Different Fitc Hydrogen Ion Chemical Sensor Development And Application

The development of non-glass pH chemical sensor for use in complex system had made remarkable advances in recent years.but generally, the detection range of normal sensors was narrow and the leaching of indicator from matrix limited their lifetime and application, nowadays, many studies concentrated on searching for new indicators and their immobilization methods. This paper reviewed the development of chemical sensors for hydrogen ion in recent years, the attention focused on the photochemical pH sensors, respects from selection of pH indicators and attachment methods to matrix were summarized. In the second part, the article for the first time studied the spectral properties of fluorescein isothiocyanate (FITC) in aqueous solution. The characteristic of FITC response to hydrogen ion had been examined nicely in acid-alkaline solution. It had been found that not only the absorption spectrum but also the fluorescent spectrum was largely dependent on the concentration of hydrogen ion in aqueous solution. In strong acidic solution FITC was excited at 300 nm and the maximum emission peak was at 364 nm; when the concentration of hydrogen ion was decreased fluorescence wavelength at 520nm was found except for 364nm, but its fluorescence intensity was lower; in weak acidic solution two excited maximum wavelength were located at 440 nm and 490nm with one emission wavelength at 520nm, as the pH value increasing only one excitation spectrum peak and emission peak were found at 490/520nm respectively. The relative fluorescence intensity of FITC depended mainly on pH value in whole pH range, the relative fluorescence intensity of FITC increased with a rise of pH in rage of 3.0 to 10.0 then decreased in the range of pH 10.0 to 13.0, and a linear relationship were obtainbetween the relative fluorescence intensity and pH in the range of pH3.43-5.26, 6.19-9.27 and 10.99-12.12 separately. FITC was one of derivatives of fluorescein, this paper had inferred the species in aqueous solution and their chemical structures of FITC according to the spectral similarity of the FITC with fluorescein in different pH medium. Based on the relationship between the relative fluorescence intensity of FITC and pH value, a novel pH chemical sensor was prepared at the third part of the article by entrapping FITC with wax on the surface of glass slide. The properties of the sensor had been evaluated including response time, leaching of indicator and the reversible lifetime. Effects of temperature and the concentration of FITC on the response to hydrogen ion had also been examined. It was found that the sensor had one maximum excitation wavelength at 250nm and two maximum emission peaks, one was at 362nm , the other located at 520nm with weak fluorescence, this was different with that of in solution. The sensor had remakble response to pH value in a wide range of pH1-12, and a excellent linear relationship was obtained between relative fluorescence intensity and pH values in the range of pH 1- 5 using 250 nm and 362 nm as excitation and emission wavelengths respectively. The pH sensor had a rapid response time below 4s over three pH unit changes. Immerging the sensor in pH5 solution for three hours there was no or little obvious reagent leaching detected; the sensor was stored at room temperature and the performance of response to hydrogen ion was stable at least 70 days. The sensor can be used below 36℃ and the concentration of FITC had little inflence on its response to pH.The principal advantages of the novel pH fluorescence sensor were simple, fast response and long lifetime. This new pH sensor was satisfied for determining pH changes in aqueous solution and biological system,the accuracy was below 0.02pH unit.