**2.2 γ-Fe2O3-based patterned nanocomposites**

Magnetic particles are useful in different biomedical applications, such as magnetically induced hyperthermia of malignant tumors, contrast enhancement agents for magnetic resonance imaging (MRI), tissue repair (Gupta et al 2005, Pankhurst et al 2003), and delivery of drugs (Voltairas et al 2002) or nucleic acids (Mair et al 2009, Buerli et al 2007), as they can be manipulated via external magnetic fields to improve transport in biological systems. They are also used in the fabrication of photonic crystals (Ding et al 2009), as nanowire contacts in electronic devices (Bangar et al, 2009), and as device components in microfluidics (Kavcic et al 2009; Fahrni et al 2009). Additionally, there has been growing interest in the use of magnetic particles in the fabrication of nanomotors and nanomachines (Ghosh & Fischer, 2009).

Among all magnetic NPs, iron oxides are possibly the most frequently used, due to their high magnetic moment, chemical stability, low toxicity, biocompatibility, easy and economical synthetic procedures. Iron oxides exist in many forms in nature, with magnetite (Fe3O4), maghemite (γ-Fe2O3) and hematite (α-Fe2O3) being the most common (Cornell & Schwertmann 2003). Magnetite is ferrimagnetic at room temperature (Cornell & Schwertmann 2003), and usually particles smaller than ≈6 nm are superparamagnetic at room temperature, although their magnetic properties depend strongly on the methods used in their synthesis (Kado 2008, Zhao et al 2007). At room temperature, maghemite is ferrimagnetic while particles smaller than ≈10 nm are superparamagnetic (Neuberger et al 2005). Aggregation of ultrafine maghemite particles sometimes leads to their magnetic coupling and ordering of their magnetic moment, which is termed superferromagnetism (Cornell & Schwertmann 2003). Hematite is paramagnetic at temperatures above 956 K. At room temperature, it is weakly ferromagnetic and undergoes a phase transition at 260 K to an antiferromagnetic state. The magnetic behavior of hematite depends also on crystallinity, particle size and on the extent of cation substitution (Cornell & Schwertmann 2003).

The magnetic properties of iron oxides have been exploited in a broad range of applications including magnetic seals and inks, magnetic recording media, catalysts, ferrofluids, contrast agents for magnetic resonance imaging, therapeutic agents for cancer treatment, and numerous others (Azhar Uddin et al 2008, Cui et al 2006, dos Santos Coelho et al 2008). These applications demand nanomaterials of specific sizes, shapes, surface characteristics, and magnetic properties, so the specific type of iron oxide is chosen every time depending on the field of use. On the top, iron oxide in polymer matrices, forming functional nanocomposites, pave the way to novel plastic devices for gas and vapor sensing, actuation, molecular separation, electromagnetic wave absorption, nonlinear optical systems, and photovoltaic solar cells (Kaushik et al 2009, Merkel et al 2002, Huo et al 2009, Long 2005). Furthermore, the magnetic properties of iron oxide can be used in future generations of electronic, magnetic, and photonic devices for information storage or magnetic imaging (Weller et al 2000, Wang et al 2004).

For enhanced performances and occasionally directional, nanocomposite systems require high density of oriented anisotropic magnetic nanostructures, like NWs, in polymer matrices. Indeed, the realization of arrays of NWs is a new interesting solution to obtain novel collective properties, different from those of isolated NPs (Tang and Kotov, 2005).

the specific area, so that the front edge of the drop is always in contact with a more hydrophilic area than the back edge (Villafiorita Monteleone et al., 2010). This kind of samples are very versatile and can be used as described above or incorporated in more

Magnetic particles are useful in different biomedical applications, such as magnetically induced hyperthermia of malignant tumors, contrast enhancement agents for magnetic resonance imaging (MRI), tissue repair (Gupta et al 2005, Pankhurst et al 2003), and delivery of drugs (Voltairas et al 2002) or nucleic acids (Mair et al 2009, Buerli et al 2007), as they can be manipulated via external magnetic fields to improve transport in biological systems. They are also used in the fabrication of photonic crystals (Ding et al 2009), as nanowire contacts in electronic devices (Bangar et al, 2009), and as device components in microfluidics (Kavcic et al 2009; Fahrni et al 2009). Additionally, there has been growing interest in the use of magnetic

particles in the fabrication of nanomotors and nanomachines (Ghosh & Fischer, 2009).

particle size and on the extent of cation substitution (Cornell & Schwertmann 2003).

