Clay/Sol-Gel-Modified Electrodes for the Selective Electrochemical Monitoring of 2,4-Dichlorophenol Mehmet Ozsoz,* ,† Arzum Erdem, † Dilsat Ozkan, † Kagan Kerman, † and Thomas J. Pinnavaia* ,‡ Department of Analytical Chemistry, Faculty of Pharmacy, Ege University, 35100 Bornova, Izmir, Turkey, and Department of Chemisty and Center for Fundamental Materials Research, Michigan State University, East Lansing, Michigan 48824 Received January 23, 2003. In Final Form: March 15, 2003 A glassy carbon electrode (GCE) and a single-use pencil graphite electrode (PGE) modified through the incorporation of a mixed-ion, amphiphilic, fluorohectorite heterostructure, wherein the galleries are regularly interstratified by hydrophilic inorganic ions (Na + ) and lipophilic onium ions, are shown to be efficient electrochemical sensors for the specific determination of the pollutant 2,4-dicholorophenol (2,4-DCP) when incorporated at the 2.5% (v/v) level into a sol-gel (triethoxysilane) matrix on the electrode surface. The voltammetric detection of 2,4-DCP resulted in low detection limits of 26.66 nM and 19.32 nM at the 2.5% (v/v) clay/sol-gel-modified GCE and PGE, respectively, based on a signal-to-noise ratio of 3. The reproducible data obtained from the single-use clay/sol-gel-modified PGE show promise for the microfabrication of a remote sensor specific for 2,4-DCP detection. Introduction The monitoring of environmental pollutants is of vital importance for the protection of public health. Biosensors are playing an important role in environmental monitoring systems because they are sensitive devices with a broad linear dynamic range. They also have the advantage of being adaptable to microfabrication technology. 1-3 The fact that functionalized aromatic compounds effect DNA oxidation at disposable electrode surfaces provided the basis for the electrochemical detection of toxicants in drinking water and wastewater samples. 4 The attractive properties of pencil graphite electrodes (PGEs), which include the ability to easily renew the electrode surface, low background current, favorable anodic potential range, and cost-effective preparation, 5 have made them especially attractive for the electrochemical detection of environ- mental pollutants. 6 Sol-gel metal oxides represent a relatively new class of materials for the immobilization of biomolecules. The design of sol-gel sensing materials, which is based on the use of various encapsulated reagents and preparation conditions, allows tailoring of the material properties over a wide range. 7 The sol-gel process provides a relatively simple way to encapsulate reagents in a stable host matrix for electroanalysis. 8 Electrons crossing the electrode/sol- gel network can be determined with good sensitivity by measuring the current and can be related to the analyte concentration or used to evaluate the analyte diffusion, reactivity, and material conductivity. Sol-gel technology provides the easy microfabrication of glasslike or ceramic materials on electrode surfaces via the hydrolysis and condensation of suitable metal alkoxides. 9 Different transducers have been employed in sol-gel-based elec- trochemistry. In a screen-printing approach, for example, graphite powder, an enzyme, and a binder were incor- porated into a silica sol. 10 Also, an amperometric glucose biosensor based on a sol-gel organic-inorganic hybrid material has been reported, 11 and redox-active reagents have been introduced into a sol-gel framework by using the organosilicon derivatives that contain electroactive functionalities. 12 In addition, a sol-gel-derived thick-film amperometric immunosensor has been described re- cently. 13 Herbicides and their hydrolysis byproducts are the most abundant pollutants found in the environment and agricultural products. 14 2,4-Dichlorophenol (2,4-DCP) is a pollutant that has been associated with the occurrence of cancer in humans. Herbicides derived from 2,4-DCP, such as 2,4-dichlorophenoxyacetic acid (2,4-D), are widely used as cereal growth regulators, pre-emergence soil sterilization agents, and weed killers. In addition, they have been used in fruit cultures to increase fruit size, reduce preharvest drop, and produce seedless fruits. Nevertheless, they can be brought by the runoff of * Authors to whom correspondence should be addressed. E- mail: ozsozs@pharmacy.ege.edu.tr (M.O.); pinnavai@cem.msu.edu (T.J.P.). † Ege University. ‡ Michigan State University. (1) Wang, J.; Rivas, G.; Cai, X.; Palecek, E.; Nielsen, P.; Shiraishi, H.; Dontha, N.; Luo, D.; Parrado, C.; Chicharro, M.; Farias, P. A. M.; Valera, F. S.; Grant, D. H.; Ozsoz, M.; Flair, M. N. Anal. Chim. Acta 1997, 347,1-8. (2) Chiti, G.; Marrazza, G.; Mascini, M. Anal. Chim. Acta 2001, 427, 155-164. (3) Marrazza, G.; Chianella, I.; Mascini, M. Anal. Chim. Acta 1999, 387, 297-307. (4) Lucarelli, F.; Palchetti, I.; Marrazza, G.; Mascini, M. Talanta 2002, 56, 949-957. (5) Wang, J.; Kawde, A.-N.; Erdem, A.; Salazar, M. Analyst 2001, 126, 2020-2024. (6) Stulik, K. Electroanalysis 1997, 4, 829. (7) Wang, J. Anal. Chim. 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