Langmuir–Blodgett films of poly(3-dodecyl thiophene) for application to glucose biosensor Rahul Singhal a , W. Takashima c , K. Kaneto c , S.B. Samanta d , S. Annapoorni b , B.D. Malhotra a,* a Biomolecular Electronics and Conducting Polymer Research Group, National Physical Laboratory, Dr. K.S. Krishnan Road, New Delhi 110012, India b Department of Physics and Astrophysics, University of Delhi, Delhi 110007, India c Department of Biological Functions and Engineering, Graduate School of Life Sciences and System Engineering, Kyushu Institute of Technology, Iizuka, Fukuoka 820-8502, Japan d Superconductivity Division, National Physical Laboratory, Dr. K.S. Krishnan Road, New Delhi 110012, India Received 28 August 2001; received in revised form 13 March 2002; accepted 22 March 2002 Abstract Monolayers of poly(3-dodecyl thiophene) (P3DT) have been obtained on indium–tin-oxide (ITO) coated glass plates by dispensing mixed solution of P3DT and stearic acid (SA) prepared in chloroform onto water subphase by a microsyringe. The pressure–area isotherms of these P3DT–SA monolayers were studied as a function of temperature and pH. The monolayer stability onto the water subphase has been experimentally studied at different temperatures, pH and surface pressure. These P3DT–SA monolayers fabricated onto the ITO-coated glass plates were characterized using FTIR and cyclic voltammetry studies. The desired enzyme monolayers were fabricated by dispensing glucose oxidase mixed with P3DT/SA in chloroform and were transferred onto desired ITO-coated glass. An attempt has been made to utilize these P3DT/SA/GOX LB films for fabrication of a glucose biosensor. Published by Elsevier Science B.V. Keywords: Poly(3-dodecyl thiophene); Glucose biosensor; Langmuir–Blodgett film; Conducting polymer; Shelf-life 1. Introduction Conducting organic polymers, in recent years have gen- erated wide-spread interest as potential materials for a variety of applications in different areas including EMI shielding, anti-static and electronic junction devices, elec- tro-chromic displays, opto-electronic systems, semiconduc- tor protection, information storage, capacitors, gas sensors and biosensors. Agbor et al. [1] have reported the effect of various gases (NO 2 ,H 2 S, CO, SO 2 ,N 2 and CH 4 ) on surface plasmon resonance of Langmuir–Blodgett (LB) films of polyaniline. Stella et al. [2] have characterized olive oil using an electronic nose based on polypyrrole. Li et al. [3] fabricated polyaniline composite ultrathin films with iso- polymolybdic acid and demonstrated that the conductivity of the films is sensitive to humidity, NO 2 and NH 3 . Besides this, the use of conducting polymer films for the develop- ment of biosensor has attracted significant attention. Umana and Waller [4] have electrochemically polymerized pyrrole in the presence of enzyme glucose oxidase (GOX) and showed that these enzyme electrodes can be used as glucose biosensors. Chaubey et al. [5] recently demonstrated that LDH immobilized PPY–PVS films can be used to estimate lactate concentration from 12 to 24 mM. A biosensor is an analytical device incorporating a bio- logical or biologically derived material, either intimately associated or integrated within a physico-chemical transdu- cer. The aim is to produce an electronic response that is proportional to the concentration of analyte. Specificity of the desired molecule can be achieved by immobilizing the appropriate enzyme into the polymer matrix. However, the usefulness of immobilized enzyme electrodes depends on factors such as the immobilization method, the chemical and physical conditions (pH, temperature and contaminants), the thickness and stability of the membrane used to couple the enzyme. Immobilization of enzyme in several matrices has been used for the fabrication of biosensors for estimation of glucose [6,7], urea [8,9], cholesterol [10], etc. A number of papers relating to development of conducting polymer sen- sors (chemical and electrochemical) self-assembled mono- layer assembly, LB deposition, etc. have recently appeared Sensors and Actuators B 86 (2002) 42–48 * Corresponding author. Tel.: þ91-11-5734273; fax: þ91-11-5852678. E-mail address: bansi@csnpl.ren.nic.in (B.D. Malhotra). 0925-4005/02/$ – see front matter. Published by Elsevier Science B.V. PII:S0925-4005(02)00145-4