Sterile saline 0.85% (w/v) is a solution of sodium chloride (NaCl) in water, where the concentration is 0.85 grams of NaCl per 100 milliliters of solution. This solution is commonly used as a diluent in microbiology for various applications like cell suspension preparation, washing cells, and preparing standardized inoculums. It's an isotonic solution, meaning it has a similar salt concentration to body fluids, which helps maintain cell viability and integrity. The solution is sterile-filtered and often used for maintaining cell viability in research and clinical diagnostics.