Optical-Fiber Medical Sensors
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Optical-Fiber
Medical Sensors
Francesco Baldini and Anna Grazia Mignani Abstract Optical-fiber sensors can be placed on the skin or inside the human body for the direct measurement of biomedical parameters. This article presents an overview of the most recent applications of optical-fiber sensors for biomedical purposes and those currently under development. Keywords: biomaterials, optoelectronic materials, optical-fiber sensors, optical properties.
Introduction Optical-fiber sensors are increasingly being used for biomedical purposes in a range of rapidly expanding applications. There are three types: noninvasive sensors, which are in contact with the skin; minimally invasive sensors, which are inserted inside body cavities; and invasive sensors, which are inserted inside organs or in blood vessels. Undoubtedly, the proliferation of these applications results from the sensors’ combined features of miniature size, versatility, and functionality: Optical-fiber sensors are small and flexible. They can be inserted uncabled inside very thin catheters and hypodermic needles to provide localized and minimally invasive monitoring. Optical-fiber sensors are nontoxic, chemically inert, and intrinsically safe for use inside the body. In addition, their electromagnetic inertness—which means they can be used without any electrical interference in the presence of other electrical equipment—is of vital importance in providing safe patient monitoring. Optical-fiber sensors are reliable and easy to use. Sensor evaluation is based mostly on performance and biocompatibility. Biocompatibility, which is the prime factor in patient comfort, is the degree to which the sensor does not affect, and is not affected by, the host body. Since, for example, performance can be notably reduced by factors in the local environment, the ability to remain unaffected by the host body is critical in devices such as chemical sensors, where a chemical transducer (or “optode”) is attached at the fiber tip. Thanks to con-
MRS BULLETIN/MAY 2002
tinual improvements in sensor design and encapsulation, their biocompatibility has made great strides in recent years. An overview of medical applications of optical-fiber sensors is given in Table I. The listed sensors are well described in many recently published reviews.1–3 The aim of this article is to provide an overview of recent developments and an outlook on emerging trends.
Blood Monitoring and Oximetry Recently, significant improvements in optical-fiber sensors for medical use have been introduced, especially in blood-gas detection sensors. In response to physicians’ demands, optical-fiber sensors now are able to monitor electrolytes in blood, such as potassium, sodium, and calcium. The CDI System 500 (Terumo Medical Corp.4) and the AVL 9180 (Roche5) are already available on the market and are capable of detecting electrolytes in blood in addition to blood gases. In the AVL system, the chemical transducers are synthesized molecules consisting of an ionophore (capable of reversibly binding the el
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