mild temperature PTT aimed at biofilm eradication. Au@mSiO2-arg/ICG nanoparticles (NPs) show excellent antibacterial effects through the generation of nitric oxide (NO) gas, heat, and reactive oxygen species (ROS) under 808nm light irradiation. The ROS generated by ICG initiates a cascade reaction with l-arg, ultimately yielding NO gas molecules. This localized release of NO not only effectively curbs the expression of heat shock proteins 70 mitigating bacterial thermoresistance, but also reduces extracellular polymeric substance allowing better penetration of the therapeutic agents. Furthermore, this nanoplatform achieves an outstanding biofilm elimination rate of over 99% in an abscess model under 808nm light irradiation (0.8 W·cm-2), thereby establishing its potential as a dependable strategy for NO-enhanced mild PTT and antibacterial photodynamic therapy (aPDT) in clinical settings.

"Turn-on" and pinhole-free ultrathin core-shell Au@SiO2 nanoparticle-based metal-enhanced fluorescent (MEF) chemodosimeter for Hg2.

This study reports a metal-enhanced fluorescence chemodosimeter for highly sensitive detection of Hg2+ ions. Silica-coated Au nanoparticles (Au@SiO2 NPs) with a pinhole-free 4-5 nm shell were synthesized and functionalized with a monolayer of turn-on fluorescent probes. Compared to other organic fluorescent probes suffering from poor biocompatibility and detection limits, this design of a monolayer of turn-on fluorescent probes immobilized on the Au@SiO2 NPs with a pinhole-free 4-5 nm shell avoids fluorescence quenching and allows the fluorescent probe within the field of the inner Au NPs to experience metal-enhanced fluorescence. With this design, the chemodosimeter permits fluorescence emission in the presence of Hg2+ ions, because they trigger the ring-opening reaction of the fluorescent probe immobilized on the Au@SiO2 NPs. Additionally, the fluorescent probe is distanced by the thin SiO2 shell from directly attaching to the metallic Au NPs, which not only avoids fluorescence quenching but allows the fluorescent probe within the long-ranged field of the inner Au NPs to experience metal-enhanced fluorescence. As a result, the detection limit for the chemodosimeter can reach up to 5.0 × 10-11 M, nearly two orders of magnitude higher than that achieved for the free fluorescent probe. We also demonstrate the acquisition of images of Hg2+ in HTC116 cells and zebrafish using a simple fluorescence confocal imaging technique. The fluorescence response results for HTC116 cells and zebrafish show that the probes can permeate into cells and organisms. Considering the availability of the many organic fluorescent probes that have been designed, the current designed metal-enhanced fluorescence chemodosimeter holds great potential for fluorescence detection of diverse species and fluorescence imaging.

Importance of the Structural and Physicochemical Properties of Silica Nanoshells in the Photothermal Effect of Silica-Coated Au Nanoparticles Suspensions.

In this work, monodisperse silica-coated gold nanoparticles (NPs) were synthesized and used for obtaining aqueous colloidal dispersions with an optimum relationship between colloidal stability and photothermal activity. The idea behind this design was to produce systems with the advantages of the presence of a silica shell (biocompatibility, potential for surface modification, and protecting effect) with a minimal loss of optical and thermal properties. With this aim, the photothermal properties of NPs with silica shells of different thicknesses were analyzed under conditions of high radiation extinction. By using amorphous, gel-like silica coatings, thicknesses higher than 40 nm could be obtained without an important loss of the light absorption capacity of the colloids and with a significant photothermal response even at low NP concentrations. The effects produced by changes in the solvent and in the NP concentration were also analyzed. The results show that the characteristics of the shell control both, the photothermal effect and the optical properties of the colloidal dispersions. As the presence of a silica shell strongly enhances the possibilities of adding cargo molecules or probes, these colloids can be considered of high interest for biomedical therapies, sensing applications, remote actuation, and other technological applications.

