Gold Nanodots Research Articles

Gold Nanostars-AIE Theranostic Nanodots with Enhanced Fluorescence and Photosensitization Towards Effective Image-Guided Photodynamic Therapy

HighlightsDevelopment of Au nanostar@AIE nanodots photosensitizers for theranostic applications.Achieving excellent metal-enhanced fluorescence and singlet oxygen generation efficiency simultaneously.Mechanism study of the role of FRET on metal-enhanced singlet oxygen generation.

Label-free sensing of virus-like particles below the sub-diffraction limit by wide-field photon state parametric imaging of a gold nanodot array.

A parallel four-quadrant sensing method utilizing a specially designed gold nanodot array is created for sensing virus-like particles with a sub-diffraction limit size (∼100 nm) in a wide-field image. Direct label-free sensing of viruses using multiple four-quadrant sensing channels in parallel in a wide-field view enables the possibility of high-throughput onsite screening of viruses.

A gold nanodot array imprinting process based on solid-state dewetting for efficient oxide-free photovoltaic devices

We report the development of an efficient imprinting process for the formation of metal (Au) nanodot arrays using a square-patterned medium substrate. Solid-state dewetting is induced by differences in the surface energy of the metal film and the interface energy between the substrate and the metal film. Thus, uniform metal nanodot arrays were transferred to the desired substrate by controlling the interfacial surface free energy between the metal film and the substrate. Optical extinction measurements showed an intense extinction peak at 550 nm, corresponding to the simulated result. Imprinting of the Au-nanodot arrays on the substrate enhanced the light trapping function and supported the electrical properties of a polymer electrode. In addition, the combination of a transparent conducting oxide-free device with the Au-nanodot arrays and a polymer electrode resulted in enhanced performance. This can be attributed to the fact that the Au-nanodot arrays allowed higher charge extraction, as confirmed by electrical analyses. Finally, a next-generation approach of imprinting metal nanodot arrays was introduced through the controlled solid-state dewetting mechanism in a specific area, which can be applicable not only in the development of optoelectronic devices but also in semiconductor processes requiring metal nanostructures.

Ultra-small nanodots coated with oligopeptides providing highly negative charges to enhance osteogenic differentiation of hBMSCs better than osteogenic induction medium

For bone regenerative engineering, it is a promising method to form skeletal tissues differentiating from human bone morrow mesenchyme stem cells (hBMSCs). However, it is still a critical challenge to efficiently control ostogenesis and clearly reveal the influence factor. To this end, the fluorescent gold nanodots (Au NDs) with highly negative charges as osteogenic induction reagent are successfully synthesized, which display better than commercial osteogenic induction medium through the investigations of ALP activity (2.5 folds) and cytoskeleton staining (1.5 folds). Two kinds of oligopeptides with different bio-structures (cysteine, Cys and glutathione, GSH) are selected for providing surficial charges on Au NDs. It is revealed that Au-Cys with more negative charges (−51 mV) play better role than Au-GSH (−19 mV) in osteogenic differentiation, when both of them have same size (∼2 nm), sphere shape and show similar cell uptake amount. To explore deeply, osteogenesis related signaling pathways are monitored, revealing that the enhancement of osteogenic differentiation was through autophagy signaling pathway triggered by Au-Cys. And the promotion of highly negative charges in osteogenic differentiation was further proved via sliver nanodots (Ag NDs, Ag-Cys and Ag-GSH) and carbon nanodots (CDs, Cys-CDs and GSH-CDs). This work indicates part of insights during hBMSCs differentiation and provides a novel strategy in osteogenic differentiation process.

Primary Amine Modified Gold Nanodots Regulate Macrophage Function and Antioxidant Response: Potential Therapeutics Targeting of Nrf2.

