Research Paper

Analytical and Bioanalytical Chemistry

, Volume 405, Issue 20, pp 6425-6436

Electrical monitoring of polyelectrolyte multilayer formation by means of capacitive field-effect devices

  • A. PoghossianAffiliated withInstitute of Nano- and Biotechnologies (INB), Aachen University of Applied Sciences, Campus JülichPeter Grünberg Institute (PGI-8), Research Centre Jülich GmbH Email author 
  • , M. WeilAffiliated withInstitute of Nano- and Biotechnologies (INB), Aachen University of Applied Sciences, Campus JülichDepartment of Informatics and Microsystem Technology, University of Applied Sciences Kaiserslautern, Campus Zweibrücken
  • , A. G. CherstvyAffiliated withMax-Planck Institute for the Physics of Complex SystemsInstitute for Physics and Astronomy, University of Potsdam
  • , M. J. SchöningAffiliated withInstitute of Nano- and Biotechnologies (INB), Aachen University of Applied Sciences, Campus JülichPeter Grünberg Institute (PGI-8), Research Centre Jülich GmbH

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Abstract

The semiconductor field-effect platform represents a powerful tool for detecting the adsorption and binding of charged macromolecules with direct electrical readout. In this work, a capacitive electrolyte–insulator–semiconductor (EIS) field-effect sensor consisting of an Al-p-Si-SiO2 structure has been applied for real-time in situ electrical monitoring of the layer-by-layer formation of polyelectrolyte (PE) multilayers (PEM). The PEMs were deposited directly onto the SiO2 surface without any precursor layer or drying procedures. Anionic poly(sodium 4-styrene sulfonate) and cationic weak polyelectrolyte poly(allylamine hydrochloride) have been chosen as a model system. The effect of the ionic strength of the solution, polyelectrolyte concentration, number and polarity of the PE layers on the characteristics of the PEM-modified EIS sensors have been studied by means of capacitance–voltage and constant-capacitance methods. In addition, the thickness, surface morphology, roughness and wettabilityof the PE mono- and multilayers have been characterised by ellipsometry, atomic force microscopy and water contact-angle methods, respectively. To explain potential oscillations on the gate surface and signal behaviour of the capacitive field-effect EIS sensor modified with a PEM, a simplified electrostatic model that takes into account the reduced electrostatic screening of PE charges by mobile ions within the PEM has been proposed and discussed.

http://static-content.springer.com/image/art%3A10.1007%2Fs00216-013-6951-9/MediaObjects/216_2013_6951_Figa_HTML.gif
Figure

Label-free electrical monitoring of polyelectrolyte multilayer formation by means of a capacitive field-effect sensor consisting of Al-p-Si-SiO2 structure. The consecutive adsorption of oppositely charged polyelectrolyte layers leads to alternating shifts of the capacitance-voltage and constant-capacitance curves, whereas the direction of these shifts correlates with the charge sign of the terminating polyelectrolyte layer

Keywords

Field-effect Capacitive sensor Polyelectrolyte multilayer Electrical monitoring ConCap