Phosphate-Buffered Saline, commonly known as PBS, is a widely used solution in biological research laboratories. It serves as a buffer system, maintaining a stable environment for cells, tissues, and biological molecules. PBS provides conditions that closely mimic the natural physiological environment of living organisms, ensuring the integrity and function of biological samples in experiments.
Composition and Key Properties
PBS is an isotonic solution, with a solute concentration similar to human or animal cells. This isotonicity is achieved through a blend of salts, including sodium chloride (NaCl), sodium phosphate (Na2HPO4), and potassium phosphate (KH2PO4). KCl may also be included. The careful balance of these salts prevents osmotic shock, where cells might either swell and burst or shrink due to water imbalance in solutions with differing solute concentrations.
The phosphate salts, sodium and potassium phosphate, are important for PBS’s buffering capacity. They form a weak acid-base system that resists changes in pH, maintaining a stable pH, commonly around 7.4. This pH closely matches the physiological pH of most biological systems, important because many cellular processes and enzyme activities are highly sensitive to pH fluctuations. A stable pH environment protects cellular components and molecules from denaturation or loss of function under acidic or basic conditions.
Beyond its isotonicity and buffering capabilities, PBS is non-toxic to cells. It is suitable for direct contact with living cells and delicate biological samples. Its inert nature prevents interference with biological reactions or processes, allowing observation without unintended chemical interactions. These properties make PBS a valuable tool for laboratory work, ensuring reliable experimental outcomes.
Common Applications of PBS
PBS finds extensive use in cell culture, maintaining cell health and experimental integrity. It is used for washing cells to remove residual media, serum, or other interfering reagents. PBS also acts as a diluent for various reagents, ensuring physiological concentration and pH of solutions added to cells. This gentle handling helps preserve cell viability during transfers or treatments.
In immunohistochemistry, PBS is used for diluting antibodies and rinsing tissue samples during staining procedures. Its stable pH and isotonic nature help maintain the structural integrity of tissues and prevent non-specific binding of antibodies. This ensures specific antibody binding to target antigens, leading to clear visualization. Rinsing also removes unbound antibodies, reducing background noise.
Molecular biology techniques also rely on PBS for applications such as DNA and RNA purification and protein extraction. When isolating nucleic acids or proteins, PBS provides a stable environment to minimize degradation and maintain structural conformation. Washing steps use it to remove impurities, ensuring biomolecule purity. Purity is important for downstream applications like PCR or electrophoresis.
PBS is also a general-purpose solution in many laboratory procedures, including sample preparation and rinsing glassware and plasticware. Its non-toxic and inert properties make it a safe and effective choice for cleaning and pre-wetting lab equipment contacting biological materials. Using PBS for these tasks helps prevent contamination and ensures that experiments are conducted in a clean and biologically compatible environment.
Basic Preparation of PBS
The preparation of PBS involves dissolving specific amounts of its component salts in high-purity water. Researchers use distilled or deionized water to ensure the absence of contaminants that could interfere with biological experiments. Accurate measurement of each salt, including sodium chloride, disodium hydrogen phosphate, and potassium dihydrogen phosphate, is important to achieve the desired isotonicity and buffering capacity.
After the salts are dissolved, the pH of the solution is adjusted. This adjustment is performed using small quantities of either hydrochloric acid (HCl) to lower the pH or sodium hydroxide (NaOH) to raise it, until the target pH, often around 7.4, is reached. Maintaining the precise pH is important for the solution’s effectiveness as a buffer and for its compatibility with biological systems. A pH meter is used to monitor the adjustment process, ensuring accuracy.
Finally, the prepared PBS solution is sterilized to prevent microbial growth, especially if it will be used in cell culture or other sterile applications. Common sterilization methods include autoclaving, which uses high-pressure steam, or filtration through a 0.22-micrometer pore size filter to remove bacteria and other microorganisms. Proper storage of the sterilized solution, often at room temperature or refrigerated, helps maintain its stability and extends its shelf life for future use in the laboratory.