SURFACE-PLASMON RESONANCE OF SELF-ASSEMBLED PHTHALOCYANINE MONOLAYERS- POSSIBILITIES FOR OPTICAL GAS-SENSING

A diphthalocyanine disulfide (Pc) molecule has been deposited as a mon olayer on gold-coated substrates through the process of self-assembly. To establish the molecular orientation of the Pc molecule on the gold surface the two complementary techniques of transmission IR and refle ction absorption IR (RAIR) spectroscopies were used, The appearance of IR absorption bands associated with the Pc nucleus in the transmissio n spectrum, and their absence in the RAIR spectrum, suggests that the Pc self-assembled monolayer (SAM) is orientated with the macrocycle pa rallel to the metal surface, The Pc SAM has been used in conjunction w ith surface plasmon resonance (SPR) to establish the utility of combin ing these techniques for optical gas sensing, The SPR reflectivity cur ves for the gold substrate and the Pc SAM on the gold substrate have b een obtained, On exposure of the Pc SAM to the environmentally importa nt NO2 gas, changes of the reflectivity signal were obtained in propor tion to the concentration of the analyte gas, The results obtained sho w that the monolayer deposition technique of self-assembly is an ideal method for the production of chemically sensitive substrates which ca n be combined with surface plasmon resonance for the optical sensing o f gaseous species.