Many mounting media for making permanent microscope slides include organic solvents and are less suitable for the use in classrooms, at home and with children. In this article I would like to show you how to make fructose syrup to be used as a safe mounting medium.
Fructose syrup is a water-based mounting medium, which is suitable for a wide variety of specimens. It is safe to use and it is easy and cheap to make. Spills can be easily washed out with water. One disadvantage is that the color of the specimens may fade and that some stains will loose intensity over time. This is due to the low pH of the medium. Fructose syrup is not suitable for making slides that last for many years, but is should be sufficient for classroom usage, where students would like to re-examine their specimens over and over again over a period of time. The medium will not completely solidify, so it is necessary to seal the cover glass at the side.
Materials: distilled water, fructose, dropper bottle or other container, optionally nail polish / nail varnish.
Method for making fructose syrup:
- Fill several grams of fructose into the dropper bottle.
- Using a marker, mark the level of the fructose on the glass bottle.
- Using the dropper, add distilled water to the fructose. The fructose will dissolve and the volume will decrease. Add more water to maintain the total volume level.
- Store the bottle for several days in a warm place, or use a warm water bath. It takes this time for all of the fructose to dissolve. At the end, you should have a clear, sticky liquid. It is then ready for use.
Method for using fructose syrup:
- The specimen to be mounted (eg. a small insect, some plant sections etc.) must be first placed into water. In most cases, fresh material is already stored in water. It could, however, be that due to previous processing or storage the specimens are soaked in alcohol or other organic solvents. This solvent must be removed first. If the specimens were stored in alcohol, then slowly transfer them into distilled water by placing them gradually into more and more dilute alcohol. If you transfer the specimen directly from concentrated alcohol into pure water, then there is the danger that the specimen changes its shape.
- Place a drop of the mounting medium on the slide, then place the specimen (not wet) into the drop. Place another drop of mounting medium on top of the specimen. The specimen is now surrounded by the medium from top and bottom. Finally, place a cover glass on top of the mounting medium.
- Store the slide for a few days horizontally. Some water will evaporate, but the syrup will not solidify completely. If you store the slide for a long time (in a dry environment), then the fructose may start to crystallize out. You can then observe the specimen under the microscope.
- Optional (careful, organic solvents involved!): Seal the corners of the cover glass with some nail polish (nail varnish). This will prevent the syrup from flowing out and will prevent moisture exchange. The slide should be stable for a few months.