alpha-Cyclodextrin-modified infrared chemical sensor for selective determination of tyrosine in biological fluids.

In this paper, we propose an evanescent wave-based infrared (IR) spectroscopic sensing method for the selective and sensitive detection of tyrosine in aqueous solution. In this approach, alpha-cyclodextrin (alpha-CTD) was chemically immobilized onto the surface of an IR-sensing element to attract tyrosine specifically to the surface of the sensing element. Theoretical equations were developed for the quantitative analysis of tyrosine. Based on its IR spectra, the synthesized alpha-CTD phase was stable in water. Optimal detection with this system occurred when the pH of the solution was ca. 10.5. Based on the absorption bands, we confirmed that alpha-CTD was most effective at attracting tyrosine under basic conditions. Using the unique absorption band of tyrosine at 1500 cm(-1), the alpha-CTD phase allowed the detection of tyrosine selectively from among a range of potentially interfering amino acids and other species commonly present in biological samples. For quantitative analysis, this CTD-modified phase was most suitable for sensing tyrosine at concentrations below 100 microM because of limits in the surface adsorption mechanism. The detection times were, in some instances, lower than 5 min. For a detection time of 10 min, the detection limit of tyrosine was ca. 0.4 microM.