Gold Nanorod Biosensors and Single Particle Spectroscopy
Jason H. HafnerMURI site visitJuly 27, 2005
Gold Nanorods
0
0.2
0.4
0.6
0.8
1
400 500 600 700 800 900 1000
Opt
ical
Den
sity
Wavelength (nm)
longitudinal
transverse
-Sharp, localized plasmon resonance.-Molecular size in short dimension
Localized Surface Plasmon Resonance Sensors
Silver nanoparticles on substrate
Antibodies conjugated to nanoparticles.
wavelength
abso
rban
ce
Localized Surface Plasmon Resonance Sensors
wavelength
abso
rban
ce
Upon analyte binding, the resonance wavelength shifts:
Silver nanoparticles on substrateBy Nanosphere Lithography
Antibodies conjugated to nanoparticles.
Localized Surface Plasmon Resonance Sensors
Haes, Van Duyne Exper Rev. Mol. Diagn. 4, p. 528 (2004).
-Simple physical mechanism: no surface enhancement, no aggregation.-Low cost technology: “label-free”, no purification or amplification of analyte. Use Gold Nanorods:More facile surface chemistry (gold).Entire substrate created by self assembly.Elongated shape and small size increases sensitivity (higher nm/RIU’s).
Seed-Mediated, Surfactant Directed
Gold colloid grows while surrounded by a surfactant bilayer which regulates the growth rate…
Gold Nanorods Synthesis
N+
Br -CTAB
Murphy, Langmuir 20, p. 6414 (2004).
… a defect forms with poor surfactant binding to create anisotropic growth…
… which results in an elongated structure.
50 mL of nanorod solution with OD=2 can be produced, but it is only stable in saturated surfactant.
PEG-SH displaces the CTAB, creating a strongly-bound buffer layer so nanorods may be put in arbitrary solutions.
HO
O
O
O
SH
100
Nanorod PEGylation
+
5000 MW PEG-thiol
0
0.25
0.5
0.75
1
1.25
1.5
Op
tica
l Den
sity
Wavelenght (nm)
400 500 600 700 800 900 1000
Nanorods in CTAB
Nanorods in buffer
PEG-Nanorods in buffer
Nanorod-Antibody Conjugation
N
O
O
O
O
NH
S
S
O
N
LC-SPDP
IgG conjugated nanorods bind a complementary strip plate (left), while nanorods that are only PEGylated do not (right).
+
Absorbance of Nanorods on a glass substrate
50:15 = 4.4 +/- 0.5 x 109 cm-1M-1
.
0
0.02
0.04
0.06
0.08
0.1
400 500 600 700 800 900 1000
Ab
sorb
an
ce
Wavelength (nm)
air water
SPR sensitivity = 150 nm/RIU
(similar to nanosphere lithography)
0.09
0.1
0.11
0.12
0.13
0.14
700 720 740 760 780 800
Abs
orba
nce
Wavelength (nm)
750.1 +/- 0.3 nm
Gold Nanorod Biosensors
0.09
0.1
0.11
0.12
0.13
0.14
700 720 740 760 780 800
Abs
orba
nce
Wavelength (nm)
750.1 +/- 0.3 nm
759.6 +/- 0.3 nm
Gold Nanorod Biosensors
0.09
0.1
0.11
0.12
0.13
0.14
700 720 740 760 780 800
Abs
orba
nce
Wavelength (nm)
750.1 +/- 0.3 nm
759.6 +/- 0.3 nm
763.0 +/- 0.2 nm
Gold Nanorod Biosensors
Single Particle Spectroscopy
To camera,CCD spectrometer,
InGaAs spectrometer.
Individual Gold Nanoshells, Dark Field
1. Determine more accurate optical properties of nanostructures.
2. Study complex nanostructure shapes.
3. Characterize tips for near field microscopy.
4. Find ultimate limit of LSPR biosensing.
Completely removes effects of structural inhomogeneity
Size Dependent Dielectric Function
= scattering rate = e-e + e-ph + e-d
Size Dependent Dielectric Function
= scattering rate = e-e + e-ph + e-d + e-surface
dA Fbulk / A = “broadening parameter”, depends on nature of surface scattering.
A = 1, high dephasingA = 0, no dephasing
Bulk: A=1 Single: A=0
Nanoshell Line Width
Single Molecule LSPR Sensing?
time
peak
Inject analyte
*Analytes (proteins) similar size to nanoparticle.
*Elongated particles: optimized for LSPR.
*Admit analyte at very low concentration.
*Observe spectral shifts at a rapid rate.
Solution: Gold Nanostars!
400 1000Wavelength (nm)
Sca
tteri
ng
Bulk
Complicated particle shapes can’t be made monodisperse. Single Particle Spectra reveal their optical properties.
Solution: Gold Nanostars!
Nanostars: large scattering cross section and sharp resonance.
Water n=1.33Sucrose n=1.45
Nanostar LSPR Shift
Oil n=1.52
584 nm / RIU 279 nm / RIU
Single Nanostar LSPR Sensing
Functionalization of gold nanostars with 16-mercaptohexadecanoic acid.
To camera,CCD spectrometer,
InGaAs spectrometer.
NSOM Tip Characterization