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Abstract

Counting is the action of finding the number of elements in a set. Past attempts at developing counters in cells have mostly attempted to mimic the binary methods that computers use to count.
Our first counter takes a new approach to counting in cells, essentially a mechanical rotary counter implemented on a micro scale. Each time the counter detects an input, it performs an excision and integration directly down-stream of the active site, turning on a reporter and rotating over one "notch" on the counter.
Our second counter operates on the wholly different principle that the statistical occurrence of a rare event in a large population can be modeled. Each cell in our population harbors a construct that when stimulated has a small chance of excising a terminator and expressing a resistance gene. The number of resistant cells is thus an accurate count of the number of input stimuli.

This counter, like the first one, can also be used in “timer” mode. Timer functionality is achieved by co-expressing with the antibiotic gene LuxI, under a promoter of our choice. When the media concentration of AHL exceeds a threshold (in part determined by the promoter we choose) YFG is expressed. To be able to count correctly, this system requires careful control of the media, so we have designed a microfluidic device to test this system.