Gallium Nanoparticles Research Articles

Self-assembly of highly ordered plasmonic gallium nanoparticles driven by nanopatterning

Ordered porous anodic alumina has become a popular template for the nanopatterning of different materials due to its ease for manufacturing. However, an aluminium nanopatterned template obtained after removing the alumina has not been widely used despite it maintains its hexagonal periodicity. In this work, we use that nanopatterned aluminium to deposit gallium nanoparticles (NPs) by thermal evaporation, resulting in highly ordered arrays of spherical-like NPs. The size and shape of the NPs are investigated by scanning electron microscopy in order to best match the template pattern. Furthermore, the improvement of the plasmonic properties of the NPs is confirmed by spectroscopic ellipsometry compared to the ones deposited on silicon substrates. Reported results show that the plasmonic intensity is increased, as well as the full width at half maximum reducing. This effect could have a direct impact on the sensing applications of these NPs.

Size-selective breaking of the core–shell structure of gallium nanoparticles

Core–shell gallium nanoparticles (Ga NPs) have recently been proposed as an ultraviolet plasmonic material for different applications but only at room temperature. Here, the thermal stability as a function of the size of the NPs is reported over a wide range of temperatures. We analyze the chemical and structural properties of the oxide shell by x-ray photoelectron spectroscopy and atomic force microscopy. We demonstrate the inverse dependence of the shell breaking temperature with the size of the NPs. Spectroscopic ellipsometry is used for tracking the rupture and its mechanism is systematically investigated by scanning electron microscopy, grazing incidence x-ray diffraction and cathodoluminescence. Taking advantage of the thermal stability of the NPs, we perform complete oxidations that lead to homogenous gallium oxide NPs. Thus, this study set the physical limits of Ga NPs to last at high temperatures, and opens up the possibility to achieve totally oxidized NPs while keeping their sphericity.

Anticancer redox activity of gallium nanoparticles accompanied with low dose of gamma radiation in female mice.

Guided treatments with nanoparticles and radiotherapy are a new approach in cancer therapy. This study evaluated the beneficial antitumor effects of γ-radiation together with gallium nanoparticles against solid Ehrlich carcinoma in female mice. Gallium nanoparticles were biologically synthesized using Lactobacillus helveticus cells. Transmission electron microscopy showed gallium nanoparticles with size range of 8-20 nm. In vitro study of gallium nanoparticles on MCF-7 revealed IC50 of 8.0 μg. Gallium nanoparticles (0.1 mg/kg body weight) were injected intraperitoneally daily on the seventh day of Ehrlich carcinoma cells inoculation. Whole-body γ-radiation was carried out at a single dose of 0.25 Gy on eighth day after tumor inoculation. Biochemical analysis showed that solid Ehrlich carcinoma induced a significant increase in alanine aminotransferase activity and creatinine level in serum, calcium, and iron concentrations in liver tissue compared to normal control. Treatment of Ehrlich carcinoma-bearing mice with gallium nanoparticles and/or low dose of γ-radiation exposure significantly reduced tumor volume, decreased alanine aminotransferase and creatinine levels in serum, increased lipid peroxidation, and decreased glutathione content as well as calcium and iron concentrations in liver and tumor tissues with intense DNA fragmentation accompanied compared to untreated tumor cells. Moreover, mitochondria in the treated groups displayed a significant increase in Na+/K+-ATPase, complexes II and III with significant reduction in CYP450 gene expression, which may indicate a synergistic effect of gallium nanoparticles and/or low dose of γ-radiation combination against Ehrlich carcinoma injury, and this results were well appreciated with the histopathological findings in the tumor tissue. We conclude that combined treatment of gallium nanoparticles and low dose of gamma-radiation resulted in suppressive induction of cytotoxic effects on cancer cells.

In Vitro Efficacy of Free and Nanoparticle Formulations of Gallium(III) meso-Tetraphenylporphyrine against Mycobacterium avium and Mycobacterium abscessus and Gallium Biodistribution in Mice.

