Spherical and Cubic Nanoparticles: Structure-Property Relationships and Enzymatic Synthesis and Degradation

Defining the influence of the shape of magnetic nanoparticles (MNPs) on their magnetic properties continues to challenge the research community. There exists a small amount of comparative data for MNPs less than 25 nm, but data for larger sizes are sorely lacking. This gap in the available data motivated my pursuit of a comparison of the magnetic properties of larger cubic and spherical Fe3O4 MNPs (>100 nm), leading to a conclusion that such comparisons should consider the degree of crystallinity of the MNPs. For MNP applications involving sensing, geometries other than spherical are preferred, where large contact areas and the resulting stronger binding to the sensor platform should lead to enhanced sensitivity. Therefore, I initially focused my research on the synthesis of cubic magnetic FeCo nanocubes with high saturation magnetization. Finally, to functionalize these nanoparticles for use in sensing, it was necessary to coat them with a thin protective layer while retaining their cubic shape. This goal was accomplished by using a silica coating followed by amine functionalization for FeCo nanocubes. Magnetic biosensing currently employs already-synthesized MNPs and giant magnetoresistive (GMR) sensors. The use of MNP labels in bioassays and diagnostics is attractive because it can overcome concerns associated with optical sensing, which relies on substrate modification to form a product that absorbs, fluoresces, luminesces, or transforms to an insoluble precipitate. The enzyme-mediated synthesis of MNPs is a new concept for magnetic sensing in which the magnetic reporter can be enzymatically synthesized in situ. The development of this project also encouraged the pursuit of a diametrically opposite system in which the magnetic component would lose its magnetism through an enzymatically-mediated reduction process. Both approaches show potential for structuring assays that use a magnetic signal that either appears or disappears in the presence of a specific enzyme. To summarize, my research has focused on two primary goals: (1) the chemical synthesis and functionalization of spherical and cubic MNPs and (2) the enzymatically-mediated synthesis or disappearance of MNPs that can be potentially used in a sensing assay.Chemistry, Department o

Latent fingermark imaging by single-metal deposition of gold nanoparticles and surface enhanced Raman spectroscopy

In forensic science, there is a high demand for a technique that allows the revelation of fingermarks invisible to the naked eye as well as the chemical information they contain. Here, we present a feasibility study consisting of using both the luminescence enhanced by surface plasmon of gold nanoparticles, and the surface enhanced Raman spectroscopy signal of fingermark chemical components to image latent fingermarks. A latent fingermark deposited on a transparent glass substrate was visually revealed using single-metal deposition employing gold nanoparticles. The resulting enhanced luminescence was monitored over a developed area of the latent fingermark, displaying light regions of 200-400 μm, corresponding to the fingermark ridges. The Raman signal of the fingermark's chemical components was enhanced into a measurable signal. Imaging those Raman peaks revealed the ridges pattern, attesting to the potential of our method. Since SMD is an end-of-sequence revelation technique for which further enhancement techniques do not exist, this work aims at demonstrating the feasibility of the technique in order to apply it on different systems, able to illuminate a complete surface of a few cm, and thus capable of both detecting contaminants in LFM and imaging features of the size of a complete LFM

