Sensors and Actuators B 125 (2007) 688–703 Review A review of fiber-optic biosensors Angela Leung a , P. Mohana Shankar b , Raj Mutharasan a,∗ a Department of Chemical and Biological Engineering, Drexel University, Philadelphia, PA 19104, United States b Department of Electrical and Computer Engineering, Drexel University, Philadelphia, PA 19104, United States Received 21 December 2006; accepted 12 March 2007 Available online 15 March 2007 Abstract Fiber-optic biosensors (FOBS) are optical fiber-derived devices which use optical field to measure biological species such as cells, proteins, and DNA. Because of their efficiency, accuracy, low cost, and convenience, FOBS are promising alternatives to traditional immunological methods for biomolecule measurements. Tapered fiber-optic biosensors (TFOBS) are a type of FOBS which rely on special geometries to expose the evanescent field to interact with samples. In order to amplify sensitivity and selectivity, TFOBS are often used with various optical transduction mechanisms such as changes in refractive index, absorption, fluorescence, and Surface Plasmon Resonance. In this review, the basic principles of TFOBS are summarized. Various common geometries for evanescent sensing and the influence of geometric parameters on optical principles are reviewed. Finally, a detailed account of the studies done to date for biomolecules detection using TFOBS will be provided. © 2007 Elsevier B.V. All rights reserved. Keywords: Biosensor; Evanescent field; Transmission; Immunosensors; Refractive index Contents 1. Introduction ............................................................................................................ 689 2. Fiber optic evanescent sensors ............................................................................................ 689 2.1. Effects of tapering on the evanescent field ........................................................................... 690 2.2. Effects of bending on evanescent field ............................................................................... 691 2.3. Effect of launch angle on evanescent field ........................................................................... 691 2.4. Effect of wavelength on evanescent field ............................................................................ 691 2.4.1. Tapered fiber geometries ................................................................................... 691 2.4.2. Detection principles in tapered fiber optic sensors ............................................................ 692 3. Applications of tapered fiber optic sensors ................................................................................. 694 3.1. Cell concentration ................................................................................................. 694 3.1.1. Pathogen detection ........................................................................................ 694 3.1.2. Clinical measurements .................................................................................... 697 3.2. Proteins or biomolecule concentration ............................................................................... 697 3.2.1. Biochemical measurements ................................................................................ 697 3.2.2. Toxins measurement ...................................................................................... 697 3.2.3. Clinical measurements .................................................................................... 698 3.3. DNA hybridisation ................................................................................................ 699 3.3.1. Pathogen detection via DNA ............................................................................... 700 4. Conclusions and future directions ......................................................................................... 700 References ............................................................................................................. 701 ∗ Corresponding author. Tel.: +1 215 895 2236; fax: +1 215 895 5837. E-mail address: mutharasan@drexel.edu (R. Mutharasan). 0925-4005/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2007.03.010