Bacterial contamination levels on various surfaces in our daily life
University of Rochester
Materials Science in Mechanical Engineering Department
507 SEM PRACTICUM
Yan Li

HOME INTRODUCTION SAMPLE PREPARATION RESULTS ACKNOWLEDGEMENTS & COLORIZATION

Sample Preparation

My samples were collected by wiping different surfaces with filter paper. Five samples were made in this project, including the surface of teeth brush; the surface of teeth; the surface of keyboard; the surface of sponge used in kitchen and the surface of cup. Since my samples contain bacteria and they are not conductive. The samples should be dehydrated and coated with gold before the observation of SEM. Usually, there are two ways to dry biological samples: one is CPD (Critical Point Drying) and the other one is HMDS (Hexamethyldisilazane) Drying. Since the bacteria are small and not containing a lot of water, the HMDS drying is good enough to dehydrate my sample.

HMDS Drying

HMDS provides a rapid, inexpensive method for drying the biolodical samples. For my samples, the procedures of sample preparation are relatively simple.

1) Immersing the filter paper with bacteria into HMDS solution for at least five minutes.
2) Waiting for half an hour untill the paper is completely dry.
3) In order to keep the samples dry sputting the samples as soon as they are completely dry.

Co2 Critical point

Sputtering

In order to increase the conductivity of the samples, they were coated with gold for 80 sec. The coating was applied using a Denton vacuum DESK II system. When a high voltage is applied to the tube, the argon in the sputter coater ionizes. Bombardment of the Gold-Palladium in the cathode by ionized argon atoms sputters off Gold-Palladium atoms from the cathode onto the specimen.