Smart and cheap assessment of microscope slide surface wettability by polysorbate 20–in aqueous buffered solutions and for increasing amounts

A smart, cheap and accurate method for measuring areas by mean of a commercial text and image processor in scaled pictures has been developed to quantify the surfaces of droplets containing increasing amounts of Polysorbate 20 surfactant onto microscope glass slides.

The effect of Polysorbate 20 in buffered aqueous solutions appears on the surfaces of electrostatically treated microscope slides: the dispensing of 100 µl or less determines the quick spreading of the liquid to form a thin and adherent film.

In this study the surfactant properties of Polysorbate 20 on optical microscope slides free of electrostatic treatment were studied under controlled temperature conditions, for increasing percentages – i.e., from 0.05% up to 5% by volume—and within 5 and 10 min after by gravity dispensation of droplets with laboratory pipettes. The areal increase was evaluated starting from pictures acquired with a smartphone and using the graphic functions of Microsoft Word: the 4-times magnification and proper scaling made it possible to avoid parallax error and to measure the areas with accuracy and reproducibility.

The tests have shown that the surfactant effect appears at the lowest concentration, with a plateau between 0.05% and 0.5% before rising again. The surface area of ​​the droplets increases over time—mainly within 5 min—due to the increase of glass surface wettability. The surfactant concentration in use at the Authors' Institution and that recommended in literature—0.1% and 0.5% by volume—are therefore apt with respect to the desired effects.

“Gutta cavat lapidem” (A drop hollows a stone).