Binary Au-Pd nanoparticles were synthesized by sonochemical reduction of solutions containing various ratios of Au3+ and Pd2+ ions (1:9, 3:7, 5:5 and 7:3) including SDS. The thickness of a Pd shell and the size of an Au core depend on the ratio of the concentrations of their ions. For these core-shell nanoparticles, expanded Pd shell lattice depending on shell thickness was observed by HRTEM. In order to study the relationship between the structure, especially the shell thickness and lattice space, of Au-Pd nanoparticle and its catalytic activity, we measured hydrogenation catalytic activity for the Au-Pd nanoparticles using 4 pentenoic acid. The core-shell nanoparticles have higher catalytic activity than Pd monometallic nanoparticles, and particles with thinner shell Pd thickness tend to show higher catalytic activities.
The quantitative nature of Electromagnetic(EM) enhancement effect on Surface Enhanced Raman Scattering (SERS) is evaluated for rhodamine 6G(R6G) molecules adsorbed on Ag dimers based on the twofold electromagnetic (EM) enhancement theory. We found large spectral changes in SERS with increasing refractive index of media around single Ag nanoaggregates. We analyzed relationship between the spectral changes in SERS and those in plasma (plasmon) resonance based on the twofold EM enhancement theory. The analysis revealed that the changes in SERS spectra are induced by changes in spectral shapes of twofold EM enhancement factors, which arise from coupling of plasma resonance with both incident and Raman scattering light. Then, the EM enhancement in SERS is quantitatively evaluated for R6G molecules adsorbed on Ag dimers. Polarization-dependence of the plasma resonance and the SERS spectra from single isolated Ag dimers was evaluated to determine oneto-one relationship between optical anisotropy of plasma resonance, that of SERS, and the morphology of the nanostructures. Experimental observations were compared with finite-difference time-domain (FDTD) calculations of the EM field induced by plasma resonance using individual morphology of the dimers. The experimental enhancement factor of SERS ~ 109 was consistent with that of the calculations within a factor of ~ 2 for three excitation wavelengths. We conclusively fortify the indispensible importance of the twofold EM enhancement theory with our results to design metal nanostructures generating strong SERS.
Gold nanorods are rod-shaped gold nanoparticles. In many cases, they are synthesized in micellar solutions of cationic amphiphiles. The nanorods showed distinctive surface plasmon (SP) bands in visible and near infrared (IR) regions. Those SP bands can be assigned to transverse and longitudinal SP oscillations of free electrons in a gold nanorod. The longitudinal SP band locating in near-IR regions can be used to sensing of bio-related materials. Gold nanorods are prepared in a micellar solution of hexadecyltrimethylammonium bromide (CTAB) which stabilizes the colloidal dispersion of nanorods. In order to remove cytotoxic CTAB from the solution and provide biocompatible nanorods, phosphatidylcholine (PC) and polyethyleneglycol (PEG) were employed as biocompatible stabilizers for the gold nanorods. The PEG-modified gold nanorods were coated with antibodies for targeted delivery without denaturation due to CTAB, and could stably circulate in the blood flow after intravenous injection into mice.
Iron-platinum (FePt) nanoparticles (NP) are an excellent magnetic material for ultra-high density magnetic storage media because of their superior magnetic properties. Meanwhile, FePt NPs are also expected to be a high-performance nanomagnet for magnetic medicine, such as magnetic hyperthermia, magnetic resonance imaging, immunomagnetic cell separation, and magnetofection, because it presents a high Curie temperature, high saturation magnetization and high chemical stability. Here we suggest a possibility of FePt NPs for various medical applications.
The magnetic particles have been studied with much interest with reference to many engineering applications. Much effort has been devoted to the preparation of nano-sized magnetic particles with well-controlled size and shape. Magnetotactic bacteria synthesize uniform and nano-sized magnetite particles enveloped by lipid membranes. Recently, several genes and proteins involved in magnetite formation in magnetotactic bacterium, Magnetospirillum magneticum strain AMB-1 have been obtained. Molecular and genetic knowledge of biogenic magnetite formation are described here. Furthermore, the tremendous biotechnological potential of biogenic magnetite was highlighted.
We described here a novel approach for pinpoint cancer diagnosis and therapy based on smart stimuli-responsive PEGylated nanogels composed of cross-linked poly[2-(N,N-diethylamino)ethyl methacrylate] (PEAMA) gel core and poly(ethylene glycol) (PEG) tethered chains bearing an acetal group as a platform moiety for the installation of tumor-specific ligand molecules. The stimuli-responsive PEGylated nanogels showed significant volume phase transition in response to the extracellular pH (7.0-6.5) of tumor environment as well as temperature. In particular, the pH-responsive PEGylated nanogels containing 19F compounds into the PEAMA gel core showed remarkable on-off regulation of 19F MR (magnetic resonance) signals in response to the extracellular pH (= 6.5) of tumor environment, demonstrating the utility of these nanogels as tumor specific smart nanoprobe for 19F MRI (magnetic resonance imaging). In addition, the cross-linked PEAMA gel core of the stimuli-responsive PEGylated nanogels also acts as nanoreactor to produce and immobilize gold nanoparticles (GNPs), viz., one-pot synthesis of stimuliresponsive PEGylated nanogels containing GNPs was successfully carried out at various temperature and N/Au ratio (molar ratio of the amino groups in the PEGylated nanogel to the Au(III) ions) through the reduction of HAuCl4 without any additional reducing agents. The stimuli-responsive PEGylated nanogels containing GNPs showed a remarkable photothermal efficacy (ΔT=6.8°C) under irradiation with Ar ion (Ar+) laser (514.5 nm) at a fluence of 39 W/cm2 for 5min (14 kJ/cm2). Note that stimuli-responsive PEGylated nanogels containing GNPs showed non-cytotoxicity in the absence of irradiation of Ar+ laser (480 μg/mL: > 90% cell viability), whereas pronounced cytotoxicity (IC50 = 90 μg/mL) was observed under irradiation with Ar+ laser at a fluence of 26 W/cm2 for 5 min (7.8 kJ/cm2), because of the heat-generation from the GNPs in the cells, which resulted in selective and noninvasive cancer photothermal therapy. Thus, stimuli-responsive PEGylated nanogels can be utilized as smart nanodevice for pinpoint cancer diagnosis and therapy.