Felix Schmidt-Stein

Amphiphilic TiO2 nanotube arrays: an actively controllable drug delivery system.

Amphiphilic TiO(2) nanotube arrays are fabricated by a two-step anodization procedure combined with hydrophobic monolayer modification after the first step. These tubes can be used as biomolecular carriers, where the outer hydrophobic barrier provides an efficient cap against drug leaching to the environment. By utilizing the photocatalytic ability of TiO(2), a precisely controlled removal of the cap and a highly controlled release of the hydrophilic payload (drug) can be achieved.

Magnetically Guided Titania Nanotubes for Site-Selective Photocatalysis and Drug Release†

The nanoscale encapsulation of ferromagnetic structures has received a great deal of attention because of the exciting possibilities to use these materials in various applications that range from novel electromagnetic to biomedical devices. For example, nanoscale magnetic entities could be transported and concentrated at pretargeted locations or organs within the human body bymeans of an external magnetic field in order to exert a specific function with high local and temporal precision. Therefore, functionalized magnetic nanodots, nanowires, or nanotubes have a high potential for in vivo applications such as magnetic resonance imaging or siteselective drug delivery systems, if the magnetic property is combined with an appropriate drug loading and release mechanism. TiO2 nanotubes are a highly promising encapsulating material for a magnetic core as a high degree of biocompatibility can be combined with a broad range of other functionalities. Since the pioneering work of Fujishima and Honda in 1971, it has been established that TiO2 is a highly active photocatalyst; this is based on the ability of TiO2 to produce electron–hole pairs upon light irradiation and thereby create highly reactive radical species. This property of TiO2 has been intensively explored in the form of photoelectrodes for the decomposition of various organic pollutants in water and air, and it has been used in self-cleaning, disinfecting, and anticancer materials. The photocatalytic ability of TiO2 can be enhanced by using nanosized TiO2 materials because of their large specific surface area. Herein, we describe a simple way of embedding magnetic properties into TiO2 nanotubes and demonstrate their different site-selective photocatalytic applications. Not only can these tubes be used as a magnetically guided photocatalyst for the decomposition of organic matter but also the photocatalytic mechanism can be exploited to release an active species (a model drug). Among the various synthetic routes used to prepare TiO2 nanotubes, [26–28] anodization approaches have gained significant attention as they lead to highly ordered nanotubular arrangements. During the past few years, our research group has contributed several generations of anodically grown self-organized TiO2 nanotube layers by anodization of Ti in aqueous and organic electrolytes. In our approach, we use nanotube layers (Figure 1a) that were produced in ethylene glycol/NH4F electrolytes [36–38] (see Section S1 and Figure S1 in the Supporting Information). These TiO2 nanotubes were filled with magnetic nanoparticles by sucking a droplet of ferrofluid placed on the top of the nanotube layer using a permanent magnet (see the Supporting Information). Figure 1b shows topand side-view SEM images of the nanotubes that are loaded with the magnetic nanoparticles. It is clear from these images that the majority of the inside tube walls were coated relatively uniformly with the magnetic particles leaving a hollow space inside the tubes. In contrast to other established but time-consuming and

TiO2 nano test tubes as a self-cleaning platform for high-sensitivity immunoassays.

Since their discovery by Iijima in 1991, carbon nanotubes have attracted tremendous scientific and technological interest due to a combination of unique inherent properties and high expectations regarding their applications. Apart from carbon, over the past fewyears a number of ‘‘inorganic’’ nanotubular or nanoporous systems have also been reported that can be grown by a self-organizing electrochemical anodization process on various metallic or semiconductor substrates. A particular advantage is that distinct tubular features can be formed in regular arrays perpendicular to the substrate surface. This arrangement makes such structures ideal for use as nano test tubes for capturing, concentrating, releasing load, or probing formolecules, and such features have been reported for silica and alumina. Herein, we show how to use titania-nanotube (TiNT) arrays as a small-volume, high-sensitivity immunoassay detection system. Due to the unique photocatalytic properties of TiO2 these arrays have self-cleaning features, which makes themmost attractive for reusable devices. TiNTarrays canbe tuned in geometry (diameter, aspect ratio), ‘‘crystal’’ structure (amorphous, anatase, rutile), electronic and biomedical properties, and even freestanding membranes can be fabricated, and therefore a very versatile nanoscale architecture can be built. Up to now an unexploited path is the direct use of such nanotube arrays as reusable immunoassay platforms. In general, one of the key goals in immunoassay research is lowering the detection threshold, ultimately reaching singlecell and single-molecule diagnostics and reducing the probe volume to aminimum. In the present work, we use high-aspectratioTiNTs (whichprovidea longobservation length combined with a small volume) to enhance the detection level of fluorescence-labeled proteins in an immunoassay concept. Self-organized TiNT arrays were grown by anodization of Ti foils in ethylene glycol electrolytes containing NH4F, as described in the Experimental Section. The resulting TiNT layers are shown in the scanning electron microscopy (SEM)

Formation of magnetic aluminium oxyhydroxide nanorods and use for hyperthermal effects

In the present work, we show that a porous alumina template can easily be filled with magnetic nanoparticles and then be sealed by a hot water treatment (by forming an aluminium oxyhydroxide (AlOOH) sealant layer). The porous layer then can be separated from the substrate by an etch to form free magnetic AlOOH nano-capsules. The process allows for a straightforward and highly defined size control of the magnetic units and can easily be scaled up. Furthermore, as AlOOH is biocompatible and has been used as a drug adjuvant for human use, the nanorod shaped capsules are highly promising for biomedical applications such as hyperthermal effects (heating in alternating magnetic fields).