Abstract
A novel chemical sensor based on a hetero-core optical fiber structure is reported where lipid films coat a
cylindrical cladding. Two lipids were applied to the fiber surface: oleic acid and phosphoric acid
di(2-ethylhexyl) ester (PAEE). An Au/lipids-coated sensor showed different shifts of the surface plasmon
resonance (SPR) peak wavelength and changes in the spectral width for different chemical solutions (i.e.,
quinine, hydroquinidine, gramine, and caffeine) whose refractive indices are close to each other. The
oleic acid- and PAEE-direct-coated sensors induced optical losses of approximately 0.4 and 0.2 dB, respectively,
for a refractive index difference of 0.0008 between water and quinine. Compared with Au/
lipid-coated sensors, the lipid monolayer showed the different sensitivities to chemical substances and
detected a wide range of chemical substances, including quinine. Changing the type of lipid in the film
controls the selectivity of chemical substances.
