Direct single-molecule dynamic detection of chemical reactions.

Single-molecule detection can reveal time trajectories and reaction pathways of individual intermediates/transition states in chemical reactions and biological processes, which is of fundamental importance to elucidate their intrinsic mechanisms. We present a reliable, label-free single-molecule approach that allows us to directly explore the dynamic process of basic chemical reactions at the single-event level by using stable graphene-molecule single-molecule junctions. These junctions are constructed by covalently connecting a single molecule with a 9-fluorenone center to nanogapped graphene electrodes. For the first time, real-time single-molecule electrical measurements unambiguously show reproducible large-amplitude two-level fluctuations that are highly dependent on solvent environments in a nucleophilic addition reaction of hydroxylamine to a carbonyl group. Both theoretical simulations and ensemble experiments prove that this observation originates from the reversible transition between the reactant and a new intermediate state within a time scale of a few microseconds. These investigations open up a new route that is able to be immediately applied to probe fast single-molecule physics or biophysics with high time resolution, making an important contribution to broad fields beyond reaction chemistry

Single‐Molecule Electronic Biosensors: Principles and Applications

Abstract Single‐biomolecule electronic sensing techniques are of great importance in many fields, from medical diagnosis to disease surveillance. As the physiological changes of single biomolecules can be converted into measurable electrical signals, single‐molecule electronic biosensors can realize real‐time, highly sensitive, and high‐bandwidth detection of individual intra‐ or inter‐molecular interactions. These powerful single‐molecule sensing devices have demonstrated key advantages in precisely providing rare and detailed intermediate information along reaction pathways and revealing unique properties hidden in ensemble measurements. This review summarizes significant advances in single‐molecule electronic biosensors, emphasizing biomolecule recognition, interaction, and reaction dynamics at the single‐molecule level. Sensor configurations, sensing mechanisms, and representative applications are also discussed. Furthermore, a perspective on the use of photoelectric integrated systems for synchronous sensing of the electrical and optical signals of single biomolecules is provided

The role of halogens in Au–S bond cleavage for energy-differentiated catalysis at the single-bond limit

The transformation from one compound to another involves the breaking and formation of chemical bonds at the single-bond level, especially during catalytic reactions that are of great significance in broad fields such as energy conversion, environmental science, life science and chemical synthesis. The study of the reaction process at the single-bond limit is the key to understanding the catalytic reaction mechanism and further rationally designing catalysts. Here, we develop a method to monitor the catalytic process from the perspective of the single-bond energy using high-resolution scanning tunneling microscopy single-molecule junctions. Experimental and theoretical studies consistently reveal that the attack of a halogen atom on an Au atom can reduce the breaking energy of Au−S bonds, thereby accelerating the bond cleavage reaction and shortening the plateau length during the single-molecule junction breaking. Furthermore, the distinction in catalytic activity between different halogen atoms can be compared as well. This study establishes the intrinsic relationship among the reaction activation energy, the chemical bond breaking energy and the single-molecule junction breaking process, strengthening our mastery of catalytic reactions towards precise chemistry