Biomedical Engineering Reference
In-Depth Information
(a)
(e)
Ag
Ag-Ag
Au
Au-Au
(b)
Ag
(c)
400
500
600
700
Wavelength (nm)
Au
(f )
s
Au
1.2
Au
s
dsDNA
3 µm
1.0
0.8
ssDNA
(d)
S
iol linker
Au
Au
0.6
DNA
0.4
0.2
Biotin
Spectral
shift
Streptavidin
Streptavidin
0.0
450
500
550
600
650
700
Au or Ag NPs
Pair
Single
Wavelength (nm)
FIGURE 5.5
(See.color.insert.).DNA-functionalized.gold.and.silver.nanoparticles.(NPs).as.molecular.plasmonic.rulers..(a).
First,.streptavidin-functionalized.nanoparticles.are.attached.to.the.BSA-biotin-coated.glass.surface.(a,.d.left)..
Then,.a.second.NP.is.modiied.by.thiol-ssDNA-biotin.bifunctional.linker.and.attached.to.the.irst.particle.via.
biotin-streptavidin.afinity.binding.(a,.d.right)..Inset:.Principle.of.transmission.dark.ield.microscopy..(b).Single.
silver.particles.appear.blue.(left).and.particle.pairs.appear.blue-green.(right)..(c).Single.gold.particles.appear.
green.(left).and.gold.particle.pairs.appear.orange.(right)..(e).Representative.scattering.spectra.of.single.particles.
and.particle.pairs.for.silver.(top).and.gold.(bottom)..The.LSPR.scattering.spectrum.for.silver.NPs.shows.a.larger.
LSPR.shift.(102.nm.vs..23.nm),.stronger.light.scattering,.and.a.smaller.half.width.at.half.maximum.(HWHM).
than.gold.particles..(f).Example.of.the.LSPR.spectral.shift.between.a.gold.particle.pair.connected.with.ssDNA.
(red).and.dsDNA.(blue),.corresponding.to.the.distance.increase.of.2.1.nm.between.the.particle.pair.upon.DNA.
hybridization..(©.2005.Macmillan.Publisher's.Ltd..Used.with.permission.)
Protein.A.was.then.immobilized.on.the.SAM.and.six.different.antibodies.were.attached.
to.protein.A.using.a.nanoliter.dispensing.system,.which.results.in.300.nanospot.arrays..A.
photograph.of.such.a.multiarray.sensor.is.shown.in.Figure.5.7a..Using.the.same.dispens-
ing.system,.they.dispensed.different.concentrations.of.speciic.antigens.onto.the.surface.
and.then.measured.the.change.in.the.absorbance.at.λ
max
.for.each.spot.that.contains.ana-
lyte.with.varying.concentrations,.as.shown.in.Figure.5.7b.and.c..The.limit.of.detection.for.
this.sensor.is.100.pg.ml
−.
,.while.the.sensor.response.scales.linearly.with.concentrations.up.