Olavarría Fullerton, Jenifier

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    Development of plasmonic nanostructures as raman sensors for the detection of arsenic antimicrobials
    (2013-12) Olavarría Fullerton, Jenifier; De Jesús Ruiz, Marco A.; College of Arts and Sciences - Sciences; Hernández Rivera, Samuel P.; Román, Félix R.; Vera, Marisol; Ríos, Robert; Department of Chemistry; Otero, Ernesto
    Pharmaceutical and Personal Care Products (PPCP’s) have been considered as a new category of emerging pollutants due to their persistence in the environment. These compounds have been a cause of concern since they have been detected at trace levels in soils and superficial and underground water. Conventional detection techniques rely on expensive, time consuming procedures and result often result in sample destruction. Surface Enhanced Raman Scattering (SERS) has been considered an attractive tool for the detection and characterization of drugs and bioactive agents since it renders large amounts of structural information which allows unequivocal identification of the analyte. In addition, analysis can be performed with small amounts of sample in aqueous media and signal enhancement allows detection at trace levels. In spite of its advantages, the technique has been limited due to the heterogeneous plasmonic responses provided by traditional substrates. The work presented herein is focused on the fabrication and development of plasmonic SERS substrates, such as silver/polydimethylsiloxane nanocomposites and hybrid nanostructured arrays, for the study of veterinary drugs in aqueous media. Silver/polydimethylsiloxane (Ag/PDMS) nanocomposites were successfully employed for the detection and characterization of trace amounts of 4-arsanilic acid, roxarsone, and acetarsone in water. The results gathered in this study show that organoarsenic species are distributed into the PDMS surface where the arsonic acid binds onto the embedded silver nanoparticles, enhancing its characteristic 792 cm-1 stretching band. The chemisorption of the drugs to the metal facilitates its detection and characterization in the parts per million to parts per billion range. An extensive analysis of the distinct spectroscopic features of each drug is also presented with emphasis on the interactions of the arsonic acid, amino, and nitro groups with the metal surface. The combination of electron beam lithography (EBL) and reactive ion etching (RIE) protocols allowed for the construction, testing and validation of nano-arrays with hybrid morphology with multi-wavelength plasmonic response for the detection of arsenic antimicrobials in water. The fabricated substrates consisted of 2500 µm2 Ag-coated SiO2/Si pillar nano-arrays of alternating hexagonal and elliptical features. Control of simple fabrication parameters such as inter-particle spacing (gap), and its orientation relative to the laser polarization vector (parallel or orthogonal), result in over a tenfold improvement in the apparent Raman response under optimized conditions. At a 632.8 nm excitation frequency, the best substrate performance was observed on parallel oriented features with a 200 nm gap, with over an order of magnitude increase in the apparent SERS signal relative to standard silver polydimethylsiloxane (Ag/PDMS) nanocomposites. Monitoring of the characteristic As-C stretching band at 594 cm-1 allowed the detection of arsenic antimicrobials in water, well within the parts per million range. The surface enhancement factors (SEF) for this substrate at 532, 632 and 785 nm excitation wavelengths were augmented by 5 to 7 orders of magnitude, respectively. The effect of substrate morphology and nanofabrication process on the Raman enhancement factor is presented.