Scanning Kelvin probe microscopy on organic field-effect transistors during gate bias stress

The reliability of org. field-effect transistors is studied using both transport and scanning Kelvin probe microscopy measurements. A direct correlation between the current and potential of a p-type transistor is demonstrated. During gate bias stress, a decrease in current is obsd., that is correlated with the increased curvature of the potential profile. After gate bias stress, the potential changes consistently in all operating regimes: the potential profile gets more convex, in accordance with the simultaneously obsd. shift in threshold voltage. The changes of the potential are attributed to pos. immobile charges, which contribute to the potential, but not to the current

Scanning Kelvin probe microscopy on organic field-effect transistors during gate bias stress

The reliability of org. field-effect transistors is studied using both transport and scanning Kelvin probe microscopy measurements. A direct correlation between the current and potential of a p-type transistor is demonstrated. During gate bias stress, a decrease in current is obsd., that is correlated with the increased curvature of the potential profile. After gate bias stress, the potential changes consistently in all operating regimes: the potential profile gets more convex, in accordance with the simultaneously obsd. shift in threshold voltage. The changes of the potential are attributed to pos. immobile charges, which contribute to the potential, but not to the current

Rational design of FRET-based sensor proteins

Real-time imaging of molecular events inside living cells is important for understanding the basis of physiological processes and diseases. Genetically encoded sensors that use fluorescence resonance energy transfer (FRET) between two fluorescent proteins are attractive in this respect because they do not require cell-invasive procedures, can be targeted to different locations in the cell and are easily adapted through mutagenesis and directed evolution approaches. Most FRET sensors developed so far show a relatively small difference in emission ratio upon activation, which severely limits their application in high throughput cell-based screening applications. In our work, we try to develop strategies that allow design of FRET-based sensors with intrinsically large ratiometric changes. This rational design approach requires a better understanding and quantitative description of the conformational changes in these fusion proteins. In this chapter, I first discuss some of the key factors and strategies that determine the ratiometric response of FRET sensors, followed by an overview of our recent work in this area. Important concepts that will be discussed are (1) the conformational behavior of flexible peptide linkers to quantitatively describe the dependence of energy transfer on linker length and (2) the control of intramolecular domain interactions using the concept of effective molecular concentration

Rational design of FRET-based sensor proteins

Real-time imaging of molecular events inside living cells is important for understanding the basis of physiological processes and diseases. Genetically encoded sensors that use fluorescence resonance energy transfer (FRET) between two fluorescent proteins are attractive in this respect because they do not require cell-invasive procedures, can be targeted to different locations in the cell and are easily adapted through mutagenesis and directed evolution approaches. Most FRET sensors developed so far show a relatively small difference in emission ratio upon activation, which severely limits their application in high throughput cell-based screening applications. In our work, we try to develop strategies that allow design of FRET-based sensors with intrinsically large ratiometric changes. This rational design approach requires a better understanding and quantitative description of the conformational changes in these fusion proteins. In this chapter, I first discuss some of the key factors and strategies that determine the ratiometric response of FRET sensors, followed by an overview of our recent work in this area. Important concepts that will be discussed are (1) the conformational behavior of flexible peptide linkers to quantitatively describe the dependence of energy transfer on linker length and (2) the control of intramolecular domain interactions using the concept of effective molecular concentration