While the overall project is the sorting of cargos on origami, we expected verification of all of the mechanisms would take longer than one summer. Therefore, this summer was spent verifying three aspects of the project:
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Simulation of Expected Results
Before undertaking our experiments, it's desirable to have an idea what our results our going to look like, particularly in the case of random walking, which we intend to investigate rather thoroughly. To do this, we use a stochastic simulation, written in MATLAB.
Derivation of Random Walk Formula
Besides the MATLAB simulation of random walking and cargo sorting, a random walk formula was developed to further investigate and verify the random walking mechanism on DNA origami. The probability of reaching the walker goal is expressed as a function of the number of steps taken.
Verification of Overall Mechanisms in Solution
All of the essential mechanisms in our system were veriﬁed in solution using polyacrylamide gel electrophoresis. These mechanisms include: walker-track binding, triggering the walker, walking from one track to another, picking up cargo, walking while carrying cargo, triggering the cargo goal, dropping oﬀ cargo, and irreversibly walking from tracks to the walker goal. We are fairly confident that all of these mechanisms work as expected in solution, with a few mysteries that do not seem to interfere with the overall behavior of the system (see Gel Verification).
Verification of Random Walking Mechanism on Origami
We used fluorescent spectroscopy (SPEX) to verify the random walking mechanism on the origami. Goals were tagged with fluorophores whereas walkers were tagged with the corresponding quenchers. Fluorescent signals will decrease when walkers reach their goals. Unlike AFM, which studied individual origami, SPEX experiments studied the collective behavior of all the origami in solution. Hence, the SPEX results were analyzed using both Matlab simulation and mathematical formulae.
We are in the process of using atomic force microscopy (AFM) to verify the random walking mechanism on origami. We plan to image individual origami rectangles (using the 1D random walking playground layout) with an inhibited, biotin/streptavidin-tagged walker at its start site, and verify that walkers begin at their intended start site at one end of the random-walking track. We will then trigger the walker, wait for some amount of time, and image the origami again to verify that walkers have left their start site and are tending to stop at their goal at the other end of the track. This research is still in progress.