Incorporation of Nafion pre-coat layers (Nafion(1/2) and Nafion(2/1)), and poly-o-phenylenediamine (PPD) on platinum disk electrodes (127 lm) for the electrochemical detection of nitric oxide (NO) is discussed. The extensive in vitro development and characterisation of Nafion(1/2) PPD and Nafion(2/1) PPD modified sensors demonstrated excellent sensitivity towards NO (1070 ± 19 pA lM1 , n = 38 and 990 ± 14 pA lM1 , n = 38) respectively which were both significantly different from bare Pt electrodes (352 ± 25 pA lM1 , n = 14). There was negligible interference, <1% of the overall signal, from the various electroactive interferents investigated at their respective physiological concentrations. The Nafion(1/2) PPD sensor demonstrated a response time of 18 ± 2 s, n = 38 at 25 C which decreased to 14 ± 1 s, n = 6 at 37 C with no significant increase in sensitivity observed (1287 ± 48 pA lM1 , n = 6). Similarly the Nafion(2/1) PPD sensor demonstrated a response time of 16 ± 2 s, n = 38 at 25 C which decreased to 10 ± 1 s, n = 6 at 37 C with a non significant decrease in sensitivity observed (791 ± 41 pA lM1 , n = 6). The limit of detection was 8 ± 1 nM, n = 12 for the Nafion(1/2) PPD modified sensor and 7 ± 1 nM, n = 12 for the Nafion(2/1) PPD modified sensor. Sensocompatibility studies undertaken in proteins (BSA), lipids (PEA) and brain tissue for 28 days resulted in an AA current which is ca. 1% of the bare Pt response (37 ± 1 nA mM1 , n = 14). Shelf-life studies for both the Nafion(1/2) PPD and Nafion(2/1) PPD modified sensors demonstrated negligible differences after 56 days storage at 4 C