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Research
Areas
Our
laboratory pursues research in the field of
nanoscale chemistry. We
explore the novel properties of nanomaterials for their
applications in molecular detection, drug delivery and
renewable energy devices. Our goal is not only to improve or
to develop novel devices for detection and treatment of
human diseases, and for conversion of clean energy by using
these nanomaterials, but also to understand at the
electronic and molecular level the correlation of their
performances and the nanomaterials’ structures. To this end,
we use a mixture of nanoscopic and macroscopic techniques to
characterize the electronic, electrochemical and optical
properties of the nanomaterials and to evaluate the
performance of the nanodevices made from the nanomaterials.
We engage in research in the following three specific areas:
1. Conducting
polymer/carbon nanotube composites
We
investigate the electronic and molecular basis understanding
of the enhanced performance and chemical stability of the
composite. We apply the composites in fuel cells, solar
cells, and chemical sensing devices.
2.
Multiplexed electrical and optical biosensors
We develop
electronic sensing devices with individually functionalized
and electronically addressable nanotransistor arrays for
sensitive biomolecular detection.
We develop
color-coded optical sensors for multiplex detection using
semiconductor QDs and metallic nanoparticles.
3.
Nanotechnology in nonviral gene delivery for cancer therapy
We study
DNA (both long plasmid DNA and short therapeutic
oligonucleotides) nanoparticles formation mechanism to
develop more efficiency gene delivery agents.
We develop
multifunctional gene delivery agents by exploring the novel
properties of inorganic engineered nanostrcutrues (carbon
nanotubes, magnetic nanoparticles, gold and silver
nanoparticles).
Research highlights
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Ma, Y. F., Cheung, W., Wei, D. G.,
Bogozi, A., Chiu, P. L., Wang, L., Pontoriero, F.,
Mendelshon, R. and He, H. X. “Improved Conductivity of
Carbon Nanotube Networks by In-situ Polymerization of a
Thin Skin of Conducting Polymer” ACS Nano, 2008, 2,
1197-1204.
There is increasing enthusiasm for the use of carbon
nanotube network films as conductive flexible electrodes
for a wide variety of applications. However, all the
reported conductivities of the single walled carbon
nanotubes (SWNTs) network films were significantly lower
than the conductivity of a carbon nanotube rope (axial
conductivity). This has been attributed to the high
contact resistance between the tubes in the networks.
Tremendous efforts have been made over the past decade to
prepare polymer and carbon nanotube composites with an aim
to synergistically combine the merits of each individual
component. However, all the reported composites show
enhanced conductivity over the polymeric side, much lower
electronic performance when compared to the carbon
nanotube network film side. In this work, we have
demonstrated experimentally, for the first time, that
in-situ polymerization of a thin “skin” of highly
conductive polymer around and along the SWNTs can greatly
decrease the contact resistance. The polymer skin also
acts as “conductive glue” effectively assembling the SWNTs
into a conductive network, which decreased the amount of
SWNTs needed to reach the high conductive regime of the
network. The highly conductive composite network and the
method to fabricate the highly conductive composite can be
widely used for large area flexible electronics, including
flexible solar cells, and organic light emitting devices.
Ma, Y. F., Chiu, P. L., Serrano, A.,
Ali, S. K., Chen, A. M, and He, H. X. “The Electronic Role
of DNA Functionalized Carbon Nanotubes: Efficacy for
In-situ Fabrication of Conducting Polymer Nanocomposites”
J. Am. Chem. Soc. 2008, 130, 7921-7928.
To truly synergistically combine the merits of each
individual component in the conducting polymer
nanocomposites, it is essential to understand the
monomer-nanotube interfacial chemical and electronic
interactions during polymerization and polymer-nanotube
interfacial interactions after the polymerization, which
has not been fully addressed.
Taking advantages of the well-documented surface chemistry
and electronic structure of single stranded DNA dispersed
and functionalized single walled carbon nanotubes (ss-DNA-SWNTs),
we systematically studied the impacts of the electronic
structure of a carbon nanotube and the monomer-nanotube
interfacial interaction on the kinetics of the
nanocomposite fabrication and the quality of the obtained
composites. For the first time, we found that the
polymerization process can be 4,500 times faster and much
less oxidant needed to initiate the reaction when a
conducting polymer was polymerized in the presence of
intact ss-DNA-SWNTs, which are electron rich. More
importantly, the quality of the composite was
synergistically improved, as demonstrated by the
significantly enhanced electrical performance of the
obtained nanocomposite. However, the synergistic
conductance enhancement cannot be obtained by simply
mixing a preformed conducting polymer with the ss-DNA/SWNTs.
