Rapid method for measurement of surface tension in multiwell plates

We describe an optical method for quantifying surface tension in 96-well microtitre plates. Absorbance and fluorescence measurements in vertical beam systems as in 96-well plate photometers are complicated by the interaction of the light with the curved surface of the liquid. If the samples do not all have the same meniscus, errors in the data proportional to the degree of curvature are produced, which may confound interpretation of the data. We have harnessed this effect by modifying a 96-well plate spectrophotometer, and show that the apparent optical density measurements correlate very closely with surface tension. The method is much quicker than conventional methods for measuring multiple samples and requires considerably less technical skill. We demonstrate the applicability of the method to the study of biomolecules by investigating the surfactant properties of two peptides (Aβ and AChE586–599) that form amyloid fibrils in vitro, in one case replicating previously published results, and in the other case highlighting the similarity, and possibly generic nature, of the biophysical properties of these amyloidogenic peptides.