The phrase “PBS plasma” does not refer to a single, distinct substance. Instead, it describes the widespread practice in scientific research and medical diagnostics of using Phosphate-Buffered Saline (PBS) in combination with blood plasma. These two components, one a synthetic buffer and the other a natural biological fluid, are used together in many laboratory procedures. Understanding their combined utility begins with appreciating what each component is and the unique properties it possesses.
Understanding Phosphate-Buffered Saline (PBS)
Phosphate-Buffered Saline is a solution routinely used in biological research, composed of a water base with dissolved salts. Its primary ingredients are sodium chloride, sodium phosphate, and often potassium phosphate and potassium chloride. These components are chosen because they are non-toxic to cells and mimic the concentrations of salts found within the fluids of the human body.
A main feature of PBS is its isotonic nature, meaning it has a similar water potential and salt concentration to the interior of living cells. This balance prevents cells from shrinking or bursting when submerged in the solution, a phenomenon caused by osmosis. Unlike pure water, which would rush into cells and cause them to rupture, PBS provides a stable osmotic environment, preserving cellular structure. This property makes it an ideal fluid for rinsing and handling cells without causing them damage.
The “phosphate” in its name points to its other principal function: acting as a pH buffer. The phosphate salts in the solution resist changes in acidity or alkalinity, maintaining a stable pH typically around 7.4. This is very close to the natural pH of human blood and is an environment where biological molecules, especially proteins, remain stable and functional. Abrupt shifts in pH can alter the shape of proteins, a process called denaturation, which destroys their biological activity.
The Composition and Function of Blood Plasma
Blood plasma is the liquid component of blood, making up about 55% of its total volume. It appears as a light-yellow fluid once the red blood cells, white blood cells, and platelets have been separated out. The vast majority of plasma, approximately 90-92%, is water. This water acts as a solvent, carrying the other components throughout the body, ensuring that cells receive necessary substances and waste products are removed.
Dissolved within this water is a complex mixture of substances, with proteins being the most abundant solids. These include albumin, which is produced by the liver and is instrumental in maintaining the osmotic pressure of the blood, and globulins, a group that includes antibodies for immune defense. Another protein is fibrinogen, which is a coagulant that plays a direct role in the blood clotting process.
Beyond proteins, plasma transports a wide array of other molecules. It carries electrolytes like sodium and potassium for nerve and muscle function, and nutrients such as glucose and amino acids for cellular energy and construction. Hormones that act as chemical messengers are also transported in plasma, as are metabolic waste products on their way to the kidneys and liver for excretion. This fluid matrix is the primary medium for transporting all these elements and maintaining blood pressure.
Why PBS is Used with Blood Plasma
When plasma is removed from the body for analysis or experimentation, it is separated from the complex, self-regulating systems that keep it stable. PBS is used to replicate these stable conditions in a laboratory setting. Its formulation provides an artificial environment that closely mimics the physiological state of the blood, thereby preserving the integrity of the plasma and its valuable components.
The most direct reason for this pairing is the maintenance of pH and osmolarity. The delicate proteins within plasma, such as antibodies and clotting factors, are sensitive to their chemical surroundings. The phosphate buffer in PBS prevents drastic pH shifts that could denature these proteins and render them useless for study. Likewise, the salt concentration of PBS ensures the osmotic environment remains stable, maintaining the native structure of the dissolved proteins.
In many diagnostic and research assays, the concentration of specific molecules in raw plasma is too high to be measured accurately. PBS serves as an ideal diluent in these situations. It allows scientists to dilute the plasma to a working concentration in a controlled manner, without altering the function or the overall chemical environment of the sample.
Key Applications in Plasma Research and Diagnostics
In medical diagnostics, the combination of PBS and plasma is fundamental to many common tests. A prime example is the Enzyme-Linked Immunosorbent Assay (ELISA), which is used to detect the presence of specific antibodies or antigens in a sample. In these tests, a plasma sample is often diluted with PBS to a specific ratio. This ensures the concentration of the target molecule falls within the assay’s detection range, allowing for accurate quantification of disease markers.
The field of proteomics, which involves the large-scale study of proteins, relies heavily on this combination for isolating specific proteins from plasma. Techniques like affinity chromatography use PBS as a base buffer. In this process, plasma is passed over a column designed to capture a target protein. PBS is then used to wash away all the other unbound plasma proteins, leaving the desired protein isolated in a purified state for further analysis.
Cell-based research frequently involves separating different blood cell populations from whole blood. For instance, when studying lymphocytes for immunological research, the cells are first separated from the plasma. These isolated lymphocytes are then washed one or more times with PBS to remove any lingering plasma components. This ensures that any observed cellular response is a direct result of the experimental treatment, not an interaction with a protein from the original plasma.
PBS is also used to prepare and reconstitute plasma-derived reagents for use in cell culture. Some cell lines require growth media supplemented with serum, which is plasma with the clotting factors removed. In other cases, specific plasma proteins that have been freeze-dried for storage must be brought back into a liquid state. PBS provides a stable, sterile, and physiologically compatible liquid for reconstituting these components into usable stock solutions.