RESEARCH ARTICLE
Copyright © 2011 American Scientific Publishers
All rights reserved
Printed in the United States of America
Journal of
Computational and Theoretical Nanoscience
Vol. 8, 1–7, 2011
Solving River Crossing Puzzle in the DNA Tile
Self-Assembly Model
Yanfeng Wang
1 2 ∗
, Yan Zheng
2
, Xuncai Zhang
1 2
, and Guangzhao Cui
1 2
1
Research and Development Center of Biological Information Technology,
Zhengzhou University of Light Industry, Zhengzhou, 450002, China
2
College of Electrical and Electronic Engineering,
Zhengzhou University of Light Industry, Zhengzhou, 450002, China
DNA computation potentially provides a degree of parallelism far beyond that of conventional silicon-
based computers. The tile assembly model of DNA molecules is a highly distributed parallel model of
nature’s self-assembly. Here we present a method for solving river crossing puzzle by DNA tile self-
assembly. The computation is nondeterministic and each parallel assembly executes in time linear
in the input. The system requires only a constant number of different tile types: 58. In addition, we
also descr ibe mechanisms for finding the successful solutions among the many parallel assemblies
and explore bounds on the probability of such a nondeterministic system succeeding.
Keywords: DNA Self-Assembly, Tile Assembly Model, River Crossing Puzzle, Nondeterministic
System.
1. INTRODUCTION
The idea of algorithmic self-assembly arose from the com-
bination of DNA computation,
1
the theory of tiling,
2
and
DNA nanotechnology.
3 4
As a computational model, algo-
rithmic DNA self-assembly first encodes the input of a
computational problem into DNA patterns and shapes, and
then manipulates these structures to produce new DNA
structures that encode the desired output of the computa-
tional problem.
Computation and self-assembly are connected by the
theory of tiling, of which Wang tiles
5
are the prime
example. Rothemund and Winfree have generalized Adle-
man’s idea to use an exponential number of independent
nodes, forming a formalized mathematical model of self-
assembly, the tile assembly model.
6
Computation and self-
assembly are connected by the theory of tiling, of which
Wang tiles
5
are the prime example. The tile assembly
model is a model of crystal growth, in which individ-
ual components are square tiles with special labels match.
Because that DNA tiles can be more easily “programmed”
to incorporate the constraints of a given problem, it is pos-
sible to exercise some degree of controlling, and therefore
parallel computation can be enhanced by self-assembling
process, in which information is encoded in the DNA tiles.
∗
Author to whom correspondence should be addressed.
The first experimental demonstrations of computation
using DNA tile self-assembly were in Ref. [7], which gave
a two-layer, linear assembly of triple-crossover (TX) DNA
molecules that executed a bit-wise cumulative XOR com-
putation. Barish et al. provided a DNA implementation of a
tile system that copies an input and counts in binary.
8
Cook
et al. used the tile assembly model to implement arbi-
trary circuits.
9
Similarly, Rothemund et al. demonstrated
DNA implementation of a tile system that computes the
XOR function, resulting in a Sierpinski triangle.
10
Brun
proposed and theoretically studied the systems that com-
pute the sums and products of two numbers by using the
tile assembly model.
11
He found that in the tile assembly
model, adding and multiplying can be done using O1
tiles, and that both computations can be carried out in a
linear time. Then, he combined these systems to create two
new systems with more complex behavior for solving two
NP-complete problems (the satisfiability and subset sum)
by using constant computational tile types.
12 13
Inspired
by Brun, we proposed two systems to compute the dif-
ference and quotient of two input numbers using the tile
assembly model with O1 tiles, and these systems can be
carried out in polynomial time. Furthermore, we provided
a scheme to factor the product of two prime numbers, and
also designed protocols to execute integer factoring.
14
The river crossing puzzle is a type of transport puzzle
in which the object is to carry items from one river bank
to another. The difficulty of the puzzle may arise from
J. Comput. Theor. Nanosci. 2011, Vol. 8, No. 4 1546-1955/2011/8/001/007 doi:10.1166/jctn.2011.1725 1