Here, we describe a quantification method, using force-distance (FD) curve based atomic force microscopy (AFM) to detect a target DNA bound to small (1.4-1.9 μm diameter) probe DNA spots, allowing mapping of entire spots to nanometer resolution. 
AFM
Quantification of Fewer than Ten Copies of a DNA Biomarker without Amplification or Labeling.Polymerase chain reaction (PCR) is a highly sensitive diagnosis technique for detection of nucleic acids and for monitoring residual disease; however, PCR can be unreliable for samples containing very few target molecules. 
PCR