Magnetic Sensing Potential of Fe3O4 Nanocubes Exceeds That of Fe3O4 Nanospheres

This paper highlights the relation between the shape of iron oxide (Fe3O4) particles and their magnetic sensing ability. We synthesized Fe3O4 nanocubes and nanospheres having tunable sizes via solvothermal and thermal decomposition synthesis reactions, respectively, to obtain samples in which the volumes and body diagonals/diameters were equivalent. Vibrating sample magnetometry (VSM) data showed that the saturation magnetization (Ms) and coercivity of 100–225 nm cubic magnetic nanoparticles (MNPs) were, respectively, 1.4–3.0 and 1.1–8.4 times those of spherical MNPs on a same-volume and same-body diagonal/diameter basis. The Curie temperature for the cubic Fe3O4 MNPs for each size was also higher than that of the corresponding spherical MNPs; furthermore, the cubic Fe3O4 MNPs were more crystalline than the corresponding spherical MNPs. For applications relying on both higher contact area and enhanced magnetic properties, higher-Ms Fe3O4 nanocubes offer distinct advantages over Fe3O4 nanospheres of the same-volume or same-body diagonal/diameter. We evaluated the sensing potential of our synthesized MNPs using giant magnetoresistive (GMR) sensing and force-induced remnant magnetization spectroscopy (FIRMS). Preliminary data obtained by GMR sensing confirmed that the nanocubes exhibited a distinct sensitivity advantage over the nanospheres. Similarly, FIRMS data showed that when subjected to the same force at the same initial concentration, a greater number of nanocubes remained bound to the sensor surface because of higher surface contact area. Because greater binding and higher Ms translate to stronger signal and better analytical sensitivity, nanocubes are an attractive alternative to nanospheres in sensing applications

Enzymatic synthesis of magnetic nanoparticles

We report the first in vitro enzymatic synthesis of paramagnetic and antiferromagnetic nanoparticles toward magnetic ELISA reporting. With our procedure, alkaline phosphatase catalyzes the dephosphorylation of L-ascorbic-2-phosphate, which then serves as a reducing agent for salts of iron, gadolinium, and holmium, forming magnetic precipitates of Fe45±14Gd5±2O50±15 and Fe42±4Ho6±4O52±5. The nanoparticles were found to be paramagnetic at 300 K and antiferromagnetic under 25 K. Although weakly magnetic at 300 K, the room-temperature magnetization of the nanoparticles found here is considerably greater than that of analogous chemically-synthesized LnxFeyOz (Ln = Gd, Ho) samples reported previously. At 5 K, the nanoparticles showed a significantly higher saturation magnetization of 45 and 30 emu/g for Fe45±14Gd5±2O50±15 and Fe42±4Ho6±4O52±5, respectively. Our approach of enzymatically synthesizing magnetic labels reduces the cost and avoids diffusional mass-transfer limitations associated with pre-synthesized magnetic reporter particles, while retaining the advantages of magnetic sensing

Magnetic Sensing Potential of Fe3O4 Nanocubes Exceeds That of Fe3O4 Nanospheres

This paper highlights the relation between the shape of iron oxide (Fe3O4) particles and their magnetic sensing ability. We synthesized Fe3O4 nanocubes and nanospheres having tunable sizes via solvothermal and thermal decomposition synthesis reactions, respectively, to obtain samples in which the volumes and body diagonals/diameters were equivalent. Vibrating sample magnetometry (VSM) data showed that the saturation magnetization (Ms) and coercivity of 100�5 nm cubic magnetic nanoparticles (MNPs) were, respectively, 1.4�0 and 1.1�4 times those of spherical MNPs on a same-volume and same-body diagonal/diameter basis. The Curie temperature for the cubic Fe3O4 MNPs for each size was also higher than that of the corresponding spherical MNPs; furthermore, the cubic Fe3O4 MNPs were more crystalline than the corresponding spherical MNPs. For applications relying on both higher contact area and enhanced magnetic properties, higher-Ms Fe3O4 nanocubes offer distinct advantages over Fe3O4 nanospheres of the same-volume or same-body diagonal/diameter. We evaluated the sensing potential of our synthesized MNPs using giant magnetoresistive (GMR) sensing and force-induced remnant magnetization spectroscopy (FIRMS). Preliminary data obtained by GMR sensing confirmed that the nanocubes exhibited a distinct sensitivity advantage over the nanospheres. Similarly, FIRMS data showed that when subjected to the same force at the same initial concentration, a greater number of nanocubes remained bound to the sensor surface because of higher surface contact area. Because greater binding and higher Ms translate to stronger signal and better analytical sensitivity, nanocubes are an attractive alternative to nanospheres in sensing applications

Cytoskeletal control of B cell responses to antigens.