BackgroundGold nanoparticles with high biocompatibility and immunomodulatory properties have potential applications in the development of new diagnostic and therapeutic strategies for nanomedicine. Nanoparticles targeting macrophages can manipulate or control immunological diseases. This study assessed the activity of dendrimer-encapsulated gold nanodots (AuNDs) with three surface modifications [ie, outfacing groups with primary amine (AuNDs-NH2), hydroxyl (AuNDs-OH), and quaternary ammonium ions (AuNDs-CH3)] regulated macrophage function and antioxidant response through Nrf2-dependent pathway.MethodsAuNDs were prepared and characterized. Intracellular distribution of AuNDs in human macrophages was observed through confocal microscopy. The activity of AuNDs was evaluated using macrophage functions and antioxidant response in the human macrophage cell line THP-1.ResultsAuNDs-NH2 and AuNDs-CH3, but not AuNDs-OH, drove the obvious Nrf2-antioxidant response element pathway in THP-1 cells. Of the three, AuNDs-NH2 considerably increased mRNA levels and antioxidant activities of heme oxygenase 1 and NAD(P)H quinone dehydrogenase 1 in THP-1 cells. IL-6 mRNA and protein expression was mediated through Nrf2 activation in AuNDs-NH2-treated macrophages. Furthermore, Nrf2 activation by AuNDs-NH2 increased the phagocytic ability of THP-1 macrophages.ConclusionAuNDs-NH2 had immunomodulatory activities in macrophages. The findings of the present work suggested that AuNDs have potential effects against chronic inflammatory diseases via the Nrf2 pathway.

Periodic Silver and Gold Nanodot Array Fabrication on Nanosphere Lithography-Based Patterns Using Electroless Deposition

Precision-controlled fabrication of metallic nanostructures is of great interest in applications such as sensing, optoelectronics, and high-capacity storage devices. However, the expense and throughput of the current methods limit the applicability of metal nanodot arrays for many of these applications. This issue is addressed by a method for generating periodic silver (Ag) and gold (Au) nanodot arrays in a straightforward, inexpensive, tunable way. Specifically, regularly placed hexagonal arrays of Ag and Au nanodots were fabricated on Si(111) surfaces via a nanosphere lithography-based approach followed by electroless deposition (ELD). Silicon surfaces with hexagonally packed nanospheres were reacted with octadecyltrichlorosilane (OTS) to form a self-assembled monolayer resist over the substrate, which leads to a hexagonal array of nanopores upon removal of the spheres. Different electroless plating solutions for Ag and Au were introduced onto the nanopore surfaces to selectively deposit metal in the nanopores, resulting in metal nanodots grown only in the nanopores, where the nanospheres were originally in contact with the substrate. Ag and Au nanodot heights can be effectively tuned from 20 to 100 nm by varying the plating time and the composition of the plating solution. Atomic force microscopy (AFM) was used to characterize the height and diameter of the nanopore and nanodot arrays along with energy-dispersive X-ray spectroscopy (EDS) to characterize the elemental composition distribution on the surface. This method provides control over the distance between nanodots and their size at the nanoscale with high reproducibility.

Improved Performance of Si Nanowire Lithium Ion Battery Anodes By Au Catalyst Nanodot Formation on TiN.

While silicon (Si) is considered to be an excellent candidate for next-generation lithium ion battery (LIB) anodes due to its abundance and high gravimetric capacity, Si suffers from large volume expansion as a result of lithiation. Nanowires (NWs) allow for radial expansion and strain release. Due to this volume expansion, the formation of bulk-like Si structures during the NWs growth process significantly degrades battery performance. Here we report suppression of bulk-like Si formation by interfacial energy contrast between the NWs nucleation catalysts (spontaneously formed gold (Au) nanodots) and titanium nitride (TiN) films. The TiN film promoted a narrow distribution of Si NWs’ diameters and a direct electrical connection to the stainless steel current collector. The characteristics of the solid electrolyte interphase and lithiation/charge transfer mechanisms in Si NWs were also investigated using electrochemical impedance spectroscopy (EIS). The EIS data suggest that the impedance to lithium diffusion within the NWs is approximately 40 % smaller in the NWs grown on TiN than the NWs grown directly on stainless steel. LIB anodes fabricated with the Au-catalyzed Si NWs on TiN films displayed enhanced specific gravimetric capacities (>30 %) under diverse charge/discharge rates and significantly improved capacity retention over 500 cycles.

