Development of high-density optical fiber arrays: New designs and applications in microscopy, microfabrication and chemical sensing

Optical imaging fibers are employed for the development of fluorescence-based chemical sensors, biosensors and optical microstructures. Optical imaging fibers comprise thousands (e.g., 3 000--100 000) of individual optical fibers that are melted and drawn together to form a coherent array, typically several hundred micrometers in diameter. The array's highly dense architecture provides thousands of spatially discrete pieces of information with a resolution as low as 2 mum. We have used these advantages to design arrays that have applications in microscopy, microfabrication and chemical sensing. In one design, the imaging fiber was coated with a thin, analyte-sensitive polymer layer to create a sensor array capable of obtaining both visual and chemical information. This technique has many potential applications because the sensing layer can be changed to measure any analyte for which there is a fluorescent indicator. The ability to combine imaging and chemical sensing in real-time was first demonstrated using sea urchin fertilization biochemistry as a model system. In these experiments, we observed both localized pH changes following fertilization as well as morphological transformations during cell division. Using the same technique, neurotransmitter release from single cells and tissue was also investigated using an acetylcholine-sensitve polymer layer. In a second design, a far-field viewing GRINscope sensor for making analytical measurements in remote locations was fabricated by coupling an imaging fiber and a micro-Gradient Index (GRIN) lens. The GRINscope sensor has the ability to view objects that are not in contact with the sensor surface. We demonstrate both single analyte and multianalyte GRINscope sensor configurations. In a third design, sensor arrays are prepared by randomly distributing a mixture of microsphere sensors on an etched imaging fiber containing thousands of micron-scale wells. The sensors occupy a different location from array to array and are identified using encoding schemes, rather than by a predetermined location in the array. High-sensitivity applications using these microsphere arrays were investigated. In a fourth design, chemical etching techniques are used to fabricate arrays of hybrid fiber optic micro- and nano-channels. Applications to chemical sensing and separation techniques are discussed.