Each step dilutes by the same factor: C_n = C₀ / DF^n
Serial dilution creates a geometric series of concentrations by repeatedly diluting by the same factor. A 1:10 serial dilution: take 0.1 mL from one tube, add to 0.9 mL diluent → concentration drops 10-fold each step. After n dilutions: C_n = C₀/DF^n. Common series: 1:2 (doubling dilutions, used in antibody titrations), 1:10 (bacterial counts), and 1:3 or 1:5 (dose-response curves). Serial dilutions are essential in: microbiology (CFU counts), immunology (ELISA, antibody titrations), pharmacology (IC50 determination), and analytical chemistry (calibration curves). Tips: use fresh pipette tips for each transfer, mix thoroughly (minimum 3× inversion), and include a blank/negative control.