DNA estimation can be done by -

A spectrophotometer measures the amount of light that a sample absorbs. The instrument operates by passing a beam of light through a sample and measuring the intensity of light reaching a detector. When a photon in the beam of light encounters an analyte molecule (the analyte is the molecule being studied), there is a chance the analyte will absorb the photon. This absorption reduces the number of photons in the beam of light, thereby reducing the intensity of the light beam. This is measured by the spectrophotometer. Nucleic acids absorb UV light at 260 nm because of nitrogenous bases purine/pyrimidines present in them. Thus the amount of DNA/RNA can be quantified using a spectrophotometer.