Porphyrin-graphene hybrids

Several papers described the use of porphyrin-graphene hybrids as sensors for biomolecules. Thus, the electrochanical interactions between hemoglobin andH2TPPmadethehydroxypropyl-p-cyclodextrin/RGO/tetraphenylporphyrin composite a material with high biorecognition capability [127]. 

As mentioned for porphyrins-graphene hybrids, electrocatalysis by porphyrins-CNTs nanoreactors can be found in oxidation or in reduction reactions. 

Xu, Y., et al., A graphene hybrid material covalently functionalized with porphyrin Synthesis and optical limiting property. Advanced Materials, 2009. 21(12) p. 1275-1279. 

Fig. 18.8 Upper part - chemical structures of a porphyrin derivative used to prepare graphene hybrids. Lower part - SEM images (left) at high (a) and low(b) magnification and photograph (right) of Ti02 electrodes soaked with nanographene hybrid for 120 hours.

Porphyrin-graphene (GO or RGO) hybrids work as nanoreactors in catalysis (either electrochemical or photochemical catalysis), in sensing (both as chemical and biochemical sensors) or in diagnostic and therapeutic applications, as illustrated in the following section. 

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. 

Tetrakis(4-pyridyl)porphyrin was covalently linked to GO and electrochemical reduction of explosive nitroaromatic compounds was obtained by the hybrid, thus performing detection of ultra-trace explosives [121]. Comparing the sensitivity and detection limit of various electrochemical sensors toward TNT detection, the resulting porphyrin/graphene-modifled GC electrode was of superior quality, allowing detection of 0.5 ppb. Detection limit for other nitroarenes were 1 (2,4-dinitrotoluene), 1 (1,3,5-trinittobenzene) and 2 (1,3-dinitrobenzene) ppb, respectively. 

Fig. 30 Scheme showing the preparation of a porphyrin/AuNPs/graphene hybrid nanomaterial by simultaneous reduction of graphene oxide/AuCLi with borohydride, and decorating with a meso-triphenyl-(4-(3-mercaptopropyloxy)phenyl)porphyrin... 

In another work, the same authors demonstrated the versatility of graphene as donor material when preparing a similar nanographene hybrid with porphycenes, a well-known electron acceptor [120], The preparation was followed along the same lines that were established for the porphyrins. By using Raman, TEM, and AFM, the nature of the graphene moiety was clearly demonstrated. Contrary to the electron ac-... 

A 2015 smdy reported hybrids of cationic porphyrins with graphene, carbon nanombes, and fuUerene, discussing their properties in view of possible applications [66]. 

Another interesting report presents the one-pot preparation of a ternary hybrid nanomaterial composed of a porphyrin-functionalized graphene, tin oxide, and gold nanoparticles [134]. This composite was applied to the simultaneous determination of epinephrine and uric acid. First, 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin was linked to GO sheets dispersed in aqueous solution, then HAuCLt was added, followed by SnCl2. The latter ensured reduction to graphene and Au nanoparticles while forming Sn02. Reduction of GO was completed with hydrazine in alkaline medium. 

Huang D, Lu J, li S, Luo Y, Zhao C, Hu B, Wang M, Shen Y. Fabrication of cobalt porphyrin. Electrochemically reduced graphene oxide hybrid films for electrocatalytic hydrogen evolution in aqueous solution. Langmuir 2014 30 6990-8. 

Covalently functionalized hybrid carbon materials can be prepared by click chemistry. This strategy is been explored by Campidelli et al. to anchor porphyrins and phthalocyanines on CNTs and graphene derivatives [191-193]. Nanomateiials based on covalently bonded GO-P was prepared by condensation reaction of GO and 5,15-pentafluorophenyl-10,20-(4-aminophenyl)porphyrin (P). RGO-P was obtained by electrochemical reduction of GO-P in pH 5 PBS solution and used in dopamine and serotonin biosensors, whose detection limits were found to be 3.5 X 10 and 4.9 x 10 pM, respectively, with negligible interference of ascorbic acid [194]. 

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