Ultrasensitive detection of specifi c DNA or peptide sequences is of great importance in disease diagnostics, environmental monitoring, gene therapy, biomolecular analysis and other biomedical applications. Polymerase chain reaction (PCR) and rolling circle amplifi cation (RCA) have been widely used for target and signal amplifi cation. Nevertheless, these methods involve complicated, high cost or time-consuming procedures. Due to the strong demands of rapid, selective and sensitive detection of DNA, optical and electrochemical detection methods relying on the fluorescent or electrochemical tags have been widely used. Another approach such as label - free electrical detection has also recently attracted extensive research efforts since no fl uorescent or electrochemical tags are required, which substantially lowers the cost of the detection. Meanwhile, many new technologies are being developed to enhance the detection sensitivity of DNA concentration. The Si-nanowire sensors based on surface-enhanced Raman scattering or fi eld-effect transistor have been demonstrated to detect the DNA at a concentration range of 0.1  ~ 1 fM. Several reports have recently made advances to approach the detection limit of sub-femtomolar level. An even higher sensitivity in the attomolar range can only be achieved with the aid of signal amplifi cations. Hence, it is of great challenge to demonstrate the label free and direct attomolar detection.