Probing Single Flavoprotein Molecules on Graphite in Aqueous Solution with Scanning Tunneling Microscopy

Abstract

Electron tunneling through redox flavoprotein molecules (glucose oxidase) is investigated at the single‐molecule level with in situ electrochemical scanning tunneling microscopy (STM; see image). By adjusting the substrate potential, the Fermi levels of the substrate and tip are shifted relative to the energy levels of the proteins, while an increasing tunneling current between the substrate and the STM tip via the flavoprotein molecules is observed.

Efficient and Stable Solid‐State Dye‐Sensitized Solar Cells Based on a High‐Molar‐Extinction‐Coefficient Sensitizer

“…The larger value of N t,0 for the aged device correlates with a shorter apparent recombination lifetime ( τ n ) in this device. This result indicates that most of the electron–hole recombination dynamics occur between the trapped electrons (by the surface and/or bulk trap states in the bandgap) and the holes in the HTM, which is consistent with previously reported results 17–22. We note a higher value of T 0 for the fresh device, corresponding to a flatter distribution of trapping states, which was confirmed by the analysis of the intensity dependence of the chemical capacitance determined by the transient photovoltage decay measurement.…”

“…The apparent charge recombination lifetime τ n ( τ n = R ct C µ ) was obtained by fitting the frequency‐dependent response in impedance measurements. According to the quasi‐static treatment,20–22 the apparent charge recombination lifetime ( τ n ) under different energy levels is related to the conduction‐band electron lifetime ( τ 0 ) by using the following expression19 where n t is the trapped electron density, τ 0 is the inverse of the pseudo first‐order rate constant for the back transfer of electrons from the conduction band, and n c is the conduction‐band electron density. Our previous impedance studies on DSCs show most of the electrons are trapped at levels in the bandgap 17–19.…”

The Influence of Charge Transport and Recombination on the Performance of Dye‐Sensitized Solar Cells

“…There are localized bulk and surface trapping states in the band gap that accommodate and release electrons. [36] In order to simplify the fitting process, only surface states formed for example, by oxygen vacancies are considered in the present work. The DOS is described by an exponential function as shown in Equation (4).…”

Imaging Single Enzyme Molecules under In Situ Conditions

“…[1] The degree of surface coverage, the surface orientation of the enzymes, that is, the position of the active site, and the activity of a single enzyme are still a question of dispute; this data can not be extracted from integral electrochemical measurements, such as cyclic voltammetry (CV). It has been shown, however, that scanning probe techniques, especially the electrochemical scanning tunneling microscopy (EC-STM), [2,3] can reveal the structure and reactivity of enzymes down to a single-molecule level, [4][5][6] although some experimental problems remain. To avoid any damage to the protein structure only small tunneling currents I T can be applied.…”