SOL-GEL ENCAPSULATION OF METALLOPROTEINS FOR THE DEVELOPMENT OF OPTICAL BIOSENSORS FOR NITROGEN-MONOXIDE AND CARBON-MONOXIDE

Three heme proteins; horse heart cytochrome c, myoglobin (Mb) and hemoglobin (Hb), have been encapsulated in a sol-gel matrix and investigated for their potential use as biological recognition centres for the biosensing of NO and CO, It has been shown that the encapsulation of these metalloproteins in sol-gels has no effect on the formation of nitrosyl or carbonyl complexes as observed using UV/VIS spectrophotometry, The metalloproteins in sol-gels could be readily reduced to the Fe-II state, using excess sodium dithionite, and re-oxidized to the Fe-III state on the addition of excess potassium ferricyanide, The observed redox capability within sol-gels enabled formation of the nitrosyl complex in both the Fe-III and Fe-II states of Mb and Db and in the Fe-III state of cytochrome c, The formation of these nitrosyl complexes was shown to be reversible, Similarly, the reversible formation of the carbonyl complex with Mb and Db in the reduced form has been achieved, Titration of a saturated solution of CO with Db contained in a sol-gel showed a Linear increase in intensity of the alpha (568 nm) and beta (540 nm) absorption bands of the metalloprotein until saturation of the iron centres of the Db occurred, A similar increase in intensity of the alpha (562 nm) absorption band of cytochrome c was observed when a saturated solution of NO was titrated against this metalloprotein contained in a sol-gel, The results show that sol-gels can be readily used as a-host for the encapsulation of cytochrome c, Mb and Db and that these metalloproteins can be used as the biological recognition centre for the biosensing of NO and CO at the micromolar level.