Single-molecule stochastic resonance

Stochastic resonance (SR) is a well-known phenomenon in dynamical systems. It consists of the amplification and optimization of the response of a systemassisted by stochastic (randomor probabilistic) noise. Here we carry out the first experimental study of SR in singleDNA hairpinswhich exhibit cooperatively transitions fromfolded to unfolded configurations under the action of an oscillating mechanical force applied with optical tweezers. By varying the frequency of the force oscillation, we investigate the folding and unfolding kinetics of DNAhairpins in a periodically driven bistable free-energy potential. Wemeasure several SR quantifiers under varied conditions of the experimental setup such as trap stiffness and length of the molecular handles used for single-moleculemanipulation. We find that a good quantifier of the SR is the signal-to-noise ratio (SNR) of the spectral density of measured fluctuations in molecular extension of the DNA hairpins. The frequency dependence of the SNR exhibits a peak at a frequency value given by the resonance-matching condition. Finally, we carry out experiments on short hairpins that show how SR might be useful for enhancing the detection of conformational molecular transitions of low SNR.