Transcript Self-Assembly at nano-Scale Binary Nanoparticles Superlattices

Chad A. Mirkin et al. Small 2005, 1, No. 1, 64 –69
Top-Down Meets Bottom-Up:
Dip-Pen Nanolithography and DNA-Directed
Assembly of Nanoscale Electrical Circuits
Student: Xu Zhang
Introduction
• Interfacing bottom-up chemical and biological assembly schemes
with top-down lithography to fabricate complex devices is presently
a major goal in nanoscience and technology.
• Bridging the gap between self-assembly techniques and modern
top-down lithography offers a way to incorporate additional
functionality (for example, in the form of chemical or biological
recognition and sensing capabilities) into conventional electronic
and optical devices, and provides a rapid means to test the potential
viability of multiple chemically synthesized device components and
self-assembly strategies.
• This paper presents a method that allows multiple, independent
chemical recognition events to be incorporated in close proximity in
a single electrical junction device by using DNA-directed assembly
of specific metal nanoparticles.
Strategy: DNA-directed assembly of Au NPs at the
gap between electrodes
DNA-directed assembly
of Au nanoparticles
modified with
oligonucleotides at the
gap between metallic
electrodes selectively
patterned with DNA via
DPN
Two different DNA
systems used to
fabricate the
devices: capture
(a,d),target
(b,e),and probe (c,f)
DNA strands.
Experimental procedure 1st:
Fabricating the electrodes
•
First, contact pads of thermally
evaporated layers of Au and Cr
were patterned using
photolithography onto a SiO2
substrate
•
Next, electron- beam lithography
(EBL) was utilized to define an
inner electrode pattern and the
inner junction “nanogap” regions
(an example is circled in the
Figure), which comprises two Au
electrode leads separated by a
gap of 20–100 nm.
Experimental procedure 2nd: Testing the process of DNAdirected nanoparticle capture into the gaps
•
•
DNA functionalization of the electrodes by
immersing the chips in solutions of hexylthiolmodified DNA strands 1a or 2d. Or by DPN,
which results devices with different DNA
sequences on neighboring junctions on the
same chip. (An APTMS modified Si3N4 AFM tip
coated with 5’ HS-DNA ink like 1a, is brought to
write on the specific electrode junctions of gold
electrode surfaces in a controlled humidity
chamber. A new tip coated with a second DNA
sequence 2d was used to pattern a second set
of nearby junctions. Then passivate the surface
with octadecanethiol (ODT).
Then apply a droplet of the solution containing
both Au nanoparticle-linker conjugates (Auoligo 1c or 2f – linker oligo 1b or 2e conjugate)
to the chip surface and hybridize 3–4 h, then
rinse the chip to remove nonspecifically bound
NPs.
Experimental procedure 3th:
Using Field emission scanning electron microscopy
(FESEM) to verify the DNA deposition on a test pattern
•
A) A low-resolution FESEM image of
the entire device;
•
B) dark-field optical microscopy image
of the test patterns on the Au bonding
pads;
•
C) FESEM image of the assembly of
complimentary oligonucleotidemodified 20-nm-diameter Au
nanoparticles on the selected area of
the test-dot arrays.
•
The dark square visible in the image
is an area that has previously been
scanned by the FESEM beam.
Experimental procedure 4th:
Using (FESEM) to verify the process of DNA-directed
nanoparticle capture into the nanogaps
FESEM image of single 20- and 30-nm-diameter Au
nanoparticles assembled from solution and bridging the two
adjacent nanoelectrode junctions.
Experimental procedure 5th:
Electrical characterization
Current–voltage (I–V) characteristics of
solution-modified, DPN-generated
nanogap devices assembled with
oligonucleotide-modified Au
nanoparticle devices: A) I–V curves of
the devices assembled with 30-nmdiameter Au NPs at various
temperatures; B,C) I–V curves of the
devices assembled with 20-nm (B) and
30-nm (C) diameter Au NPs at T=4.2 K
showing the experimental data and the
fit to the orthodox Coulomb
blockade model (c); D) I–V and the
corresponding conductance (numerical
dI/dV) plot of the device assembled
with 30-nm-diameter Au nanoparticles
at T=4.2 K. The inset picture shows a
model circuit of the system with a
double-barrier junction used for fitting
the experimental data.
Conclusions
The authors have demonstrated that
• DNA hybridization can be used to direct the assembly of single
DNA-functionalized nanoparticles into single-electrode junctions;
• DPN can be used to interface DNA-directed nanoparticle assembly
with conventional microfabrication techniques to produce primitive
tunnel junction circuits.
• And these junctions provide the opportunity to measure electrical
transport through well-defined biochemical tunnel junctions, as well
the opportunity to develop simple biosensors based on basic on/offtype recognition events.
Learn from the paper
How to develop the scientific thinking:
Top-Down Or Bottom-Up?
• This paper gave me an example for develop the
scientific story using Bottom-Up method.
• And also a good example for compose the paper using
Top-Down method.