Erick S. Vasquez

Janus magnetic nanoparticles with a bicompartmental polymer brush prepared using electrostatic adsorption to facilitate toposelective surface-initiated ATRP.

Utilizing the inherent negative charge of mica surfaces, amine-functionalized magnetic nanoparticles (Fe3O4/NH2) were electrostatically adsorbed onto the mica such that surface-initiated ATRP could be used to grow poly(n-isopropylacrylamide) (PNIPAM) from the exposed hemisphere. By reducing the solution pH, a positive charge generated on the mica was used to release the nanoparticles from the substrate. A second ATRP reaction was carried out to grow poly(methacrylic acid) (PMAA) from the initiated surfaces. As a result, the Fe3O4/NH2 core has a polymer shell with one hemisphere PMAA and the other hemisphere PNIPAM-b-PMAA resulting in the PMAA-Fe3O4-PNIPAM-b-PMAA bicompartmental polymer Janus nanoparticles. Elemental and functional group compositions were confirmed using ATR-FTIR, XPS, and EDS. Imaging with AFM, SEM, and TEM showed the evolution of the Janus nanoparticle morphology. This study demonstrates a facile and innovative scheme involving a noncovalent solid protection technique combined with sequential, surface-confined controlled radical polymerizations for the production of multicomponent nanocomposites.

Bioluminescent magnetic nanoparticles as potential imaging agents for mammalian spermatozoa

BackgroundNanoparticles have emerged as key materials for developing applications in nanomedicine, nanobiotechnology, bioimaging and theranostics. Existing bioimaging technologies include bioluminescent resonance energy transfer-conjugated quantum dots (BRET-QDs). Despite the current use of BRET-QDs for bioimaging, there are strong concerns about QD nanocomposites containing cadmium which exhibits potential cellular toxicity.ResultsIn this study, bioluminescent composites comprised of magnetic nanoparticles and firefly luciferase (Photinus pyralis) are examined as potential light-emitting agents for imaging, detection, and tracking mammalian spermatozoa. Characterization was carried out using infrared spectroscopy, TEM and cryo-TEM imaging, and ζ-potential measurements to demonstrate the successful preparation of these nanocomposites. Binding interactions between the synthesized nanoparticles and spermatozoon were characterized using confocal and atomic/magnetic force microscopy. Bioluminescence imaging and UV–visible-NIR microscopy results showed light emission from sperm samples incubated with the firefly luciferase-modified nanoparticles. Therefore, these newly synthesized luciferase-modified magnetic nanoparticles show promise as substitutes for QD labeling, and can potentially also be used for in vivo manipulation and tracking, as well as MRI techniques.ConclusionsThese preliminary data indicate that luciferase-magnetic nanoparticle composites can potentially be used for spermatozoa detection and imaging. Their magnetic properties add additional functionality to allow for manipulation, sorting, or tracking of cells using magnetic techniques.

Fetuin-A adsorption and stabilization of calcium carbonate nanoparticles in a simulated body fluid

Fetuin-A is a serum glycoprotein identified as a calcification inhibitor, and a key player in bone formation and human metabolic processes. A study on binding mechanisms of Fetuin-A with calcium carbonate nanoparticles in a simulated body fluid (DMEM) environment is presented. Observed interactions between Fetuin-A and the CaCO3 nanoparticles reveal an initial adsorption process, followed by a stabilization stage, and then a solubilization period for the Fetuin-A/CaCO3 complex. FTIR and XPS are used to monitor functional group and elemental composition changes during the initial adsorption process between Fetuin-A and the CaCO3 nanoparticles. Distinctive Fetuin-A/CaCO3 complex structures-also known as mineralo-protein particles-are imaged with TEM and SEM. DLS and UV-Vis methods are used to further characterize the in situ binding mechanisms. Results of this study can guide the design of complex organic-inorganic hybrid materials, improve current drug delivery methods, and provide insight in monitoring and controlling interactions between Fetuin-A and external calcium ions.

Electromagnetic induction by ferrofluid in an oscillating heat pipe

Thermal-to-electrical energy conversion was demonstrated using an oscillating heat pipe (OHP) filled with ferrofluid and equipped with an annular-type solenoid. The OHP was subjected to a 100 °C axial temperature difference allowing the ferrofluid to passively oscillate through the solenoid, thus accomplishing electromagnetic induction. The measured solenoid voltage consisted of aperiodic pulses with dominant frequencies between 2 and 5 Hz and peak-to-peak amplitudes approaching 1 mV. Despite exposure to the thermal and phase change cycling within the OHP, nanoparticle morphologies and magnetic properties of the ferrofluid remained intact. This energy harvesting method allows for combined thermal management and in-situ power generation.