Optical Properties of Silica-Coated Au Nanorods: Correlating Theory and Experiments for Determining the Shell Porosity

Optical Properties of Silica-Coated Au Nanorods: Correlating Theory and Experiments for Determining the Shell Porosity

Enhanced performance of organic solar cells with multifunctional silica-coated Au nanobowtie core-shell structure

The multifunctional silica-coated Au nanobowtie (GNB@SiO2) core-shell structure was embedded in organic solar cells (OSCs), and an intense performance promotion of the devices was achieved by optimizing the shape and the size of the GNB@SiO2. The light absorption of the active layer was increased with GNB@SiO2 doping concentration increasing until the doping concentration exceeds 10 nM. The devices obtain the best J-V characteristics when GNB@SiO2 doping concentration is 10 nM. Comparing with that of the control cells, the optimal performance of the devices with GNB@SiO2 incorporated was significantly increased by 47%. The finite-difference time-domain method was used to simulate the special asymmetry shape and the size of the multifunctional GNB@SiO2 impact on the performance of the OSCs. The electric field intensity |E|2 in the different planes revealed that the local surface plasmon resonance (LSPR) and far-field scattering effect played an important role in the light absorption of the devices. The cooperation effect of LSPR near-field and the far-field scattering resulted in the electric field redistribution of the active layer as the result of the absorption enhanced.

Hybrid Hydrogels for Synergistic Periodontal Antibacterial Treatment with Sustained Drug Release and NIR-Responsive Photothermal Effect.

BackgroundPeriodontal pathogenic bacteria promote the destruction of periodontal tissues and cause loosening and loss of teeth in adults. However, complete removal of periodontal pathogenic bacteria, at both the bottom of the periodontal pocket and the root bifurcation area, remains challenging. In this work, we explored a synergistic antibiotic and photothermal treatment, which is considered an alternative strategy for highly efficient periodontal antibacterial therapy.MethodsMesoporous silica (MSNs) on the surface of Au nanobipyramids (Au NBPs) were designed to achieve the sustained release of the drug and photothermal antibacterials. The mesoporous silica-coated Au NBPs (Au NBPs@SiO2) were mixed with gelatin methacrylate (GelMA-Au NBPs@SiO2). Au NBPs@SiO2 and GelMA-Au NBPs@SiO2 hybrid hydrogels were characterized, and the drug content and photothermal properties in terms of the release profile, bacterial inhibition, and cell growth were investigated.ResultsThe GelMA-Au NBPs@SiO2 hybrid hydrogels showed controllable minocycline delivery, and the drug release rates increased under 808 nm near-infrared (NIR) light irradiation. The hydrogels also exhibited excellent antibacterial properties, and the antibacterial efficacy of the antibiotic and photothermal treatment was as high as 90% and 66.7% against Porphyromonas gingivalis (P. gingivalis), respectively. Moreover, regardless of NIR irradiation, cell viability was over 80% and the concentration of Au NBPs@SiO2 in the hybrid hydrogels was as high as 100 µg/mL.ConclusionWe designed a new near-infrared light (NIR)-activated hybrid hydrogel that offers both sustained release of antibacterial drugs and photothermal treatment. Such sustained release pattern yields the potential to rapidly eliminate periodontal pathogens in the periodontal pocket, and the photothermal treatment maintains low bacterial retention after the drug treatment.

Enhancing Catalytic Activity and Selectivity by Plasmon-Induced Hot Carriers.

SummaryPlasmon-assisted chemical transformation holds great potential for solar energy conversion. However, simultaneous enhancement of reactivity and selectivity is still challenging and the mechanism remains mysterious. Herein, we elucidate the localized surface plasmon resonance (LSPR)-induced principles underlying the enhanced activity (∼70%) and selectivity of photoelectrocatalytic redox of nitrobenzene (NB) on Au nanoparticles. Hot carriers selectively accelerate the conversion rate from NB to phenylhydroxylamine (PHA) by ∼14% but suppress the transformation rate from PHA to nitrosobenzene (NSB) by ∼13%. By adding an electron accepter, the as-observed suppression ratio is substantially enlarged up to 43%. Our experiments, supported by in situ surface-enhanced Raman spectroscopy and density functional theory simulations, reveal such particular hot-carrier-induced selectivity is conjointly contributed by the accelerated hot electron transfer and the corresponding residual hot holes. This work will help expand the applications of renewable sunlight in the directional production of value-added chemicals under mild conditions.

