Abstract

In recent years, many (bio)chemical sensors for detecting important constituents of human body, such as Na⁺,. Ca²⁺, K⁺, and Cl⁻, etc., have been reported. Generally, these sensors are based on electrode has been known to have low sensitivity, which make it difficult to sense materials of very small reactivity. Meanwhile, absorption spectro-photometry and ATR (Attenuated Total Reflection) spectrometry have the high sensitivity and are suitable to sensing required high level sensitivity. However, a common problem with absorption spectro-photometry is nonlinearity of the absorbance with concentration caused by stray ray when the sample has high absorbance at the selected wavelength. It is complex and tedious for this method to be applied to the analysis of turbid biochemicals because of multiple dilutions of the sample and the need for a special setup, etc. One of the limitations of ATR spectrometry is that it shows poor sensitivity for weakly light-absorbing samples. This arises because the effective sample thickness is in the order of the penetration length of the evanescent wave into the sample, which is small. In this study, we propose a thin-film optical waveguide type ion sensor for solving the limits of conventional transmission or reflection measurements as mentioned above. The proposed sensor improves sensitivity and selectivity by taking in ionophore and chromoionophore in sensing layer. The sensing layer (refractive index;1.51 at λ=488nm) was made and deposited by spincoating of ionophore (HDOPP-Ca for Ca²⁺ or Valynomycin for K⁺), chromoionophore, PVC-PVA-PVAc copolymer and BEHP on waveguide layer. The waveguide layer was fabricated by rf sputtering of Corning 7059 glass (refractive index;1.59 at λ=488nm) on Pyrex glass (refractive index;1.48 at λ=488nm) substrate. The fabricated waveguide sensor was placed on stage, and laser light of 488nm or 633nm was coupled into the waveguide by the prism coupling method. The decoupled light was measured with an optical powermeter. To evaluate the characteristics of this sensor, CaCl₂ solution and KCl solution of pH5.3 (Acetate Buffer) was used, and during the experiment its concentration was gradually increased from 10⁻⁵ to 10⁻²mol.

© 1998 IEEE