Microtensiometer for Confocal Microscopy Visualization of Dynamic Interfaces

Steven V Iasella, Sourav Barman, Clara O Ciutara, Boxun Huang, Michael L. Davidson, Joseph A. Zasadzinski

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

Adsorption of surface-active molecules to fluid-fluid interfaces is ubiquitous in nature. Characterizing these interfaces requires measuring surfactant adsorption rates, evaluating equilibrium surface tensions as a function of bulk surfactant concentration, and relating how surface tension changes with changes in the interfacial area following equilibration. Simultaneous visualization of the interface using fluorescence imaging with a high-speed confocal microscope allows the direct evaluation of structure-function relationships. In the capillary pressure microtensiometer (CPM), a hemispherical air bubble is pinned at the end of the capillary in a 1 mL volume liquid reservoir. The capillary pressure across the bubble interface is controlled via a commercial microfluidic flow controller that allows for model-based pressure, bubble curvature, or bubble area control based on the Laplace equation. Compared to previous techniques such as the Langmuir trough and pendant drop, the measurement and control precision and response time are greatly enhanced; capillary pressure variations can be applied and controlled in milliseconds. The dynamic response of the bubble interface is visualized via a second optical lens as the bubble expands and contracts. The bubble contour is fit to a circular profile to determine the bubble curvature radius, R, as well as any deviations from circularity that would invalidate the results. The Laplace equation is used to determine the dynamic surface tension of the interface. Following equilibration, small pressure oscillations can be imposed by the computer-controlled microfluidic pump to oscillate the bubble radius (frequencies of 0.001-100 cycles/min) to determine the dilatational modulus The overall dimensions of the system are sufficiently small that the microtensiometer fits under the lens of a high-speed confocal microscope allowing fluorescently tagged chemical species to be quantitatively tracked with submicron lateral resolution.

Original languageEnglish (US)
Article numbere64110
JournalJournal of Visualized Experiments
Volume2022
Issue number187
DOIs
StatePublished - Sep 2022

Bibliographical note

Funding Information:
All the confocal microscopy images were obtained using the Nikon A1RHD Multiphoton upright confocal microscope. We acknowledge the guidance and assistance of the support staff, especially Guillermo Marques, at the University Imaging Center at the University of Minnesota. This work was supported by NIH Grant HL51177. SI was supported by a Ruth L. Kirschstein NRSA Institutional Research Training Grant F32 HL151128.

Publisher Copyright:
© 2022 JoVE Journal of Visualized Experiments.

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