Nitric oxide (NO) is a gaseous free radical that turned out to have vital physiological roles in mammals including humans. The detection and quantification of nitric oxide has been accomplished to a certain extent, but major challenges in the determination of this reactive molecule are yet to be fully overcome for reliable measurements in biological media. We developed electrochemical sensor for NO detection by electropolymerization of 3, 4-ethylenedioxythiophene (EDOT) on 7- and 30-µm carbon fiber electrode (CFE). Our data indicate that the sensor exhibits great sensitivity for NO (10- fold enhancement than the bare CFE). The modified microelectrode has rapid and reproducible response to NO at virtually low applied potential (0.5V). Also, since our previous studies show that a transition metal catalyst enhances significantly the sensitivity for NO detection, the metal catalyst-PEDOT (Poly EDOT) layer-by-layer modified electrode was used to investigate the performance of the resulting sensor. We show that this "third generation" modified sensor has high sensitivity (more than 100 times than bare CFE), and excellent linearity on a wide range, including low concentrations (sub-nanomolar) of NO, which can be use for reliable detection of NO in biological systems. Preliminary application results will be presented and discussed.