Experimental characterization of methanol-acetic acid fixative sessile drop dynamics in dry and humid air by video imaging and interference analysis

Dynamics of methanol and acetic acid (3:1, v/v) fixative sessile drop is important for metaphase chromosomal spreads in cytogenetic assays. However, it has not been well characterized by biologists from a physical science point of view. In this work, a simple optical setup was built to record the fixative drop spreading and evaporation process. Drop film thickness, cross-sectional profile and surface thinning speed were constructed from the observed interference patterns to show evolution of the process in both dry and humid air. Surface thinning speed analysis at the drop center suggested different evaporation regimes. The ability of characterizing fluid behavior at a scale comparable to the size of cells by interference fringes is expected to facilitate further understanding of the metaphase spreading process at micro- and nano-scale.