Fluorinated xerogel-derived microelectrodes for amperometric nitric oxide sensing.

An amperometric fluorinated xerogel-derived nitric oxide (NO) microelectrode is described. A range of fluorine-modified xerogel polymers were synthesized via the cohydrolysis and condensation of alkylalkoxy- and fluoroalkoxysilanes. Such polymers were evaluated as NO sensor membranes to identify the optimum composition for maximizing NO permeability while providing sufficient selectivity for NO in the presence of common interfering species. By taking advantage of both the versatility of sol-gel chemistry and the "poly(tetrafluoroethylene)-like" high NO permselective properties of the xerogels, the performance of the fluorinated xerogel-derived sensors was excellent, surpassing all miniaturized NO sensors reported to date. In contrast to previous electrochemical NO sensor designs, xerogel-based NO microsensors were fabricated using a simple, reliable dip-coating procedure. An optimal permselective membrane was achieved by synthesizing xerogels of methyltrimethoxysilane (MTMOS) and 20% (heptadecafluoro-1,1,2,2-tetrahydrodecyl)trimethoxysilane (17FTMS, balance MTMOS) under acid-catalyzed conditions. The resulting NO microelectrode had a conical tip of approximately 20 microm in diameter and approximately 55 microm in length and exhibited sensitivities of 7.91 pA x nM (-1) from 0.2 to 3.0 nM (R (2) = 0.9947) and 7.60 nA x microM (-1) from 0.5 to 4.0 microM ( R (2) = 0.9999), detection limit of 83 pM (S/ N = 3), response time ( t 95%) of <3 s, and selectivity (log K NO, j (amp)) of -5.74, <-6, <-6, <-6, <-6, -5.84, and -1.33 for j = nitrite, ascorbic acid, uric acid, acetaminophen, dopamine, ammonia/ammonium, and carbon monoxide. In addition, the sensor proved functional up to 20 d, maintaining >or=90% of the sensor's initial sensitivity without serious deterioration in selectivity.