Slides 101

Would you eat your spaghetti dinner without a plate? No, of course not! It would make a big mess and be ugly to look at. Instead you NEED something to put that spaghetti on, to contain it, to keep it clean, to make it look nice – a bowl, a plate, SOMETHING!

By the same token, you wouldn’t image your sample without a microscope slide either. So the question is not “do you use a microscope slide?” but “what type of microscope slide do you use?” and with what accessories?

Microscope Slide Features

The job of all microscope slides is to hold your specimen in place for examination. However, the shape, size, material of slides can vary tremendously:

Size

A typical microscopy slide is about 75 x 25 mm and 1 mm thick, although you can find longer ones and skinnier ones.

Materials

Most slides are made of optical quality glass (soda lime glass or borosilicate) with polished edges, although plastic can also be used. Fused quartz glass is preferred if ultraviolet transparency is a factor.

Shape

Most microscope slides are flat but this is not your only choice. Concave slides have wells that may help you hold thicker samples or liquids from cell culture.

Markings

Most slides have a frosted or enamel end. This is used for labeling of the slide with a pen or pencil. I would always recommend pencil though as many solvents are used during microscopy sample preparations and will wash away pen markings (not good). You can even spice up your microscope slide racks by buying ones with colored frosted ends. Picture it now: Your bench littered in rainbow colored slides. Wheeeee!

Graticule slides have grid markings on them. This can help you estimate the size of your sample under magnification and, if need be, provide reference areas for accurate scorings. Sometimes these grids can be very fine and are used for special applications, like cell counting.

Coatings

Uncoated slides can be just fine, but often slides are coated to help samples stick better – this is especially necessary if you are mounting tissue sections or cells on your slides. (To learn more about how to mount charged slides with tissue sections, suspension cells, or adherent cells, see my other articles.) Coatings can include poly-L-lysine, gelatin, silanes, epoxy resins or even gold. You can either buy slides with these coatings pre-applied by the manufacturer or you can apply them yourself – it is up to you depending on what you have more of: time or money.

Microscope Slide Accessories

It isn’t just the slides themselves that vary. How you mount your slides also varies. Do you use a coverslip? Mounting Media? What type?

Cover slips

You might think that all coverslips are created the same. You might think that you can grab just any ol’ piece of glass sold as a cover slip, put it over your sample and be fine. But you’d be wrong!

In fact, cover slips come in multiple sizes. And lets face the hard truth…size matters! Cover slips come in a variety of thicknesses, #0 to #4, and you need to use the ideal cover slip size if you are to get ideal images.

Your ideal thickness is engraved on your microscope’s objective. For most, this is 1.7 mm. This means you should use a #1 coverslip, which is 0.13 mm to 0.16 mm thick. “But wait!” you say “0.13 mm to 0.16 mm is not 0.17 mm – shouldn’t you go a size up?” No. This is because you must also take into account the thickness of the mounting media when selecting the ideal coverslip for your objective. So to achieve your objective’s ideal thickness of 0.17 mm you need to use a coverslip that is a little less (a #1 at 0.13 mm to 0.16 mm) and anticipate your mounting media adding 1–2 ? m of thickness.

Mounting Medias

• Dry (no media). Dry mounting is the simplest way to mount your specimen. It involves nothing more than your microscope slide, your sample, and a coverslip. This method is most commonly used with inorganic and dead matter, such as hair, feathers, pollens, etc. It is not appropriate for most cell and tissue imaging.
• Wet Media. In wet mounting there is liquid between your microscope slide and cover slip, covering your sample. This is a good method because liquid refracts light and can make your specimen easier to see.
• Adherent Media. These media harden over time and fix your coverslip and slide together. They are excellent for preserving your sample.

Good luck and happy imaging!