Name two methods to quantify DNA concentration.

• A. PCR and gel electrophoresis
• B. Spectrophotometry (A260/A280) and fluorometry (Qubit or PicoGreen)
• C. Mass spectrometry and NMR
• D. Western blot and ELISA

Answer: (B)

Two common ways to quantify DNA concentration are spectrophotometry and fluorometry. Spectrophotometry measures how much UV light DNA absorbs at 260 nm, and the absorbance value can be converted to concentration; the A260/A280 ratio also helps assess purity, with typical pure DNA giving roughly 1.8–2.0. However, this method can overestimate if contaminants like RNA, phenol, or salts are present. Fluorometry uses DNA-specific fluorescent dyes, such as those used in Qubit or PicoGreen assays, which bind to DNA and emit light proportional to the amount of double‑stranded DNA; these assays are more sensitive and less affected by contaminants, making them ideal for precise quantification, especially at low concentrations or with impure samples, though they require a standard curve. Other approaches like PCR with gel or protein-focused techniques (mass spectrometry, NMR, Western blot, ELISA) don’t provide a direct, reliable DNA concentration measurement in routine practice, so they aren’t used for quantifying DNA concentration.