Hydrological tracers using nanobiotechnology: proof of concept.

In order to answer questions that involve differentiating among multiple and potentially interacting hydrological flowpaths, it would be ideal to use multiple tracers with identical transport properties that can nonetheless be distinguished from each other. This paper describes the development and proof of concept of a new kind of engineered tracer system that allows a large number of individual tracers to be simultaneously distinguished from one another. This new tracer is composed of polylactic acid (PLA) microspheres into which short strands of synthetic DNA and paramagnetic iron oxide nanoparticles are incorporated. The synthetic DNA serves as the "label" or "tag" in our tracers that allow us to distinguish one tracer from another, and paramagnetic iron oxide nanoparticles are included in the tracer to facilitate magnetic concentration of the tracers in potentially dilute water samples. Some potential advantages of this tracer concept include: virtually limitless uniquely labeled tracers, highly sensitive detection, and relatively moderate expense. Three proof-of-concept experiments at scales ranging from orders of 10 cm to 100 m demonstrated the use of the tracer system.