Elements for surface microfluidics in diamond

Abstract

Surface microfluidic elements are an essential part of lab-on-a-chip systems to perform complex chemical and biochemical synthesis as well as analyical tasks. These systems typically consist of channels, mixers and reaction chambers but also of actuators like pumps, heaters, etc., and sensors, measuring temperature, flow, impedance, pH, etc. To integrate these different functionalities, it is usually necessary to utilize different material systems [Eur. J. Pharm. Sci., 20(2) (2003) 149–171; Adv. Drug Delivery Rev., 55(3) (2003) 349–377]. Due to the unique properties of diamond, e.g. chemical inertness, UV transparency, high thermal conductivity and its semiconducting property, diamond can be universally used as base material for both passive and active elements. In previous work, the realization of temperature sensors, UV sensors and experimental ion sensitive FETs [Diamond Relat. Mater. 12 (2003) 554–559] has already been demonstrated. Various actuation principles like electrostatic [Diamond Relat. Mater. 12 (2003) 418–421], bubble-jet [Diamond Relat. Mater. 10 (2001) 722–730] and bi-metal actuators [Technical Proceedings of the 2003 Nanotechnology Conference, San Francisco, USA, February 23–27, (2003) pp. 380–383] have also been employed. This paper presents a new approach to the fabrication of all-diamond surface channels and chambers to link the different elements together and to provide a covered fluidic pathway. This needs high aspect ratio geometries and was obtained by modifying the common dielectric sacrificial layer technology used for MEMS [J.W. Gardner, Microsensors-Principles and Applications, John Wiley and Sons, Chichester, UK, 1994, p. 52ff], that is replacing the silicon dioxide by electroplated metal. Using an electroplating process, high thicknesses can be obtained. The sacrificial metal layer is then overgrown with diamond. As a first example, an integrated micro-membrane pump with thermal actuation is discussed.