- Dr. Petra Uhlmann
- Dr. Pagra Truman
The aim of our work is the development of a Lab on a Chip device for the separation of emulsions on chemically patterned surfaces with integrated semiconductor sensing elements. Our work is supported by the DFG priority program SPP 1164 "Nano- and Microfluidics".
The work is devided into three parts:
- development of chemically patterned surfaces: nanoscale hydrophobic coatings for the separation of liquid mixtures
- separation on chemically patterned surfaces: separation dynamics of binary liquid mixtures – theory and experiment
- development of a semiconductor sensor: liquid transport detection using single FET devices
Each topic is described briefly below.
1. Nanoscale hydrophobic coatings for the separation of liquid mixtures 
Summary: Organofunctional silane containing coatings are widely used to modify surface chemistry and have many applications in micro- and nanofluidics because liquid motion on these scales is strongly influenced by capillary or wall effects. In this work we focus on the development of nanoscale coatings for chemically patterned surfaces using fluorosilane SAMs and fluorine containing methacrylate coatings for the novel approach to separate emulsions on surfaces with an abrupt change of wettability from hydrophilic to hydrophobic. As a model system we investigate the separation of Toluene- Water- emulsions on such surfaces and thus aim for coatings easy to apply resulting in contact angles bigger 90° the same time being solvent resistant. We study the fastness to solvents (Toluene and Acetone) as a function of the deposition parameters and demonstrate emulsion separation. The fluorosilane SAMs are patterned by combinig CVD and UV-lithography while the methacrylate coatings are deposited by dipcoating.
2. Separation dynamics of binary liquid mixtures - Theory & Experiment 
Summary: Differences of wettability on chemically patterned surfaces allow to drive or guide liquid and even can be used to separate emulsions. It is conceivable to extend this concept to more complex systems like mixtures of multiple liquids, objects in liquids or mixtures of liquids with a higher degree of compatibility. But to do so it is necessary to understand which processes are relevant for separation and which parameters describe these processes. Using surfaces with an abrupt change of wettability and monodisperse Toluene- Water- mixtures as model emulsions we show that the separation process is a highly complex multiscale phenomena and present two theoretical approaches: On the one hand we consider the system to be a purely hydrodynamic system and transform differences of wettability into corresponding pressures. On the other hand we analyze the dynamics of single droplets. Comparing open and confined systems we find that the driving forces for separation are different.
3. Liquid transport detection using single FET devices ,
Summary: Observation and monitoring liquid transport and transport in liquids is a major task for lab on a chip applications and research. We use novel thin film FET devices based on silicon-on-insulator (SOI) substrates as planar sensors for the detection of liquid transport in capillaries to overcome the drawbacks of optical flow observation techniques the same time providing chemical composition analysis capabilities of ISFET technologies. Based on a newly developed theoretical model for Field-Effect liquid movement detection we demonstrate fundamental applications like the detection of capillary filling speed and level. To proof compatibility with ISFET technologies we demonstrate chemical composition analysis capabilities pH-detection and sensitivity to ionic strength. Furthermore we show how the sensitivity of the devices can be tuned as a unique feature provided by the use of silicon-on-insulator substrates.
- Prof. Dr. Dierk Raabe, Dr. Fathollah Varnik
Max-Planck-Institut für Eisenforschung, Düsseldorf
- Prof. Dr. Jörg Weber
Stiftungslehrstuhl für Halbleiterphyisk, Technische Universität Dresden
- Prof. Dr. Yurii A. Shchipunov, Dr. Marina Petuhova
Institut für Chemie an der Russischen Akademie der Wissenschaften, Wladiwostok
- Prof. Dr. Johann Wolfgang Bartha
Institut für Halbleiter- und Mikrosytemtechnik, Technische Universität Dresden
- Prof. Dr. Steffen Hardt
Leibniz Universität Hannover, Institut für Nano- und Mikroprozesstechnik
- Dr. Magnus Jäger
Universiät des Saarlandes, Fachrichtung Medizintechnik
- Dr. Steffen Howitz
GeSiM Gesellschaft für Silizium-Mikrosysteme, Großerkmannsdorf
Most important publications
- Truman, P.; Uhlmann, P.; Stamm, M.
Sensor für die Bestimmung der Fließbewegungen von und/oder in Flüssigkeiten sowie seine Verwendung
DE 10 2005 030 200.9.52, IPF Dresden
- Truman, P.; Uhlmann, P.; Stamm, M.
Monitoring liquid transport and chemical composition in lab on a chip systems using ion sensitive FET devices more
Lab on a Chip 6 (2006) 1220-1228
- Drechsler, A.; Petong, N.; Bellmann, C.; Busch, P.; Stamm, M.; Grundke, K.; Reichelt, J.
The Effect of Adsorbed Cationic Surfactant on the Pattern Collapse of Photoresist Lines in Photolithographic Processes more
Progress in Colloid and Polymer Science 132 (2006) S 82-94