A CMOS MICROSYSTEM COMBINING MAGNETIC ACTUATION AND IN-SITU OPTICAL DETECTION OF MICROPARTICLES U. Lehmann 1) , M. Sergio 2) , S. Pietrocola 1) , C. Niclass 2) , E. Charbon 2) and M.A.M. Gijs 1) 1 Institute of Microelectronics and Microsystems, Microsystems Laboratory 2 2 School of Computer and Communication Sciences, Ecole Polytechnique Fédérale de Lausanne (EPFL) Lausanne, SWITZERLAND ABSTRACT: We present a CMOS-based hybrid microfluidic system that combines the manipulation of magnetic microparticles through a magnetic field with in situ optical detection via single photon avalanche diodes (SPADs). Magnetic particles are actuated within a glass micro-capillary and are detected upon passage over the SPAD, where they block incident light and thus lower the photon count. The optical sensors, which are not influenced by the magnetic actuation forces, allow detecting the presence of magnetic particles of 30, 5 and 1 µm diameter, while being able to distinguish between different sizes. Keywords: Magnetic Actuation, Optical Detection, CMOS, Single Photon Avalanche Diode 1. INTRODUCTION Magnetic microparticles and their application in microfluidics and bioanalytical microsystems have been steadily gaining interest in recent years [1-3]. The manipulation of such particles can be achieved by modulating the topology of a magnetic field over the chip surface via an array of micro-coils [4, 5]. This method allows a very precise control of the microparticles and does not require external moving parts. In our system the magnetically actuated particles are detected optically. Thus, advantageously, the principles used for actuation and detection are not coupled and permit high sensitivity. In addition, due to the speed and accuracy of sensing, it is conceivable to implement stable and effective feedback mechanisms to ensure actuation reliability and precision. 1.1. System Setup The CMOS chip presented here comprises four metal layers. The upper two levels form overlapping square coils, while the lower pair contains the SPADs, which are positioned under the opening at the center of each coil. Fig. 1 presents schematic views of the system, while Fig. 2 shows a photomicrograph of the chip with close- ups of a coil and a center SPAD. Figure 1: Schematic views of the system. a: Explosion view of the system, where the integrated microcoils generate the field for magnetic actuation and the SPADs at the coil centers perform the optical detection. b) Side view of the chip with micro-capillary.