© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 2384 www.advmat.de www.MaterialsViews.com wileyonlinelibrary.com COMMUNICATION Two-Dimensional Programmable Manipulation of Magnetic Nanoparticles on-Chip Anandakumar Sarella, Andrea Torti, Marco Donolato, Matteo Pancaldi, and Paolo Vavassori* Remote and precise manipulation of magnetic particles is required to meet the demands for high-throughput and loca- tion-specific analysis in lab-on-chip applications. In the last decade many techniques have been developed for the remote manipulation of fluid-borne magnetic particles for accom- plishing different tasks in biology, medicine and chemistry. Magnetic tweezers [1] are commonly employed for the handling of individual magnetic micro- and nano-particles with nano- scale accuracy over a limited spatial area. Micro fabricated cur- rent wires [2] and micro-magnets [3,4] allow simple transport of magnetic particles as well as complex operations such as con- tinuous sorting [5,6] and enhanced mixing, [7] however, with a loss in the spatial accuracy. Although the individual strategies men- tioned above have been developed to separately address one or more of the required tasks, techniques that permit an encom- passing approach have yet to be achieved. Successful attempts in this direction were recently reported using discrete patterned magnetic thin films micro-structures tailored to form transport lines that enable the programmable motion of single micrometer-sized magnetic particles by the application of time-variable external magnetic fields. [8,9] Alter- natively, thin film-based devices have been developed to trap and transport magnetic micro-particles via strong localized fields and gradients found at domain walls in garnet films. [10–12] More recently, magnetically controllable artificial and bio- logical micro-robots, the so called magnetotactic artificial robots, [13] have been explored for micro-scale applications such as drug delivery and micro-assembly. However, none of these approaches combines capture, translocation along multiple tra- jectories, and release of individual magnetic particles of size not only in the micrometer range but also far below the micron, and with a control of the manipulation of the individual entity at both the micro- and nano-scale. In recent studies, it was demonstrated that spatially constrained magnetic domain walls (CDWs) propagating in ferromagnetic nano-strips (nano- conduits) predefined over a chip, can magnetostatically couple to fluid-borne magnetic nano-particles. [14–18] This property, together with the possibility of manipulating CDWs with nano- meter scale accuracy in specifically designed magnetic conduits, have been combined in technology platforms, which encom- pass remote manipulation of individual as well as large popula- tion of magnetic particles, transportation over large distances, and fine manipulation with nano-scale resolution. However, till date, the manipulation capabilities of this class of devices were limited to predefined patterned paths, albeit, more than one path could be selected. [16] For instance, in drug discovery the efficacy of chemotherapeutic drugs is often hampered by a lim- ited understanding of their mechanism of action. Achieving a 2-dimensional (2D) accurate manipulation over large areas with a control at the single molecule level is crucial (for example, in order to monitor the interaction dynamics with single cells [19] ), and will open the way to single molecule biophysics in on-chip devices for drug discovery. Furthermore, such manipulation and positioning capabilities could also be used in photonic applications since they would allow assembling nano-particles in ordered structures on a surface by remotely controlling the distance and symmetry of the assembly, thereby enabling the formation of 2D lattices with adjustable photonic band gaps (so called colloidal photonic crystals [20] ). In this communication, a novel device concept is presented that vastly extends the functionalities of CDWs based single par- ticle conveyors defined on a chip surface by allowing for the cap- ture, manipulation, and release of individual or multiple fluid- borne magnetic nano-particles, without any priori fixed pathway. The herein proposed technology is easy to reproduce on different functional substrates [21] and can be used for a variety of applica- tions in biology, chemistry, medicine as well as photonics, where a precise magnetic particle positioning is required. The central aspect to this approach includes an array of magnetic nano- or micro-ring structures patterned on a chip surface. A magnetic ring sustains the continuous and precise displacement of CDWs as well as of magnetic nano-particles that couples magneto-statically to the displacing CDWs. [22,23] As shown in Figure 1(a), two CDWs can be easily created and positioned at predefined positions on the perimeter of the cir- cular ring shaped magnetic conduit by applying a momentary external magnetic field Hs, intense enough to saturate the ring along the desired in-plane direction. Each CDW separates two regions of oppositely aligned magnetizations. Each magnetic region, a magnetic domain, has a head (a positive or north pole) and a tail (a negative or south pole). The resulting CDWs are therefore classified as head-to-head (HH) or tail-to-tail (TT). The Dr. A. Sarella, M. Pancaldi, Prof. P. Vavassori CIC nanoGUNE Consolider Tolosa Hiribidea 76, E-20018, Donostia – San Sebastian, Spain E-mail: p.vavassori@nanogune.eu Dr. A. Torti STMicroelectronics Via C. Olivetti 2, IT-20864, Agrate Brianza, Italy Dr. M. Donolato DTU Nanotech Building 345 East, DK-2800, Kongens Lyngby, Denmark Prof. P. Vavassori IKERBASQUE, Basque Foundation for Science E-48011, Bilbao, Spain DOI: 10.1002/adma.201304240 Adv. Mater. 2014, 26, 2384–2390