Best sensor for number small water droplets count

Dear All, I am spraying water droplets using humidifier. I need sensor which can help me to determine or count number of very tiny water droplets on plane surface or on cotton thread...please suggest.

By weight ?
The water droplets will anyway have lost their original form when absorbed onto a cotton thread.
Assume a standard weight for a water droplet from an atomiser.

Why would you want to do this ? Pretty nigh on impossible IMO.

Why not measure the amount of water sprayed out and assume it’s misting ok

Sounds like a task for CV.

What if I spray it on glass or on mirror and can I use any light sensor and how to measure the condensation on glass?? and how ??

I want to compare something with two different mist sprayer on two different sample collector. I would like to use glass or mirror instead of cotton fiber.

You realize that droplets on a surface will evaporate depending on the temperature of the surface, that even counting the droplets doesn't tell you their actual volume anyway? You can probably get some vague signal from the optical parameters of the glass (such as back-scattering?), but if you want to accurately measure its not really meaningful unless you can control all the variables like air humidity, air temperature, glass temperature etc etc

Are you trying to determine the coarseness or fineness of the spray coverage?
Or do you real need to know the droplet size?
To measure particle size as is, you would need to have some seriously deep pockets and buy yourself a Coulter Counter.
You could look at industries where particle size is important like spray shops or smoke detection.
I wonder if a very small array of electrodes or some sort of optical device?
Maybe a camera and some AI and a frosted glass screen might work.
It's going to be hard, and one thing for certain is that the size will change between nozzle and surface as particles coalesce or surface charge affects results.
Particles in water is relatively easy with turbidity - you need the equivalent for water droplets.