Manipulating Superparamagnetic Microparticles with an Electromagnetic Needle

DOI: 10.1002/admt.201700177 organisms. The manipulation of superparamagnetic microparticles, in particular, has a wide range of applications, including magnetic logic;[13] sorting and trapping of magnetically tagged proteins,[14] cells,[15] and microorganisms;[16] microfluidic mixing;[17] magnetoresistive biosensing;[18] immunoassays;[19] and lab-on-a-tube devices.[20] In principle, the manipulation methods of these microparticles can be cate gorized into two groups: batch and individual particle manipulation. In batch manipulation, the magnetic field and field gradient originate from sources, such as external permanent magnet,[19] micropatterned current wires,[21,22] and microfabricated arrays of permanent magnets.[23] These systems are usually coupled with fluidic flows within fluidic chips. The microparticles are treated collectively as a lot with the manipulation strategies being mainly limited to trapping, separation (e.g., magnetic from nonmagnetic particles) or unidirectional transportation.[24] The individual particle manipulation, on the contrary, allows 1D, 2D, and 3D positioning, as well as possible orientation control of an individual magnetic microparticle. 1D transportation has been carried out by serpentine microcurrent lines[25] or by zig-zag Selective, precise, and high-throughput manipulation of individual superparamagnetic microparticles has profound applications in performing locationtailored in vitro biomedical studies. The current techniques for manipulation of microparticles allow only a single particle in the manipulation workspace, or simultaneous transportation of multiple microparticles in batches. In this work, a method based on a robotized electromagnetic needle for manipulation of individual superparamagnetic microparticles within a microparticle population is introduced. By automatically controlling the highly localized magnetic field of the needle, a single microparticle is selectively picked when its neighboring particle is few micrometers away. Supported by the nanometer resolution of the robotic positioner, particles are placed at sub-micrometer precision. This manipulation technique allows the creating of arbitrary patterns, sorting of microparticles based on size and morphology, and transporting of individual microparticles in 3D space. Therefore, this approach has the potential to enable more deterministic and quantitative microanalysis and microsynthesis using superparamagnetic microparticles. Micromanipulation