The magnetic properties of iron oxides have been exploited in a broad range of applications including magnetic seals and inks, magnetic recording media, catalysts, ferrofluids, contrast agents for magnetic resonance imaging, therapeutic agents for cancer treatment, and numerous others (Azhar Uddin et al 2008, Cui et al 2006, dos Santos Coelho et al 2008). These applications demand nanomaterials of specific sizes, shapes, surface characteristics, and magnetic properties, so the specific type of iron oxide is chosen every time depending on the field of use. On the top, iron oxide in polymer matrices, forming functional nanocomposites, pave the way to novel plastic devices for gas and vapor sensing, actuation, molecular separation, electromagnetic wave absorption, nonlinear optical systems, and photovoltaic solar cells (Kaushik et al 2009, Merkel et al 2002, Huo et al 2009, Long 2005). Furthermore, the magnetic properties of iron oxide can be used in future generations of electronic, magnetic, and photonic devices for information storage or magnetic imaging

For enhanced performances and occasionally directional, nanocomposite systems require high density of oriented anisotropic magnetic nanostructures, like NWs, in polymer matrices. Indeed, the realization of arrays of NWs is a new interesting solution to obtain novel collective properties, different from those of isolated NPs (Tang and Kotov, 2005).

Among all magnetic NPs, iron oxides are possibly the most frequently used, due to their high magnetic moment, chemical stability, low toxicity, biocompatibility, easy and economical synthetic procedures. Iron oxides exist in many forms in nature, with magnetite (Fe3O4), maghemite (γ-Fe2O3) and hematite (α-Fe2O3) being the most common (Cornell & Schwertmann 2003). Magnetite is ferrimagnetic at room temperature (Cornell & Schwertmann 2003), and usually particles smaller than ≈6 nm are superparamagnetic at room temperature, although their magnetic properties depend strongly on the methods used in their synthesis (Kado 2008, Zhao et al 2007). At room temperature, maghemite is ferrimagnetic while particles smaller than ≈10 nm are superparamagnetic (Neuberger et al 2005). Aggregation of ultrafine maghemite particles sometimes leads to their magnetic coupling and ordering of their magnetic moment, which is termed superferromagnetism (Cornell & Schwertmann 2003). Hematite is paramagnetic at temperatures above 956 K. At room temperature, it is weakly ferromagnetic and undergoes a phase transition at 260 K to an antiferromagnetic state. The magnetic behavior of hematite depends also on crystallinity,

complicated systems and devices, such as microfluidics, labs on chip etc.

**2.2 γ-Fe2O3-based patterned nanocomposites** 

(Weller et al 2000, Wang et al 2004).

One-dimensional magnetic NWs can be produced by the assembly of isotropic magnetic NPs, under external magnetic field (MF). This is an attractive technique for the fabrication of NWs, due to its simplicity and at the same time, high effectiveness. In this perspective, several studies have recently demonstrated the possibility of producing oriented magnetic nanocomposites through the dispersion of magnetic NPs in polymer or prepolymer solutions, and subsequent evaporation or polymerization under a weak magnetic field (Park et al 2007, Jestin et al 2008, Fragouli & Buonsanti et al 2010, Fragouli & Torre et al 2010). Here, we present photolithographically realized patterned nanocomposites of PMMA or SU-8 polymers which incorporate magnetic NWs, formed starting from spherical iron oxide (γ-Fe2O3) colloidal NPs. Indeed, applying a homogeneous magnetic field produced by two magnets to the nanocomposites solutions, NWs are formed, which are aligned along the magnetic field lines. We demonstrate that the photolithography process does not affect the NPs alignment, and, more importantly, that it allows the creation of polymeric patterns with magnetic properties in specific areas.
