Nanoparticle-based biosensors: development and application

Baltazar, Raul

http://hdl.handle.net/10400.1/334

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Authors

Baltazar, Raul

Advisor(s)

Ferreira, Guilherme

Abstract(s)

The development of technologies for imaging systems is a key issue in Medical Bioengineering. Within that context, the establishment of methodologies to link biomolecules to metallic and/or semiconductor nanoparticles, generating biologically active colorimetric sensors, constitutes an important research field towards the detection of molecular interactions both in vivo and in vitro. This thesis deals with the study and application of nanoparticle-based colorimetric sensors, namely gold nanoparticles (AuNPs) and quantum dots (QDs), for the study of biomolecular interactions and for biosensing purposes. AuNPs are well known for their strong interactions with light that result on surface plasmon resonances (SPRs) which are transduced by characteristic optical absorption profiles. The wavelength peak of those plasmon resonances is found to depend greatly on three major factors: the nanoparticles morphology, the dielectric characteristics of the medium in which the nanoparticles are embedded and the interparticle distances. Since the SPR peak shifts to higher wavelengths and broadens when nanoparticles are brought close together, due to interparticle plasmon coupling, the biorecognition-induced aggregation of AuNPs has become a very attractive tool as colorimetric transduction signal in a variety of biosensing platforms. In this thesis, the colorimetric signal changes generated upon AuNPs aggregation was explored for the development of strategies for immunosensing and DNA-detection. QDs, on their hand, possess unique photophysical properties for the development of robust and efficient fluorescent sensors, including high quantum yields, broad absorption spectra, narrow size-tunable photoluminescent emissions and exceptional resistance to both photobleaching and chemical degradation. Additionally, scientific research over the last few years proved that these nanometer-sized semiconductor particles can be linked with a range of biomolecules (including: peptides, antibodies, nucleic acids, and small-molecule ligands) and be used as biological labels. In this thesis, a few critical steps were taken on the characterization of the QDs photoluminescence properties, namely: under long-term photo-excitation with laser light and, when exposed to range of different temperatures.