Active optical thin-film waveguide sensor for ion sensing

In this paper, an active PVC optical thin-film waveguide sensor is proposed which can select a specific ion and measure its concentration. The waveguide was fabricated using the plasticized poly(vinyl chloride) (PVC), bis ethyl hexyl phthalate (BEHP), lipophilic anionic dye (LAD-3), and ionophores (K23E1 for calcium, or C14DD16C5 for sodium) in which the PVC membrane plays important roles for both incident light propagation and selective ion sensing. In order to investigate the applicability of this sensor to Ca²⁺ and Na⁺ measurement, the sensor was applied to sample solutions whose CaCl₂ concentration was gradually altered. Also, we applied it to a NaCl solution. In this experiment, we found that this PVC thin-film waveguide possessed good light propagation for argon laser light at 488 nm. Also, the comparison of the experimental responses between the active waveguide sensor and a commonly utilized waveguide sensor (evanescent waveguide spectrometry), indicated that the sensitivity of the active waveguide sensor is obviously higher than that of the conventional waveguide sensor. These findings suggested that the proposed PVC waveguide ion sensor is applicable to the determination of various ions with high sensitivity.