How would you define a figure of merit (FOM) for optical nanosensors based on the aggregation of gold or other plasmonic nanoparticles?

In our latest

Article Plasmonic Absorption in Antigen-Induced Aggregated Gold Nano...

we proposed an adimensional FOM based on the following 5 parameters:

1- the number of Au NPs in the aggregate (#NPs)

2- the average of the minimum interparticle distance among next-neighbor NPs (⟨gap⟩)

3- the aspect ratio of the aggregate (i.e., the ratio of its length to its width, ar)

4- the average size of the NPs in the aggregate (⟨d⟩)

5- the corresponding standard deviation [expressed in percentage, sd(%)]

Can a better FOMs be identified (for instance at different wavelengths)?