There are two possible causes for the condensation on the bottom of your sliding glass door. The first is air infiltration caused by damaged or improper weather stripping. If air can leak past your sliding glass door, then it will cool the interior surface of the door and condensation can form on the metal bottom section. The best way to determine whether there is air infiltration is to use a smoke stick, or a cigarette to look for drafts. Move the smoke stick around the edges of the door, preferably on windy day, and any air infiltration will become obvious. If you discover a problem, it may be possible to adjust the door or the weather stripping.
The second cause is a lot more difficult to deal with, because it is an inherent design flaw in the door. It's called thermal bridging. In less expensive doors, heat or cold passes readily through the metal parts by conduction. A well-designed door or window has thermal breaks in it to prevent heat transfer. These can be seen in the window illustration below.
If you're door has no thermal breaks, there is little that you can do in some cases. Depending on how the doors slide, it may be possible to glue a decorative piece of wood or low density plastic on the bottom of the door to act as insulation. In many cases, this is only possible on one of the two doors. If installed on the other door, it would prevent the doors from sliding.