The nontuberculous mycobacterial (NTM) pathogens, M. avium complex (MAC) and M. abscessus, can result in severe pulmonary infections. Current antibiotics confront significant challenges for treatment of these NTM infections due to emerging multidrug-resistance. Thus, development of new antibiotics targeted against these agents is needed. We examined the inhibitory activities of Ga(NO3)3, GaCl3, gallium meso-tetraphenylporphyrine (GaTP), and gallium nanoparticles (GaNP) against intra- and extracellular M. avium and M. abscessus. GaTP, an analogue of natural heme, inhibited growth of both M. avium and M. abscessus with MICs in Fe-free 7H9 media of 0.5 and 2 μg/mL, respectively. GaTP was more active than Ga(NO3)3 and GaCl3. Ga(NO3)3 and GaCl3 were not as active in Fe-rich media compared to Fe-free media. However, GaTP was much less impacted by exogenous Fe, with MICs against M. avium and M. abscessus of 2 and 4 μg/mL, respectively, in 7H9 OADC media (Fe rich). Confocal microscopy showed that GaNP penetrates the M. avium cell wall. As assessed by determining colony forming units, GaNP inhibited the growth of NTM growing in THP-1 macrophages up to 15 days after drug-loading of the cells, confirming a prolonged growth inhibitory activity of the GaNP. Biodistribution studies of GaNP conducted in mice showed that intraperitoneal injection is more effective than intramuscular injection in delivering Ga(III) into lung tissue. GaTP exhibits potential as a lead compound for development of anti-NTM agents that target heme-bound iron uptake mechanisms by mycobacteria and inhibit growth by disrupting mycobacterial iron acquisition/utilization.

Plasmonics in the Ultraviolet with Aluminum, Gallium, Magnesium and Rhodium

Ultraviolet plasmonics (UV) has become an active topic of research due to the new challenges arising in fields such as biosensing, chemistry or spectroscopy. Recent studies have pointed out aluminum, gallium, magnesium and rhodium as promising candidates for plasmonics in the UV range. Aluminum and magnesium present a high oxidation tendency that has a critical effect in their plasmonic performance. Nevertheless, gallium and rhodium have drawn a lot of attention because of their low tendency of oxidation and, at the same time, good plasmonic response in the UV and excellent photocatalytic properties. Here, we present a short overview of the current state of UV plasmonics with the latest findings in the plasmonic response and applications of aluminum, gallium, magnesium and rhodium nanoparticles.

Tunable plasmonic resonance of gallium nanoparticles by thermal oxidation at low temperatures

The effect of the oxidation of gallium nanoparticles (Ga NPs) on their plasmonic properties is investigated. Discrete dipole approximation has been used to study the wavelength of the out-of-plane localized surface plasmon resonance in hemispherical Ga NPs, deposited on silicon substrates, with oxide shell (Ga2O3) of different thickness. Thermal oxidation treatments, varying temperature and time, were carried out in order to increase experimentally the Ga2O3 shell thickness in the NPs. The optical, structural and chemical properties of the oxidized NPs have been studied by spectroscopic ellipsometry, scanning electron microscopy, grazing incidence x-ray diffraction and x-ray photoelectron spectroscopy. A clear redshift of the peak wavelength is observed, barely affecting the intensity of the plasmon resonance. A controllable increase of the Ga2O3 thickness as a consequence of the thermal annealing is achieved. In addition, simulations together with ellipsometry results have been used to determine the oxidation rate, whose kinetics is governed by a logarithmic dependence. These results support the tunable properties of the plasmon resonance wavelength in Ga NPs by thermal oxidation at low temperatures without significant reduction of the plasmon resonance intensity.

High Ultraviolet Absorption in Colloidal Gallium Nanoparticles Prepared from Thermal Evaporation.

