Sensors and Actuators B 168 (2012) 62–73 Contents lists available at SciVerse ScienceDirect Sensors and Actuators B: Chemical j o ur nal homep a ge: www.elsevier.com/locate/snb Miniaturized F - -selective all-solid-state potentiometric sensors with conductive polymer as an intermediate layer Alexey Matusevich, Mariusz Pietrzak ∗ , El ˙ zbieta Malinowska Warsaw University of Technology, Faculty of Chemistry, Institute of Biotechnology, Department of Microbioanalytics, 00-664 Warsaw, Poland a r t i c l e i n f o Article history: Received 18 October 2011 Received in revised form 29 December 2011 Accepted 9 January 2012 Available online 11 April 2012 Keywords: Potentiometric sensor Fluoride-selective electrode Polyurethane membrane Solid-state sensor a b s t r a c t In this work, miniaturized F - -selective all-solid-state potentiometric sensors were prepared and char- acterized. Poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) was used as an intermediate layer between gold internal electrode and polymer membrane of fluoride-selective sensors. The method of PEDOT:PSS deposition was optimized in order to prepare a layer with the best parameters for sensors preparation. Fluoride-selective ionophores working according to different car- rier mechanisms (neutral and charged one) and appropriate lipophilic ionic additives were used for membrane preparation. The influence of membrane components on PEDOT:PSS intermediate layer properties has been evaluated. It is shown that the use of PEDOT:PSS deposited between fluoride- selective membrane and sensor internal electrode can enhance charge transfer between them only if membrane is able to provide sufficient cation movement. Working parameters of electrodes with membranes made of polyurethane (PU) and various amounts of plasticizer or non-plasticized PU were compared with electrodes based on conventional poly(vinyl chloride) (PVC) membranes. It was found that non-plasticized PU can successfully replace plasticized PVC in membranes doped with Al-based fluoride-selective ionophores, while for Zr-based ionophore it caused dramatic deterioration of elec- trodes’ working parameters. Using PU as membrane matrix, the best working parameters were achieved for electrodes based on Al(III)-tetra-tert-butyltetraazaporphine (log K pot. F - ,Y - : Cl - -3.9, Br - -3.8, NO 3 - -3.6, SCN - -2.1, ClO 4 - -2.5). As a result of studies, miniaturized fluoride-selective all-solid-state potentio- metric sensors with response time less than 12 s, lifetime more than 3 months and enhanced standard potential (E 0 ) stability, were prepared. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Fluoride anion determination is of high importance for many real-world applications, including analysis of oral hygiene prod- ucts and fluoridated municipal water. Crystalline electrode based on LaF 3 doped with EuF 2 is one of most useful tools for F - anal- ysis [1], however it also has certain shortcomings, including a relatively high price and the difficulty in preparation of a truly miniaturize versions of this device. Due to these drawbacks, some receptors were tested as potential fluoride-selective ionophores in order to devise a much simpler polymer membrane-based fluoride electrode [2–4]. Among these compounds, Al(III)-tetra- tert-butyltetraazaporphine has been recently proposed by our group as ionophore of the best F - -selectivity among all fluoride ionophores described in the literature [4]. For the successful design of a truly useful miniaturized ion- selective electrode (ISE) with polymer membrane, some important ∗ Corresponding author. E-mail address: mariusz@ch.pw.edu.pl (M. Pietrzak). issues should be taken into account. Poor adhesion of a polymeric membrane to the electrode transducer might result in a prema- ture sensor failure due to detachment of the membrane. Among polymer membranes commonly used to date for miniaturized cation-selective electrodes preparation, polyacrylic matrices are known to provide the best adhesion and durability of membranes [5–9], however they also have some limitations in use. In contrast to commonly used technique of membrane preparation consist- ing of the dissolution of membrane components and subsequent evaporation of a solvent, polyacrylic membranes are usually pre- pared in situ on a transducer. The mixture of monomers, crosslinker, ionophore, ionic sites and initiator is usually dropped on a trans- ducer and then treated with heat or UV radiation. However, some of the ionophores can be destroyed during the polymerization process and other can block the initiation of polymerization process due to their high molar absorptivity (e.g. metalloporphyrins – often used as anion-selective ionophores). Polyurethane (PU), owing good adhesion to certain substrates, is often much better choice, as compared to typically employed poly(vinyl chloride) (PVC) when constructing miniaturized pla- nar ion-selective electrodes [10–13]. Polyurethanes demonstrate a 0925-4005/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2012.01.026