Control of Triplet Blinking Using Cyclooctatetraene to Access the Dynamics of Biomolecules at the Single‐Molecule Level

To explore the dynamics of biomolecules, tracing the kinetics of photo-induced chemical reactions via the triplet excited state (T1) of probe molecules offers a timescale that is ~10^6 times wider than via the singlet excited state (S1). Here, using cyclooctatetraene (COT) as a triplet energy acceptor and at the same time as a photostabilizer, the triplet-triplet energy transfer (TTET) kinetics governed by oligonucleotide (oligo) dynamics were studied at the single-molecule level by measuring fluorescence blinking. TTET kinetics measurement allowed us to access the length- and sequence-dependent dynamics of oligos, and realize the single-molecule detection of a model microRNA biomarker. In sharp contrast to the singlet-singlet Forster resonance energy transfer (FRET) that occurs in the 1-10 nm range, TTET requires a Van der Waals contact. Thus, the present method serves as a complementary method to FRET and provides direct information on biomolecular dynamics on the μs to ms timescale.