New methods for the production of colloidal Ga nanoparticles (GaNPs) are introduced based on the evaporation of gallium on expendable aluminum zinc oxide (AZO) layer. The nanoparticles can be prepared in aqueous or organic solvents such as tetrahydrofuran in order to be used in different sensing applications. The particles had a quasi mono-modal distribution with diameters ranging from 10 nm to 80 nm, and their aggregation status depended on the solvent nature. Compared to common chemical synthesis, our method assures higher yield with the possibility of tailoring particles size by adjusting the deposition time. The GaNPs have been studied by spectrophotometry to obtain the absorption spectra. The colloidal solutions exhibit strong plasmonic absorption in the ultra violet (UV) region around 280 nm, whose width and intensity mainly depend on the nanoparticles dimensions and their aggregation state. With regard to the colloidal GaNPs flocculate behavior, the water solvent case has been investigated for different pH values, showing UV-visible absorption because of the formation of NPs clusters. Using discrete dipole approximation (DDA) method simulations, a close connection between the UV absorption and NPs with a diameter smaller than ~40 nm was observed.

Gallium nanoparticles facilitate phagosome maturation and inhibit growth of virulent Mycobacterium tuberculosis in macrophages.

New treatments and novel drugs are required to counter the growing problem of drug-resistant strains of Mycobacterium tuberculosis (M.tb). Our approach against drug resistant M.tb, as well as other intracellular pathogens, is by targeted drug delivery using nanoformulations of drugs already in use, as well as drugs in development. Among the latter are gallium (III) (Ga)-based compounds. In the current work, six different types of Ga and rifampin nanoparticles were prepared in such a way as to enhance targeting of M.tb infected-macrophages. They were then tested for their ability to inhibit growth of a fully pathogenic strain (H37Rv) or a non-pathogenic strain (H37Ra) of M.tb. Encapsulating Ga in folate- or mannose-conjugated block copolymers provided sustained Ga release for 15 days and significantly inhibited M.tb growth in human monocyte-derived macrophages. Nanoformulations with dendrimers encapsulating Ga or rifampin also showed promising anti-tuberculous activity. The nanoparticles co-localized with M.tb containing phagosomes, as measured by detection of mature cathepsin D (34 kDa, lysosomal hydrogenase). They also promoted maturation of the phagosome, which would be expected to increase macrophage-mediated killing of the organism. Delivery of Ga or rifampin in the form of nanoparticles to macrophages offers a promising approach for the development of new therapeutic anti-tuberculous drugs.

Ga(III) Nanoparticles Inhibit Growth of both Mycobacterium tuberculosis and HIV and Release of Interleukin-6 (IL-6) and IL-8 in Coinfected Macrophages.

ABSTRACTTreatment of individuals coinfected with human immunodeficiency virus (HIV) type 1 and Mycobacterium tuberculosis is challenging due to the prolonged treatment requirements, drug toxicity, and emergence of drug resistance. Mononuclear phagocytes (MP; macrophages) are one of the natural reservoirs for both HIV and M. tuberculosis. Here, the treatment of HIV and M. tuberculosis coinfection was studied by preloading human macrophages with MP-targeted gallium (Ga) nanoparticles to limit subsequent simultaneous infection with both HIV and M. tuberculosis. Ga nanoparticles provided sustained drug release for 15 days and significantly inhibited the replication of both HIV and M. tuberculosis. Addition of Ga nanoparticles to MP already infected with M. tuberculosis or HIV resulted in a significant decrease in the magnitude of these infections, but the magnitude was less than that achieved with nanoparticle preloading of the MP. In addition, macrophages that were coinfected with HIV and M. tuberculosis and that were loaded with Ga nanoparticles reduced the levels of interleukin-6 (IL-6) and IL-8 secretion for up to 15 days after drug loading. Ga nanoparticles also reduced the levels of IL-6 and IL-8 secretion by ionomycin- and lipopolysaccharide-induced macrophages, likely by modulating the IκB kinase-β/NF-κB pathway. Delivery of Ga nanoparticles to macrophages is a potent long-acting approach for suppressing HIV and M. tuberculosis coinfection of macrophages in vitro and sets the stage for the development of new approaches to the treatment of these important infections.

