Biomedical Engineering Reference
In-Depth Information
3.00 nm
3.00 nm
A
B
120 nm
100 nm
0.00 nm
0.00 nm
2.50 nm
C
D
8.00 mV
120 nm
70 nm
-7.00 mV
0.00 nm
FIGURE 1.5
6His-SP1-GNP-DNA.tri-block.conjugates..(A).AFM.topography.of.a.1D.structure.based.on.the.tri-block.conju-
gate..The.6His-SP1-GNP.hybrids.appear.as.bright.spots.on.the.DNA.strand..(B,C).DNA.junction.based.on.the.
tri-block.conjugates..The.enlarged.image.in.Figure.1.5C.shows.multiple.DNA.molecules.anchored.to.the.same.
hybrid.(dashed.square.in.B)..(D).EFM.image.of.the.junction.in.Figure.1.4B..One.can.see.a.polarization.signal.at.
the.positions.of.6His-SP1-GNP..The.SP1.protein.is.electrically.silent.and.exhibits.no.polarization.signal.
1.4 SP1-GNPTubes
Another.1D.structure.formed.using.the.SP1-GNP.hybrids.is.a.tubular.chain.composed.of.
alternating.stacked.units.of.protein.and.GNP..Such.structures.spontaneously.form.upon.
incubation.of.6His-SP1-GNP.hybrids.in.buffer.solution..The.inter-GNP.separations.within.
the.protein-GNP.chains.made.of.this.protein.variant.are.irregular.and.depend.on.the.rela-
tive.position.of.the.GNP.with.regard.to.the.protein,.mainly.due.to.the.lexible.long.6His.
tags.(at.the.end.of.each.of.the.12.N.termini),.such.that.the.GNPs.are.not.in.direct.electrical.
contact..Figure 1.6A.shows.a.scheme.of.a.6His-SP1.protein-GNP.chain..A.TEM.image.of.
several.6His-SP1-GNP.chains.can.be.seen.in.Figure 1.6B:.the.GNPs.appear.as.dark.spots.
between.the.6His-SP1.rings.(that.are.“standing”.in.a.side.view)..A.HAADF-TEM.image.of.
one.of.the.protein-GNP.chains.is.shown.in.Figure 1.6C..The.GNPs.appear.as.bright.spots,.
revealing.a.distance.of.~4.nm.
In.order.to.improve.the.packing.of.the.6His-SP1s.and.reduce.the.inter-GNP.separation.
(and.6His-SP1.separations),.another.SP1.derivative.was.engineered.by.adding.a.six-histi-
dine.tag.to.a.truncated.N.terminal.SP1.(ive.N.terminal.amino.acid.residues.were.deleted.
