e  •  00  •  ~  ~  ~  ~  =  ~  ~  ~  N  ’"\,Ci  N  0  ....  QO  rJJ  =› (’D  (’D  .....  O’I  0  ....  N  0  d  r.,;_  _."-0  "-0  00  "’""’  ’N  ~  =  "’""’  FIG. SA  First reaction  Second reaction  Droplet-~~nera~ing  Fluid 2  /  microfluidic region  /  microfluidic region  microflu1~c  region  ____  1 ________  , __  ..l{  _________ ,,  ___________  .…;_ 1  "’- ,-----+:  l  I  d  !!!ff  Wll#ffl  t ________  -4’-_________  J  !  --- Fluid 2  /  /  First trigger  Second  trigger  First trigger source  <---- Second trigger  source 