Fabrication Of Fiber Optic Sensor Research Articles

A sensitive and selective optical detection of Ni2+ based on gold nanoparticles synthesized using Nocardiopsis

In the present report, a sensitive and selective sensor has been developed for the detection of Ni2+ using optical properties of gold nanoparticles. Gold nanoparticles used for the sensing has been synthesized using Nocardiopsis dassonvillei NCIM 5124. Synthesized gold nanoparticles were found to be aggregated in presence of Ni2+ ions with concomitant change in the surface plasmon resonance (SPR) peak intensity of gold nanoparticles. This Ni2+ induced change in the optical properties of gold nanoparticles has been explored for the fabrication of fiber optic sensor for the detection of Ni2+. The selectivity of the sensor towards Ni2+ was tested by measuring the sensing response of the sensor towards various metal ions such as, Zn2+, Cd2+, Cr3+, Mo2+, Cu2+, Pd2+, Hg2+ and Ni2+at 100 ppm concentrations. The developed sensor showed linear response in the range of 2–10 ppm (R2 = 0.98). Detection limit of the sensor was found to be 2 ppm.

New insights into sensors based on radical bisphthalocyanines

The unique semiconducting, optical and electrochemical properties of radical lanthanide bisphthalocyanines make them ideal materials for sensing applications. A variety of chemical sensors have been developed using rare-earth bisphthalocyanine thin films. In this paper, the characteristics of sensors based on bisphthalocyanines are reviewed. The advantages of these sensors with respect to sensors developed using other metallophthalocyanines are discussed. Resistive sensors based on bisphthalocyanines change their conductivity when exposed to a variety of pollutant gases and volatile organic compounds. Because bisphthalocyanines are intrinsic semiconductors, the conductivity of their thin films is higher than the conductivity of metallophthalocyanine thin films. This facilitates the electrical measurements and enhances the sensitivity of the sensors. Optical sensors have also been developed based on the rich optical properties shown by bisphthalocyanines. Films characterized by a bright green color change to red or to blue upon oxidation or reduction. The changes also affect the charge-transfer band associated to the free radical that bisphthalocyanines show in the near infrared region. This band coincides with telecommunication wavelengths, making possible the fabrication of fiber optic sensors where a phthalocyanine film is deposited at one of the ends of the fiber. Electrochemical sensors have been developed taking advantage of the unique electrochemical behavior associated to the one-electron oxidation and one-electron reduction of the phthalocyanine ring. These reversible processes are extremely sensitive to the nature of the electrolytic solution. This has made possible the development of voltammetric sensors able to produce particular signals when immersed in different liquids. In the last part of the paper, the fundamentals and performance characteristics of electronic noses and electronic tongues based on bisphthalocyanines are described. Such devices have been successfully exploited in quality control, classification, freshness evaluation and authenticity assessment of a variety of food, mainly wines and olive oils.

Focused ion beam fabrication of metallic nanostructures on end faces of optical fibers for chemical sensing applications

Focused ion beam (FIB) fabrication of fiber optic sensors, mainly chemical sensors, which are based on plasmonics-active nanostructures formed on the cleaved tips of optical fibers, is reported. The nanostructures fabricated included nanoholes in optically thick metallic films as well as metallic nanopillars and nanorods. The sensing mechanism is based on detecting shifts in surface plasmon resonances (SPRs) associated with nanoholes in metallic films and localized SPRs of metallic nanopillars and nanorods, when the refractive index of the medium surrounding the nanostructures is changed. These sensors can be employed for the detection of chemical agents in air as well as liquid media surrounding the sensors. FIB milling was employed to fabricate ordered arrays of nanoholes in optically thick (100–240nm) metallic films deposited on cleaved end faces of multimode, four-mode, and single-mode optical fibers. Separately, metallic nanorods and nanopillars were formed by first depositing a metallic (gold or silver) film on tips of optical fibers, which was followed by FIB milling large area patterns to form freestanding nanorods and nanopillars. Utilizing FIB allows engineering nanostructure geometries, i.e., nanostructure shapes and sizes that are chosen based on the plasmon resonances associated with them. Formation of periodic arrays of nanoholes provides a means of tuning plasmon resonance peaks, associated with extraordinary transmission of light through the array of nanoholes in the metallic films, based on periodicity and shape of the nanoholes as well as on refractive index changes to form sensitive chemical sensors.