Biosensors and Bioelectronics 22 (2006) 145–152 Potentiometric sensor for atrazine based on a molecular imprinted membrane G. D’Agostino ∗ , G. Alberti, R. Biesuz, M. Pesavento Dipartimento di Chimica Generale, Universit` a degli Studi di Pavia, Via Taramelli 12, 27100 Pavia, Italy Received 24 January 2006; received in revised form 21 April 2006; accepted 4 May 2006 Available online 3 July 2006 Abstract A molecular imprinted polymer (MIP) membrane for atrazine, not containing macropores, was synthesized and implemented in a potentiometric sensor. It is expected to work like a solid ISE (where the specific carrier are the imprinted sites) the specific carrier being the imprinted site. The active ion is the protonated atrazine, positively charged. To form this species the determination is carried out in acidic solution at pH lower than 1.8, in which atrazine is prevalently monoprotonated. At these conditions the membrane potential increases with atrazine concentration over a wide concentration range (3 × 10 -5 to 1 × 10 -3 M). The slope of the function E versus log c is about 25 mV/decade, showing that the atrazine form sorbed on MIP is the biprotonated one. The detection limit is determined by the relatively high concentration of atrazine released by the membrane in the sample solution at the considered conditions. It seems to be independent of the atrazine concentration in the internal solution of the sensor, but it depends on the acidity of the solution. The response time is less than 10 s and the sensor can be used for more than 2 months without any divergence. © 2006 Elsevier B.V. All rights reserved. Keywords: Molecular imprinted polymer; Potentiometric sensor; Atrazine; Ion selective electrode 1. Introduction The molecular imprinted polymers for triazinic herbicides, particularly atrazine, were the subject of many investigations in recent years with interesting application in chemical analysis. MIPs are used for solid phase extraction (SPE) and chromato- graphic separation (Matsui et al., 1995, 1997; Muldoon and Stanker, 1997; Olsen et al., 1998; Takeuchi et al., 1999; Lanza and Sellergren, 1999; Bjarnason et al., 1999; Ferrer et al., 2000). The use of these polymers for the recognition in chemical sen- sors has been also proposed. Some authors prepared polymeric membranes for conductimetric and capacimetric (Piletsky et al., 1995, 1998; Sergeyeva et al., 1999; Panasyuk-Delaney et al., 2001), for piezoelectric detection (Pogorelova et al., 2002), and other signal transduction methods, for example through the bulk acoustic wave and fluorescence (Liang et al., 2000; Jenkins et al., 2001) Despite the relatively simple transduction of the poten- tiometric signal, only a few sensing devices of this kind have ∗ Corresponding author. Tel.: +39 0382 987 580; fax: +39 0382 528 544. E-mail address: girolamo.dagostino@unipv.it (G. D’Agostino). been developed. All of them were based on the use of very thin membranes or films (Kitade et al., 2004; Zhou et al., 2005), with problems due to difficulties in preparation, reproducibility and possible interferences. Recently a sensor has been developed, based on a MIP polymeric film deposited on the gate surface of an ion-sensitive field-effect transistor, obtaining good results in terms of specificity and low detection limit (Pogorelova et al., 2002). Potentiometric sensors have been previously proposed for charged analytes, for example for nitrate anion based on imprinted conducting polymers (Hutchins and Bachas, 1995). Atrazine is protonated, and as a consequence, positively charged in aqueous solution at sufficiently low pH, its protona- tion constant being log K a = 1.7 (Smolkova and Pacakova, 1978; Skopalov´ a and Kotouˇ cek, 1995). The combination of the pos- itively charged species with the imprinted membrane should produce a variation of the membrane charge. This can be mea- sured potentiometrically by a conventional ISE device, in which the membrane is placed between an internal filling solution at constant composition in contact with a reference electrode, and the sample solution (Craggs et al., 1974). This configu- ration is very simple, and gives a Nernstian response to the analyte concentration, which is very convenient for quantifi- 0956-5663/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.bios.2006.05.014