Target-induced autonomous synthesis of G-quadruplex sequences for label-free and amplified fluorescent aptasensing of mucin 1

Highly sensitive and simple detection of biomarkers can significantly facilitate early disease diagnosis and treatment. Using a new target-triggered autonomous synthesis of G-quadruplex sequences via primer exchange signal amplification strategy, we developed an ultrasensitive and simple label-free aptamer-based method for sensing mucin 1 (MUC1), a protein biomarker, in this work. The target molecules bind and cause the change in conformation of the aptamer region in the hairpin probes to expose the primer complementary sequences, which subsequently hybridize with the primers to initiate the ssDNA synthesis process with the aid of the DNA polymerase. By encoding the G-quadruplex complementary sequence in the template, numerous G-quadruplex sequences with various lengths can therefore be produced. The thioflavin T further binds these G-quadruplex sequences to yield substantially enhanced fluorescence for ultrasensitively detecting MUC1 within the linear range from 5 to 1000 pM with the 1.9 pM detection limit in a non-label approach. The high selectivity and potential application of this sensing method for diluted human serums have also been verified. Showing high sensitivity with convenient signal amplification, such an aptamer-based protein sensing strategy thus exhibits promising potentials for establishing various platforms for detecting different cancer markers at trace levels.