www.MaterialsViews.com 1 © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.small-journal.com Magnetometry of Individual Polycrystalline Ferromagnetic Nanowires Naveen Shamsudhin,* Ye Tao, Jordi Sort, Bumjin Jang, Christian L. Degen, Bradley J. Nelson, and Salvador Pané magnetic agents by spatio-temporally designed magnetic fields are used for their locomotion and site-targeted locali- zation in bodily fluids. [1–3] Body-endogenous and exogenous magnetic nanoparticles have enabled on-demand in vivo trig- gering of localized hyperthermia, [4] neuronal stimulation, [5,6] and activation of cellular signaling pathways. [7,8] In vitro, they are used as wireless actuators to exert and measure forces and torques on single molecular systems, [9] and on individual cells to investigate their mechano-responsive behavior. [10–12] Additionally, they are increasingly used as mobile sensors for probing local microrheological properties. [13,14] The applica- tion of nanomagnetic components in structures with fluidic mobility, incorporating sensing, actuation, and advanced on- demand functionalities is known as magnetic nanorobotics. [15] While the majority of current magnetic particle-based biophysical assays have used μm and sub-μm sized spherical superparamagnetic, paramagnetic, and ferromagnetic parti- cles, magnetic nanostructures in a variety of geometries like helices, coils, solid wires, and chains of beads have been inves- tigated for their enhanced mobility and maneuverability in fluids. [16–19] An important class of magnetic nanostructures for DOI: 10.1002/smll.201602338 Ferromagnetic nanowires are finding use as untethered sensors and actuators for probing micro- and nanoscale biophysical phenomena, such as for localized sensing and application of forces and torques on biological samples, for tissue heating through magnetic hyperthermia, and for microrheology. Quantifying the magnetic properties of individual isolated nanowires is crucial for such applications. Dynamic cantilever magnetometry is used to measure the magnetic properties of individual sub-500 nm diameter polycrystalline nanowires of Ni and Ni 80 Co 20 fabricated by template-assisted electrochemical deposition. The values are compared with bulk, ensemble measurements when the nanowires are still embedded within their growth matrix. It is found that single-particle and ensemble measurements of nanowires yield significantly different results that reflect inter-nanowire interactions and chemical modifications of the sample during the release process from the growth matrix. The results highlight the importance of performing single-particle characterization for objects that will be used as individual magnetic nanoactuators or nanosensors in biomedical applications. Nanorobotics N. Shamsudhin, B. Jang, Prof. B. J. Nelson, Dr. S. Pané Multi-Scale Robotics Laboratory ETH Zurich Zurich 8092, Switzerland E-mail: snaveen@ethz.ch Dr. Y. Tao, Prof. C. L. Degen Department of Physics ETH Zurich Zurich 8092, Switzerland Prof. J. Sort Institució Catalana de Recerca i Estudis Avançats (ICREA) and Departament de Física Universitat Autònoma de Barcelona Bellaterra, Barcelona 08193, Spain 1. Introduction Magnetic nanostructures are ideal platforms for transducing external control signals to target sites deep within bio- logical tissues. Physical forces and torques exerted on these small 2016, DOI: 10.1002/smll.201602338