Optical Fiber Microarrays for Chemical and Biological Measurements

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1133-AA02-01

Optical Fiber Microarrays for Chemical and Biological Measurements.

David R. Walt, Christopher LaFratta, Michael Webb, Zhaohui Li, Hans-Heiner Gorris, and Ryan Hayman Chemistry Department, Tufts University, 62 Talbot Ave., Medford, MA 02155, U.S.A.

ABSTRACT We have used coherent imaging fiber arrays as a platform for preparing chemical sensors and biosensors. Sensors can be made with spatially-discrete sensing sites for multi-analyte determinations. Micrometer sized sensors have been fabricated by etching the cores of an optical imaging fiber to create microwells and loading them with microspheres. These arrays possess both high sensitivity and reproducibility and can be used for making thousands of measurements simultaneously such as for genetic analysis or for the analysis of complex biological fluids. Both optical and optoelectrochemical arrays have been used for multiplexed sensing. In another scheme, the arrays can be used for single molecule detection. In this format, individual molecules, such as enzymes, can be trapped in the microwells by sealing each microwell with a silicone gasket. The enzyme molecules catalyze the formation of a fluorescent product that can be detected readily. The kinetic properties of hundreds to thousands of single enzyme molecules can be monitored simultaneously using this format. By observing the stochastic nature of the single molecule responses, new mechanistic insights into the fundamental nature of the enzymes can be obtained.

INTRODUCTION Optical fibers have been used for chemical sensing for nearly three decades. A variety of sensing formats have been employed. Optical fibers can carry light signals due to the refractive index difference between the clad and core materials comprising the fiber. By attaching chemically-sensitive species to the distal end of the fiber, one can interrogate these species by illuminating the proximal fiber end. Our laboratory has used a fluorescence transduction mechanism because fluorescence enables a simple optical setup. In our implementation, excitation light is carried down the fiber core via total internal reflection and the isotropicallyemitted fluorescence signal can be collected by the same fiber core. In this way, the fiber provides the ability to interrogate a sample remotely. Chemical sensing often requires the measurement of either multiple analytes or of the spatial distribution of a single analyte. To address these sensing needs, we have developed optical fiber array sensors [1]. In this approach, a unitary coherent fiber bundle comprising thousands of single micron-sized individual fibers is used (Figure 1-left). The most common implementation of this format involves etching one end of the fiber array. The composition of the fiber cores is slightly different from the clad, resulting in a preferential etch when the array is placed in an acid solution [2]. Etching results in an array of user-defined wells at the end of the fiber where each well is optically “wired” by the fiber core that defines each well’s bottom