Surprisingly, the enhancement was not achievable by
in-situ polymerization with pre-oxidized SWNTs, which are
electron deficient. In addition, the polymerization
process is also much slower in the presence of
pre-oxidized ss-DNA-SWNTs. Understanding these reaction
characteristics is important to effectively optimize the
fabrication parameters and ensure the formation of
composites in a controllable fashion for a variety of
potential applications. Based on these remarkable
observations, currently they are developing a “greener”
approach for the fabrication of nanocomposites.
In-situ
Fabrication of A Water-Soluble, Self-Doped Polyaniline
Nanocomposite: the Unique Role of DNA Functionalized
Single-Walled Carbon Nanotubes
Yufeng Ma, Shah K
Ali, Ling Wang, Pui Lam Chiu, Richard Mendelsohn and
Huixin He,
J. Am. Chem. Soc., 128,
12064-12065.
Dispersion of carbon
nanotubes into solvents affects their surface chemistries,
electronic structures, and subsequent functionalization. In
this communication, a water-soluble self-doped
polyaniline nanocomposite was
fabricated by in-situ polymerization of the
3-aminophenylboronic acid
monomers in the presence of single-stranded DNA dispersed- and
functionalized- single-walled carbon nanotubes.
For the first time, we found that the carbon nanotubes became
novel active stabilizers due to the DNA
functionalization. The nanotubes reduced the polyaniline
backbone from the unstable, degradable, fully oxidized
pernigraniline state to the stable, conducting emeraldine
state due to their reductive ability,
which could improve the chemical stability of the self-doped
polyaniline. Electrical measurements demonstrate that the
conductivity of the nanocomposite was much higher than that of
the pure self-doped polyaniline in both acidic and neutral
solutions.
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Yufeng Ma, Shah R Ali, Afua S. Dodoo, and Huixin He,
J. Phys. Chem. B, 2006, 110, 16359-16365
A nanocomposite of poly(anilineboronic acid), a self-doped
polyaniline, with ss-DNA wrapped single walled carbon
nanotube (ss-DNA/SWNTs) was fabricated on a gold electrode
by in-situ electrochemical polymerization of
3-aminophenylboronic acid monomers in the presence of ssDNA/SWNTs.
We used this nanocomposite to detect nanomolar
concentrations of dopamine and found that the sensitivity
increased four orders of magnitude compared to the detection
only neat poly(anilineboronic acid) was used to modify the
electrode. For the first time, this work reports the
multiple functions of the ss-DNA/SWNTs in the fabrication
and biosensor application of a self-doped polyaniline/ssDNA/SWNT
nanocomposite. First, the ssDNA/SWNTs acted as effective
molecular templates during polymerization of self-doped
polyanline so that not only was the polymerization speed
increased, but also the
quality of the polymer was greatly improved. Second, they
functioned as novel active stabilizers after the
polymerization, which significantly enhanced the stability
of the film. Furthermore, the ss-DNA/SWNTs also acted as
conductive polyanionic doping agents in
the resulting polyaniline film, which showed enhanced
conductivity and redox activity. Finally, the large surface
area of carbon nanotubes greatly increased the density of
the functional groups available for sensitive detection of
the target analyte. We envision that polyaniline with other
functional groups, as well as other conducting polymers, may
be produced for different targeted
applications by this approach. This work is published in
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Zhang, J. M., Ma, Y. F., Stachura, S. He, H. X.,
Langmuir, 2005, 21, 4180-4184
This work reports a robust and efficient approach to
assemble highly aligned DNA strands onto Si chips. The
method combines advantages from molecular combing and
microcontact printing to realize controlling both the
density and direction of DNA strands on the Si chip. In
addition, it also can be utilized to prepare stretched DNA
structures on solid surfaces. Compared to approaches that
use molecular combing directly on silanated surfaces, the
stretched single-chain DNA structures are straighter.
Furthermore, by exploiting the hydrophobic property of the
intrinsic poly(dimethylsiloxane) (PDMS) stamp, this study
also describes a simple way to simply produce straight
bundled DNA arrays on Si and other substrates.