Tailoring a novel Au nanodot arrays on graphene substrate for a highly active Surface-Enhanced Raman Scattering (SERS)

In this work, gold nanodots (Au NDs) were arrayed on the thin graphene (GR) layer, prepared by chemical vapor deposition, by focused ion beam technique. Following, GR/Au NDs substrates was evaluated of Surface-Enhanced Raman Scattering (SERS) by using rhodamine 6G (R6G) as a molecular probe. As expected, GR/Au NDs significantly enhanced the SERS signals. The limit of detection for R6G was as low as 10−12 M and the Raman enhancement factor was as large as 108 times. GR/Au NDs SERS-active substrate showed a promising technique to enhance the trace detection and quantitative detection of organic contaminants.

Time-resolved temperature-jump measurements and steady-state thermal imaging of nanoscale heat transfer of gold nanostructures on AlGaN:Er3+ thin films.

For a nanostructure sitting on top of an AlGaN:Er3+ thin film, a new thermal imaging technique is presented where dual cameras collect bandpass filtered videos from the H and S bands of Er3+ emission. We combine this thermal imaging technique with our newly developed time-resolved temperature measurement technique which relies on luminescence thermometry using Er3+ emission. This technique collects time-resolved traces from the H and S bands of Er3+ emission. The H and S signal traces are then used to reconstruct the time-resolved temperature transient when a nanostructure is illuminated with a pulsed 532 nm light. Two different types of samples are interrogated with these techniques (drop-casted gold nanosphere cluster and lithographically prepared gold nanodot) on the AlGaN:Er3+ film. Steady-state and time-resolved temperature data are collected when the samples are immersed in air and water. The results of time-resolved temperature-jump measurements from a cluster of gold nanospheres show extremely slow heat transfer when the cluster is immersed in water and nearly 200-fold increase when immersed in air. The low thermal diffusivity for the cluster in water suggests poor thermal contact between the cluster and the thermal bath. The lithographically prepared nanodot has much better adhesion to the AlGaN film, resulting in much higher thermal diffusivity in both air and water. This proof-of-concept demonstration opens a new way to measure the dynamics of the local heat generation and dissipation at the nanoparticle-media interface.

Tailor-engineered plasmonic single-lattices: harnessing localized surface plasmon resonances for visible-NIR light-enhanced photocatalysis

A platform material composed of 2D gold (Au) nanodot plasmonic single-lattices (Au-nD-PSLs) featuring tailor-engineered geometric features for visible-NIR light-driven enhanced photocatalysis is presented.

Cu(II)-Regulated On-Site Assembly of Highly Chemiluminescent Multifunctionalized Carbon Nanotubes for Inorganic Pyrophosphatase Activity Determination.

A novel signal-on chemiluminescence (CL) assay for pyrophosphatase (PPase) activity determination was innovatively developed based on the Cu(II)-regulated on-site assembly of highly chemiluminescent Cu(II), N-(aminobutyl)-N-(ethylisoluminol) (ABEI), gold nanodot, and chitosan multifunctionalized carbon nanotubes (Cu(II)/ABEI-Au/cs-CNTs). First, ABEI-functionalized gold nanodots (ABEI-Au) were assembled on the surface of chitosan-modified carbon nanotubes (cs-CNTs) via the reduction of HAuCl4 with ABEI in a cs-CNT suspension to form ABEI-Au/cs-CNTs. Then, it was found that the catalyst Cu(II) can be selectively, efficiently, and quickly adsorbed onto ABEI-Au/cs-CNTs via the high-affinity interactions between Cu(II) and cs-CNTs to form novel hybrid nanomaterials Cu(II)/ABEI-Au/cs-CNTs. The CL intensity of Cu(II)/ABEI-Au/cs-CNTs was enhanced by about 2 orders of magnitude compared with that of ABEI-Au/cs-CNTs. Furthermore, it was found that in the presence of pyrophosphate ions (PPi), PPi could coordinate with Cu(II) to form a stable PPi-Cu(II) complex and block the assembly of Cu(II)/ABEI-Au/cs-CNTs. After the addition of PPase, PPase could catalyze the hydrolysis of PPi into Pi and release Cu(II) from the PPi-Cu(II) complex. The released free Cu(II) could trigger the on-site assembly of highly chemiluminescent Cu(II)/ABEI-Au/cs-CNTs, resulting in an enhanced CL intensity. The enhanced CL intensity had a good linear relationship with the activity units of PPase ranging from 0.025 to 0.5 U, with a detection limit of 9 mU. The method was employed to monitor the PPase inhibitor efficiently. Cu(II)/ABEI-Au/cs-CNTs with excellent CL may also find more applications in the development of novel CL analytical methods.

