Figure 1: Proposed remote monitoring system for a potable water distribution network. Optical fibers (black) bearing many sensors (red) are contained in the water pipes. The status of these sensors is interrogated from one single central monitoring station. Spatially resolved readout of all sensors in the network is obtained.

Figure 2: Spatially resolved sensor readout. Short (0.5 ns) laser pulses coupled into the fiber end excite closer regions first. The resulting fluorescence pulse is captured by the fiber and propagates to the fiber ends, where it is detected. The time delay between exciting pulse and returning pulse provides the location of the emitting sensor.


Figure 3: One of many possible chemosensor schemes for the identification of the presence of toxins. The optical fiber is coated with a permeable gel, to which various chemical receptors are attached. The fluorescence signal is provided by a fluorescent group (“fluorophore”), which is also attached to the gel matrix. Binding of a toxin to the receptor changes the fluorescence characteristics of the fluorophore. The laser pulses “interrogating” the fluorophore report this change to the monitoring station.

Project Summary:
One goal of this project is the development of a technology to enable real-time monitoring of potable water during its distribution from the water filtration plant to the consumer. Although up to now this threat has received less attention than the airborne distribution of deadly agents, the fact that biological and chemical agents represent credible threats against water supply systems was reaffirmed in a report by the President’s Commission on Critical Infrastructure Protection. Continuous monitoring of even a few major trunk lines at only few locations along these lines, for example by taking water samples and subjecting them to standard chemical analyses, involves significant time and effort.

Our work is directed toward a system whereby an optical fiber, bearing an array of chemosensors and placed inside a water conduit, can report on the chemical composition and physical properties of the water stream in real time at many discrete locations over a long distance (see Fig. 1). The sensor status is evaluated remotely by laser pulses sent through the fiber from a central monitoring station to the sensor locations (see Fig. 2). Since the fluorescence signals returning from the sensors to the monitoring stations encode the sensor locations in the network, a spatial map containing the status of all sensors can be displayed in the central monitoring station. This allows for the rapid implementation of targeted countermeasures should chemical and/or biological agents be injected into the water distribution network.

Our work targets simultaneously many aspects of such a technology. We are studying new coatings for optical fibers that serve as hosts for chemosensors and biosensors (see Fig. 3), are working on combinatorial chemistry techniques for the efficient fabrication of optical fibers carrying thousands of such sensors, and are developing chemical identification methods for trace amounts of chemical and biological pollutants.