Fluorescence correlation spectroscopy (FCS) is a well-established method for the analysis of freely diffusing fluorescent particles in solution. In a two-colour setup, simultaneous detection of two different dyes allows the acquisition of both the autocorrelation of the signal of each channel and the cross-correlation of the two channels (fluorescence cross-correlation spectroscopy, FCCS). The cross-correlation function is related to the amount of diffusing particles carrying both dyes and can be used for monitoring a binding reaction. Here we develop a formalism for a quantitative analysis of ligand binding from a combination of the auto-and the cross-correlation amplitudes. Technical constraints, like the focal geometry, background signal and cross-talk between the detection channels as well as photophysical and biochemical effects which modulate the brightness of the particles are included in the analysis. Based on this framework a comprehensive treatment for the determination of two-component binding equilibria by FCS/FCCS is presented.

Micrometer-sized highly sensitive strain sensors are presented. The sensors are based on magnetic tunneling junctions (MTJs) incorporating magnetostrictive free layers. The influence of mechanical strain upon the free layer is explained by a model taking into account the total free energy of the sensing layer. Those MTJ devices prepared in situ with magnetostrictive Fe50Co50 layers exhibit a tunneling magnetoresistance (TMR) ratio of 48%. The changes in strain Δε on the order of 0.4 parts per thousand (‰) result in resistance changes of 24%, which in turn leads to gauge factors [(ΔR/R)/Δε] on the order of 600, whereas gauge factors of 2–4 are typical for metal based, and 40–180 for piezoresistive semiconductor strain gauges.

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