Preparation and plasmon resonance properties of Au nanorods and Aunanorods@SiO2

Au nanorods were prepared through seed growth method. Their lengths and diameters were controlled by adjusting Ag+ content in the growth solution. Ethyl orthosilicate were hydrolyzed in alkali solutions to obtain SiO2-coated Au nanostructures. Au nanorods with ideal morphologies and sizes could only be obtained under the presence of a certain Ag+ concentration in the growth solution. Without Ag+, only some irregular nanoparticles were generated without nanorods. Longitudinal plasma absorption of Au nanorods shifts first to red shift and then to blue with the increase of Ag+ in the growth solution, while transverse plasma absorption hardly changes. However, longitudinal plasma absorption of silica-coated Au nanorods has a blue shift with the increase of the thickness of silica, while the transverse plasma has a slight red shift. Therefore, by coating Au nanorods with silica and by adjusting their aspect ratio by using different Ag+ concentration in the growth solution, Au nanoparticles can be synthesized for applications requiring absorption in specific UV regions.

Osteogenic Differentiation of Mesenchymal Stem Cells with Silica-Coated Gold Nanoparticles for Bone Tissue Engineering.

Multifunctional nanofibrous scaffolds for effective bone tissue engineering (BTE) application must incorporate factors to promote neovascularization and tissue regeneration. In this study, silica-coated gold nanoparticles Au(SiO2) were tested for their ability to promote differentiation of human mesenchymal stem cells (hMSCs) into osteoblasts. Biocompatible poly-ε-caprolactone (PCL), PCL/silk fibroin (SF) and PCL/SF/Au(SiO2) loaded nanofibrous scaffolds were first fabricated by an electrospinning method. Electrospun nanofibrous scaffolds were characterized for fiber architecture, porosity, pore size distribution, fiber wettability and the relevant mechanical properties using field emission scanning electron microscopy (FESEM), porosimetry, determination of water contact angle, measurements by a surface analyzer and tabletop tensile-tester measurements. FESEM images of the scaffolds revealed beadless, porous, uniform fibers with diameters in the range of 164 ± 18.65 nm to 215 ± 32.12 nm and porosity of around 88–92% and pore size distribution around 1.45–2.35 µm. Following hMSCs were cultured on the composite scaffolds. Cell-scaffold interaction, morphology and proliferation of were analyzed by FESEM analysis, MTS (3-(4,5-dimethyl thiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium inner salt) and CMFDA (5-choromethyl fluorescein acetate) dye assays. Osteogenic differentiation of MSCs into osteogenic cells were determined by alkaline phosphatase (ALP) activity, mineralization by alizarin red S (ARS) staining and osteocalcin expression by immunofluorescence staining. The results revealed that the addition of SF and Au(SiO2) to PCL scaffolds enhanced the mechanical strength, interconnecting porous structure and surface roughness of the scaffolds. This, in turn, led to successful osteogenic differentiation of hMSCs with improved cell adhesion, proliferation, differentiation, mineralization and expression of pro-osteogenic cellular proteins. This provides huge support for Au(SiO2) as a suitable material in BTE.

Synthesis of porphyrin-conjugated silica-coated Au nanorods for synergistic photothermal therapy and photodynamic therapy of tumor

