Gold Nanorod Biosensors and Single Particle Spectroscopy

Jason H. HafnerMURI site visitJuly 27, 2005

Gold Nanorods

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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

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0.25

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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).

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Absorbance of Nanorods on a glass substrate

50:15 = 4.4 +/- 0.5 x 109 cm-1M-1

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Ab

sorb

an

ce

Wavelength (nm)

air water

SPR sensitivity = 150 nm/RIU

(similar to nanosphere lithography)

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700 720 740 760 780 800

Abs

orba

nce

Wavelength (nm)

750.1 +/- 0.3 nm

Gold Nanorod Biosensors

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700 720 740 760 780 800

Abs

orba

nce

Wavelength (nm)

750.1 +/- 0.3 nm

759.6 +/- 0.3 nm

Gold Nanorod Biosensors

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0.1

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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