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    Gold-nanoparticle-based fiber optic sensor for sensing the refractive index of environmental solutions
    (2018-08-01)
    Houngkamhang, Nongluck
    ;
    Charoensuwan, Sittan
    ;
    Sonthipakdee, Onanong
    ;
    Nawattanapaiboon, Kawin
    ;
    Somboonkaew, Armote
    Here an optical fiber modified with gold nanoparticles was successfully fabricated to sense the refractive index of a chemical solution surrounding its surface, with the potential of utilizing this sensor as a biosensing device. Gold nanoparticles, with an average diameter ~20 nm, were synthesized via the citrate reduction method and used to functionalize the glass core of an optical fiber. The sensing principle, which is based on localized surface plasmon resonance, requires the metal gold nanoparticles to be exposed to both the incident and absorbing lights, with the potential detection capabilities determined from the observed light intensity measurement. The optical fiber was uncladded at its center to expose the glass core fiber, and gold nanoparticles were immobilized on the exposed surface using a silane coupling agent. The sensitivity of the gold-nanoparticle-modified optical fibers in measuring the refractive index changes of a solution was compared for unclad lengths ranging between 1 and 2 cm. The attenuation of light depended on both the refractive index of solution and the length of the unclad fiber. The results showed that the fiber sensitivity increased as the unclad length increased due to greater amount of gold on the surface. Antibody-A, which has a specific binding to antigen-A, was then covalently linked to the fiber surface via an amide bond to demonstrate the potential bio-sensing platform of this sensor. The antibody-A functionalized optical fiber was used to detect the red blood cell samples in groups A, B, and O, where it effectively detected both the specific and non-specific binding signals. This fiber optic biosensor therefore provides a low-cost and simple fabrication setup that has potential field applications. Moreover, this setup could potentially be applied to detect other types of whole cell samples.
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    Morphology-controlled seed-assisted hydrothermal ZnO nanowires via critical concentration for nucleation and their photoluminescence properties
    (2015-01-01)
    Kasamechonchung, Panita
    ;
    Horprathum, Mati
    ;
    Boonpavanitchakul, Kanittha
    ;
    Supaka, Nuttapun
    ;
    Prompinit, Panida
    Here we demonstrate the controllability on morphology of hydrothermal ZnO nanowires through the critical concentration for nucleation. When Zn ion concentration is relatively low, the nucleation process preferentially occurs on the (0001) plane, promoting nanowire growth. In contrast, for relatively high Zn ion concentration, the (10-10) plane emerges, suppressing nanowire growth. The occurrence of this nucleation competition on the crystal planes as a function of concentration is caused by differences in the critical nucleation sizes between the (0001) plane and the (1010) plane. Furthermore, we found that the density of ZnO nanowires trend to decrease with increasing the growth time due to the lateral growth effect. Photoluminescence measurement of ZnO nanowires exhibited that the near band emission peak of 380nm decreased with decreasing nanowire diameter while the broad emission peak below band gap appears the opposite trend because of surface to volume ratio effect.