Porphyrin-based electrochemical sensors

Center for Biomedical Research and Department of Chemistry, Oakland University, Rochester, Michigan 48309-4477 USA 

Preparation and Measurement of Nitric Oxide with Amperometric Sensors.245 

Preparation of Porphyrin-Based Potentiometric Sensors for Anions.252 

Copyright 2000 by Academic Press 231 All rights of reproduction in any form reserved. 

Porphyrin-based electrochemical sensors possess a unique set of characteristics that may make them of fundamental importance in solving some of the problems in pure and applied biology and medicine. Sensor properties that are particularly advantageous are small size and fast response time, as well as the ability to provide both qualitative and quantitative information about an electroactive analyte. The main challenge in the development of a successful electrochemical sensor is the improvement of its selectivity. 

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Porphyrin-Based Electrochemical Sensors Tadeusz Malinski... 

Malinski T (2000) Porphyrine-based electrochemical sensors. In Kadish KM, Smith KM, Guilard R (eds) The porphirin handbook, vol 6. Acad Press, Amsterdam/ Boston/London/New York/Oxford/Paris/San Diego/San Francisco/Singapore/Sydney/ Tokyo, pp 231-256... 

Excellent recent reviews on graphene-based electrochemical sensors [113] and on analytical devices in biomolecules detection and cancer diagnostics [114] appeared recently, where the superior electrochemical sensing performances of graphene-based electrodes toward the detection of various biomolecules and chemicals have been demonstrated. Also in this field, porphyrin-functionalized graphene hybrids resulted in interesting analytical applications, as will be discussed next. 

It should be noted that 86 also functions as an electrochemical anion sensor, where the Zn(II) porphyrin-based oxidation potential is sensitive to... 

Studies of synthetic porphyrin-based anion receptors should form the basis for more effective sensors. Metallocene-substituted porphyrins examined by Beer and coworkers have proven successful in the solution-phase binding of ions such as chloride, bromide and nitrate." The cobaltocenium-substituted and ferrocene-substituted porphyrins (Figure 134) bind ions in solution, as shown by H NMR and electrochemical studies. The latter measurements reveal that the porphyrin and ferrocene redox... 

This is a typical example of the unique application of the electrochemical sensor for detection of NO release ftom normotensive and hypertensive rats." - It has been reported based on spectroscopic measurements, that endothelium of hypertensive rats produced more NO2/NO3 than endothelium of normotensive rats. However these reports were in contradiction to data obtained on smooth-muscle relaxation, hindered in hypertensive rats. This means that the endothelium of hypertensive rats should produce less NO. Electrochemical measurements with porphyrinic sensor clearly show that net concentration of NO produced by endothelium of SHR rats is lower than that produced by the endothelium of WKY rats. These results correlate well with previously reported smooth-muscle relaxation data. Total production of NO by the endothelium of hypertensive rats is slightly higher than in normotensive rats. However, the endothelium of SHR rats also generated... 

The cucurbit [n]uril family (CB[n]) of molecular containers possess remarkable binding affinities and selectivities (Ka values up to 1012M-1, Krei values up to 106) which renders them useful as a component of molecular machines, sensors, and biomimetic systems (123-125). Recently, Wagner and coworkers have reported (126) that CB[10] - with its spacious 870A3 cavity - is capable of acting as a host for free base and metalated tetra (Af-methylpyridinium)porphyrins 19a-d (Fig. 17). Despite the large ellipsoidal deformation of CB[10] upon complexation, the complexed porphyrins retain their fundamental UV/VIS, fluorescence, and electrochemical properties. The CB[ 10] porphyrin... 

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. 

Currently available amperometric and voltammetric porphyrinic sensors for detection of electroactive analytes are based on their electrochemical oxidation or reduction on polymeric conductive films of metalloporphyrins. If the current generated during the process is linearly proportional to the concentration of an andyte, the current can be used as an analytic signal. This current can be measured in either the... 

Figure 8. Schematic diagram of electrochemical nitric oxide sensor based on conductive polymeric porphyrin.

Electrochemical methods for NO determination offer several features that are not available with spectroscopic approaches. Perhaps the most important is the capability of microelectrodes to directly measure NO in single cells in situ, in close proximity to the source of NO generation. Figure 2 shows sensors that have been developed for the electrochemical measurement of NO. One is based on the electrochemical oxidation of NO on a platinum electrode (the classical Clark probe for detection of oxygen) and operates in the amperometric mode [17]. The other is based on the electrochemical oxidation of NO on conductive polymeric porphyrin (porphyrinic sensor) [24]. The Clark probe uses a platinum wire as a working electrode (anode) and a silver wire serves as the counterelectrode (cathode). The electrodes are mounted in a capillary tube filled with a sodium chlo-ride/hydrochloric acid solution separated from the analyte by a gas-permeable membrane. A constant potential of 0.9 V is applied, and direct current (analytical signal) is measured from the electrochemical oxidation of NO on the platinum anode. In the porphyrinic sensor, NO is catalytically oxidized on a polymeric metalloporphyrin... 

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