Single-Molecule Sensing of Interfacial Acid–Base Chemistry

Abstract

Bronsted acid and base interactions are a cornerstone of chemistry describing a wide range of chemical phenomena. However, probing such interaction at the solid–liquid interface to extract the elementary and intrinsic information at a single-molecule level remains a big challenge. Herein, we employ an STM break junction (STM-BJ) technique to investigate the acid–base chemistry of carboxylic acid-based molecules at a Au (111) model surface and propose a prototype of a single-molecule pH sensor for the first time. The single-molecule measurements in different environmental conditions verify that the formation probability of molecular junctions is determined by the populations of deprotonated -COO– form in a self-assembled monolayer. Furthermore, the variation of the intensity of the conductance peaks (i.e., junction-forming probability) with the pH of the bulk solution fits well to the Henderson–Hasselbalch type equation. From the equation, a good linear relation is found between the degree of dissociation of the immobilized -COOH group and the environmental pH, providing a feasible way to design chemicals and biosensors and a detector at the single-molecule scale.

Electrochemically activated carbon–halogen bond cleavage and C–C coupling monitored by in situ shell-isolated nanoparticle-enhanced Raman spectroscopy

“…The as-prepared 55 nm Au @ ca. 2 nm SiO 2 nanoparticles synthesized according to the reported method 30,37 are dropped on the SAM on the smooth Au electrode as Raman signal amplifiers, which offer a tremendous improvement in sensitivity (10 7 -10 8 times) to detect surface species. 38 Their SEM and TEM images are shown in Fig.…”

Enhanced Gating Performance of Single-Molecule Conductance by Heterocyclic Molecules

“…Fabricating single-molecule devices has been the ultimate goal of electronic device minimization since Aviram and Ratner proposed a prototype molecular rectifier in 1974. − Benefiting from the development of the single-molecule break junction technique, numerous investigations have successfully constructed and explored metal–molecule–metal junctions over the past two decades. − To date, electron transport through single molecules could be tuned under external stimulus, such as electricity, , light, − and pH. − Among them, electrochemical modulation provides a promising method for manipulating the energy alignment between molecular frontier orbitals and Fermi level of metal electrodes. ,− Significant results, such as redox-enhanced tunneling, ,− molecule structure transforms, and quantum interference , via electrochemical gating, have been reported. In order to realize functionally electronic components like a single-molecule switch or transistor, much effort has been devoted to improving gating efficiency of conductance within the limited gate potential range, but it remains an outstanding challenge.…”

Recent Advances in Single-Molecule Sensors Based on STM Break Junction Measurements

“…Thus, the formation probability of molecular junctions strongly relies on the population of deprotonated carboxylic acid molecules, which provides a unique platform for designing a single-molecule pH sensor. As shown in Figure 6 a, Zhou and co-authors used the STM-BJ techniques to probe the acid−base chemistry of SAM of 4-(methylthio)benzoic acid (4-MTBA) on the Au(111)/aqueous solution interface [ 31 ]. With changing the pH of solution from 0 to 5, the conductance peaks at about 10 −2.90 G 0 ascribed to the formations of single-molecule junctions become intense, shown in Figure 6 b.…”