NO microsensor

Figure 1.3 shows a typical calibration curve generated using an NO microsensor and the SNAP method described. 

Simonsen s group has performed some elegant work over the years on NO release characteristics from rat superior mesenteric artery. Initially, Simonsen s group simultaneously monitored artery relaxation and NO concentration in the artery using a NO microsensor in response to various drugs [120], NO concentration was monitored via an ISONOP30 electrode, purchased from WPI and inserted into the artery lumen using... 

Fig. 37.11. Use of an NO microsensor for detection of the NO release from cultured endothelial cells. The sensor is a dual probe microsensor. The small sensor is a bare Pt UME used to position the sensor in the feedback mode. Onto the larger Pt electrode a polymer was deposited from an acrylic resin containing Ni(4-lV-tetramethyl) pyridyl porphyrin and served as amperometric NO sensor, (a) Schematic of the sensor, (b) optical microphotograph of the sensor surface, (c) Response of the NO sensor to the stimulation of the cells with bradykinin at different distances of the sensor to the surface of the cells. Reprinted with permission from Ref. [104], Copyright 2004, American Chemical Society.

Fig. 8.17 Biogeochemical profiles of sulfur, manganese and iron species in a coastal marine sediment (Aarhus Bay, Denmark, 16 m water depth). A) Oxygen and nitrate profiles measured with and NO microsensors. B) Pore water profiles of dissolved manganese, iron and H S. C) Profiles of solid phase oxidized manganese and iron and of pyrite. D) Distribution of sulfate reduction rates (SRR) measured hy S-technique. The broken line at 4 cm depth indicates the transition between the suboxic zone and the sulfidic zone. Data in A) were measured at the same site but a different year than data in B)-D). (Data from Kjaer 2000 and Thamdrup et al. 1994a reproduced from Jorgensen and Nelson 2004).

Zhu et al. (2002) reported about a sensitive, selective, and stable NO microsensor with an electrode which was modified by nano-Au colloid supported on Nation. A low detection limit, high selectivity. 

Planar NO microsensors are constructed similarly to the planar metal disk microelectrodes commonly used in scanning electrochonical microscopy (SECM, see Chapter 12). The working electrodes are prepared as follows (i) The metal (e.g., Pt) disk electrode is encased in glass and the surrounding glass sheath reduced as described in Section 6.3.1 and in reference (19). The bare metal electrode is then chonicaUy modified to enhance the kinetics for electrochemical oxidation of NO on its surface. 

For a platinized Pt-based Clark-type NO microsensor (13), the surface of a bare Pt disk electrode is electrochemically platinized by cyclic voltammetry in a platinizing solution (3% chloroplatinic acid in water). As the potential is scanned (from -t-0.6 to -0.35 V vs. Ag/AgCl) using cycUc voltammetry (see Chapter 11), Pt(TV) ions are electroplated on the bare Pt disk electrode to create a porous and roughened electrode surface. The platinized Pt electrode has a larger active surface area as demonstrated by the larger recorded currents and lower detection limits for NO measurements compared with bare Pt electrodes as shown in Figme 6.3.10.1. 

In this Clark-type NO microsensor, a PTFE gas permeable membrane was used for selectivity specific to NO. A capillary structure with the bottom end simply covered with a thin PTFE gas permeable membrane ( 30 pm thick) was used as an outer sleeve of the sensor. A platinized Pt working electrode with a Ag wire reference electrode coiled around its glass sheath was inserted into the outer sleeve filled with an internal solution (aqueous 30 mM NaCl and 0.3 mM HCl solution as recommended by Shibuki) to optimize kinetics of NO oxidation at the platinum working electrode of the NO gas sensor (20). The Pt... 

Figure 6.3.10.1 (a) Typical dynamic response curves for bare Pt-based NO microsensors and pla-... 

Other types of planar NO microsensors include Pt microelectrodes chemically modified by electrodeposition of metaUoporphyrin-like nickel(II) complexes. For example, tetrasul-fonated phthalocyanine tetrasodium (NiTSPc) was electrodeposited on the bare electrode surface by repetitive cychc voltammetry (21). Alternatively, electrode functionalization using nickel(4-iV-tetramethyl)pyridyl porphyrin (NiTmPyP) as an electrocatalyst was also carried out by applying multiple pulses in differential pulse amperometry (22). In this case, the electrocatalyst was entrapped in a NO selective polymer network of a negatively charged acrylic acid resin that prevented access by anionic interfering species. 

Ion-selective microsensors have some disadvantages. Often their selectivity is not very high. Because of interference by Na or CP ions, measurements cannot be made in marine environments, with the exception of pH, and Ca ". However, their value for studies in freshwater environments is high, and no alternative exists for NH4, N02, and NOs microsensors. They last only ca. 1 day however, they are easy to construct. Finally, these sensors have behaved unpredictably in some circumstances, readings drifting radically, for example, upon penetration of the biofilm. Most likely this is caused by dissolution of hydrophobic biofilm compounds in the LIX membrane. The microsensor can be protected from this phenomenon with a hydrophilic protein layer (De Beer et aL 1997). 

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