What is difference between micro- and nano-encapsulation - (Aug/18/2014 )

Dear all, 

I always heard about microencapsulation of probiotic cells. May I know is there any technique can form nanoencapsuted cells instead of micro- size? Besides that, what does it mean by microencapsulation? Is it necessary must corporate with freeze dry/ spray dry process in order to form the cells protective layer? Thanks. 

Think it would be tough to "encapsulate" a microbe(s) of around a micrometer in  a particle of ~ a nanometer.