Quantifying Cell Confluency by Plasmonic Nanodot Arrays to Achieve Cultivating Consistency.

The determination of cell confluency and subculture timing for cell culture consistency is crucial in the field of cell-based research, but there is no universal standard concerning optimal confluence. In this study, gold nanodot arrays on glass substrates were used as culture substrates, and their spectral shifts of localized surface plasmon resonance (LSPR) were employed to monitor cell growth and quantify cell confluency. Experiments including cell counting, metabolic activity, focal adhesion, and cell cycle were also performed to confirm the cell growth monitoring accuracy of the LSPR signals. The LSPR signal exhibited the same trends like the increase of cell numbers and cell metabolic activity and reached the maximum as the cell growth achieved confluency, suggesting its great capability as an effective indicator to predict suitable subculture timing. The proposed sensing approach is a noninterventional, nondestructive, real-time, and useful tool to help biologists quantify the optimal subculture timing, achieve cell culture consistency, and obtain reproducible experimental results efficiently.

Novel design of NIR-triggered plasmonic nanodots capped mesoporous silica nanoparticles loaded with natural capsaicin to inhibition of metastasis of human papillary thyroid carcinoma B-CPAP cells in thyroid cancer chemo-photothermal therapy

In the search for developing a biomedicine based nanomaterial for therapeutic applications, here we described a new benign development of Photo-triggered Gold nanodots capped mesoporous silica nanoparticles Au@MSNs loaded with capsaicin (Cap) for photothermal therapy of cancer cells. Electron microscopic techniques (SEM and TEM) studies depict the anisotropic shape of Cap-Au@MSNs with mean size ≈110 nm. The successful amine functionalization and covalent interaction of Au nanodots on the mesoporous silica surface were confirmed from the results of FTIR, XPS and UV–vis spectral analyses, which directly indicates the composition of synthesized mesoporous silica surface. Additionally, Dynamic Light Scattering (DLS) revealed that synthesized cap-AuMSNs were stable with highly negatively charged. Cap-AuMSNs exhibited extraordinary in vitro antitumor activity against the tested twp thyroid cancer cell lines (i.e., FTC-133 and B-CPAP). 3-(4, 5-Dimethyl-2-thiazolyl)-2, 5-diphenyl-2H tetrazolium bromide (MTT) assay determined that capsaicin and Cap-AuMSNs conferred strong cytotoxicity against the FTC-133 and B-CPAP cell lines. Further, evaluation of the mechanism showed that anticancer activity was achieved by inducing apoptosis in thyroid cancer cells. In addition, we found that such compounds exhibited promising antimetastatic activity and reduced the invasiveness of cancer cells. Hence, we suggesting that these Cap-Au@MSNs can be used as promising candidates for cancer therapy and deserve further investigation.