Synergistic therapy of tumor has attracted the attention of an increasing number of researchers because of its higher efficiency compared to single therapy. Herein, 4-carboxyphenyl porphyrin-conjugated silica-coated gold nanorods (AuNR@SiO2-TCPP) were synthesized. The synergistic treatment of photothermal therapy and photodynamic therapy on A549 cancer was researched in vivo and in vitro. In the AuNR@SiO2-TCPP, Au NRs and TCPP act as photothermal agent and photosensitizer, respectively. The temperature of the AuNR@SiO2-TCPP (0.11 nmol L−1) rises to 56.8 °C for 10 min under the illumination of 808 nm laser (2 Wcm−2). In MTT assays, the viability of A549 cancer cell treated with AuNR@SiO2-TCPP (100 μg ml−1) is only 21%. In animal experiments, the relative tumor volumes in mice receiving AuNR@SiO2-TCPP (5 mg kg−1) with 660 and 808 nm irradiations were significantly inhibited and the average value is decreased to 0.78 while the average value of the control group is increased to 7.2. These results demonstrate that the AuNR@SiO2-TCPP is a potential nanomedicine against tumor for clinical application in the near future.

Au Nanobottles with Synthetically Tunable Overall and Opening Sizes for Chemo-Photothermal Combined Therapy.

Highly asymmetric Au nanostructures, such as split Au nanorings and Au nanocups, exhibit attractive plasmonic properties because of their asymmetric geometries. To facilitate their plasmonic applications, effective and facile synthetic methods for producing asymmetric Au nanostructures with controllable sizes and uniform shapes are highly desirable. Herein, we report on an approach for the synthesis of largely asymmetric colloidal Au nanobottles with synthetically tunable overall and opening sizes. Au nanobottles with overall sizes in the range of ∼100-230 nm are obtained through sacrificial templating with differently sized PbS nano-octahedra. The opening sizes of the produced Au nanobottles can be tailored from ∼10 to ∼120 nm by either adjusting the Au/PbS molar ratio in the growth process or controlling the oxidation degree. The achieved size tunability allows the plasmon resonance wavelength of Au nanobottles to be varied in the range of ∼600-900 nm. Our uniform Au nanobottles, which possess controllable sizes, large cavity volumes, and tunable plasmon resonance wavelengths in the visible to near-infrared range, have been further applied for anticancer drug delivery and photothermal therapy. The effects of surface coating and the opening size of Au nanobottles on the drug encapsulation efficiency (EE) and initial burst drug release are systemically evaluated. A high doxorubicin EE and low initial burst drug release are realized with the dense silica-coated Au nanobottles having an opening size of 44 nm. In addition, chemo-photothermal combined therapy has been demonstrated with the doxorubicin-loaded Au nanobottles. Our results will be helpful for the design of Au nanobottles with different sizes and plasmonic properties as well as provide ample opportunities for exploring various plasmon-enabled applications of Au nanobottles.

A dual signal amplification nanosensor based on SERS technology for detection of tumor-related DNA.

A dual signal amplification method based on surface-enhanced Raman scattering (SERS) is developed by photo-triggered release of SERS probes from mesoporous silica-coated Au nanorods (SiO2@Au) and the use of a specially-designed SERS substrate with an internal reference. Two metal carbonyl (metal-CO) labels (Os-SCO and Re-SCO) are proposed here as novel interference-free labels. Results demonstrate that tumor-related DNA can be quantitatively detected by this reliable and ultra-sensitive SERS platform.

Porous Silica-Coated Gold Sponges with High Thermal and Catalytic Stability.

A method to fabricate porous silica-coated Au sponges that show high thermal and catalytic stability has been developed for the first time. The method involves dense surface functionalization of Au sponges (made by self-assembly of Au nanoparticles) with thiolated poly(ethylene glycol) (SH-PEG), which provides binding and condensation sites for silica precursors. The silica coating thickness can be controlled by using SH-PEG of different molecular weights. The silica-coated Au sponge prepared by using 5 kDa SH-PEG maintains its morphology at temperature as high as 700 °C. The calcination removes all organic molecules, resulting in porous silica-coated Au sponges, which contain hierarchically connected micro- and mesopores. The hierarchical pore structures provide an efficient pathway for reactant molecules to access the surface of Au sponges. The porous silica-coated Au sponges show an excellent catalytic recyclability, maintaining the catalytic conversion percentage of 4-nitrophenol by NaBH4 to 4-aminophenol as high as 93% even after 10 catalytic cycles. The method may be applicable for other porous metals, which are of great interests for catalyst, fuel cell, and sensor applications.

