e  •  00  •  ~  ~  ~  ~  =  ~  ~  ~  ?  N  ’"\,Ci  N  0  ....  \,Ci  rJJ  =› (’D  (’D  .....  --.J  0  ....  N  0  d  r.,;_  "’""’  ’"=  "’""’  00  \0  ~  "’""’  00  =  "’""’  FIG. 5B  /  //  /  First set of particles  ;•  (assernbled}  /  Second set of particles  (unassen1bled)  Trigger applied for pH› control substance  (gradually reduces  surface charge)  Second set of particles  (assembled as shell on  assernbled array of first  set of particles) 