To create complex colloidal hybrid nanoparticles—materials with various types of nanoparticles fused together—nanoscience researchers at Pennsylvania State University are taking a cue from their colleagues in organic synthesis. Guided by mechanistic considerations, Raymond E. Schaak, Matthew R. Buck, and James F. Bondi use chemical transformations to tack together simpler pieces of the structure in a predictable manner (Nat. Chem., DOI: 10.1038/nchem.1195). “We are trying to bring the elegance of organic total synthesis to the world of inorganic nanostructures,” Schaak tells C&EN. “We approach the synthesis in a stepwise manner; identify plausible reaction mechanisms; and develop, define, and exploit unique solid-state analogs of concepts that underpin organic synthesis but that are not typically in the nanomaterials chemist’s toolbox, such as chemoselective and regioselective reactions, coupling chemistry, and substituent effects.” For example, the researchers create gold-platinum-iron oxide hybrid nanoparticles from the reduction of gold ions in the presence of Pt-Fe3O4. One might expect the resulting gold nanoparticle to fuse to the Pt, the Fe3O4, or both regions of the particle, but the Penn State team found that the gold particle fused exclusively to Pt, demonstrating regioselectivity in their synthetic scheme.
To dissolve blood clots, biomedical engineer Donald Ingber of Harvard University and colleagues modelled nanoparticles after platelets—cells that circulate in the blood and help stop bleeding by forming clots. The nanoparticles are less than 100 nm wide and made of synthetic polymers stuck together like a ball of wet sand. Like platelets, clumps of the particles flow freely in the blood and gravitate toward blocked vessels by sensing a change in blood flow. Once there, they break apart into individual particles that stick to the clot, releasing a drug called tissue plasminogen activator (tPA) that dissolves it.
A three-component metal alloy mediates electrocatalytic reduction of oxygen to water more effectively than pure platinum and platinum-based bimetallic catalysts.
Oxygen reduction is a critical reaction
in fuel cells and metal-air batteries.
Nanoparticulate platinum supported
on carbon is considered the best catalyst
for that reaction, but kinetic factors
prevent platinum from reaching its
theoretical catalytic effectiveness. In
addition, the metal is costly and relatively
scarce. Recent investigations have focused on platinum-based bimetallic substitutes, but three-component systems have not been explored systematically. Vojislav R. Stamenkovic and coworkers prepared bimetallic and trimetallic thin films of platinum alloyed with iron, cobalt, and nickel and compared their measured electrocatalytic activities with their predicted oxygen binding energies. The group’s tests show that a catalyst consisting of 6-nm-diameter particles of PtCoNi (atomic ratio roughly 3:0.5:0.5) is more active for oxygen reduction than platinum-based bimetallic catalysts and four times as active as pure platinum. Check the paper out here.
Catalytic nanowire motors are of interest for biomedical applications including drug delivery and gene therapy due to their ability to pick up, tow, and release particles. For example, Joseph Wang and co-workers, University of California, San Diego, USA, recently demonstrated the guided transport of drug-loaded liposomes, pancreatic cancer cells, and nucleic acids by fuel-driven nanomotors. Despite the advances in cargo-towing by catalytic nanomotors, future ex-vivo and in-vivo biomedical transport applications require the use of biocompatible, fuel-free nanomotors.
Wang and co-workers now report magnetically driven (fuel-free) nanomotors. These two- or three-segment, flexible nanowire motors consist of a rotating magnetic nickel head (≈ 1.5 μm long), along with a flexible silver segment (≈ 4 μm long). They are able to pick-up and transport various drug carriers from a loading zone to a predetermined destination through a predefined route. The transport occurs at a rate order of magnitude faster than that expected from Brownian motion and they are among the fastest fuel-free synthetic nanomotors reported to date. Check details out here.
Amanda Silva et al. in Claire Wilhelm's lab wrote an interesting article about investigating magnetic targeting efficiency at the nanoscale. For their magnetophoretic mobility measurements, they developed a simple chamber including a microtip as a magnetic attractor for use under bright field or fluorescence microscopy. Different sets of magnetic nanocontainers were produced and their magnetophoretic mobility was investigated. The combination of the analysis of Brownian motion together with the magnetophoretic mobility inferred both the size, the magnetophoretic velocity and the magnetic content of the nanocontainers.
Additionally, nanomagnetophoresis experiments under fluorescence microscopy provided information on the constitutive core/shell integrity of the nanocontainers and the co-internalization of a fluorescent cargo. To see for yourself, check out their paper here.
David Kennedy from Ikotech LLC just informed me that the LinkedIn "Magnetic Particles Interest Group" has already grown to over 100 members in less than 30 days since he first set it up at the Minneapolis conference -- including over 20 organic connections from people that neither attended the recent conference nor have any connection to David. It thus seems that the LinkedIn "Magnetic Particles Interest Group" is a tool that can help promote our field, industry, and the Magnetic Carriers conferences.
Please consider joining the LinkedIn group and/or participating, posting, or promoting your activities or the activities of others in the field on this group site. Information for the group, including how to join, can be reached at this link.
The May 2012 issue of Pharmaceutical Research is a theme issue about "Magnetic Nanoparticles for Biomedical Applications" edited by Alexander Pfeifer and Katrin Zimmermann from the Institute of Pharmacology and Toxicologie, University of Bonn; und Christian Plank from the Institute of Experimental Oncology and Therapy Research at the Technical University in Munich.
Research papers and reviews are presented that deal with MNPs in various - mostly biomedical - applications. Based on the scientific background of the guest editors, a focus of this theme issue is magnetic drug targeting, in particular magnetically guided and enhanced nucleic acid delivery, also known as magnetofection. Considerable progress in this particular field has been accomplished during the last decade. This focus is not intended to neglect the formidable achievements with magnetic particles in other biomedical applications, such as cell tracking and positioning, magnetic cell separation, imaging and diagnostics, theranostics, magnetic actuation of cellular functions, AC magnetic field hyperthermia, etc. Most contributions to this theme issue report on applications of magnetic particles as opposed to theoretical / physical considerations. However, several papers focus on chemical and physical topics implied in the preparation and imaging/detection of MNPs as well as on mathematical models to better understand the physics of magnetofection.
To see for yourself, see http://www.springerlink.com/
Procedures such as MRI, magnetic hyperthermia, and maybe magnetically induced drug release require the application of rapidly changing magnetic fields. Irving Weinberg from Bethesda, MD recently published a study where he shows that increasing the frequency of the fields actually reduces the occurence of peripheral nerve stimulation (PNS). PNS is consistent with Maxwell’s equations that relate changing magnetic fields (i.e., dB/dt) with induced electromotive forces; the switching of magnetic gradient coils can result in the local induction of electrical currents in the human body, leading to PNS which can be unpleasant or even painful if sufficiently strong.
To check out if this is important for your applications and to learn more, check here.
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