  In contrast to electronic computation, chemical computation is noisy and
susceptible to a variety of sources of error, which has prevented the
construction of robust complex systems. To be effective, chemical algorithms
must be designed with an appropriate error model in mind. Here we consider the
model of chemical reaction networks that preserve molecular count (population
protocols), and ask whether computation can be made robust to a natural model
of unintended "leak" reactions. Our definition of leak is motivated by both the
particular spurious behavior seen when implementing chemical reaction networks
with DNA strand displacement cascades, as well as the unavoidable side
reactions in any implementation due to the basic laws of chemistry. We develop
a new "Robust Detection" algorithm for the problem of fast (logarithmic time)
single molecule detection, and prove that it is robust to this general model of
leaks. Besides potential applications in single molecule detection, the
error-correction ideas developed here might enable a new class of
robust-by-design chemical algorithms. Our analysis is based on a non-standard
hybrid argument, combining ideas from discrete analysis of population protocols
with classic Markov chain techniques.
