Sensors from porphyrins

Flgure 14. Exponential decrease of NO concentration with Increasing distance of porphyrinic sensor from the membrane of single Isolated endothelial cell (dashed line) and single endothelial cell in cell culture (solid line). Rabbit aorta endothelial cells were stimulated with calcium ionophore. 

Bouvet, M., Parra, V., Locatelli, C. Xiongb, H. (2009). Electrical transduction in phthalocyanrne-based gas sensors from classical chemiresistors to new functional stmc-tures J. Porphyrins Phthalocyanines, 13, 84-91. 

Fig. 12 Exponential decrease of NO concentration with increasing distance of porphyrin sensor from the membrane of a single isolated eNOS cell (solid line), a single eNOS cell in cell culture and a single eNOS cell in culture (3 x 10 cells). NO release was stimulated from HUVECwith Cal.

Fig. 12a,b. The sensorgrams for the binding of the antibody dendrimer (a) or IgG (b) to the anionic porphyrin immobilized onto the surface of the sensor chip. Phosphate borate buffer (0.1 M, pH 9.0) was used. TCPP was immobilized via hexamethylenediamine spacer onto the sensor chip and then a solution of IgG or the dendrimer was injected to the flow cell. After 60 s from the injection of the antibody solutions, flow ceU was filled with buffer... 

Surface modified NO sensors incorporate an electrode surface that has been modified or treated in some way so as to increase the selectivity of the sensor for NO and promote catalytic oxidation of NO. An early example of such a sensor was presented by Malinski and Taha in 1992 [27], In this publication an —500nm diameter carbon fiber electrode was coated with tetrakis(3-methoxy-4-hydroxyphenyl)porphyrin, via oxidative polymerization, and Nation. This electrode was shown to have a detection limit of — lOnM for NO and great selectivity against common interferences. However, recently it has been shown that this electrode suffers severe interference from H202 [28],... 

Brovkovych et al. [38] applied the electrochemical porphyrinic sensor technique for the direct measurement of NO concentrations in the single endothelial cell. It was found that NO concentration was the highest at the cell membrane (about 1 pmoll-1) and decreased exponentially with distance from the cell, becoming undetectable at the distance of 50 pm. Now we will consider the principal reactions of nitric oxide relevant to real biological systems. 

This effect is complete in the case of porphyrins 6-8,13, which behave in the same way, independent of metal present in the inner core of the macrocycle. In conclusion, the introduction of these alkyl chains from one side gives a higher porosity to the molecular film and, as a consequence, both a speed up of the response and an increase of the sensor response. On the other hand there is a significant decrease of the importance of the selective interactions in the sensing mechanism of the organic material and, as a consequence, a lowering of the selectivity of the sensor. 

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.

Figure 15.23 Zinc (II) porphyrin-derived anion sensor 15.5 and the mixed nanoparticle derived from it (reproduced by permission of The Royal Society of Chemistry).

Figure 16.20 Examples of sensor molecules (a) tetraphenyl porphyrin, solvatochromic Rei-chardt s dye and pH indicator (phenol red) (b) image of the 36-dye matrix before exposure, after exposure, and the resulting difference map and (c) colour change profiles for common beverages. (Reprinted with permission from Zhang and Suslick [90], Suslick et at. [91], and Janzen et al. [147]. American Chemical Society 2006-2007)...

Electrochemical NO sensors based on platinized or electrocatalyst-modified electrodes often in combination with a permselective and charged membrane for interference elimination were proposed. Although the catalytic mechanism is still unknown, it can be assumed that NO is co or dinative ly bound to the metal center of porphyrin or phthalocyanine moieties immobilized at the electrode surface. The coordinative binding obviously stabilizes the transition state for NO oxidation under formation of NO+. Typically, sub-pM concentrations of NO can be quantified using NO sensors enabling the detection of NO release from individual cells. 

D Urso A, Mammana A, Balaz M et al (2009) Interactions of a tetra-anionic porphyrin with DNA from a Z-DNA sensor to a versatile supramolecular device. J Am Chem Soc 131 2046-2047... 

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