AC electrokinetic immobilization of organic dye molecules
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RESEARCH PAPER
AC electrokinetic immobilization of organic dye molecules Eva-Maria Laux 1 & Christian Wenger 2,3 & Frank F. Bier 1,4 & Ralph Hölzel 1 Received: 22 October 2019 / Revised: 28 January 2020 / Accepted: 31 January 2020 # The Author(s) 2020
Abstract The application of inhomogeneous AC electric fields for molecular immobilization is a very fast and simple method that does not require any adaptions to the molecule’s functional groups or charges. Here, the method is applied to a completely new category of molecules: small organic fluorescence dyes, whose dimensions amount to only 1 nm or even less. The presented setup and the electric field parameters used allow immobilization of dye molecules on the whole electrode surface as opposed to pure dielectrophoretic applications, where molecules are attracted only to regions of high electric field gradients, i.e., to the electrode tips and edges. In addition to dielectrophoresis and AC electrokinetic flow, molecular scale interactions and electrophoresis at short time scales are discussed as further mechanisms leading to migration and immobilization of the molecules. Keywords AC electrokinetics . AC electrophoresis . Molecular dielectrophoresis . Interdigitated electrodes . Organic dyes
Introduction Spatial manipulation and immobilization of small objects is a central experimental step in a broad spectrum of scientific applications that aim at ordered structures in the nanorange as well as in bioanalytic applications, where analytes of interest can be concentrated or moved to specific sites for further reactions or detection. The method of choice for the movement of these diverse objects is very often the application of alternating current (AC) electric fields. Dielectrophoresis (DEP) is one of the most prominent mechanisms that can be exploited for spatial
Published in the topical collection Bioanalytics and Higher Order Electrokinetics with guest editors Mark A. Hayes and Federica Caselli. * Eva-Maria Laux [email protected] 1
Fraunhofer Institute for Cell Therapy and Immunology, Branch Bioanalytics and Bioprocesses (IZI-BB), Am Mühlenberg 13, 14476 Potsdam-Golm, Germany
2
IHP GmbH - Leibniz Institut fuer Innovative Mikroelektronik, 15236 Frankfurt/Oder, Germany
3
Brandenburg Medical School Theodor Fontane, 16816 Neuruppin, Germany
4
Institute of Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Potsdam-Golm, Germany
manipulation and even immobilization of microscopical and submicroscopical objects regardless of their charge. The objects’ dimensions that have been spatially manipulated by dielectrophoretic forces are getting smaller and smaller, from biological objects like cells [1] with dimensions of tens of micrometers or carbon nanotubes with diameters of few nanometers and lengths of several micrometers [2], reaching down to nanoparticles with diameters of only a few nanometers in all three dimensions [3], e.g., zinc oxide nanoparticles with a diameter of 9 nm [4], core-shell CdSe quantum dots w
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