BRET-based biosensor DNA DNA aptamer DNA-protein conjugate NLS PNA PUF RNA binding protein RNA nanostructure RNA nanotechnology RNA regulation RNA-peptide conjugate RNA-protein complex Schiff base Technology: general issues abasic site anticancer drug aptamer artificial viral capsid camptothecin derivative catalytic RNA cellular uptake conjugate crosslink cytosine methyltransferase cytotoxicity drug delivery drug delivery system encapsulation fluorescent probe