Gelatin coated slides can hold sections on slides more securely therefore preventing sections from falling off slides. Here we introduce a method on how to make gelatin coated slides. This technique has been proven successful.

Coating

1.   Chrome Alum Gelatin Solution:

      Gelatin, type A, 220 or 275 Bloom -------- 1.5 g

      Chromium potassium sulfate -------------- 0.25 g

      Distilled water ------------------------------- 500 ml

Heat the water to 60 ºC and completely dissolve the gelatin with the aid of a magnetic stirrer. Stir in the chromium potassium sulfate (The solution should turn a pale blue). Add a few crystals of thymol as a preservative.

2.  Procedure:

Dip racks of clean slides in the warm gelatin solution (40-50 ºC), drain the slides onto paper tissue, and then stand the slides (covered with foil to keep off dust) on end to air dry or 37 ºC incubator overnight. Store in dust-free container at room temperature. Throw out the gelatin mixture after use. 

Mounting:

1.   Paraffin Sections (up to 50um):

Cut 20-50 um paraffin sections with the aid of a warm water drop on the block face by using hair brush gently. Briefly, trim paraffin block to cutting surface, dip hair brush in warm water in water bath, brush paraffin block surface gently to make sure the block surface is fully moisturized. Then cut and transfer the section to water bath (set water bath temperature to 50 ºC or higher. If temperature is too low, the folds will not be flatten). Allow the sections remain in water bath for 5-10 minutes or until they are flatten (no wrinkles, some sections, especially middle part of brain, will not be completely flatten, and some wrinkles will go away during air dry). Mount the sections onto gelatin-coated slides. Air dry slides overnight to several days or bake slides in 45ºC oven overnight (NEVER allow oven temperature go higher than 50 ºC or sections will crack). Take slides out of oven and proceed with deparaffinization.

2.   Frozen/vibratome sections (20-50um):

      Before or after staining of frozen/vibratome sections, mount the sections on gelatin-coated slides and air dry overnight or 2-3 days.

Note:

This protocol has been tested successfully on formalin-fixed, paraffin embedded brain tissue sections at 50 um thick. The sections went through antigen retrieval (steam) procedure and still intact without detaching from slides.

Regular slides (uncoated slides) can be used to replace gelatin-coated slides for 20-50 um paraffin embedded brain sections, but additional gelatin powder in water bath is needed at 0.03% concentration (3 g gelatin needed in 10L of water bath).