Liquid Nanoparticles Research Articles

The mechanism of laser-assisted generation of aluminum nanoparticles, their wettability and nonlinearity properties

Aluminum nanoparticles (NPs) demonstrate a variety of applications. Here we study the laser-assisted generation of Al based NPs in liquids and in vacuum, and their ability to change the wettability and nonlinear optical properties of the surfaces, suspensions and plasmas. By means of Molecular Dynamics method we analyzed the formation process of aluminum NPs during the ablation of bulk targets. The numerical simulations allowed identifying the main mechanisms of NPs formation in liquid media and the existence of the optimal laser irradiation parameters for producing Al NPs of the desired size and morphology. We experimentally analyze the variations of the wettability of glass surfaces under the deposition of the NPs produced during laser ablation of aluminum in water and in vacuum. In the former case we demonstrate a significant decrease of contact angle leading to superhydrophilic properties of deposited NPs from water suspension. Meanwhile, the NP-contained films deposited on the glass substrates during ablation of Al in vacuum demonstrated the superhydrophobic features. The low-order nonlinear optical properties of Al NPs produced during ablation of the bulk metal by nano-, pico-, and femtosecond pulses are determined. The coefficients of nonlinear refraction and absorption of Al NPs using 40 fs pulses at λ = 400 nm were measured to be ~ 10-9 cm2 W−1 and 10-7 cm W−1, respectively. Al NPs allowed generation of 37th harmonic using 40 fs pulses propagating nearby to the ablating aluminum target.

Chelation, formulation, encapsulation, retention, and in vivo biodistribution of hydrophobic nanoparticles labelled with 57Co-porphyrin: Oleylamine ensures stable chelation of cobalt in nanoparticles that accumulate in tumors

Background and motivationWhile small molecules can be used in cancer diagnosis there is a need for imageable diagnostic NanoParticles (NPs) that act as surrogates for the therapeutic NPs. Many NPs are composed of hydrophobic materials so the challenge is to formulate hydrophobic imaging agents. To develop individualized medical treatments based on NP, a first step should be the selection of patients who are likely responders to the treatment as judged by imaging tumor accumulation of NPs. This requires NPs with the same size and structure as the subsequent therapeutic NPs but labelled with a long-lived radionuclide. Cobalt isotopes are good candidates for NP labelling since 55Co has half-life of 17.5 h and positron energy of 570 keV while 57Co (t1/2 271.6 d) is an isotope suited for preclinical single photon emission tomography (SPECT) to visualize biodistribution and pharmacokinetics of NPs. We used the hydrophobic octaethyl porphyrin (OEP) to chelate cobalt and to encapsulate it inside hydrophobic liquid NPs (LNPs). We hypothesized that at least two additional hydrophobic axial ligands (oleylamine, OA) must be provided to the OEP-Co complex in order to encapsulate and retain Co inside LNP. Results1. Cobalt chelation by OEP and OA. The association constant of cobalt to OEP was 2.49 × 105 M−1 and the formation of the hexacoordinate complex OEP-Co-4OA was measured by spectroscopy. 2. NP formulation and characterization: LNPs were prepared by the fast ethanol injection method and were composed of a liquid core (triolein) surrounded by a lipid monolayer (DSPC:Cholesterol:DSPE-PEG2000). The size of the LNPs loaded with the cobalt complex was 40 ± 5 nm, 3. Encapsulation of OEP-Co-OA: The loading capacity of OEP-Co-OA in LNP was 5 mol%. 4. Retention of OEP-57Co-4OA complex in the LNPs: the positive effect of the OA ligands was demonstrated on the stability of the OEP-57Co-4OA complex, providing a half-life for retention in PBS of 170 h (7 days) while in the absence of the axial OA ligands was only 22 h. 5 Biodistribution Study: the in vivo biodistribution of LNP was studied in AR42J pancreatic tumor-bearing mice. The estimated half-life of LNPs in blood was about 7.2 h. Remarkably, the accumulation of LNPs in the tumor was as high as 9.4% ID/g 24 h after injection with a doubling time for tumor accumulation of 3.22 h. The most important result was that the nanoparticles could indeed accumulate in the AR42J tumors up to levels greater than those of other NPs previously measured in the same tumor model, and at about half the values reported for the molecular agent 57Co-DOTATATE. ConclusionsThe additional hydrophobic chelator OA was indeed needed to obtain a stable octahedral OEP-Co-4OA. Cobalt was actually well-retained inside LNP in the OEP-Co-4OA complex. The method described in the present work for the core-labelling of LNPs with cobalt is now ready for labeling of NPs with 55Co, or indeed other hexadentate radionuclides of interest for preclinical in vivo PET-imaging and radio-therapeutics.