Hierarchical Cu@CuxO nanowires arrays-coated gold nanodots as a highly sensitive self-supported electrocatalyst for L-cysteine oxidation

The sensitivity, selectivity, and stability of an electrochemical sensor for detecting small biomolecules can be significantly upgraded through properly controlling the morphology and chemical structure of electrocatalyst. Herein, we fabricated a unique hierarchical nanostructure based on Cu@CuxO nanowires (NWs) array uniformly depositing with a layer of gold nanoparticles (2–3 nm) through a simple electroless deposition process. The Au–Cu@CuxO NWs hybrid was successfully applied as a novel binder-free self-supported biosensor towards L-cysteine detection with low limit of detection (1.25 μM), wide linear detection range (1.25 μM–1.94 mM), long-term stability (four weeks), and excellent selectivity. In addition, the hybrid-based sensor accurately detected L-cysteine in real samples. It was found that the obtained nanostructure with the formation of strong interaction between Au and Cu phase produces synergistic effects, which improve exposed electroactive site number, accelerate charge transfer rate, and increase surface area, thereby boosting the sensing performance. The results open a potential way to develop electrochemical sensor for efficiently detecting not only L-cysteine but also other small molecules with high sensitivity, accuracy, stability, and cost-effectiveness in health care and disease diagnosis.

Effect of Gold Nanospheres and Nanodots on the Performance of PEDOT:PSS Solar Cells.

Gold nanospheres were synthesized using a modified Turkevich method (d = 14±4 nm, λmax = 531 nm), while gold nanodots made of spheres (5±2 nm) and non-spherical nanodots (aspect ratio of 1.7±0.4) were synthesized using a modified seed mediated method. The spherical gold nanodots exhibited a transverse excitation mode at 525 nm while the non-spherical gold nanodots showed an additional longitudinal excitation mode observed in the UV-vis spectrum at 794 nm. The gold nanodots also exhibited a surface enhanced Raman effect which significantly influenced the electronic properties of the photovoltaic device. The incorporation of Au nanospheres in a PEDOT:PSS hole transport layer increased the photovoltaic device efficiency by 51%. This was attributed to a decrease in the series resistance which improved the hole transport pathways in the PEDOT:PSS and enhanced the current density of the photovoltaic device. In contrast, incorporation of spherical and non-spherical gold nanodots into the PEDOT:PSS hole transport layer resulted in a decrease in current density and a consequent decrease in efficiency. This can be attributed to the electron-hole recombination and accumulation of space charges by the non-spherical gold nanodots in PEDOT:PSS resulting in an increased series resistance and leakage currents and hence a reduced device performance. Thus, the morphological, structural and opto-electrical properties of the gold nanospheres and nanodots influenced the device performance of the PEDOT:PSS solar cells.

Length-controlled and selective growth of individual indium nitride nanowires by localized laser heating

Length-controlled indium nitride (InN) nanowires are grown by localized laser-assisted metal organic vapor phase epitaxy. Laser irradiation results in spatially confined, rapid heating that enables precise nucleation control and subsequent nanowire growth. This localization of the laser-driven growth can realize on-demand and site-selective direct synthesis of length-controlled nanowires on catalytic gold nanodots. The length of the InN nanowires is controlled by the laser irradiation time at a fixed power. Energy dispersive X-ray, Raman and photoluminescence spectroscopic analyzes respectively characterize the elemental composition, crystallinity, and emission properties of as-grown InN nanowires.

Targeted and imaging-guided chemo-photothermal ablation achieved by combining upconversion nanoparticles and protein-capped gold nanodots

For precise targeting therapy, nanocarriers are typically employed to realize tumor-guided delivery of chemotherapeutic drugs, which should ideally kill cancer cell without side effect under controlled release. Besides, as the temperature is fatal for photothermal therapy (PTT), enhancing photothermal conversion efficiency is essential for improving PTT efficacy. Moreover, as PTT is a localized therapy technique, maintaining high penetration depth and simultaneously achieving multimodal imaging during theranostics are conducive to clinical application. Aiming at resolving these plaguing challenges, here we developed a novel anti-tumor platform by combining upconversion nanoparticles with protein-capped gold nanodots through a facile route, following by loading chemotherapeutic drug (doxorubicin, DOX) and conjugating targeting agent (folic acid, FA). Such nanoplatform with luminescence resonance energy transfer (LRET) effect showed enhanced PTT efficacy under near-infrared (NIR) laser irradiation, and FA conjugation is capable of further targeting cancer cells, namely the focus location in vivo. Meanwhile, the nanocarrier with pH-sensitive DOX release ability would contribute to intensive release responding to acidic tumor microenvironment assisted by NIR light excitation induced heat effect, further improving in vivo anti-tumor efficiency. Additionally, by combining our upconversion/Au nanohybrid with multimodal imaging, direct cancer cell killing responses could be obtained at a deeper penetration depth, promising for completely inhibiting tumor proliferation.

