Analytica Chimica Acta 399 (1999) 21–27 Sol–gel materials for electrochemical biosensors Joseph Wang ∗ Department of Chemistry and Biochemistry, New Mexico State University, MSC 3C, Las Cruces NM 88003, USA Received 3 December 1998; received in revised form 22 March 1999; accepted 1 April 1999 Abstract An overview is presented of the state-of-the art of electrochemical biosensors employing sol–gel materials. Low-temperature, porous sol–gel ceramics represent a relatively new class of materials for the immobilization of biomolecules. The rational design of sol–gel sensing materials, based on the judicious choice of the starting alkoxide, encapsulated reagents, and prepa- ration conditions, allows tailoring of material properties in a wide range, and offers great promise for the development of electrochemical biosensors. The various advantages of biogels for amperometric biosensing are discussed, along with com- mon designs of sol–gel-derived bioelectrodes, recent advances and trends, and future prospects. ©1999 Elsevier Science B.V. All rights reserved. Keywords: Biosensors; Electroanalysis; Sol–gel processes; Immobilization; Enzyme electrodes 1. Introduction 1.1. Protein immobilization for electrochemical biosensors Electrochemical biosensors, particularly enzyme electrodes, have enjoyed considerable popularity, culminating in commercial devices, ranging from self-testing meters for blood glucose to high through- put analyzers for various metabolites [1,2]. Such devices rely on the intimate coupling of a biological element and an electrode transducer that converts the specific biorecognition event to a useful electrical signal. Effective immobilization of the biological entity onto the transducer surface is thus one of the key features for the successful operation of electrochem- ∗ Tel.: +1-505-646-2505; fax: +1-505-646-2649 E-mail address: joewang@nmsu.edu (J. Wang) ical biosensors. The objective of this important step is to provide a simple means for attaching the pro- tein, so that it retains its affinity and stability over prolonged periods, while providing accessibility to- wards the target analyte and an intimate contact with the electrode surface. Commonly used immobiliza- tion protocols include physical entrapment (behind semi-permeable membranes or within a polymeric film), co-valent binding or cross-linking using multi- functional reagents, and non-co-valent schemes such as surface adsorption or mixing within the bulk of composite electrode materials. While offering an effective interface, some of these procedures are tedious, result in poor stability and perturbed func- tion, require expensive reagents, or environmentally unattractive solvents. New immobilization schemes and advanced sensing materials are highly desired for improving the analytical capabilities of biosens- ing devices, and for meeting the challenges posed by complex environmental and clinical samples. 0003-2670/99/$ – see front matter ©1999 Elsevier Science B.V. All rights reserved. PII:S0003-2670(99)00572-3