Base sequence dependence of deoxyribonucleic acid studied by scanning tunneling microscopy

In order to identify high-order structures and pitch length of deoxyribonucleic acid (DNA), poly(dA-dT).poly(dA-dT) and poly(dG-dC).poly(dG-dC) were adsorbed on Cu(111) substrates by the pulse injection method and were observed by ultra high vacuum (UHV) scanning tunneling microscopy (STM). In large-scale STM images, the high-order structure of poly(dC-dC)poly(dG-dC) has a higher divergence and shorter dimension compared with those of poly(dA-dT) poly(dA-dT). High-resolution STM images revealed that the pitch lengths of poly(dA-dT)poly(dA-dT) and poly(dG-dC)poly(dG-dC) adsorbed onto the surface were longer than those possessed in the aqueous solution.