Disposable Optical Sensor Chip for Medical Diagnostics: New Ways in Bioanalysis Karsten Schult, ² Andreas Katerkamp, ² Dieter Trau, ‡ Frank Grawe, ² Karl Cammann, ² and Markus Meusel* ,² Institut fu ¨ r Chemo- und Biosensorik, Mendelstr. 7, D-48149 Mu ¨ nster, Germany, and Hong Kong University of Science and Technology, Department of Chemistry, Clear Water Bay, Kowloon, Hong Kong An optical sensor system is described which is particularly well suited for medical point-of-care diagnostics. The system allows for all kinds of immunochemical assay formats and consists of a disposable sensor chip and an optical readout device. The chip is built up from a ground and cover plate with in- and outlet and, between, of an adhesive film with a capillary aperture of 5 0 μm. The ground plate serves as a solid phase for the immobilization of biocomponents. In the readout device, an evanescent field is generated at the surface of the ground plate by total internal reflection of a laser beam. This field is used for the excitation of fluorophor markers. The generated fluorescence light is detected by a simple optical setup using a photomultiplier tube. Because of the evanescent field excitation, washing or separation steps can be avoided. With this system the pregnancy hormone chori- onic gonadotropin (hCG) could be determined in human serum with a detection limit of 1 ng/ mL. Recovery values were 8 6 , 1 0 6 , and 1 0 2 % for 5 , 5 0 , and 1 0 0 ng/ mL hCG, respectively. The SD in repeated measurements (n ) 10) was 5 .6 %. Furthermore, the feasibility of the system in competitive-type immunoassays was demonstrated for serum theophylline. A linear calibration curve of signal vs theophylline between 1 and 50 mg/ L was obtained. Recovery values varied between 1 1 8 % (1 0 mg/ L) and 81.0% (20 mg/ L). Today, immunoassay is the predominant analytical technique for quantitative determination of analytes in the field of laboratory medicine. The specificity of the analysis is provided by the antibody molecule which recognizes the corresponding antigen. One of the key features of most immunoassays is the solid phase which facilitates washing and separation steps and serves as a matrix for the immobilization of either the antibody or the antigen. Another important feature is the label used in the immunoassay. Most commonly, radioisotopes or, for example, fluorescent and enzyme labels are applied. In particular, the advent and use of enzyme labels paved the way for rapid immunoassay testing. In comparison with complex and sophisticated immunoassay equipment used in laboratory medicine, rapid immunoassays are mainly manual, single-use devices that are particularly well suited for point-of-care (POC) testing. Thus, these assays can readily be applied when the measurement has to be performed in emergency rooms, in ambulances, at the bedside, or at the doctor’s office. According to Hesterberg and Crosby, 1 rapid immunoassays are defined as those that produce a result in less than 30 min, that are rated as moderately complex or waived by the Clinical Laboratory Improvement Amendments of 1988 (CLIA ’88), and that can be completed without the aid of additional equipment. The four primary rapid immunoassay formats in use today are latex agglutination, horizontal flow devices, tangential flow devices (the so-called dipsticks), and optical immunoassays. 1 Up to now, one of the drawbacks of these test kits was the complicated handling procedure and often the lack of sensitivity. Moreover, in most cases, these tests are qualitative or semiquantitative although strong efforts are undertaken to eliminate these limitations. 2-4 An analytical device based on reflectometry, for example, was developed by Boehringer Mannheim (the “Cardiac Reader”) 5 for the readout of troponin T and myoglobin rapid tests. Some of the disadvantages of conventional rapid tests can be circumvent with the relatively new technology of the so-called biosensors. These devices consist per definition of a biological component that provides the required specificity and the trans- ducer that generates the signal. Both components have to be in close contact with each other. The most successful biosensor to date is obviously the one for blood glucose determination. 6 Biosensors that take advantage of the antibody/ antigen interaction are called immunosensors. 7 Similar to conventional immunoassays, these devices are based on an immobilized ligand and a labeled component. Biosensors are useful analytical devices in various fields such as process control (for a review see ref 8), environ- mental analysis, 9 and laboratory medicine (for a review see ref * Corresponding author: (fax) +49-251-980-2890; ( e-mail) meusel@ uni-muenster.de. † Institut fu ¨ r Chemo- und Biosensorik. ‡ Hong Kong University of Science and Technology. (1) Hesterberg, L. K.; Crosby, M. A. Lab. Med. 1996 , 27, 41-6. (2) Stephenson, J. IVD Technol. 1998 ,7/8, 51-6. (3) Scheyer, R. D.; Hochholzer, J. M.; Mattson, R. H. Epilepsia ( NY) 1995 , 36, 1152-4. (4) Anderson, D. J.; Guo, B.; Xu, Y.; Ng, L. M.; Kricka, L. J.; Skogerboe, K. J.; Hage, D. S.; Schoeff, H.; Wang, J.; Sokoll, L. J.; Chan, D. W.; Ward, K. M.; Davis, K. A. Anal.Chem. 1997 , 69, 165R-229R. (5) Waldenhofer, U.; Hirschl, M. M.; Laggner, A. N.; Katus, H. A.; Mu ¨ ller- Bardorff, M.; Sylven, C.; Rasmanis, G.; Collinson, P. O.; Gerhardt, W.; Hafner, G.; Zerback, R.; Leinberger, R. Crit. Care 1998 , 2, P53. (6) Arens, S.; Moons, V.; Meuleman, P.; Struyf, F.; Zaman, Z. Clin. Chem. Lab. Med. 1998 , 36, 47-52. (7) Byfield, M. P.; Abuknesha, R. A. Biosens. Bioelectron. 1994 , 9, 373-400. (8) Mulchandani, A.; Bassi, A. S. Crit. Rev. Biotechnol. 1995 , 15, 105-24. (9) Kra ¨ mer, P. J. AOAC Int. 1996 , 79, 1245-54. Anal. Chem. 1999, 71, 5430-5435 5430 Analytical Chemistry, Vol. 71, No. 23, December 1, 1999 10.1021/ac9907686 CCC: $18.00 © 1999 American Chemical Society Published on Web 10/29/1999 Author’s copy - only for private use!!!