Electron Microscopy and X-Ray Diffraction Analysis of Titanium Oxide Nanoparticles Synthesized by Pulsed Laser Ablation in Liquid

A femto-second pulsed laser ablation in liquid (PLAL) procedure for the generation of titanium oxide nanoparticles (NP) is reported with the purpose of understanding morphology and structure of the newly generated NPs. Ablation duration was varied for optimization of NP generation processes between 10 and 90 min. Surface morphology of NPs as well as their size and shape (distribution) were analysed by various complementary electron microscopy techniques, i.e. SEM, TSEM and TEM. The crystalline structure of titanium oxide particles was investigated by XRD and HR-TEM. Concentration of generated titanium oxide NPs in liquid was analysed by ICP-MS. A mix of crystalline (mainly anatase), partly crystalline and amorphous spherical titanium oxide NPs can be reported having a mean size between 10 and 20 nm, which is rather independent of the laser ablation (LA) duration. A second component consisting of irregularly shaped, but crystalline titanium oxide nanostructures is co-generated in the LA water, with more pronounced occurrence at longer LA times. The provenance of this component is assigned to those spherical particles generated in suspension and passing through the converging laser beam, being hence subject to secondary irradiation effects, e. g. fragmentation.

Morphology and structure of TixOy nanoparticles generated by femtosecond laser ablation in water

In this work femto-second pulsed laser ablation in liquid (PLAL) procedure for the generation of titanium oxide nanoparticles (NP) is reported with the purpose of understanding morphology and structure of the newly generated NPs. Ablation duration was varied for optimization of NP generation processes between 10 and 90 min. Surface morphology of NPs as well as their size and shape (distribution) were analysed by various complementary electron microscopy techniques, i.e. SEM, TSEM and TEM. The crystalline structure of titanium oxide particles was investigated by XRD (two instruments operated in different geometries) and HR-TEM. Concentration of generated titanium oxide NPs in liquid was analysed by ICP-MS. A mix of crystalline (mainly anatase), partly crystalline and amorphous spherical titanium oxide NPs can be reported having a mean size between 10 and 20 nm, which is rather independent of the laser ablation (LA) duration. A second component consisting of irregularly shaped, but crystalline titanium oxide nanostructures is co-generated in the LA water, with more pronounced occurrence at longer LA times. The provenance of this component is assigned to those spherical particles generated in suspension and passing through the converging laser beam, being hence subject to secondary irradiation effects, e. g. fragmentation.

Encapsulation and retention of chelated-copper inside hydrophobic nanoparticles: Liquid cored nanoparticles show better retention than a solid core formulation

