Surface-plasmon resonance sensing of alcohol with electrodeposited polythiophene and gold nanoparticle-oligothiophene films

Electrodeposited films of polythiophene or gold nanoparticles (NPs) capped with conjugated oligothiophenes prepared on thin gold films are employed in a Kretschmann-type surface-plasmon resonance detector. The polythiophene films selectively respond to alcohol (ethanol or methanol) and toluene vapors but not to hexanes or water vapors, while the nanoparticle/oligothiophene films respond only to alcohol vapors of the solvents tested. For both films, the response to vapors consisted of the minimum in the reflectance curve (theta(0)) shifting to a higher angle as the thickness of the film increased. Slight increases in dielectric constant were also observed. The NPs do not result in an enhancement in sensitivity, contrary to theoretical predictions that suggest greater sensitivity may be achieved due to localized surface-plasmon effects associated with the presence of the Au NPs in the dielectric.