Important question regarding capacitive sensors on molecular/nano level

I'm doing a research project on different kind of sensors and I'm
interested especially in their sensitivities.

Concerning capacitive sensors I'm interested in measuring the presence
of molecules or nanoparticles either in air or liquids.

1. What capacitive measuring technologies are available for measuring
molecules or nanoparticles either in air or liquids?
2. I have the following setup:
A capacitive sensor and on top of that a thin film coated with a
certain polymer having affinity to certain molecules. The thin film and
the polymer have an entire thicknes of let's say 50 micron. Now the
sensor is calibrated. After that, molecules or nanoparticles on a ppm
or ppt (or whatever concentration level) get trapped on the polymer
which means that weight is added and actually matter is added. But can
anyone tell me how many atoms/molecules/nanoparticles have to be added
in order to measure a difference (pr square mm or something else).
3. How would you measure ppm or ppt concentrations by capacitive means?
3. Are there any webpages dealing with sensors and their sensitivities?

Thank you in advance,

Lucas Jensen