Nano-SnO2/polyaniline composite films for surface plasmon resonance

Synthesized nanocomposites of protonated polyaniline with camphor sulfonic acid (PANI-CSA) doped with tin oxide nanoparticles (SnO2 NPs) were coated as films on fused silica substrates using the dip-coating technique. The optical, electrical, chemical and thermal properties of the produced (PANI-CSA)/SnO2 were investigated. The refractive index for (PANI-CSA)/SnO2 nanocomposite films increases with increasing SnO2 NPs mole fraction. The optical bandgap energy of undoped PANI-CSA thin films is 4.34 eV, being this value decreased in a monoexponentially decay to 4.08 eV for samples up to a 0.11-mol fraction of SnO2 NPs in PANI-CSA. For a 0.20-mol fraction the bandgap has a substantial decrease (3.93 eV) due to SnO2 NPs percolations. Upon inceasing SnO2 MPs content the electrical conductivity of the (PANI-CSA)/SnO2 nanocomposite films reaches a threshold of 2.25 [S.cm(-1)]. A surface plasmon resonance (SPR) theoretical model consisting in a prism with Au/(PANI-CSA)/ SnO2 layers shows that the SPR sensitivity for particle detection increases with increasing SnO2 NPs concentration.