Biomedical Engineering Reference
In-Depth Information
A
C
GNP
SP1
11 nm
B
D
SP1
11 nm
GNP
FIGURE 1.2
6His-SP1-GNP.hybrids..(A,B).HAADF-STEM.(vanadium.staining).images.of.the.6His-SP1-GNP.hybrid.in.top.
and. side. views,. respectively.. (C,D). Computer. simulations. of. the. 6His-SP1-GNP. hybrid. top. and. side. views,.
respectively..(From.Medalsy.et.al..2008.)
The. formation. of. SP1-GNP. hybrids. was. validated. using. electron. microscopy. and.
atomic. force. microscopy. (AFM).. High-angle. annular. dark-ield. scanning. transmis-
sion. electron. microscopy. (HAADF-STEM). revealed. the. existence. of. the. GNP. in. the.
SP1.inner.pore..Figure 1.2A.shows.the.GNP.(bright.white).centered.within.the.darker.
round.protein.ring..The.side.view.(Figure 1.2B).shows.GNPs.attached.to.both.faces.of.
the.dodecameric.ring..This.hybrid.formation.is.consistent.with.the.crystal.structure,.as.
there.are.six.N.termini.on.each.face.of.the.6His-SP1,.pointing.in.opposite.directions..
Figure 1.2C.and.D.shows.illustrations.of.6His-SP1.attached.to.two.GNPs.on.both.sides.
in.top.and.side.views,.respectively.
Electrostatic. force. microscopy. (EFM). is. capable. of. distincting. between. a. polarizable.
object,.for.instance,.a.GNP,.and.an.isolating.object.like.the.SP1.protein..By.scanning.over.
the.investigated.object.in.EFM.mode,.the.biased.tip.induces. an.electric. ield.component.
normal.to.the.surface..The.charge.carriers.in.a.polarizable.object.are.polarized.according.
to.the.ield.direction,.and.therefore,.for.both.positive.and.negative.tip.voltages,.there.will.
be.an.electrostatic.attraction.between.the.tip.and.the.object..An.insulating.object.will.not.
respond.to.the.electric.ield,.and.thus.will.not.produce.any.electrostatic.signal.
23,24
EFM.measurements.performed.on.6His-SP1.and.on.6His-SP1-GNP.hybrids.(Figure 1.3).
revealed. a. clear. difference. between. the. two. species.. The. EFM. scan. was. repeated. for. -5.
V.(Figure 1.3B),.0.V.(Figure 1.3C),.and.+5.V.(Figure 1.3D)..The.phase.shift.reaction.above.
