Peptide-bridged assembly of hybrid nanomaterial and its application for caspase-3 detection

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).