English: (A) A sandwich type genosensor model: A capture probe is employed to capture the target (DNA/RNA) from the solution phase to the electrode surface. The electrode bound target DNA is quantified indirectly by binding the reporter probes conjugated with a redox signal amplifier. The redox signal amplifier could be an enzyme or a nanomaterial, which produces the redox-active molecules. The redox-active molecules undergo an oxidation/reduction reaction, which is then quantified as an electrical response (current–voltage response) using electrochemical analytical methods. The whole strategy depends solely on hybridization efficiency between the nucleic acid probes and the target molecules (RNA/DNA/PNA). In this approach, target DNA does not need any modification. (B) The double-helical structure of DNA and Watson and Crick base pairing in DNA. DNA consists of two strands. The two strands are held together by complementary base pairing between the bases, i.e., hydrogen bonds (A with T and G with C). Two hydrogen bonds attach A to T; three hydrogen bonds attach G to C. High temperature can denature the double-stranded DNA into single-strands. These complementary single-stranded DNAs can specifically rehybridized to form a double-stranded helix by reducing the reaction temperature.