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Yufeng Ma, Jianming Zhang, Guojin Zhang and Huixin He*,
J. Am. Chem. Soc. 2004, 126, 7097 –7101
It is essential to put individual, freestanding nanowires
onto insulating substrates and integrate them to useful
devices. Here we report a strategy for fabrication of
conducting polymer nanowires on thermally oxidized Si
surfaces using DNA as templates. The direct use of stretched
and immobilized DNA strands as templates avoided the
agglomeration of DNA caused by shielding of charges on DNA
when polyaniline/DNA complexes formed in solution. Most
importantly, the oriented DNA strands immobilized on Si
surface predetermined the position and the orientation of
the nanowires. The approach described here is the first step
toward uniting the programmable-assembly ability of DNA with
the unique electronic properties of conducting polymers for
high-density functional nanodevices. The conductivity of the
nanowires is very sensitive to the proton doping-undoping
process suggesting that the nanowires hold a great promise
for sensitive chemical sensor applications.
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Oligodeoxynucleotide nanostructure formation in the
presence of polypropyleneimine dendrimers and their uptake
in breast cancer cells
Alex M. Chen, Latha M. Santhakumaran, Sandhya K. Nair,
Peter S. Amenta, Thresia Thomas, Huixin He, and T. J.
Thomas, Published in Nanotechnology, 2006.
This is a collaboration study with
Drs. Thomas at University of Medicine and Dentistry at New
Jersey. We studied the efficacy of 5 generations of
polypropyleneimine (PPI) dendrimers to provoke
nanoparticle formation from a 21-nt antisense
oligodeoxynucleotide (ODN). Nanoparticle formation was
observed with all generations of dendrimers by light
scattering and microscopic techniques. The efficacy of the
dendrimers increased with generation number. Atomic force
microscopy (AFM) was used to study the morphology of the
structures at different condensation stages.
Based on the observed nanofibers in the beginning
of condensation,
we propose a zipping condensation mechanism, which is very
different from the condensation pathways of high molecular
weight DNA polymers. Electron microscopy showed the
presence of toroidal nanoparticles. Confocal microscopic
analysis showed that the nanoparticles formed with G-4 and
G-5 dendrimers could undergo facile cellular uptake in a
breast cancer cell line, MDA-MB-231, whereas particles
formed with G-1 to G-3 dendrimers lacked this ability.
Nanoparticles formed with G-1 to G-3 dendrimers showed
significantly lower zeta potential (5.2-6.5 mV) than those
(12-18 mV) of particles formed with G-4 and G-5
dendrimers.
These results show that the structure
and charge density of the dendrimers are important in ODN
nanoparticle formation and cellular transport and that G-4
and G-5 dendrimers are useful in cellular delivery of
antisense ODN.
Figure 1. AFM images of condensates formed by the
21-nt ODN in the presence of PPI dendrimers after
10-minute condensation. ODN had a concentration of 0.4
µM and dendrimer was 2.5 µM in a solution containing the
approximate physiological concentration of salts. Panels
are (A) G-1, (B) G-2, (C) G-3, (inset) Phase image with
the same scale of the main image indicated by a red
arrow. (D) G-4, (E) G-5, and (F) G-5. Bar represents
250 nm in all panels.
Figure 2.
AFM images of condensates formed by the 21-nt ODN in
the presence of PPI dendrimers after 1 hour of
condensation (panels A, B, C, D, E and F). ODN had a
concentration of 0.4 µM and dendrimer was 2.5 µM in a
solution containing the approximate physiological
concentration of salts. (A) G-1, (B) G-1 (zoom image
of one part of panel (A)), (C) G-2, (D) G-3, (E) G-4,
(F) G-5. Bar represents 4 µm in panel (A), 1 µm in
panels (B, C, D, F) and 300 nm in panel (E).
Figure 3.
Representative images of cellular uptake of
fluorescein-labeled 21-nt ODN by MDA-MB-231 cell by
confocal microscopy. ODN uptake in the absence (A, B,
C, D) or the presence (E, F, G, H) of G-4 dendrimer is
shown. Differential interference contrast (DIC) images
of cells are shown in panels A and E. Nuclei stained
with DAPI (B and F), detection of fluorescein-labeled
oligonucleotide (C and G) and overlay of images (D and
H) are shown. Final concentration of ODN and G-4
dendrimer in the cell culture medium were 0.2 µM each.
Figure 4. Schematic representation of the
proposed zipping mechanism for the condensation of the
21-nt ODN by PPI dendrimers. PPI dendrimers first
“zip” the ODN molecules by electrostatic interactions
to form extended chains. The extended chains could
wrap around to form aggregated complex structures,
which then further condense into spheroidal
structures. The extended chains could also interact
with each other in parallel to form ribbon- and
rod-like structures and then wrap around to form
toroidal structures.
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