rXXXX American Chemical Society A dx.doi.org/10.1021/am100805y | ACS Appl. Mater. Interfaces XXXX, XXX, 000–000 RESEARCH ARTICLE www.acsami.org Electropolymerized Molecularly Imprinted Polymer Films of a Bis-Terthiophene Dendron: Folic Acid Quartz Crystal Microbalance Sensing Dahlia C. Apodaca, †,‡ Roderick B. Pernites, † Ramakrishna R. Ponnapati, † Florian R. Del Mundo, ‡ and Rigoberto C. Advincula* ,†,‡ † Department of Chemistry and Department of Chemical and Biomolecular Engineering, University of Houston, Houston, Texas 77204-5003, United States ‡ Institute of Chemistry, University of the Philippines, Diliman, Quezon City, Philippines 1101 b S Supporting Information ABSTRACT: A folic acid sensor was prepared via an electropolymerized molecularly imprinted polymer (E-MIP) film of a bis-terthiophene dendron on a quartz crystal microbalance (QCM). The cyclic voltammetry (CV) electrodeposition of the im- printed polymer film was monitored by electrochemical QCM or E-QCM, enabling in situ monitoring and characterization of E-MIP film formation and the viscoelastic behavior of the film. A key component of the E-MIP process is the use of a bifunctional monomer design to precomplex with the template and function as a cross-linker. The complex was electropolymerized and cross-linked by CV to form a polythiophene matrix. Stable cavities were formed that specifically fit the size and shape of the folic acid template. The same substrate surface was used for folic acid sensing. The predicted geometry of the 1:2 folic acid/terthiophene complex was obtained through semiempi- rical AM1 quantum calculations. The analytical performance, expressed through the figures of merit, of the sensor in aqueous solutions of the analyte was investigated. A relatively good linearity, R 2 = 0.985, was obtained within the concentration range 0-100 μM folic acid. The detection limit was found to be equal to 15.4 μM (6.8 μg). The relative cross selectivity of the folic acid imprinted polymer against the three molecules follows this trend: pteroic acid (= 50%) > caffeine (= 41%) > theophylline (= 6%). The potential and limitations of the E-MIP method were also discussed. KEYWORDS: sensing, MIP, imprinting, electropolymerization, QCM, film, folic acid ’ INTRODUCTION Molecular imprinting (MIP) is a technique widely used for the preparation of polymeric materials for molecular recognition. 1-4 In MIP, the specific interaction of a functional monomer with the template is manifested through the organization of specific binding sites, which usually occur during fabrication of a three- dimensional polymer monolith or film. Regardless of the type of interaction, i.e., whether covalent or noncovalent, the preorga- nized interaction creates a geometry that is complementary to the size and shape of the template or target molecule. This enables recognition of the template by the polymer matrix in subsequent rebinding studies or applications. MIP is a valuable component in the preparation of sensors. 5-10 The biomimetic properties of MIPs render them attractive as chemical recognition elements in sensors or artificial receptors. For recognition, MIP offers a very promising alternative to natural receptors such as antibodies and enzymes, which have relatively poor stability and a short shelf- life. 11 Because of low cost, ease of preparation, robustness, coupled with a wide choice of templates and functional mono- mers, and an increase in demand in the fields of food analysis, environmental monitoring, pharmaceutical assays, and security monitoring that includes the detection of explosives, chemical warfare agents, and illicit drugs, 12 MIP has become one of the most widely used methods for the preparation of sensor films. 13 However, MIP has some limitations, which include poor recog- nition properties in water, long equilibrium binding kinetics, and slow leaching of the template from the polymer matrix, which must be addressed appropriately. 13,14 A main challenge in the design of MIP-based chemical sensors is that these materials are usually prepared in bulk as monoliths, thus lacking the ability to form a smooth film that is directly interfaced with a transducer or electrode. Other groups have resorted to obtaining bulk polymer films or membranes. 15-19 Another option is surface imprinting by spray- or spin-coating techniques that have been used to obtain thin films on piezoelectric devices 20 . Spin coating, in particular, often suffers from the following drawbacks: di fficulty in depositing high-quality films of submicrometer thickness, tendency to form coating defects (e.g., the orange-peel effect), poor homogeneity in composition, and unwanted precipitation of the polymer due to the premature evaporation of solvents. 21 To this end, direct electroche- mical deposition of polymers offers a viable means of introducing the recognition domain as films on the surface of a transducer. 22 Received: August 29, 2010 Accepted: November 1, 2010