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Preparation and Characterization of Functionalized Multi-Dimensional Nanostructural Materials and Their Applications in VI Brational Spectroscopic Chemical Sensing Systems
Vibrational spectroscopy is a powerful tool in obtaining chemical information of amolecule itself and its surroundings. Both infrared and Raman spectroscopy are frequentlyused to acquire vibrational spectra of organic species. For infrared spectroscopic method, itcommonly suffers low applicability and sensitivity in determination of analytes in aqueoussamples. Attempts have been made to increase the sensitivity by treating the surface ofsensing element with a thin layer of polymer. Through partition, analytes can be attractedand concentrated into the polymer thin film. However, slow in response and strong spectralinterferences from polymer film are observed. To overcome these weaknesses,nanomaterials have been applied to replace the polymeric sensing phase. However, due tothe prepared substrates are mainly 2-dimensional structures, short linear (dynamic) range ofresponse and low sensitivity in detection of low absorptivity compounds were observed.Similarly, Raman spectroscopy offers advantages in handling aqueous solution but suffersfrom low sensitivity in detection. Efforts have been given to utilize metallic nanoparticles toincrease the Raman scattering through the so-called surface enhancement effects. On theother hand, either IR or Raman method, the preparation of highly sensitive substrates fordetection of analytes is critical to increase the sensitivity in obtaining high qualityvibrational spectra. To have a more sensitive sensing substrate, a reasonable approach is toincrease the thickness of the nanomaterials to form multi-dimensional structures. Theadvantages over the convensional two-dimensional structures include the better matching ofthe depth of penetration of evanescent wave in infrared spectroscopic method and also highchances to interact with Laser radiation in Raman spectroscopic method. Also, a properstacking of the nanomaterials can increase the chances to have the so-called hot-spot effectand further increase of the sensitivity can be expected. Therefore, in this project, thepreparation of multi-dimensional structural nanomaterials is first focused. Two types ofmulti-dimensional structural nanomaterials are classified and designed. In the first class,high surface area templates are first prepared following attaching metallic nanoparticles bychemical reduction reactions. The materials to form templates can be metal oxide nanowires,fibers, surfactant-roughen polymer film, chemical roughen crystals and porous membranes.The second class of multi-dimensional structures can be prepared by stacking of metalnanoparticles, i.e. seed-mediated, surface-controlled method, and self-assemblynanoparticles. Metals of Ag, Au, Pd, Pt, and Cu will be selected to form the metallicnanoparticles. In terms of applications, the surface of the metallic materials formed on thesensing elements (i.e. optical fibers or sensing chip) will be further treated with selectivechemicals, i.e. chelating agents, complexing agents, and biomaterials, to approach the realapplications.
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