Modification of block copolymer lithography masks by O2/Ar plasma treatment: insights from lift-off experiments, nanopore etching and free membranes

Block copolymer lithography allows for the large-area patterning of surfaces with self-assembled nanoscale features. The created nanostructured polymer films can be applied as masks in common lithography processing steps, such as lift-off and etching for pattern replication and transfer. In this work, we discuss an approach to improve the pattern replication efficiency by modification of the polymer mask prior to lithographical use by means of an O2/Ar plasma treatment. We present a much better quality of pattern replication without loss of features, along with a precise tunability of feature sizes, that can be achieved by short mask treatment. We point out a correlation between nanopore position within the ordered arrays, expressed by its coordination number, the nanopore shape and the replication efficiency. Our experimental strategy to explain these correlations combines the indirect investigation of patterns replicated from the modified polymer masks and direct investigation of the mask top and bottom. Pattern replication is performed either in the form of gold nanodot arrays created via lift-off or nanopores transferred into a SiO2 substrate by reactive ion etching. The direct analysis of free polymer membranes released from the substrate reveals the nanopore shape at the mask top and bottom surfaces.

Morphology-Controlled Versatile One-Pot Synthesis of Hydrophobic Gold Nanodots, Nanobars, Nanorods, and Nanowires and Their Applications in Surface-Enhanced Raman Spectroscopy

Many previously reported syntheses of gold nanoparticles required lengthy reaction times, complicated operations, high temperatures, or multi-step manipulations. In this work, a morphology-controlled versatile one-pot synthesis of hydrophobic gold nanodots, nanobars, nanorods, and nanowires has been developed. A series of gold nanomaterials ranging from round nanodots, short nanobars, and long nanorods to ultrathin and ultralong nanowires (diameter <2 nm, length >2 μm) have been readily prepared by simply adjusting the feeding ratio of chloroauric acid to oleylamine, oleic acid, and triphenylsilane. The silk-like ultralong and ultrathin nanowires were found to have a single crystalline structure and may have significant potential applications in microelectronics and biosensors. Large sizes of gold spherical nanoparticles were obtained from gold nanodots via a seed-mediated growth approach. These nanoparticles and ultralong nanowires showed excellent surface-enhanced Raman scattering (SERS) activity in organic solvents and, therefore, were employed as efficient organic-soluble SERS substrates for the detection of hydrophobic food toxicants, such as 3,4-benzopyrene, and carcinogens, such as benzidine.

Pnipam-covered gold nanodots for reversible adsorption of biomolecules

Thermoresponsive polymer poly(N-isopropylacrylamide) (Pnipam) can undergo a phase transition from a hydrophilic, water-swollen state to a hydrophobic, collapsed state when heated above its lower critical solution temperature, around 32°C in water. A temperature-induced change in the hydration of Pnipam can render its surface adhesive or non-adhesive to biomolecules. The author thus exploited a hybrid plasmonic nanostructure including a lithographic gold nanodots array covered with Pnipam brushes for reversible adsorption of protein molecules. Microscopic and spectroscopic analysis – e.g. scanning electron microscope, force microscope and far-field extinction microspectroscopy – will be carried on prepared hybrid nanomaterial to characterize the morphology and the optical properties. This thermoresponsive hybrid nanostructure was demonstrated to be able to switch efficiently the adsorption/desorption of bovine serum albumin proteins, by convenient temperature stimuli. This work could provide an important step toward the use of thermosensitive plasmonic structures in biomedical and biological applications such as enzyme immobilization, cell sorting, protein adsorption and purification.