A sensitive electrochemical sensor based on chitosan and electropolymerized Meldola blue for monitoring NO in brain slices

We report the development of a novel electrochemical NO microsensor using electrodeposited Meldola blue (MB) as an electron mediator, o-phenylenediamine (o-PD) as a permselective membrane and a natural biocompatible polymer, chitosan as a protective coating, all deposited sequentially on a platinum microelectrode with a diameter of 125 μm. The electron transfer kinetics and the role of each component in the sensing layer were systematically studied in relation to the analytical performance of the corresponding chemically modified Pt microelectrodes. The use of an electropolymerized MB layer ensured stability of the mediator while the chitosan biopolymer provided a protective layer for the o-PD and MB as well as some sieving function against interferents, ascorbic acid and dopamine. The new NO microsensor demonstrated an extended linear range between 10 nM and 600 μM, with a R2 value of 0.9993, one order of magnitude wider than that of other NO microsensors reported to date, and a sensitivity of 20 nA μM−1. The detection limit of the sensor was 1 nM and the response time was 8 s. The chemically modified microelectrode was able to measure induced NO production in brain slices in a dose dependent manner. The stability of the active sensing surface was established both in standard NO solutions and in rat brain slices, and the sensitivity decreased by only 4% post-NO measurement in the brain slice.