MotivationIn the field of imaging, 18F-fluorodeoxyglucose (FDG) PET imaging allows evaluation of glucose metabolism and is the most widely used imaging agent clinically for metastatic cancer. While it can certainly detect the metastatic disease, in order to provide a more fully “individualized medicine” strategy of detection and pharmaceutical treatment, what is needed are additional imaging nanoparticles that resemble the subsequently-administered nanoparticle drug delivery system itself. Both of these nanoparticles must also be able to take advantage of what may well be a limited EPR effect in human tumors, which in and of itself still needs to be characterized in the clinic. Administration of FDG, followed by a nanoparticle imaging agent, followed by a therapeutic nanoparticle would constitute such an “individualized medicine strategy”, especially for anti-metastasis approaches. It is here that our endogenous-inspired nanoparticle strategies for imaging and therapeutics are focused on encapsulating and retaining imaging ions such as copper inside novel hydrophobic nanoparticles. In this paper, we describe a new approach to label the core of hydrophobic nanoparticles composed of Glyceryl Trioleate (Triolein) with copper using the hydrophobic chelator Octaethyl porphyrin (OEP). Research plan and methodsThe research plan for this study was to (1) Formulate nanoparticles and control nanoparticle size using a modification of the solvent injection technique, named fast ethanol injection; (2) Chelate copper into the octaethyl porphyrin; (3) Encapsulate OEP-Cu in nanoparticles: the encapsulation efficiency of copper into liquid nanoparticles (LNP), solid nanoparticles (SNP) and phospholipid liposomes (PL) was evaluated by UV–Vis and atomic absorption spectroscopy; (4) Retain the encapsulated OEP-Cu in the liquid or solid cores of the nanoparticles in the presence of a lipid sink. Results(1) The size of the nanoparticles was found to be strongly dependent on the Reynolds number and the initial concentration of components for the fast injection technique. At high Reynolds number (2181), a minimum value for the particle diameter of ∼30nm was measured. (2) Copper was chelated by OEP in a 1:1mol ratio with an association constant of 2.57×105M−1. (3) The diameter of the nanoparticles was not significantly affected by the presence of OEP or OEP-Cu. The percentage of encapsulation of copper to nanoparticles was >95% at low OEP-Cu concentrations. In the absence of OEP, copper was not detected in nanoparticles demonstrating the role of the hydrophobic chelator OEP in the encapsulation of the otherwise water-soluble copper inside lipid nanoparticles. (4) The in vitro retention upon incubation at 37°C over a 48h period in the presence of a lipid sink showed a slow transfer of OEP-Cu into the lipid sink (t1/2=7.7h) for SNP; for PL there was an almost instantaneous transfer of OEP-Cu into the lipid sink (t1/2=0.5h), while for the LNP, all OEP-Cu was retained in the LNP over the full 48h period. ConclusionsThe main conclusion of this study was that a very hydrophilic ion such as Cu2+ can indeed be solubilized and retained in the core of hydrophobic nanoparticles when a hydrophobic molecule (OEP) is used as a chelator. The fast-injection technique was shown to provide a very convenient method to formulate both liquid and solid nanoparticles labeled with Cu (well chelated by OEP), with diameters as small as 30nm, and encapsulation efficiencies higher than 95% when the concentration of OEP-Cu loaded into the nanoparticles was equal to or below 2.5mol%. This is expected to be sufficient for PET-imaging studies.

Nanoparticle Liquids for Surface Modification and Lubrication of MEMS Switch Contacts

Contact failures in microelectromechanical system (MEMS) switches, particularly during hot switching, prevent their widespread use. In this paper, a nanoparticle liquid (NPL) lubricant is synthesized and deposited on MEMS switch contacts as a nanotechnology-based lubricant. NPLs are monolithic hybrid materials comprised of an inorganic nanosized metallic core and an organic low viscosity corona. The NPL used here utilizes either Au or Pt nanoparticles as the core and a mercaptoethanesulfonate ionic liquid as the corona. Performance, reliability, and chemical/physical processes on hot-switched NPL-lubricated contact surfaces were investigated at high (1 mA) and low (10 ) currents using a micro/nanoadhesion apparatus as a MEMS switch simulator with in situ monitoring of contact resistance and adhesion force. This was coupled with ex-situ analyses of the contacts using scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and scanning Auger spectroscopy. NPLs exhibited improved electrical performance and durability (orders of magnitude improvement) as compared to uncoated and self-assembled monolayer-coated switch contacts. Improved performance and reliability results from the following: 1) controlled nanoscale surface roughness that spreads current through multiple nanocontacts; 2) restricted size melting regions and termination of nanowire growth (prevents shorting) during contact opening; 3) enhanced thermal and electrical conductivity that reduces lubricant degradation; and 4) lubricant self-healing (flow to damaged areas) as confirmed with physical and chemical analyses. Based on these results, NPLs show excellent potential as surface modifiers/lubricants for MEMS switch contacts.