  In 2011 the DNA seesaw gate motif was introduced. It is a powerful
feed-forward DNA nanodevice that can perform digital logic computations. The
landmark of that work managed to evaluate moderately large Boolean circuits by
cascading multiple DNA seesaw gates. Although the design is robust in solution
and scalable, it is designed for one time use and is not reusable. This
prevents pursuing important applications such as feedback and sequential
digital circuits. We present a novel design for DNA nanodevices that can
perform digital logic computations and are furthermore renewable. First, we
modified the prior DNA seesaw gate motif into a hairpin. We call the resulting
motif a DNA hairpin-seesaw gate. We show the feed-forward digital computation
reaction imitates the seesaw gate motif. Second, we added a reporting phase
that provides increased scalability to our device. Third, we designed input and
fuel extracting hairpins that when added, initiate a renewing process. This
results in a renewed functional gate, in its original configuration, which is
able to make a new logical computation with new inputs. Finally, we introduced
a renewable two-input Boolean logic OR gate. After calculating the output of a
certain input set, the circuit is restored and a new set of inputs is
introduced to compute the new output. We provide experimental fluorescent data
on three repeated rounds of executions of our hairpin gate motif and its
restoration, indicating gradual loss of response. Finally, we calculated rate
constants of our experimental data by fitting it to a second order reaction
model using maximum likelihood estimation method.