The actin cytoskeleton is essential for cell mechanics and has increasingly been implicated in the regulation of cell signalling. In B cells, the actin cytoskeleton is extensively coupled to B cell receptor (BCR) signalling pathways, and defects of the actin cytoskeleton can either promote or suppress B cell activation. Recent insights from studies using single-cell imaging and biophysical techniques suggest that actin orchestrates BCR signalling at the plasma membrane through effects on protein diffusion and that it regulates antigen discrimination through the biomechanics of immune synapses. These mechanical functions also have a role in the adaptation of B cell subsets to specialized tasks during antibody responses

Vibrational response of clusters of Fe\u3csub\u3e3\u3c/sub\u3eO\u3csub\u3e4\u3c/sub\u3e nanoparticles patterned on glass surfaces investigated with magnetic sample modulation AFM

© 2018 The Royal Society of Chemistry. The vibration of Fe3O4 nanoparticles in response to an alternating magnetic field can be sensitively detected using contact mode atomic force microscopy (AFM) combined with selective modulation of magnetic domains. While imaging patterned samples of magnetic nanoparticles with contact mode AFM, a magnetic field was applied to drive sample vibration. The field altered in polarity and strength according to parameters of an AC current applied to a solenoid located under the sample. The vibration of Fe3O4 nanoparticles was detected by a nonmagnetic AFM tip to map the changes in frequency and amplitude of the vibrating sample at the level of individual Fe3O4 nanoparticles and clusters. Colloidal lithography, was used to prepare patterns of Fe3O4 nanoparticles on a glass surface using the basic steps of mixing, drying and removing the surface template of latex spheres. Monodisperse latex spheres were used to guide the deposition of magnetic nanoparticles in the spaces between the close-packed spheres of the latex film. With a mixture approach of two-particle lithography, 2D arrays of patterned aggregates of metal nanoparticles were generated which formed a periodic, well-defined arrangement that was suitable for subsequent characterizations with magnetic sample modulation (MSM)

Divalent cations regulate glucagon binding. Evidence for actions on receptor-Ns complexes and on receptors uncoupled from Ns

The effects of Mg2+ or ethylenediaminetetraacetic acid (EDTA) on 125I-glucagon binding to rat liver plasma membranes have been characterized. In the absence of guanosine 5'-triphosphate (GTP), maximal binding of 125I-glucagon occurs in the absence of added Mg2+. Addition of EDTA or Mg2+ diminishes binding in a dose-dependent manner. In the presence of GTP, maximal binding occurs in the presence of 2.5 mM Mg2+ (EC50 = 0.3 mM) while EDTA or higher concentrations of Mg2+ diminish binding. Response to exogenous Mg2+ or EDTA depends on the concentration of Mg2+ in the membranes and may vary with the method used for membrane isolation. Solubilized 125I-glucagon-receptor complexes fractionate on gel filtration columns as high molecular weight, GTP-sensitive complexes in which receptors are coupled to regulatory proteins and lower molecular weight, GTP-insensitive complexes in which receptors are not coupled to other components of the adenylyl cyclase system. In the absence of GTP, 40 mM Mg2+ or 5 mM EDTA diminishes receptor affinity for hormone (from KD = 1.2 +/- 0.1 nM to KD = 2.6 +/- 0.3 nM) and the fraction of 125I-glucagon in high molecular weight receptor-Ns complexes without affecting site number (Bmax = 1.8 +/- 0.1 pmol/mg of protein). Thus, while GTP promotes disaggregation of receptor-Ns complexes, Mg2+ or EDTA diminishes the affinity with which these species bind hormone. In the presence of GTP, hormone binds to lower affinity (KD = 9.0 +/- 3.0 nM), low molecular weight receptors uncoupled from Ns.(ABSTRACT TRUNCATED AT 250 WORDS