nano cube syn and dimer
TRANSCRIPT
THE END GOAL
REAL-TIME MOLECULAR
DETECTION
Gold nanocluster and pH indicator
(4-mercapto benzoic acid) Single
plasmonic nanoparticles for
biosensing, Takumi et al.
Functionalizing metallic nano
structures with environmentally
sensitive molecules allows for single
molecule detection.
Example: Disassociation of 4-MBA
carboxyl group causes a shift in
adsorbed spectra. Thus intracellular
detection of pH gradients is possible.
As a specific frequency of light is absorbed into the
resonance of plasmons, the transmitted and reflected
spectrum is altered.
Ref: nanocomposix.com
ENHANCEMENT FACTOR
• Raman scattering a LOW probability
phenomena that is enhanced with
particle geometry.
• Geometry results in hotspots in areas of
small radius
Rycenga et al.
WHAT ARE NANO ANTENNA?
1. WHEN LIGHT INTERACTS WITH THE SURFACE OF A METAL, ITS ENERGY IS TRANSFERRED TO THE
FREE ELECTRONS ON THE SURFACE. THESE FREE ELECTRONS COLLECTIVELY OSCILLATE AS A
PLASMON
2. WHEN THE OSCILLATION IS RESTRICTED TO A DOMAIN COMPARABLE TO THE WAVELENGTH
USED TO EXCITE IT, THEN IT IS A LOCALIZED SURFACE PLASMON(LSP).
3. THE ELECTRIC FIELD OF THE SURFACE IS GREATLY EFFECTED BY PLASMONS AND PROXIMITY TO
OTHER OBJECTS CAN RESULT IN RESONANCE.
4. RESONANCE RESULTS IN ENHANCEMENT OF ELECTRIC FIELDS DUE TO GEOMETRY AND AREAS
OF HEIGHTENED ELECTRIC FIELDS ARE KNOWN AS NANO ANTENNA.
5. RAMAN SCATTERING IS THEORIZED TO BE THE RESULT OF LIGHT INTERACTING WITH
RESONATING PLASMONS TO EMIT RADIATION.
REAGENTS
Ethylene Glycol: Heat to 150-160 c is necessary for equilibrium shift to favor formation of acetaldehyde. Purity of low metallic ion concentration is important as it is competes with
sulfur ions.
Sodium Hydrosulfide: Initiator that dramatically decreases reaction time 10 fold. Acutuallymolar concentration is difficult to know because it is an unknown hydrate. Suggest moving to
Sodium sulfide. Ratio of sodium sulfide to silver nitrate is 1:10,000.(Panfilova)
PVP: Poly vinyl pyrrolidone. Regardless of molecular weight of polymer, it needs to exist in
reaction in a ratio of 1:1.9-2.25 silver ions per repeating unit of PVP (C6H9NO).
Silver Trifluoroacetate: Source of silver ions for reaction. Use of silver nitrate has been more
widely used, but it is sensitive to heat.
E. V. Panfilova et al, “Study of polypol synthesis reaction parameters controlling high yield of silver nanocubes.”
PUBLISHED DATA OF REAGENT VARIATION
E. V. Panfilova et al, “Study of polypol synthesis reaction parameters controlling high yield of silver nanocubes.”
2006
Altering sodium sulfide from 26-32uM
concentration in reaction vessle
Altering Silver:PVP ratio (0.77, 1.155,
1.5, 2.3, .7)
Results of varying NaSH were inconclusive due to incorrect PVP concentration.
1.5mL 2/3/15
1.5mL 1/24/15
1.7mL 2/3/15 1.9mL 2/3/151.25mL 1/24/15
Larger Size Distribution Rare cube formationLarge Shape Distribution 35-45% Yield
Notice over passivation decreases particle size
DIMERIZING
Hydrophobic Sonication
in Ethanol
1. PVP Ag Nanocubes
2. Deposition to substrate
3. Functionalize with
hydrophobic ligand
4. Release from substrate in
ethanol
5. Wash and storage
1) PDMS stamp hydrophobic octadecanethiol (ODT) on to top face of cube for 10
seconds.
2) Allow 5 minutes reaction time.
3) Rinse with toluene(???)
4) Sonicate in hydrophilic 16-mercaptohexandecanoic acid (MHA)
5) Wash in ethanol.
POLY DIMETHYLSILOXANE - PDMS
• Biologically inert. Food additive.
• Resistant to polar solvents, swells with
non polar.
• Two part polymer.
• Elasticity can by tuned by mixing ratio.
• Easy to make and inexpensive
FUNNEL OF LOVE
1. Create a disperse monolayer at the
surface of a filled funnel.
2. Slowly drain fluid from funnel, thereby
reducing surface area.
3. Cubes should form compact monolayer.
The current procedure is
extremely crude as a true
monolayer is not being formed
prior to stamping. Rather 3D
structures are dominating the
surface preventing single face
functionalization.
More commonly we see this…
FUNCTIONALIZATION OF SILVER SURFACE
• Stabilizing PVP must be removed in order
to functionalize surface.
• Thiol-terminated molecules for a stronger
covalent bond with silver than PVP and
will irreversibly replace PVP.
• If a specific percentage of replaced PVP
is required, this can be accomplished by
use of low thiol concentration and
monitoring change in SERS spectrum.