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The Impact of Microscope Slides on Immunohistochemistry
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Several factors go into successful Immunohistochemistry ("IHC"). One specific factor that I will discuss in this article is the microscope slide. While the advent of positively-charged or adhesive coated slides has definitely helped to improve tissue retention, tissue lifting may still occur. The best way to prevent this from happening is to properly fix and process the tissue. But to augment performance, the slide you use is important. And if you want a slide with enhanced ability to prevent tissue section loss or lifting in harsher environments (like IHC) then you may want to learn more about what manufacturers are doing.
Contrary to popular belief there is no such thing as a "magically" charged slide. All adhesion slides are treated and the coating that is applied provides the adhesive properties we need for successful IHC. The coating that is applied does covalently bond to the slide and impart a positive charge that attracts the formalin fixed "negatively" charged tissue proteins. Traditional slide coatings are hydrophobic ("afraid of water") but over the last 4-5 years, manufacturers have been quietly introducing hydrophilic ("love water") slides. In order to understand the differences between hydrophobic and hydrophilic glass properties I thought the pictures and chart below may help.
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Feature/Property
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Hydrophobic Slides
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Hydrophilic Slides
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Water Collection on Slide
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Hydrophobic glass has taller, more round, water droplets which can collect under the tissues and trap water underneath.
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Hydrophilic glass water drops are flatter. They pool under the tissue sections but do not trap the water under the sections
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"Movability" of Section
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Paraffin section is not moveable once picked up on the slide. If tissue is not optimally positioned on the slide; may need to discard/start over with fresh slide.
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Paraffin sections will be moveable until the water has dissipated and section has touched the surface of the slide
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Dry Time
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Slides require a longer drying time due to trapped water which could lead to tissue loss and/or nuclear bubbling.
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Two ways to reduce required dry time.
1. Allowing slide to lay flat for 10-15 seconds after picking up tissue.
2. Pick up the sections in a more vertical manner from the water bath (helps avoid collecting excess water).
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Hydrophobic Slide with trapped water beneath tissue-This can cause longer drying periods to remove water.
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Hydrophilic Slides-sections are more prone to moving on the slide.
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Picking up the sections in a more vertical manner from the water bath may help to avoid collecting excess water with hydrophobic slides as well as helping to avoid larger pools of water to collect under sections on hydrophilic slides...so when in doubt so straight in and straight out when picking up sections on slides.
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As with all new processes, it may take a bit of practice to develop your way of handling and picking up sections on hydrophilic slides but it will be worth the effort. While I am not advocating the use of either in this article, recent studies show that the hydrophilic slides have 2x -- 3x times the number of binding sites that hydrophobic slides have. More binding sites means better adherence of tissue sections to the slides. If nothing else, its information I thought everyone in our community should have so you can make the most informed decision possible.
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Happy Thanksgiving Everyone! Debbie Siena, HT (ASCP) QIHC Technical Manager StatLab Medical Products
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