Fluorescence Imaging of Intracellular Telomerase Activity Using Enzyme-Free Signal Amplification

A novel enzyme-free signal amplification-based assay for highly sensitive in situ fluorescence imaging and detection of intracellular telomerase activity was developed by using a gold nanoflare probe-triggered mimic-hybridization chain reaction (mimic-HCR) coupled with a graphene oxide (GO) surface-anchored fluorescence signal readout pathway. The nanoflare probe consists of gold nanoparticles (AuNPs) functionalized with a dense shell of nucleic acid sequences by Au-S bond formation. The nucleic acid sequence is composed of three segments: a long thiol-labeled sequence (HS-DNA) and two short sequences (a telomerase primer sequence, "Primer-DNA", and an FAM-terminated reporter sequence, "Flare-DNA"), both of which are complementary to HS-DNA. The mimic-HCR system is formed by two FAM-modified hairpin sequences that are adsorbed on GO. Upon endocytosis of the AuNP/GO combinatorial probe, the Primer-DNA can be extended by intracellular telomerase at its 3' end to produce the telomeric repeated sequence, which leads to inner chain substitution and not only releases the Flare-DNA to turn on the fluorescence of FAM but also initiates the subsequent signal amplification and enrichment for the mimic-HCR system anchored on GO. The proposed approach can sensitively detect telomerase activity in living cells, distinguish normal cells from cancer cells, and monitor the change in telomerase activity in response to a telomerase inhibitor.