Templated assembly of metal nanoparticle films on polymer substrates

We report on directed self-assembly of ordered, vapor-deposited gallium nanoparticles on surface-relief-structured polymer substrates. Grating templates impose periodic order in one dimension, most effectively when the grating half-period is of the order of the mean unperturbed center-to-center particle spacing for a given mass-thickness of Ga. Self-organized order also emerges in the perpendicular direction as a consequence of the liquid-phase particles' nucleation, growth, and coalescence on the ridges of the grating pattern in relative isolation from the adjacent slots, and vice versa.

Targeted Delivery of Glucan Particle Encapsulated Gallium Nanoparticles Inhibits HIV Growth in Human Macrophages.

Glucan particles (GPs) are hollow, porous 3–5 μm microspheres derived from the cell walls of Baker's yeast (Saccharomyces cerevisiae). The 1,3-β-glucan outer shell provides for receptor-mediated uptake by phagocytic cells expressing β-glucan receptors. GPs have been used for macrophage-targeted delivery of a wide range of payloads (DNA, siRNA, protein, small molecules, and nanoparticles) encapsulated inside the hollow GPs or bound to the surface of chemically derivatized GPs. Gallium nanoparticles have been proposed as an inhibitory agent against HIV infection. Here, macrophage targeting of gallium using GPs provides for more efficient delivery of gallium and inhibition of HIV infection in macrophages compared to free gallium nanoparticles.

Biocompatible nano-gallium/hydroxyapatite nanocomposite with antimicrobial activity.

Intensive research in the area of medical nanotechnology, especially to cope with the bacterial resistance against conventional antibiotics, has shown strong antimicrobial action of metallic and metal-oxide nanomaterials towards a wide variety of bacteria. However, the important remaining problem is that nanomaterials with highest antibacterial activity generally express also a high level of cytotoxicity for mammalian cells. Here we present gallium nanoparticles as a new solution to this problem. We developed a nanocomposite from bioactive hydroxyapatite nanorods (84 wt %) and antibacterial nanospheres of elemental gallium (16 wt %) with mode diameter of 22 ± 11 nm. In direct comparison, such nanocomposite with gallium nanoparticles exhibited better antibacterial properties against Pseudomonas aeruginosa and lower in-vitro cytotoxicity for human lung fibroblasts IMR-90 and mouse fibroblasts L929 (efficient antibacterial action and low toxicity from 0.1 to 1 g/L) than the nanocomposite of hydroxyapatite and silver nanoparticles (efficient antibacterial action and low toxicity from 0.2 to 0.25 g/L). This is the first report of a biomaterial composite with gallium nanoparticles. The observed strong antibacterial properties and low cytotoxicity make the investigated material promising for the prevention of implantation-induced infections that are frequently caused by P. aeruginosa.

Stay weird, gallium

Gallium has doubled down on its status as a quirky element by showing that it can support both liquid and solid phases simultaneously over a wide range of temperatures (Nat. Mater. 2016, DOI: 10.1038/nmat4705). Bulk gallium liquefies at 30 °C, the temperature of a warm summer’s day and a melting point much lower than most metals. Scientists led by April S. Brown of Duke University have discovered that gallium nanoparticles exhibit another thermal anomaly, existing as liquid blobs with solid cores from about –90 °C to 525 °C when the particles rest on rigid, inert sapphire substrates. Within the nanoparticle, the pressure is sufficiently high to crystallize the gallium near the core. Meanwhile, a balance between surface and interfacial forces creates an equilibrium that favors a liquefied shell. Although this balance stands up to large changes in temperature, it is upset by changing the chemical and mechanical properties of the

Thermally stable coexistence of liquid and solid phases in gallium nanoparticles.

