Caspase-3 plays an important role in the initiation and propagation of apoptosis which is involved in various kinds of diseases including neurodegenerative diseases and inflammatory diseases. The capase-3 cleavable site of Asp-Glu-Val-Asp (DEVD) connected to a partial sequence of Escherichia coli RNAI was labeled with tetramethyl-6-carboxyrhodamine (TAMRA) as an optical probe. Graphene oxide (GO) was synthesized by a modified Hummer's method and exploited for the preparation of nano-sized GO (NGO) conjugated with polyethylene glycol (PEG). After binding the NGO-PEG by π-π stacking, the quenched fluorescence of TAMRA-DEVD-single stranded DNA (ssDNA) conjugate was recovered via the enzymatic cleavage by caspase-3 in live A549 cells. The comparative study with terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay clearly confirmed the specific detection of apoptosis by the non-covalent TAMRA-DEVD-ssDNA/NGO-PEG complex. Furthermore, the self-assembled NGO complex was successfully exploited for in vivo diagnosis of apoptosis-related diseases like hypoxic-ischemic encephalopathy (HIE) and liver cirrhosis.
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