Researchers from the National Institute of
Standards and Technology (NIST), the Naval Research Laboratory (NRL)
and the University of Maryland (UMD) have demonstrated a deceptively
simple technique for chemically bonding single strands of DNA to gold.
Among other features, they report in a forthcoming issue* of the
Proceedings of the National Academy of Sciences, the technique offers
a convenient way to control the density of the DNA strands on the
substrate, which could be important for optimizing DNA sensor arrays.
Single-strand DNA can be anchored to a gold
substrate for use in biodetectors by attaching a tail of adenine
bases. Adenine's strong affinity for gold not only bonds the
strands in place but also allows some control over the spacing by
adjusting the length of the tail.
Short DNA sequences arrayed on substrates like
glass, silicon or gold are used in biochemical sensors that can detect
specific "target" sequences of DNA or analyze complex sequences. In
such arrays, DNA strands are attached to the substrate by one end and
stand up like bristles on a brush. Specific "target" DNA sequences
from a test sample can be identified because they will bond (hybridize)
only to a complementary sequence on the array--microarray "gene chips"
are the best-known example of the technology. The properties of gold
are well-known, so it is a practicaland convenient substrate for some
sensors. One popular technique for making DNA sensors (developed at
NIST) is to use DNA with a sulfur atom attached to one end, which acts
as "glue" because sulfur readily reacts with gold.
But a potentially less expensive and even simpler
approach, according to the NIST, NRL and UMD team, might be to use a
string of adenine nucleotides as an anchor. Of the four nucleotides
that comprise DNA molecules, adenine, turns out to have a particularly
high affinity for gold. Short strands composed entirely of adenine
will adhere to a gold surface even if they have to muscle aside other
strands in the process. As a result, say the researchers, short blocks
of adenine at the end of DNA strands can serve as bonding anchors--but
even better, they say, these adenine blocks can be used to control the
spacing of the DNA strands on the substrate. This is because each
adenine tail lies flat on the substrate, taking up space. Within
limits, the longer the adenine tail is, the larger is its footprint on
the substrate, and the lower the total density of DNA strands.
Controlling the density of DNA "brushes" on a
substrate is important for sensor design because an overly dense
thicket does not leave enough room for "target" DNA strands from the
test sample to bond, while too sparse an array doesn't produce a
strong enough signal.
Source / Further
information:
-
Publishing date: 22-Dec-2006
-
A. Opdahl, D. Petrovykh, H. Kimura-Suda, M.J.
Tarlov and L.J. Whitman. Independent control of grafting density
and conformation of single-stranded DNA brushes. Proceedings of
the National Academy of Sciences, 104:9-14 (2007)
The authors have applied for a patent on the
technique. The research was supported by Office of Naval Research
and the Air Force Office of Scientific Research.
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