Direct and precise length measurement of single, stretched DNA fragments by dynamic molecular combing and STED nanoscopy

A combination of DNA stretching method and super-resolution nanoscopy allows an accurate and precise measurement of the length of DNA fragments ranging widely in size from 117 to 23,130 bp. BstEII- and HindIII-treated lambda DNA fragments were stained with an intercalating dye and then linearly stretched on a coverslip by dynamic molecular combing. The image of individual DNA fragments was obtained by stimulated emission depletion nanoscopy. For DNA fragments longer than 1000 bp, the measured lengths of DNA fragments were consistently within 0.5 to 1.0 % of the reference values, raising the possibility of this method in a wide range of applications including facile detection for copy number variations and trinucleotide repeat disorder.