Chem 8157

1. It appears that one of the key features in detecting a response in the gold nanohole arrays is the change in the index of refraction (See Figure 5).

This figure shows a quadratic (or higher order) dependence on the index of refraction.

On the other hand, Equation 1 suggests a square root dependence. Explain.

2. If this system was used to measure a biointeraction, describe the respective binding isotherm. [Hint: here, we cannot measure mobility shifts to determine the fraction of bound analytes].

For the question 1, because they use the index of refraction (n) as x-axis value, we have to change the dielectric terms in equation 1 to index of refraction. However, when I use n~E^1/2 to replace the dielectric terms in equation 1, I still can't get the quadratic relationship between wavelength shift to index of refraction. Does anyone have another method to answer this question?

Thanks

1. There is a simple relation between the index of refraction n of a non-magnetic material

and the dielectric constant.
dielectric constant=square of n. In equation 1, the square root part is composed of

multiplication of two dielectric constants. So it's similar with figure 5. The wavelength

shows a quadratic dependence on the index of refraction.
There is also another complex equation to describe the relationship between dielectric

constant and index of refraction. So it's possible that the wavelength shows higher order

deendence on the index of refraction.
2. The SPR signal(peak wavelength shift(R)) of antibody and antigen binding at each

concentration was plotted against the antibody concentration(C). Req=Rmax*C/(C+Kd). Req is

the SPR signal at equilibrium, Rmax is the maximum binding capacity.This equation can be

used to draw the binding isotherm.
For SPR, Kd is measured by the association and dissoaciation rate.Kd=k1/k-1.

I found one question on the comments of my presentation. It was: what's this array advance this area?
In my opinion, the array has more energy that is transfered to the surface than single hole. So it has higher sensitivity. Other reference said the nano hole can focus on the subject better than big holes. It seems much more bright compared with big holes. Other importance is the same as in the summary, like transmission mode operation, a relatively small footprint and repeatability.