CONSTRUCTING A HANGING DROP OSMOMETER**

Abstract

We designed an osmometer based on a hanging drop design by Weatherley (1960) for measuring osmolarities of small volume, botanical samples. An osmometer measures solute concentrations and can be used to indirectly quantify interactions between solutes.  We constructed an osmometer prototype that we are displaying by the poster. It is constructed from gas-tight syringes, capillary tubing, and 3D printed supports. Changes in solution volume will be measured with a cell phone camera, magnifying lenses, and image analysis software. We are working to generate calibration curves for solutions of known osmolarity. Upon successful calibration of the osmometer, we will be able to measure interactions between osmolytes and native proteins and nucleic acids. Equivalent measurements have been limited in solute choice and concentration and temperature ranges by the constraints of commercially available osmometers. This instrument has the potential to permit measurements over a range of temperatures (through submerging the apparatus in a water bath or temperature-controlled chamber) and between solutes like osmolytes and lipid membranes—all things that are impossible with current, commercial instruments. These measurements of interactions between biological molecules will extend the power of predictive and analytical models used to help answer many biochemical questions