Vitamin C-Conjugated Nanoparticle Protects Cells from Oxidative Stress at Low Doses but Induces Oxidative Stress and Cell Death at High Doses.

Although the antioxidant property of vitamin C is well-known for protecting cells from oxidative stress, a recent study shows that it can also generate oxidative stress under a high intracellular concentration and induce cell death. However, poor chemical stability and low biological concentration (micromolar) of vitamin C restrict its function primarily as an antioxidant. Here, we report two different nanoparticle forms of vitamin C with its intact chemical stability, glucose-responsive release from nanoparticle, and efficient cell delivery in micro to millimolar concentrations. Nanoparticles are composed of silica-coated Au nanoparticles or lipophilic polyaspartic acid-based polymer micelles which are conjugated with vitamin C via phenylboronic acid. Surface chemistry of nanoparticles is optimized for an efficient cellular interaction/uptake and for cell delivery of vitamin C. We found that vitamin C protects cells from oxidative stress at micromolar concentrations, but at millimolar concentrations, it induces cell death by generating oxidative stress. In particular, high-dose vitamin C produces H2O2, disrupts the cellular redox balance, and induces cell death. This study highlights the concentration-dependent biological performance of vitamin C and the requirement of a high-dose cell delivery approach for enhanced therapeutic benefit.

Fabrication of multilayered Au/silica/gadolinium compound core–shell particles and their imaging properties

The present work proposes a preparation method for multilayered Au nanoparticle/silica/gadolinium compound core–shell (Au/SiO2/GdC) particles. Silica-coated Au core–shell (Au/SiO2) particles with a size of 38.0 nm were prepared by a sol-gel reaction in the presence of the Au nanoparticles with a size of 15.5 nm. Multilayered Au/SiO2/GdC particles with sizes of ca. 35–52 nm were prepared by a homogeneous precipitation reaction in the presence of Au/SiO2 particles. The computed tomography (CT) value of the Au/SiO2/GdC colloid solution containing 4.3 × 10−2 M Au was 344.1 HU: Its converted CT value (CT divided by Au concentration) was as large as 8.0 × 103 HU/M. The r1 value of the Au/SiO2/GdC colloid solution was as large as 3.5 mM−1 s−1.

Highly Stable Silica-Coated Gold Nanoflowers Supported on Alumina.

Shape-controlled nanocrystals, such as nanowires and nanoflowers, are attractive because of their potential novel optical and catalytic properties. However, the dispersion and morphological stabilities of shape-controlled nanocrystals are easily destroyed by changing the dispersion solvent and temperature. Methods of support and the silica coating are known to improve the dispersion and morphological stabilities of metal nanocrystals. The silica-coating method often causes morphological changes in shape-controlled nanocrystals because the silica coating is formed in mixed solutions of water and organic solvents such as ethanol, and this results in aggregation due to changes in the dispersion solvent. Furthermore, ligand exchange, designed to improve the dispersion stability in the solvent, often causes morphological changes. This article introduces a method for the preparation of highly stable silica-coated Au nanoflowers (AuNFs) supported on Al2O3. The method of support prevents the aggregation and precipitation of AuNFs when the solvent is changed from water to water/ethanol. Through stability improvement, silica coating of AuNFs/Al2O3 was conducted in water/ethanol without ligand exchange that causes morphological changes. Furthermore, silica-coated AuNFs/Al2O3 exhibit high morphological stability under high-temperature conditions compared to uncoated AuNFs/Al2O3. These results are very useful when preparing highly morphologically stable, silica-coated, shape-controlled nanocrystals without ligand exchange.

