Recovery and ampli®cation of plasmid DNA with atomic force microscopy and the polymerase chain reaction

Mapping the force on plasmid DNA molecules with the atomic force microscope (AFM) showed an increased adhesion force between a silicon nitride tip and DNA strands in a mildly acidic solution. With this adhesion force, the plasmid DNA could be stretched off the mica surface, and the silicon nitride tip occasionally picked up one or several molecules of plasmid DNA from the mica surface. We have been able to develop a polymerase chain reaction (PCR) method, with which one molecule of plasmid DNA could be speci®cally and ef®ciently ampli®ed, to prove the presence of plasmid DNA on the silicon nitride AFM tip. It opens up a possibility for recovering one or several DNA molecules with an AFM tip from biological sample surfaces including that of a chromosome. # 1998 Elsevier Science B.V.