Keywords:molecular electronics, thermodynamics, intercalation
The investigation on thermodynamics equilibrium at the single-molecule level is seldom reported despite its significance for characterizing reactions. To address this issue, we developed a novel strategy based on electrical single-molecule detection. Specifically, we showed the determination of an equilibrium constant of a single-molecule chemical reaction. The intercalation reaction of ethidium bromide (EB) to DNA was studied in the present work. The single-molecule conductance of reactants (DNA and EB) and product (the DNA–EB complex) was measured by the break-junction technique based on scanning tunneling microscopy. The three compounds differed in the conductance from one another. The concentration of DNA–EB was related to the observation probability of its single-molecule conductance, and the association constant of DNA–EB intercalation was successfully determined by the single-molecule measurements.