Imaging Single Enzyme Molecules under In Situ Conditions

High‐Resolution Imaging of the Initial Stages of Oxidation of Cu(111) with Scanning Electrochemical Potential Microscopy

“…At distances far away from the sample surface (> 1 nm), the tip potential converges to a constant value of E SECPM = À0.26 V. This value is different from the OCP of a W wire with a macroscopic surface area, E OCP = À0.32 V, which is in agreement with literature values. [6] In the present case of an extended tip with its non-insulated volume extending completely through the double layer region in the z direction, the potential is measured at different positions between the tip apex and the boundary between the insulated and non-insulated area, [9] which should lead to the detection of an integral potential over the non-insulated area of the tip. The reason for this deviation will be discussed below.…”

“…[3,4] They all differ from the exponential and linear potential profiles through the EDL, as described by the GCS theory and predicted by theoretical simulations of SECPM potential profiling. [6] In the present case of an extended tip with its non-insulated volume extending completely through the double layer region in the z direction, the potential is measured at different positions between the tip apex and the boundary between the insulated and non-insulated area, [9] which should lead to the detection of an integral potential over the non-insulated area of the tip. In the EDL region, where the potential is z-dependent, this integral signal is different from that at the tip apex; hence, even at closest tip-sample distances, it is not possible to measure the potential applied to the WE.…”

“…Higher current densities have been obtained for smaller free-tip surface areas and vice versa. [9,10] All SECPM images presented in this paper have been recorded at potential set-points of DE = 25 mV, that is, with the tip potential very close to the WE potential. Hence, if the anodic tip dissolution changes the free-tip surface, a deviation from the ideal Tafel behavior is expected (see Figure 6) for higher values of I STM À1 [corresponding to smaller tip surfaces according to Eq.…”

“…[9] SECPM was also used for the investigation of single-crystal metal surfaces in combination with atomic force microscopy (AFM) and STM, [10] but, although SECPM is supposed to have a similar lateral resolution to STM, no examples of atomically resolved structures imaged with SECPM have been reported to date. The same technique was successfully employed to image enzymes immobilized on a highly ordered pyrolytic graphite (HOPG) electrode, which delivered a better spatial resolution of the large organic molecules compared to electrochemical STM (EC-STM).…”

“…The same technique was successfully employed to image enzymes immobilized on a highly ordered pyrolytic graphite (HOPG) electrode, which delivered a better spatial resolution of the large organic molecules compared to electrochemical STM (EC-STM). [9] SECPM was also used for the investigation of single-crystal metal surfaces in combination with atomic force microscopy (AFM) and STM, [10] but, although SECPM is supposed to have a similar lateral resolution to STM, no examples of atomically resolved structures imaged with SECPM have been reported to date.…”