Hybrid nanostructures of gold/polyelectrolyte for optical biosensor
authors Sónia Oliveira Pereira
supervisors Ana Margarida Madeira Viegas de Barros-Timmons; Tito da Silva Trindade
thesis type Mestrado
author keywords Biotecnologia, Nanoestruturas, Biossensores, Polielectrólitos
abstract Gold nanoparticles (Au NPs) have been receiving significant attention due to the fact that their optical properties are very sensitive to characteristics such as size, shape, state of aggregation and surrounding environment which can find potential applications in biosensors. In the present work Au NPs were prepared by two distinct methods: (i) the standard citrate method which yielded Au NPs with 14.9 ± 2.7 nm diameter and an absorption maximum (λmax) at around 522 nm, and (ii) an in situ procedure using poly(allylamine hydrochloride) (PAH) as reducing agent. The ensuing Au NPs had a diameter of 22.0 ± 3.3 nm and an absorption maximum (λmax) at around 538 nm. The effect of the reaction conditions on the materials properties was assessed by optical spectroscopy, dynamic light scattering (DLS), zeta potential measurements and transmission electron microscopy. To investigate the robustness of the ensuing citrate nanostructures, the samples were submitted to a series of washing cycles in order to assess PAH removal. Upon each cycle the materials were analyzed by visible spectroscopy and zeta potential measurements. These studies indicated that from the third cycle the amount of PAH was residual. In order to use the Au colloidal suspensions as biosensors, different strategies to modify PAH were used. The PAH chains were first functionalized with fluorescein isothiocyanate (FITC) and biotin. The chemically modified polyelectrolyte was used to coat the Au NPs prepared via the citrate method. The functionalization of the nanostructures with biotin a posteriori yielded a more sensitive system. For the Au NPs prepared in situ four different functionalization and purification routes have been explored. Only the following sequence proved successful: in situ synthesis of Au NPs, followed by reaction with FITC to ensure the pH is kept around 9; the ensuing nanostructures were then purified by centrifugation and re-dispersion to slightly acid pH and finally modification with biotin was preformed. The resulting hybrid nanostructures were characterized by visible spectroscopy, fluorescence and measurements of zeta potential. Finally, the optical response and specificity of the functionalized nanostructures towards avidin was evaluated using visible and fluorescence spectroscopies. For comparison purposes, the original Au NPs coated with PAH were used as blanks as well as nanostructures prepared specifically for this purpose which were functionalized either with FITC or with biotin. The results show that these hybrid nanostructures have potential to be used as biosensor, since a specific response was observed namely when the gold NPs were prepared via the citrate method.
year published 2011
subject category Mestrado em Biotecnologia
link http://hdl.handle.net/10773/7974