Small But Powerful Optically: Glass Microcapillaries for Studying Complex Fluids or Biological Systems with Submicrolitre Samples under Harsh Conditions

Abstract

Glass micro-capillaries are the simplest yet most versatile, robust, practical and cheap microfluidic devices. Their small size and high optical quality favour detailed investigation under the optical microscope. Here we first review some of their applications, such as determining contact angles and the observation of tenuous wetting films under harsh conditions of pressure and temperature. We further explore how an optical cusp formed by reflection off the inner wall of a glass capillary may be used to monitor the refractive index of its fluid content. Finally, we illustrate how the above advantages may be put to use in the study of extremophile microorganisms, for example in recreating under the microscope the conditions prevailing on the ocean floors. RÉSUMÉ :Les microcapillaires de verre sont les outils microfluidiques les plus simples, et né anmoins ils sont polyvalents, robustes et bon marché . Leur petite taille et grande qualité optique favorisent leur utilisation sous le microscope optique. Nous passons en revue quelques unes de leurs applications, comme la dé termination d'angles de contact et l'observation de films de mouillage en conditions sé vè res de pression et tempé rature. Nous explorons ensuite comment la caustique formé e par ré flexion sur la paroi interne du capillaire est relié e à l'indice de ré fraction du contenu fluide. Finalement, nous illustrons comment ces avantages peuvent servir à l'é tude d'organismes extré mophiles, par exemple en recré ant sous le microscope les conditions des fonds océ aniques.

Traceability of the Primary Nano-flow Measurement System: Measuring the Local Inner Diameter of a Glass Capillary

“…Covering the capillary with glycerol and filling it with DMSO that is necessary to dissolve the Nile Red dye, ensures to reduce the distortions caused by the light's refraction at the different air/glass and liquid/glass interfaces [17,18], since they have similar refractive indices as the capillary's glass. A drop of water was deposited on the lens of the objective and the coverslip placed on the support, perpendicularly to the objective's axis, in contact with the drop.…”

“…N. Hobeika et al propose an optical method which takes advantage of the refraction of light through capillaries in order to study the contact angle of immiscible fluids and detect thin films on the inner wall of the capillary. In their paper, they propose a mathematical equation relating the inner diameter of the capillary with an apparent diameter that appears in images of the capillaries and under certain focus conditions, as two white lines [17,18]. The adjustment of the focus in order to make the white lines appear is however difficult and the associated uncertainty has not been evaluated in their paper.…”