overview towards precise patterning of nanoparticles for nanoelectronic and plasmonic devices dna...
TRANSCRIPT
Overview• Towards precise patterning of nanoparticles for
nanoelectronic and plasmonic devices• DNA used to from complex nanostructures
• Authors present method of fabricating nanoparticle arrays with controlled periodicity with 3-D DNA nanotubes
-Rothemund, P. W. K. Nature 440, 297-302 (16 March 2006)
Design
• One long DNA strand (black) with 170 short ‘staple’ strands (red)
• (A), (B), (C) are clustered biotin
• DNA forms 6-helix nanotube bundle (412 x 6 nm)
Assembly & Binding
• Height = 1.7- 3.5 nm (6 nm)
• Length = 436 +/- 14 nm (412 nm)
Assembly & Binding
• Successful attachment of 9 streptavidin (height increase ~0.5 nm)
• Periodicity of 45 nm (43 nm expected)
Assembly & Binding
• QDs have similiar spacing
• 5.5 nm height cross section
• 49 nm periodicity
Spatial Control
Conclusion
• Powerful and convenient pathway to control nanoparticle patterning
• Self-assembling scaffold for nanoscale electronic and photonic devices
• Variations available for spacing, length, QD size, and QD material
Controlled Drug Deliver
• Self-assembled micelles– Biocompatible and biodegradable– Amphiphilic block copolymers (PEG, PCL,
PLA)
• Inefficient drug release
PEG Alternative
• Dextran (Dex)– Aqueous soluble, biocompatible, branching– -OH functionality for conjugation
• Authors report shell-sheddable biodegradable Dex-SS-PCL micelles for drug delivery
Reduction-Responsive Delivery
Synthesis
Micelle Formation
• Average micelle size increased from 60 to 200 nm with DTT addition– Aggregates from lose of
solubilizing shell
• Little change after 24hrs w/o DTT
DOX Release
Cellular Uptake
2 hr
4 hr
24 hr
Cellular Uptake
2 hr
4 hr
24 hr
Free DOX
No DOX
Toxicity
• Free DOX and cleavable micelle show similar response
• Control and non-DOX loaded micelle show similar response
Conclusion
• Nontoxic Dex-SS-PCL diblock copolymers with high drug loading efficiency were developed
• Micelles are stable and allow for rapid drug release in response to intracellular levels of reducing potential
Overview
• Effort to mix nanoparticles (NP) with polymers to combine unique physical properties with processibility
• Need efficient ways to control NP arrangement in polymer matrix– Dispersion of NP impacts electronic,
transport, and mechanical properties
NP Incorporation
Phase Dispersion
Conclusions
• Initially NPs are randomly incorporated in swollen polymers
• Polymers pack more densely with water and NPs phase segregate to polymer core-shell interface
Nano Lett., Article ASAPPublication Date (Web): January 26, 2010
Goals
• Efficient, highly portable energy sources for hand-held electronics
• Decreasing power requirements– Augment batteries with ‘scavenger’ systems– Salvage otherwise wasted energy
Wasted Energy…
• Work by the human body– Breathing
• Lung expansion/contraction generate ~1 W (charge pacemakers?)
– Walking• A heel strike during walking has 67 W of power
available (~1-5% energy to power cell phones)
Piezoelectrics
• Crystals become electrically polarized by mechanical stress (and vice versa)
• Processing - high temperature, rigid inorganic substrates• Authors present approach to incorporate crystalline
piezoelectric lead zirconate titanate (PZT) onto rubber substrates for flexible energy conversion
-http://www.piezomaterials.com/
Production
Processed into nanothick ribbons and printed onto polydimethyl-siloxane (PDMS) stamps via dry transfer
Function(a) Schematic of a specimen indicating
piezoelectric bending and measurement.
(b) Oscillating pressure (left axis) and induced dielectric displacement (right axis)
Characterization
Summary
• Highly crystalline piezoelectric ceramic ribbons have been transferred onto flexible rubber substrates
• Efficient electromechanical energy converters towards wearable/implantable energy harvesters
• Challenges to overcome: stretchable substrates, cycling longevity, storage/power conversion on substrates…
Light Concentration
• Surface plasmons– Electromagnetic surface waves carried by
density fluctuations of electrons
• Patterned metals– Films, trenches, gaps, tips for control and
delivery of surface plasmons
Surface Plasmons
• Focusing on tip or apex allows for excitation of highly local and extremely intense optical fields– ‘Optical lightning rod’
• Authors present three-dimensional plasmonic nanofocusing with patterned gold and silver pyramids
Nanopyramids
500 nm
500 nm
200 nm
1000 nm
Light incident from above is backscattered into plasmons that travel up sides and corners, converging at the apex
Fabrication
-Xu, Q., Tonks, I., Fuerstman, M., Love, C., Whitesides, G. Nano Lett., 2004, 4 (12), 2509.- Henzie, J., Kwak, E., Odom, T. Nano Lett, 2005, 5 (7), 1199.
Fabrication
-Xu, Q., Tonks, I., Fuerstman, M., Love, C., Whitesides, G. Nano Lett., 2004, 4 (12), 2509.- Henzie, J., Kwak, E., Odom, T. Nano Lett, 2005, 5 (7), 1199.
Simulations
Simulations
Imaging
Pyramids in Action
Conclusion
• 3-D nanofocusing with well-defined plasmonic hot spots
• Applications in scanning-probe microscopy, optical trapping, high-density data storage
• Thin films allow for backside excitation