What instrument is used to measure the concentration of proteins or DNA?

The spectrophotometer is the instrument used to measure the concentration of proteins or DNA because it operates on the principle of light absorption. When a sample containing these biomolecules is exposed to specific wavelengths of light, the amount of light absorbed correlates with the concentration of the substance in the solution, based on Beer-Lambert law.

For proteins, the spectrophotometer can detect the absorbance at 280 nanometers, which is useful for quantifying proteins due to the presence of aromatic amino acids. For nucleic acids like DNA, absorbance is typically measured at 260 nanometers, allowing for the quantification of DNA based on its unique absorbance characteristics.

The other instruments mentioned have different functions. A microscope is used for observing small objects or organisms and provides visual detail rather than concentration measurements. A thermometer measures temperature but has no application in quantifying concentrations of biological molecules. An electrophoresis unit separates molecules based on their size and charge, providing information about the composition but not direct measurements of concentration.