Fabrication of silica-coated gold nanorods and investigation of their property of photothermal conversion

This study described the preparation of silica-coated Au nanorods (AuNR/SiO2) in a colloidal solution, assessed their property of photothermal conversion, and investigated their ability to kill cancer cells using photothermal conversion. Au-seed nanoparticles were produced by reducing hydrogen tetrachloroaurate (HAuCl4) with sodium borohydride (NaBH4) in aqueous n-hexadecyltrimethylammonium bromide (CTAB) solution. AuNRs were then fabricated by reducing HAuCl4 and silver nitrate (AgNO3) with l-ascorbic acid in the aqueous CTAB solution in the presence of Au-seed nanoparticles. The as-prepared AuNRs were washed by a process composed mainly of centrifugation to remove the CTAB. The washed AuNRs were coated with silica by mixing the AuNR colloidal solution, an aqueous solution of (3-aminopropyl)trimethoxysilane, and tetraethylorthosilicate/ethanol solution with a water/ethanol solution. We found that the addition of AuNR/SiO2 in water, in mice, and in a culture medium with cancer cells, followed by irradiation with a laser, cause an increase in temperature, demonstrating that AuNR/SiO2 have the ability of photothermal conversion. In addition, the cancer cells in the culture medium were found to be killed due to the increase in temperature caused by the photothermal conversion.

Hollow Mesoporous Silica Nanoparticles with Tunable Structures for Controlled Drug Delivery.

A size-controllable and facile synthetic strategy has been developed to fabricate a series of hollow mesoporous silica nanoparticles (HMSNs) with tunable hollow cores or shell thicknesses by employing gold nanoparticles (Au NPs) and cetyltrimethylammonium bromide (CTAB) as dual templates. Various sizes of Au NPs and different amounts of tetraethyl orthosilicate contributed to structure-tailored mesoporous silica-coated Au NPs. After calcination, CTAB molecules were completely removed, and Au NPs could still support the silica shell due to the high melting point. HMSNs were ultimately obtained by etching Au NPs. Applications of HMSNs as nanocarriers for delivering drugs were investigated. Significantly, it was flexible and convenient to control drug-loading/releasing behavior of HMSNs just by tuning the hollow cores or shell thicknesses. Intracellular experiments have proven that HMSNs are suitable for delivering drugs. We anticipate that this study could provide an important avenue for the synthesis of HMSNs and further contribute to advancing practical applications of HMSNs in drug delivery systems.

Strong Fluorescence Enhancement with Silica-Coated Au Nanoshell Dimers

Fluorescence intensity is vital for fluorescence sensing and imaging because it determines the sensing sensitivity and imaging brightness. This study reports plasmon-enhanced fluorescence by engineering plasmonic nanostructures, that are SiO2-coated Au nanoshell dimers with a high yield exceeding 60 %. With this elaborately designed nanostructure, we show that the thin SiO2 shell can conveniently distance the fluorophore from the underneath metal, thereby effectively avoiding fluorescence quenching. Meanwhile, the inner Au nanoshell dimers create abundant hot spots at particle-particle junctions and enable near-infrared fluorescence enhancement. The largest fluorescence enhancement achieved is 69 times for the design with a 9 nm external SiO2 shell, as is also confirmed by three-dimensional finite-difference time-domain simulations. This dramatically increased fluorescence has great significance in fluorescence-based sensing and imaging.

Influence of SiO2 shell thickness on power conversion efficiency in plasmonic polymer solar cells with Au nanorod@SiO2 core-shell structures.

Locating core-shell metal nanoparticles into a photoactive layer or at the interface of photoactive layer/hole extraction layer is beneficial for fully employing surface plasmon energy, thus enhancing power conversion efficiency (PCE) in plasmonic organic photovoltaic devices (OPVs). Herein, we first investigated the influence of silica shell thickness in Au nanorods (NRs)@SiO2 core-shell structures on OPV performances by inserting them into poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) and thieno[3,4-b]thiophene/benzodithiophene (PTB7) interface, and amazedly found that a 2–3 nm silica shell onto Au NRs induces a highest short-circuit current density of 21.2 mA cm−2 and PCE of 9.55%. This is primarily due to an extremely strong local field and a much slower attenuation of localized surface plasmon resonance around ultrathin silica-coated Au NRs, with which the field intensity remains a high value in the active layer, thus sufficiently improves the absorption of PTB7. Our work provides a clear design concept on precise control of the shell of metal nanoparticles to realize high performances in plasmonic OPVs.