nanoparticle acceptor surface (smaller r), hence increasing energy transfer efficiency.
This, in turn, explains why the larger gold nanoparticles in the ruler resulted in better
fluorescence quenching. The plot of quenching efficiency (0) versus different gold
nanoparticle diameters (d) (Figure 5-10) shows a plateau after the particle diameter
reached ~18nm, indicating that the surface of the particle had reached the antibody
binding site and had thus achieved maximum fluorescence quenching. Consequently,
particles with diameters larger than d=18nm would not reach a higher degree of
quenching.
The distance-dependent quenching data were fit to the Nanoparticle Surface
Energy Transfer model employed by Jennings et. a/.70:
1
+-1 (1-4)
l+ rl
In equation (1-4), 0 is the energy transfer efficiency; ro is a constant value for a specific
dye-metal system, corresponding to the distance at which a dye will display equal
probabilities for energy transfer and spontaneous emission66; and r is the distance from
the dye molecule to the gold nanoparticle surface.
Substitution of r from equation (5-1) and rearranging gives:
1 =- + (5-2)
(1 J 2r, r,
4
By letting Y= -1 and X=d, (3) is simplified to:
X R
Y=- +-R (5-3)
2ro ro
122