At which wavelength is nucleic acid absorbance highest?

The absorbance of nucleic acids is highest at 260 nm due to the presence of aromatic bases in their structure, such as adenine, thymine, cytosine, and guanine. When ultraviolet light at this specific wavelength passes through a sample containing nucleic acids, the energy of the light is effectively absorbed by these bases, causing an increase in absorbance. This property is commonly utilized in laboratory settings for quantifying nucleic acid concentrations, as the degree of absorbance correlates with the amount of nucleic acids present in the sample.

At wavelengths significantly lower or higher than 260 nm, the absorbance contributions from nucleic acids decrease. For example, absorbance at 230 nm is primarily associated with contaminants like phenol or other organic compounds, while 280 nm is mainly linked to protein absorbance, particularly due to amino acids like tryptophan and tyrosine. The wavelength of 300 nm does not typically provide reliable measurements for nucleic acids as the absorbance is significantly lower, leading to less distinct differentiation between nucleic acids and other components in a sample. Therefore, the choice of 260 nm is reinforced by its specificity and reliability for nucleic acid quantification in molecular biology assays.