Gallium (Ga), a group III metal, is of fundamental interest due to its polymorphism and unusual phase transition behaviours. New solid phases have been observed when Ga is confined at the nanoscale. Herein, we demonstrate the stable coexistence, from 180 K to 800 K, of the unexpected solid γ-phase core and a liquid shell in substrate-supported Ga nanoparticles. We show that the support plays a fundamental role in determining Ga nanoparticle phases, with the driving forces for the nucleation of the γ-phase being the Laplace pressure in the nanoparticles and the epitaxial relationship of this phase to the substrate. We exploit the change in the amplitude of the evolving surface plasmon resonance of Ga nanoparticle ensembles during synthesis to reveal in real time the solid core formation in the liquid Ga nanoparticle. Finally, we provide a general framework for understanding how nanoscale confinement, interfacial and surface energies, and crystalline relationships to the substrate enable and stabilize the coexistence of unexpected phases.

Reversible Size Control of Liquid-Metal Nanoparticles under Ultrasonication.

This paper describes the reversible control of the size of liquid-metal nanoparticles under ultrasonication. Gallium was utilized as a liquid metal, which has a melting point of 29.8 °C. Investigating the effects of ultrasonication (power, time, and temperature) on the formation of gallium nanoparticles revealed that the process is similar to the formation of oil in water (O/W) or water in oil (W/O) emulsions, as the temperature significantly affects the size of the gallium nanoparticles (GaNPs). Under ultrasonication, the balance between the break-up and coalescence of the GaNPs can be adjusted by changing the temperature or adding acid through modulating the natural surface oxide layer (which can be removed with acid) and the stabilizing effect of the surfactant dodecanethiol. Coalescence was predominant at higher temperatures, whereas particle break-up was found to be predominant at lower temperatures. Furthermore, the change in size was accompanied by a shift in the plasmonic absorption of the GaNPs in the UV region.

Reversible Size Control of Liquid‐Metal Nanoparticles under Ultrasonication

AbstractThis paper describes the reversible control of the size of liquid‐metal nanoparticles under ultrasonication. Gallium was utilized as a liquid metal, which has a melting point of 29.8 °C. Investigating the effects of ultrasonication (power, time, and temperature) on the formation of gallium nanoparticles revealed that the process is similar to the formation of oil in water (O/W) or water in oil (W/O) emulsions, as the temperature significantly affects the size of the gallium nanoparticles (GaNPs). Under ultrasonication, the balance between the break‐up and coalescence of the GaNPs can be adjusted by changing the temperature or adding acid through modulating the natural surface oxide layer (which can be removed with acid) and the stabilizing effect of the surfactant dodecanethiol. Coalescence was predominant at higher temperatures, whereas particle break‐up was found to be predominant at lower temperatures. Furthermore, the change in size was accompanied by a shift in the plasmonic absorption of the GaNPs in the UV region.

Immunosensing platform based on gallium nanoparticle arrays on silicon substrates.

Gallium nanoparticles (GaNPs) of different sizes are deposited on Si(100) substrates by thermal evaporation. Through ellipsometric analysis, it is possible to investigate the plasmonic effects in the GaNPs and exploit them to develop biosensors. The excitation of the resonant modes for certain incidence angles leads to negative values of the imaginary part of the pseudodielectric function (<εi>) obtained in ellipsometry. Furthermore, there is an abrupt sign change when the difference between the phase shifts of p- and s-polarization components reaches 180° at an energy of around 3.15 eV. At that energy, reversal of the polarization handedness (RPH) occurs for an elliptically-polarized input beam. The energy of the RPH condition reduces as the evaporation time increases. The slope of <εi> at the RPH condition is extremely sensitive to changes in the surrounding medium of the NP surface and prompts the use of the GaNP/Si system as sensor platform. Fourier transformed infrared spectroscopy (FTIR) is used before and after functionalization with 3,3'-dithiodipropionic acid di(N-succinimidyl ester) and a glutathione-specific antibody to confirm the chemical modification of the sample surface. The developed immunosensor is exposed to different concentrations of glutathione (GSH) showing a linear relationship between the slope of the pseudodielectric function at the RPH condition and the GSH concentration. The immunosensor shows a limit of detection of 10nM enabling its use for the detection of low GSH levels in different medical conditions.

