DNA NANOTECHNOLOGY AND ITS BIOLOGICAL APPLICATIONS - Bio-Inspired and Nanoscale Integrated Computing - page 373

T , T

s , s

S

s , s ,

T

s s

T , S

Figure 13.22. Autonomous molecular cascade for signal amplification.

13.10. AUTONOMOUS MOLECULAR CASCADE DEVICES
FOR MOLECULAR SENSING

Another type of task that can be done at the molecular scale (and would be
considerably aided by this technology) is to sense a particular molecule and amplify
a response signal to achieve detection with extremely few starting target molecules.
There are a number of protocols, such as PCR, used to detect and amplify a given
sequence of DNA, but most of these require a repeated temperature-cycling and so
are not autonomous [24]. Demonstrated an autonomous system using DNA
nanostructures that initiated a hybridization cascade reaction in response to
detection of a given ssDNA sequence S. It is described in Figure 13.22.
The experiment made use of multiple copies of two distinct DNA nanos-
tructures T and T

that are initially added to a test tube.
When ssDNA sequence S is added to the test tube, S initially has a
hybridization reaction with a part of T, thus exposing a second ssDNA S

u

u that

had been previously hidden within the nanostructure of T.
Next, S

u u

, thus exposing a second
copy of S that had been previously hidden within the nanostructure of T

has a hybridization reaction with a part of T

. That
other copy of S then repeats the process of other similar (but so far unaltered)
copies of T and T

u

, allowing a cascade effect to occur completely autonomously.
Such autonomous molecular cascade devices have applications to a variety of
medical applications, where a larger response (e.g., a cascade response) is required
in response to one of multiple molecular detection events.

u

13.11. CONCLUSIONS

We have provided an overview of a number of methods for assembling computa-
tional patterns within the molecular fabric of DNA lattices. We have surveyed the