How to do damage if touching a particle?

You can create particle zones with status effects

A relatively new entity, area_effect_cloud, is a region of particles that applies a status effect, modeled after the Ender Dragon's breath attack.

Try something like this, but replace every x with a number.

/summon area_effect_cloud ~ ~ ~ {Particle: <.put your particle here> ,ReapplicationDelay:5,Radius:xf,Duration:x,DurationOnUse:xf,Age:x,WaitTime:x,Effects:[{Id:20,Amplifier:1,Duration:20}]}

You could also add in some cool stuff by using the execute command

/execute @e[minecraft:area_effect_cloud] ~ ~ ~ /<put youre command here>