Prolonged-acting, multi-targeting gallium nanoparticles potently inhibit growth of both HIV and mycobacteria in co-infected human macrophages.

Human immunodeficiency virus (HIV) infection and Mycobacterium tuberculosis (TB) are responsible for two of the major global human infectious diseases that result in significant morbidity, mortality and socioeconomic impact. Furthermore, severity and disease prevention of both infections is enhanced by co-infection. Parallel limitations also exist in access to effective drug therapy and the emergence of resistance. Furthermore, drug-drug interactions have proven problematic during treatment of co-incident HIV and TB infections. Thus, improvements in drug access and simplified treatment regimens are needed immediately. One of the key host cells infected by both HIV and TB is the mononuclear phagocyte (MP; monocyte, macrophage and dendritic cell). Therefore, we hypothesized that one way this can be achieved is through drug-targeting by a nanoformulated drug that ideally would be active against both HIV and TB. Accordingly, we validated macrophage targeted long acting (sustained drug release) gallium (Ga) nanoformulation against HIV-mycobacterium co-infection. The multi-targeted Ga nanoparticle agent inhibited growth of both HIV and TB in the macrophage. The Ga nanoparticles reduced the growth of mycobacterium and HIV for up to 15 days following single drug loading. These results provide a potential new approach to treat HIV-TB co-infection that could eventually lead to improved clinical outcomes.

Gallium plasmonics: deep subwavelength spectroscopic imaging of single and interacting gallium nanoparticles.

Gallium has recently been demonstrated as a phase-change plasmonic material offering UV tunability, facile synthesis, and a remarkable stability due to its thin, self-terminating native oxide. However, the dense irregular nanoparticle (NP) ensembles fabricated by molecular-beam epitaxy make optical measurements of individual particles challenging. Here we employ hyperspectral cathodoluminescence (CL) microscopy to characterize the response of single Ga NPs of various sizes within an irregular ensemble by spatially and spectrally resolving both in-plane and out-of-plane plasmonic modes. These modes, which include hybridized dipolar and higher-order terms due to phase retardation and substrate interactions, are correlated with finite difference time domain (FDTD) electrodynamics calculations that consider the Ga NP contact angle, substrate, and native Ga/Si surface oxidation. This study experimentally confirms previous theoretical predictions of plasmonic size-tunability in single Ga NPs and demonstrates that the plasmonic modes of interacting Ga nanoparticles can hybridize to produce strong hot spots in the ultraviolet. The controlled, robust UV plasmonic resonances of gallium nanoparticles are applicable to energy- and phase-specific applications such as optical memory, environmental remediation, and simultaneous fluorescence and surface-enhanced Raman spectroscopies.

Spectropolarimetric Properties of a Gallium Nanoparticle Layer on a Sapphire Substrate

Gallium nanoparticles (Ga NPs) are currently the subject of vigorous research as possible substrates in surface-enhanced Raman scattering (SERS) experiments in the ultraviolet spectral domain. Verification of any comprehensive model of the interaction of electromagnetic radiation with Ga NPs requires that complete polarimetric measurements be made. These spectropolarimetric properties can be obtained using a Mueller matrix spectropolarimeter (MMSP). The position of localized surface plasmon resonances (LSPRs) and spectral depolarization data of Ga NPs in the 300 to 1100 nm spectral region are presented. Spectral depolarization data may be of value in creating a better understanding of how light couples to individual nanoparticles, as well as the role played by interparticle coupling and the connection to phenomena such as SERS.