This work presents two examples of biosensors that employ DNA as the recognition element. The transduction technique chosen is electrochemical impedance spectroscopy, which makes labeless detection possible. In the first case, a DNA probe was used to hybridize and detect a complementary DNA target; this principle may be used to construct biosensors to confirm a microbial, vegetal or animal species. The working example shown is the detection of enterohaemorragic Escherichia coli O104:H4 bacteria, blamed of an epidemic outbreak in vegetables in Germany in 2011. As a second example, a specific DNA aptamer able to interact with proteins, is used to develop a biosensor to detect thrombin, an important protein mediating in blood coagulation. Following the current trend in the field, these DNA biosensors have been prepared with help of nanocomponents in order to improve or to confirm and visualize the detection capabilities.