Rheological characterization of mammalian lung mucus

Mammalian lung mucus is a complex fluid that demonstrates non-linear viscoelastic responses, strain-stiffening at low and strain-softening at large strain values, as measured using large amplitude oscillatory shear (LAOS) experiments. The mechanical properties of lung mucus reported here can be linked to high-strain rate physiological processes, such as coughing, and can guide drug delivery development.

Functional holey graphene oxide: a new electrochemically transformed substrate material for dopamine sensing

Increasing active sites through generating holes within the basal plane of graphene sheets is an effective strategy to enhance catalytic performance in various applications such as sensors, electrocatalysis, and electronics. In this study, we report a simple two-step electrochemical approach to convert graphene oxide (GO) into holey graphene oxide (HGO)—graphene sheets with holes ranging from several to tens of nanometers in diameter. The resultant HGO graphene has an order of magnitude more effective surface area than GO, and behaves almost as a reversible electrode system in terms of peak-to-peak seperation value (ΔE) and heterogeneous electron transfer rate constant (k0) towards the Fe(CN)63−/4− redox probe. Characterization of the HGO surface using atomic force microscopy (AFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and cyclic voltammetry confirmed generation of holes on the graphene sheets. β-Cyclodextrin (β-CD) was immobilized on ‘as prepared’ HGO demonstrating an additional advantage from the presence of oxygen-containing functional groups on the resultant HGO surface. The β-CD-HGO nanocomposite was investigated as a potential dopamine (DA) sensor material using amperometric techniques. The linear range for DA detection was 0.1–800 μM (N = 3), sensitivity was 4.4 nA μM−1 cm−2, and the detection limit was 7.6 nM (S/N = 3). In addition to enhanced catalytic performance, HGO can be easily modified with materials such as β-cyclodextrin, as well as nanoparticles, bioactive molecules, and stimuli responsive polymers, providing a promising sensor platform.

Fabricated nanogap-rich plasmonic nanostructures through an optothermal surface bubble in a droplet

A rapid and cost-effective method for the fabrication of nanogap-rich structures is demonstrated in this Letter. The method utilizes the Marangoni convection around an optothermal surface bubble inside a liquid droplet with a nanoliter volume. The liquid droplet containing metallic nanoparticles reduces the sample consumption and confines the liquid flow. The optothermal surface bubble creates a strong convective flow that allows for the rapid deposition of the metallic nanoparticles to form nanogap-rich structures on any substrate under ambient conditions. This method will enable a broad range of applications such as biosensing, environmental analysis, and nonlinear optics.

Energy harvesting via ferrofluidic induction

A series of experiments were conducted to investigate and characterize the concept of ferrofluidic induction - a process for generating electrical power via cyclic oscillation of ferrofluid (iron-based nanofluid) through a solenoid. Experimental parameters include: number of bias magnets, magnet spacing, solenoid core, fluid pulse frequency and ferrofluid-particle diameter. A peristaltic pump was used to cyclically drive two aqueous ferrofluids, consisting of 7-10 nm iron-oxide particles and commercially-available hydroxyl-coated magnetic beads (~800 nm), respectively. The solutions were pulsated at 3, 6, and 10 Hz through 3.2 mm internal diameter Tygon tubing. A 1000 turn copper-wire solenoid was placed around the tube 45 cm away from the pump. The experimental results indicate that the ferrofluid is capable of inducing a maximum electric potential of approximately +/- 20 μV across the solenoid during its cyclic passage. As the frequency of the pulsating flow increased, the ferro-nanoparticle diameter increased, or the bias magnet separation decreased, the induced voltage increased. The type of solenoid core material (copper or plastic) did not have a discernible effect on induction. These results demonstrate the feasibility of ferrofluidic induction and provide insight into its dependence on fluid/flow parameters. Such fluidic/magneto-coupling can be exploited for energy harvesting and/or conversion system design for a variety of applications.

Experimental and numerical investigation of the Silicon particle distribution in electro-spun nano-fibers

The properties of ceramic materials are dependent on crystal sizes and their distribution. These parameters can be controlled using electrospinning of the two-phase mixed system. The preceramic solution consists of silicon nanoparticles and polyacrylonitrile (PAN) polymer mixture. Particle distribution during the electrospinning technique was characterized using transmission electron microscopy and modeled using the finite element method. The experimental and numerical results were in agreement. Large silicon particles were located in the skin and the smaller ones were located at the core. This was illustrated by the migration rate from the core, which was the fastest for large particles and diminished as the particles become smaller in size. The threshold for Stokes number was found to be around 2.2 × 10-4 with a critical particle size of 1.0 × 10-7 m in diameter. The current results are very promising, as it demonstrated a novel way for the fabrication of PAN/Si ceramic nanofibers with a gradient of particle size and properties from the skin to the core.