Positively Charged Slides
Many methods of adhering sections to slides depend on using some material, usually protein, to act as a contact glue between the glass and the tissue. Charged slides are different in that the adhesive compound has a positive charge and either coats the glass or bonds to it chemically. The positively charged coating attaches to the tissue through negative charges in the tissue.
There are two compounds used for this, polylysine, which coats the slide, and 3-Aminopropyltriethoxysilane (also referred to as TES, AES, APS, APES, APTS or APTES), which bonds to the glass. Kiernan discusses these two adhesives along with chrome alum gelatin, which acts in a similar manner. Wheaton Scientific has a pdf sheet with full instructions for preparing both polylysine and APES coated slides.
Slides to be coated must be clean and the following is recommended before coating:–
|Cleaning slides for coating|
• Clean slides thoroughly with detergent or 2N sodium hydroxide.
• Wash slides thoroughly with distilled water to remove all traces of cleaning solution.
• Dry the slides.
• Continue with the procedure for polylysine or APES coating.
Polylysine coated slides
Kiernan notes that any kind of polylysine may be used for coating slides and refers to Thibodeau et. al. for a simple method which involves spraying a 1:10 dilution of polylysine onto clean slides then drying. Scientific Solutions gives a simple method, as does Nikilab.
There are many variations on the theme, but most are similar to the following:–
|Preparing polylysine coated slides|
• Immerse in 0.01% polylysine for 15 to 45 minutes.
• Rinse well with distilled water.
• Dry and store in boxes
Silane coated slides
A straightforward method for silanising slides is given by the University of Nottingham, and there is another on the Thermo Scientific web site. Kiernan gives technical details for preparing them and discusses the chemistry behind their adhesive capabilities.
The actual preparation and coating with APES should be done in a fume hood. Reserve the glassware used to dilute and apply APES for that purpose alone as it will also be coated. Most instructions include the following:–
|Preparing silanised slides|
• Immerse in 2% APES in absolute acetone, 5 seconds to 45 minutes.
• Rinse with a few changes of fresh absolute acetone.
• Dry and store in boxes
Kiernan, J A., (1999).
Strategies for preventing detachment of sections from glass slides.
Microscopy Today v. 99-6, p. 22-24.
Thibodeau, T R, Shah, I A, Mukherjee, R & Hosking, M B,, (1997).
Economical spray-coating of histologic slides with poly-L-lysine.
Journal of Histotechnology, v. 20, p. 369-370