Optical Fiber Immunosensor 117 Applied Biochemistry and Biotechnology Vol. 89, 2000 Copyright © 2000 by Humana Press Inc. All rights of any nature whatsoever reserved. 0273-2289/00/89/0117/$12.50 117 *Author to whom all correspondence and reprint requests should be addressed. Development of a Chemiluminescent Optical Fiber Immunosensor to Detect Streptococcus pneumoniae Antipolysaccharide Antibodies ROBERT S. MARKS,* ,1,2 ALON MARGALIT, 2 ALEXEI BYCHENKO, 2 EFIM BASSIS, 1 NURITH PORAT, 3 AND RON DAGAN 3 1 Unit of Biotechnology, 2 Institute for Applied BioSciences, and 3 Pediatric Infectious Disease Unit, Soroka University and the Faculty of Health Sciences, Ben-Gurion University of the Negev, PO Box 653, Beer-Sheva 84105, Israel, E-mail: Rsmarks@bgumail.bgu.ac.il Abstract A chemiluminescent-based optical fiber immunosensor was developed for the detection of antipneumococcal antibodies. This was accomplished by developing a different chemical procedure utilizing 3-aminopropyl tri- methoxysilane and cyanuric chloride to conjugate pneumococcal cell wall polysaccharides to the optical fiber tips, and by improving the sensitivity of the photodetection system. The lowest titer of antipneumococcal antibodies detected by the optical fiber was at a 1:819,200 dilution. The lowest corre- sponding value by standard enzyme-linked immunosorbent assay was at a 1:98,415 dilution. It was concluded that the optical immunosensor system is an accurate and sensitive method to detect antipneumococcal antibodies and may be an adequate tool to monitor antibodies in specimens such as saliva and urine. Index Entries: Optical fiber; chemiluminescence; immunosensor; Strepto- coccus pneumoniae. Introduction Streptococcus pneumoniae (pneumococcus) is a bacterial pathogen associated with life-threatening invasive diseases such as meningitis,