Description

A semi-permanent mounting media for immunofluorescence microscopy.

Method

1. Add the following reagents to a 250 ml flask or beaker:

• 24 g analytical grade glycerol (Sigma #G-6279)
• 9.6 g Mowiol 4-88 (Fluka, #81381, can be purchased through Sigma-Aldrich)
• 24 ml distilled water
• 48 ml 0.2M Tris buffer, pH 8.5

2. Stir with a clean stir bar on a hot plate on warm (not boiling)at least 4-5 hours until the majority of the Mowiol powder goes into solution.
3. Aliquot into 50 ml centrifuge tubes, weigh and balance
4. Centrifuge at 5000g for 15 minutes. Carefully remove the supernatant without disturbing the pellet at the bottom of the flask.
5. Aliquot into 15 ml conical tubes – add only 10 mls to each tube to allow for expansion with freezing.
6. Aliquots may be stored at -20C for 12 months. Store at room temperature no more than one month.
7. To use, warm solution to room temperature to eliminate bubble formation. use approximately 10 ul of mounting media for an 18 mm coverslip.
8. Allow slides to dry overnight at room temperature in a light-tight box.

Phosphate buffered saline (abbreviated as PBS) is a buffer solution commonly used in biological research. It is a salty solution containing sodium chloride, sodium phosphate, and (in some formulations) potassium chloride and potassium phosphate. The buffer helps to maintain a constant pH. The osmolarity and ion concentrations of the solution usually match those of the human body (isotonic).

Applications

PBS has many uses because it is isotonic and non-toxic to cells. It can be used to dilute substances. It is used to rinse containers containing cells. PBS can be used as a diluent in methods to dry biomolecules, as water molecules within it will be structured around the substance (protein, for example) to be ‘dried’ and immobilized to a solid surface. The thin film of water that binds to the substance prevents denaturation or other conformational changes. Carbonate buffers may be used for the same purpose but with less effectiveness. PBS can be used to take a reference spectrum when measuring the protein adsorption in ellipsometry.

Additives can be used to add function. For example, PBS with EDTA is also used to disengage attached and clumped cells. Divalent metals such as zinc, however, cannot be added as this will result in precipitation. For these types of applications, Good’s buffers are recommended.

Preparation

There are many different ways to prepare PBS. Some formulations do not contain potassium, while others contain calcium or magnesium^[1]. One of the most common preparations is described below.

A 10 liter stock of 10x PBS can be prepared by dissolving 800 g NaCl, 20 g KCl, 144 g Na₂HPO₄ · 2H₂O and 24 g KH₂PO₄ in 8 L of distilled water, and topping up to 10 L. The pH is ~6.8, but when diluted to 1x PBS it should change to 7.4. When making buffer solutions, it is good practice to always measure the pH directly using a pH meter. If necessary, pH can be adjusted using hydrochloric acid or sodium hydroxide.

On dilution, the resultant 1x PBS should have a final concentration of 137 mM NaCl, 10 mM Phosphate, 2.7 mM KCl, and a pH of 7.4.
Another preparation is described in Molecular Cloning by Sambrook, Fritsch and Maniatis, Apendix B.12^[2] as follows:

For 1 litre of 1X PBS, prepare as follows:

1. Start with 800 ml of distilled water:
2. Add 8 g of NaCl.
3. Add 0.2 g of KCl.
4. Add 1.44 g of Na₂HPO₄.
5. Add 0.24 g of KH₂PO₄.
6. Adjust the pH to 7.4 with HCl.
7. Add distilled water to a total volume of 1 liter.

Dispense the solution into aliquots and sterilize them by autoclaving (20 min, 121°C, liquid cycle). Store at room temperature.

References

1. Dulbecco, R. et al. (1954): Plaque formation and isolation of pure lines with poliomyelitis viruses. In: J. Exp. Med. vol. 99 (2), pp. 167-182. PMID 13130792
2. Sambrook, Fritsch, and Maniatis (1989) Molecular Cloning: A Laboratory Manual, 2nd ed., Cold Spring Harbor Laboratory Press, Cold Spring Harbor, New York, volume 3, apendix B.12
3. Portions of this article are from “Phosphate buffered saline. In Wikipedia, the free encyclopedia. Retrieved September 17, 2008, from http://en.wikipedia.org/wiki/Phosphate_buffered_saline.” This article has been reviewed for scientific accuracy and is used in accordance with Wikipedia’s GNU Free Documentation License (GFDL).