e  •  00  •  ~  ~  ~  ~  =  ~  ~  ~  N  ’"\,Ci  N  0  ....  QO  rJJ  =› (’D  (’D  .....  ~  0  ....  N  0  d  r.,;_  _."-0  "-0  00  "’""’  ’N  ~  =  "’""’  FIG.3  Prepare a first fluid consisting of particles  to be assembledt a solvent, and pH  control substance  \~  Prepare a second fluid substantially  immiscible in the first fluid  ,v  Flow both fluids into a droplet generating  microfluidic region  \~  Trigger pH control substance in a reaction  microfluidic region  ,v  Titrate the pH towards the isoelectric  point 