• ELSEVIER Sensors and Actuators B 32 (1996) 149-155 • CHEMICAL Sensing fatty acid binding protein with planar and fiber-optical surface plasmon resonance spectroscopy devices Ulrich Kunz a,*, Andreas Katerkamp a, Reinhard Renneberg b, Friedrich Spener a, Karl Cammann a alnstitlltft/r Chemo- lind Biosensorik, Mendelstrape 7, D-48149 Munster. Germany b Biosensor Unit. Hong Kong Univer.'ity of Science and Technology, Departments of Chemistry and Chemical Engineering, Clear Water Bay, Kowloon, Hong Kong Received 16 November 1995; revised 21 February 1996; accepted 29 February 1996 Abstract The human heart-type fatty acid binding protein (H-FABP) can be used as an early heart infarction marker in clinical diagnostics because its concentration in blood plasma increases about 1.5 to :3 hours after the onset of an acute myocardial infarction. Hence, it is of main interest to determine an infarct with a fast immunosensor. Surface plasmon resonance spectroscopy (SPRS) is one of the most versatile and sensitive direct optical technologies used for biochemical sensors. The aim of this study is the development of a direct optical immunosensor for the detection of H·FABP. Two different SPRS devices have been constructed: the well-known planar configuration and a new promising fiber- optical transducer. Both transducers are compared under the same conditions with regard to the measurement of H-FABP. They show a similar response and an excellent correspondence of the calibration curves. The detection limit of H-FABP in a competitive assay is about 200 ng mr I in both cases. Keywords: Human heart-type fally acid binding protein; Fiber optics; Surface plasmon resonance spectroscopy 1. Introduction The human heart-type fatty acid binding protein (H- FABP) is one species of a family of nonenzymic proteins that bind hydrophobic ligands. Highest contents of H-FABP are found in those tissues which show high rates of fatty acid handling, for example, the intestine. liver and heart. The localization of these fatty acid binding proteins is with con- centrations up to 5% of soluble proteins mainly cytosolic. The bovine H-FABP used in this study is very similar to the human H-FABP. It has a clam-like structure with the ligand accommodated between the two halves of the clam and a molecular mass of about 15 kDa; for more details, see Refs. [ 1.2]. The appearance of human H-FABP in plasma within 1.5 to 3 h after the onset of the first clinical symptoms of acute myocardial infarction is of special interest. The concentration ofH-FABP increases from the threshold of about 20 ng ml-- I up to 400 ng ml- 1 during the infarction period [3]. Other possible infarction markers like creatine kinase isoenzyme MB reach their highest concentration only after 8 h [3]. .. Corresponding author. 0925-4005/96/$15.00 © 1996 Elsevier Science SA All rights reserved PII 80925-4005 (96)01886-2 Furthermore, the plasma H-FABP concentration returns to its normal value within 20 h after acute myocardial infarction. Therefore. it can be used to indicate a reinfarction [3]. These results allow the application of H-FABP as an early plasma marker of acute myocardial infarction. However, n rapid assay system is required to monitor cardiac patients. One promising approach is the use of a direct optical immunosen- sor based on surface plasmon resonance spectroscopy. This method allows a visualization of macromolecularinteractions in real time without labeling of proteins [4,5]. Surface plasmons are the quanta of charge-density waves of free electrons in a metal propagating along the interface of a metal and a dielectric medium such as buffer or air. The electromagnetic field of these surface waves reaches its high- est intensity at the metal surface and decreases exponentially into the adjacent phase. Therefore, it is influenced by the optical properties of this phase. The strong dependence of the surface plasmons on the refractive index of the dielectric medium can be used for sensor development purposes. Different configurations are employed to excite sarface plasmons. but for sensor application the planar attenuated total reflection (ATR) configuration is mostly used [6.7]. A thin silver or gold layer is deposited on a glass slide which is Only for private use!