A novel and highly selective signal amplification strategy was developed based on target-assisted self-cleavage DNAzyme probes for imaging of miRNA-222 and miRNA-223.
DNA
nanomachines have received great interest due to their potential
to mimic various natural biomolecular machines. Intracellular pH sensing
and imaging are of great significance to understand cellular behaviors
and disease diagnostics. In this work, we report the novel molecular
switching of a self-assembled 3D DNA triangular prism nanomachine
(TPN) for pH sensing and imaging in living cells. The TPN was self-assembled
in quantitative yields by hybridization with two DNA triangles and
three I-strands (containing i-motif sequences). At acidic conditions,
the TPN was compressed due to the I-strand that formed an intramolecular
i-tetraplex, which was in between the fluorophores Cy3 and Cy5, resulting
in a significant fluorescence resonance energy transfer (FRET) signal.
At neutral or weakly alkaline conditions, the TPN adopted an extended
state due to the random coil form of the I-strand, leading to spatial
separation of the two fluorophores and the FRET being blocked. The
TPN was fully reversible and could rapidly respond to the pH changes,
entered into living cells automatically via an endocytic pathway,
monitored spatiotemporal pH changes during endocytosis, maintained
its structural integrity after escape from lysosomes, still had the
ability for pH sensing, and also visualized pH fluctuations under
varying stimuli in living cells. We foresee that this TPN can become
a generic platform for a pH-related cell biology study and in disease
diagnostics.
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