No abstract

A novel fiber-optic evanescent wave sensor (FOEWS) for O(2) detection based on [Ru(bpy)(3)](2+)-doped hybrid fluorinated ORMOSILs (organically modified silicates) has been developed. The sensing element was fabricated by dip-coating the optical fiber with [Ru(bpy)(3)](2+)-doped hybrid fluorinated ORMOSILs composed of n-propyltrimethoxysilane (n-propyl-TriMOS) and 3, 3, 3-trifluoropropyltrimethoxysilane (TFP-TriMOS). Fluorophores of [Ru(bpy)(3)](2+) were excited by the evanescent wave field produced on the fiber core surface and the emission fluorescence was quenched by O(2). Spectroscopic properties have been characterized by FTIR and UV-VIS absorption measurements. By using the presented hybrid fluorinated ORMOSILs, which enhances the coating surface hydrophobicity, the quenching response is increased. The sensitivity of the sensor is 7.5, which is quantified in terms of the ratio I (N2)/I (O2) (I (N2) and I (O2) represent the fluorescence intensities in pure N(2) and pure O(2) environments, respectively). The limit of detection (L.O.D.) is 0.01% (3sigma) and the response time is about 1 s. Meanwhile, the proposed FOEWS has the advantages of easy fabrication, low cost, fast response and suitable sensitivity for oxygen monitoring using a cheap blue LED as light source and coupling a miniature PMT detector directly to the optical fiber probe.

A novel small-volume fiber-optic evanescent-wave absorption sensor based on the Griess-Ilosvay reaction has been developed and evaluated for nitrite determination. The sensor was constructed by inserting a decladded optical fiber into a transparent capillary to form an annular column microchannel. The Evanescent wave (EW) field produced on the optical fiber core surface penetrated into the surrounding medium and interacted with the azo dye, which was generated by the reaction of nitrite and nitrite-sensitive reagents. The detector was designed to be parallel to the axis of the optical fiber. The defined absorbance was linear with the concentration of nitrite in the range from 0.05 to 10 mg L(-1), and the detection limit was 0.02 mg L(-1) (3sigma) with the relative standard deviation (RSD) of 2.6% (n = 8). The present sensor was successfully used to determine nitrite in real samples of mineral water, tap water, rain water, and seawater. The results were consistent with the data obtained by standard spectrophotometric method, showing potential of the proposed sensor for practical application.