Recent　developments　in　the　rational　design　and　the　controlled　assembly　of　nanoscale　building　blocks　have　resulted　in　functional　devices　such　as　nano-optoelectronics,　novel　contrast　probes　for　molecular　imaging,　and　nanosensors.　In　the　present　study,　we　designed　and　synthesized　a　hybrid　nanomaterial　consisting　of　[Ru(bpy)3]2+-encapsulated　silica　nanoparticles　(SiNPs)　and　gold　nanoparticles　(AuNPs)　through　peptide-bridged　assembly　in　a　controllable　way.　A　peptide　that　contains　recognition　sequence　DEVD　specific　for　active　caspase-3　cleavage　was　employed　to　bring　SiNPs　and　AuNPs　into　close　proximity　through　specific　molecular　recognition.　A　FRET　system　with　SiNPs　as　energy　donors　and　AuNPs　as　energy　acceptors　has　been　thus　developed　and　applied　for　caspase-3　detection.　A　change　in　distance　between　the　two　building　blocks　resulted　in　a　change　in　FRET　efficiency,　causing　a　ratiometric　change　in　emission.　Caspase-3　triggers　the　cleavage　of　the　peptide　links　between　the　two　nanoparticles　and　releases　AuNPs　from　the　nanohybrids,　inducing　the　activation　of　SiNPs　to　the　＇ON＇　state.　The　fluorescence　turn-on　response　is　specific　to　caspase-3　and　allows　the　detection　of　caspase-3　as　low　as　0.05　U　mL-1　(∼6　pM).　©　2013　American　Chemical　Society.