A pH-dependent optical sensor based on ultraviolet-treated liquid crystals to detect xanthine

초록

We report an ultraviolet (UV)-treated liquid crystal (LC)-based optical sensor for monitoring the xanthine (Xn) levels. The sensing mechanism is based on the orientation change of UV-treated 4-cyano-4 '-pentylbiphenyl (5CB) by the pH-dependent adsorption and desorption of 4-cyano-4 '-biphenylcarboxylate (CB) at the aqueous-5CB interface. The areal density of CB adsorbed at the interface has an effect on the orientation of the LCs and de-pends on the pH of the solutions. When the pH levels increased, the optical image of the UV-treated 5CB appeared dark due to the self-assembled CB at the interface. When the pH levels decreased, the optical image appeared bright due to the desorption of CB from the interface to the aqueous phase. Xanthine oxidase (XO) catalyzes the Xn degradation reaction, forming uric acid and hydrogen peroxide. These acidic products contribute to decreasing pH levels and the tilted ordering of 5CB. A transition from the homeotropic to tilted orientation as the Xn concentration increased was visible as a change from dark to bright images under a polarizing microscope. This pH-driven optical sensor had low detection limits of 1.733 pM in the phosphate -buffered saline and could be applicable in human urine and spoiled fish.

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